US20050107835A1

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Publication number: US20050107835A1
Application number: US10/993,799
Authority: US
Inventors: Gust Bardy; Riccardo Cappato; William Rissmann; Alan Ostroff
Original assignee: Cameron Health Inc
Current assignee: Cameron Health Inc
Priority date: 2000-09-18
Filing date: 2004-11-19
Publication date: 2005-05-19
Also published as: US20020042634A1; US7039465B2; WO2003018119A1

Abstract

An implantable cardioverter-defibrillator for subcutaneous positioning between the third rib and the twelfth rib within a patient, the implantable cardioverter-defibrillator including a housing, wherein at least a portion of the housing is curved; an electrical circuit; and at least one electrically conductive surface integrally positioned on at least one portion of the house, wherein at least one electrically conductive surface is coupled to the electrical circuit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser. No. 09/940,371, filed Aug. 27, 2001; which is a continuation-in-part of U.S. application Ser. No. 09/663,606, filed Sep. 18, 2000, now U.S. Pat. No. 6,647,292; and U.S. application Ser. No. 09/663,607, filed Sep. 18, 2000, now U.S. Pat. No. 6,721,597, the disclosures of all which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Defibrillation/cardioversion is a technique employed to counter arrhythmic heart conditions including some tachycardias in the atria and/or ventricles. Typically, electrodes are employed to stimulate the heart with electrical impulses or shocks of a magnitude substantially greater than pulses used in cardiac pacing.

Defibrillation/cardioversion systems include body implantable electrodes and are referred to as implantable cardioverter/defibrillators (ICDs). Such electrodes can be in the form of patches applied directly to epicardial tissue, or at the distal end regions of intravascular catheters, inserted into a selected cardiac chamber. U.S. Pat. Nos. 4,603,705; 4,693,253; 4,944,300; and 5,105,810, the disclosures of which are all incorporated herein by reference, disclose intravascular or transvenous electrodes employed either alone or in combination with an epicardial patch electrode. Compliant epicardial defibrillator electrodes are disclosed in U.S. Pat. Nos. 4,567,900 and 5,618,287, the disclosures of which are incorporated herein by reference. A sensing epicardial electrode configuration is disclosed in U.S. Pat No. 5,476,503, the disclosure of which is incorporated herein by reference.

In addition to epicardial and transvenous electrodes, subcutaneous electrode systems have also been developed. For example, U.S. Pat. Nos. 5,342,407 and 5,603,732, the disclosures of which are incorporated herein by reference, teach the use of a pulse monitor/generator surgically implanted into the abdomen and subcutaneous electrodes implanted in the thorax. This system is far more complicated to use than current ICD systems using transvenous lead systems together with an active can electrode and therefore it has o practical use. It has in fact never been used because of the surgical difficulty of applying such a device (3 incisions), the impractical abdominal location of the generator and the electrically poor sensing and defibrillation aspects of such a system.

Recent efforts to improve the efficiency of ICDs have led manufacturers to produce ICDs which are small enough to be implanted in the pectoral region. In addition, advances in circuit design have enabled the housing of the ICD to form a subcutaneous electrode. Some examples of ICDs in which the housing of the ICD serves as an optional additional electrode are described in U.S. Pat. Nos. 5,133,353; 5,261,400; 5,620,477; and 5,658,321 the disclosures of which are incorporated herein by reference.

ICDs are now an established therapy for the management of life threatening cardiac rhythm disorders, primarily ventricular fibrillation (V-Fib). ICDs are very effective at treating V-Fib, but are therapies that still require significant surgery.

As ICD therapy becomes more prophylactic in nature and used in progressively less ill individuals, especially children at risk of cardiac arrest, the requirement of ICD therapy to use intravenous catheters and transvenous leads is an impediment to very long term management as most individuals will begin to develop complications related to lead system malfunction sometime in the 5-10 year time frame, often earlier. In addition, chronic transvenous lead systems, their reimplantation and removals, can damage major cardiovascular venous systems and the tricuspid valve, as well as result in life threatening perforations of the great vessels and heart. Consequently, use of transvenous lead systems, despite their many advantages, are not without their chronic patient management limitations in those with life expectancies of >5 years. The problem of lead complications is even greater in children where body growth can substantially alter transvenous lead function and lead to additional cardiovascular problems and revisions. Moreover, transvenous ICD systems also increase cost and require specialized interventional rooms and equipment as well as special skill for insertion. These systems are typically implanted by cardiac electrophysiologists who have had a great deal of extra training.

In addition to the background related to ICD therapy, the present invention requires a brief understanding of automatic external defibrillator (AED) therapy. AEDs employ the use of cutaneous patch electrodes to effect defibrillation under the direction of a bystander user who treats the patient suffering from V-Fib. AEDs can be as effective as an ICD if applied to the victim promptly within 2 to 3 minutes.

AED therapy has great appeal as a tool for diminishing the risk of death in public venues such as in air flight. However, an AED must be used by another individual, not the person suffering from the potential fatal rhythm. It is more of a public health tool than a patient-specific tool like an ICD. Because >75% of cardiac arrests occur in the home, and over half occur in the bedroom, patients at risk of cardiac arrest are often alone or asleep and can not be helped in time with an AED. Moreover, its success depends to a reasonable degree on an acceptable level of skill and calm by the bystander user.

What is needed therefore, especially for children and for prophylactic long term use, is a combination of the two forms of therapy which would provide prompt and near-certain defibrillation, like an ICD, but without the long-term adverse sequelae of a transvenous lead system while simultaneously using most of the simpler and lower cost technology of an AED. What is also needed is a cardioverter/defibrillator that is of simple design and can be comfortably implanted in a patient for many years.

SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is now made to the drawings where like numerals represent similar objects throughout the figures where:

FIG. 1 is a schematic view of a Subcutaneous ICD (S-ICD) of the present invention;

FIG. 2 is a schematic view of an alternate embodiment of a subcutaneous electrode of the present invention;

FIG. 3 is a schematic view of an alternate embodiment of a subcutaneous electrode of the present invention;

FIG. 4 is a schematic view of the S-ICD and lead ofFIG. 1 subcutaneously implanted in the thorax of a patient;

FIG. 5 is a schematic view of the S-ICD and lead ofFIG. 2 subcutaneously implanted in an alternate location within the thorax of a patient;

FIG. 6 is a schematic view of the S-ICD and lead ofFIG. 3 subcutaneously implanted in the thorax of a patient;

FIG. 7 is a schematic view of the method of making a subcutaneous path from the preferred incision and housing implantation point to a termination point for locating a subcutaneous electrode of the present invention;

FIG. 8 is a schematic view of an introducer set for performing the method of lead insertion of any of the described embodiments;

FIG. 9 is a schematic view of an alternative S-ICD of the present invention illustrating a lead subcutaneously and serpiginously implanted in the thorax of a patient for use particularly in children;

FIG. 10 is a schematic view of an alternate embodiment of an S-ICD of the present invention;

FIG. 11 is a schematic view of the S-ICD ofFIG. 10 subcutaneously implanted in the thorax of a patient;

FIG. 12 is a schematic view of yet a further embodiment where the canister of the S-ICD of the present invention is shaped to be particularly useful in placing subcutaneously adjacent and parallel to a rib of a patient;

FIG. 13 is a schematic of a different embodiment where the canister of the S-ICD of the present invention is shaped to be particularly useful in placing subcutaneously adjacent and parallel to a rib of a patient;

FIG. 14 is a schematic view of a Unitary Subcutaneous ICD (US-ICD) of the present invention;

FIG. 15 is a schematic view of the US-ICD subcutaneously implanted in the thorax of a patient;

FIG. 16 is a schematic view of the method of making a subcutaneous path from the preferred incision for implanting the US-ICD;

FIG. 17 is a schematic view of an introducer for performing the method of US-ICD implantation;

FIG. 18 is an exploded schematic view of an alternate embodiment of the present invention with a plug-in portion that contains operational circuitry and means for generating cardioversion/defibrillation shock waves;

FIG. 19 is a top perspective view of an alternative S-ICD canister of the present invention depicting the top side of the canister housing and a lead electrode coupled to the S-ICD canister;

FIG. 20 is an exploded bottom perspective view of the S-ICD canister ofFIG. 19 showing an electrode in the shape of a thumbnail positioned on the bottom surface of the canister housing;

FIG. 21 is a front elevational view of the S-ICD canister ofFIG. 19 depicting the curved canister housing;

FIG. 22 is a partial schematic view of the S-ICD canister of the present invention implanted subcutaneously in the thorax of the recipient patient;

FIG. 23A is a top plan view of an alternative S-ICD canister of the present invention having a duckbill-shaped end to the canister housing at the proximal end;

FIG. 23B is a top plan view of an alternative S-ICD canister of the present invention having a duckbill-shaped canister housing with an alternative proximal head configuration;

FIG. 24A is a top plan view of an alternative S-ICD canister of the present invention having a rectangular-shaped canister housing;

FIG. 24B is a top plan view of an alternative S-ICD canister of the present invention having a square-shaped canister housing with a triangular shaped electrode;

FIG. 24C is a top plan view of an alternative S-ICD canister of the present invention having a square-shaped canister housing with a square shaped electrode;

FIG. 25A is a top plan view of an alternative S-ICD canister of the present invention having a tongue depressor-shaped canister housing;

FIG. 25B is a top plan view of an alternative S-ICD canister of the present invention having a modified tongue depressor-shaped canister housing;

FIG. 26A is a top plan view of an alternative S-ICD canister of the present invention having a multi-segment canister housing;

FIG. 26B is a front elevational view of the S-ICD canister ofFIG. 26A depicting the curved proximal segment and the planar distal segment of the multi-segment canister housing;

FIG. 26C is a front elevational view of the S-ICD canister ofFIG. 26A depicting the curved proximal segment and the curved distal segment of the multi-segment canister housing;

FIG. 27 is a plan view of an alternative S-ICD canister made of nonconductive materials according to an embodiment of the present invention; and

FIG. 28 is a plan view of an alternative S-ICD canister made of a mixture of conductive and nonconductive materials according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now toFIG. 1, the S-ICD of the present invention is illustrated. The S-ICD consists of an electricallyactive canister11 and asubcutaneous electrode13 attached to the canister. The canister has an electricallyactive surface15 that is electrically insulated from theelectrode connector block17 and thecanister housing16 via insulatingarea14. The canister can be similar to numerous electrically active canisters commercially available in that the canister will contain a battery supply, capacitor and operational circuitry. Alternatively, the canister can be thin and elongated to conform to the intercostal space. The circuitry will be able to monitor cardiac rhythms for tachycardia and fibrillation, and if detected, will initiate charging the capacitor and then delivering cardioversion/defibrillation energy through the active surface of the housing and to the subcutaneous electrode. Examples of such circuitry are described in U.S. Pat. Nos. 4,693,253 and 5,105,810, the entire disclosures of which are herein incorporated by reference. The canister circuitry can provide cardioversion/defibrillation energy in different types of waveforms. In the preferred embodiment, a 100 uF biphasic waveform is used of approximately 10-20 ms total duration and with the initial phase containing approximately ⅔ of the energy, however, any type of waveform can be utilized such as monophasic, biphasic, multiphasic or alternative waveforms as is known in the art.

In addition to providing cardioversion/defibrillation energy, the circuitry can also provide transthoracic cardiac pacing energy. The optional circuitry will be able to monitor the heart for bradycardia and/or tachycardia rhythms. Once a bradycardia or tachycardia rhythm is detected, the circuitry can then deliver appropriate pacing energy at appropriate intervals through the active surface and the subcutaneous electrode. Pacing stimuli will be biphasic in the preferred embodiment and similar in pulse amplitude to that used for conventional transthoracic pacing.

This same circuitry can also be used to deliver low amplitude shocks on the T-wave for induction of ventricular fibrillation for testing S-ICD performance in treating V-Fib as is described in U.S. Pat. No. 5,129,392, the entire disclosure of which is hereby incorporated by reference. Also the circuitry can be provided with rapid induction of ventricular fibrillation or ventricular tachycardia using rapid ventricular pacing. Another optional way for inducing ventricular fibrillation would be to provide a continuous low voltage, i.e., about 3 volts, across the heart during the entire cardiac cycle.

Another optional aspect of the present invention is that the operational circuitry can detect the presence of atrial fibrillation as described in Olson, W. et al. “Onset And Stability For Ventricular Tachyarrhythmia Detection in an Implantable Cardioverter and Defibrillator,” Computers in Cardiology (1986) pp. 167-170. Detection can be provided via R—R Cycle length instability detection algorithms. Once atrial fibrillation has been detected, the operational circuitry will then provide QRS synchronized atrial defibrillation/cardioversion using the same shock energy and waveshape characteristics used for ventricular defibrillation/cardioversion.

The sensing circuitry will utilize the electronic signals generated from the heart and will primarily detect QRS waves. In one embodiment, the circuitry will be programmed to detect only ventricular tachycardias or fibrillations. The detection circuitry will utilize in its most direct form, a rate detection algorithm that triggers charging of the capacitor once the ventricular rate exceeds some predetermined level for a fixed period of time: for example, if the ventricular rate exceeds 240 bpm on average for more than 4 seconds. Once the capacitor is charged, a confirmatory rhythm check would ensure that the rate persists for at least another 1 second before discharge. Similarly, termination algorithms could be instituted that ensure that a rhythm less than 240 bpm persisting for at least 4 seconds before the capacitor charge is drained to an internal resistor. Detection, confirmation and termination algorithms as are described above and in the art can be modulated to increase sensitivity and specificity by examining QRS beat-to-beat uniformity, QRS signal frequency content, R—R interval stability data, and signal amplitude characteristics all or part of which can be used to increase or decrease both sensitivity and specificity of S-ICD arrhythmia detection function.

In addition to use of the sense circuitry for detection of V-Fib or V-Tach by examining the QRS waves, the sense circuitry can check for the presence or the absence of respiration. The respiration rate can be detected by monitoring the impedance across the thorax using subthreshold currents delivered across the active can and the high voltage subcutaneous lead electrode and monitoring the frequency in undulation in the waveform that results from the undulations of transthoracic impedance during the respiratory cycle. If there is no undulation, then the patent is not respiring and this lack of respiration can be used to confirm the QRS findings of cardiac arrest. The same technique can be used to provide information about the respiratory rate or estimate cardiac output as described in U.S. Pat. Nos. 6,095,987; 5,423,326; and 4,450,527, the entire disclosures of which are incorporated herein by reference.

The canister of the present invention can be made out of titanium alloy or other presently preferred electrically active canister designs. However, it is contemplated that a malleable canister that can conform to the curvature of the patient's chest will be preferred. In this way the patient can have a comfortable canister that conforms to the shape of the patient's rib cage. Examples of conforming canisters are provided in U.S. Pat. No. 5,645,586, the entire disclosure of which is herein incorporated by reference. Therefore, the canister can be made out of numerous materials such as medical grade plastics, metals, and alloys. In the preferred embodiment, the canister is smaller than 60 cc volume having a weight of less than 100 gms for long term wearability, especially in children. The canister and the lead of the S-ICD can also use fractal or wrinkled surfaces to increase surface area to improve defibrillation capability. Because of the primary prevention role of the therapy and the likely need to reach energies over 40 Joules, a feature of the preferred embodiment is that the charge time for the therapy, intentionally e relatively long to allow capacitor charging within the limitations of device size. Examples of small ICD housings are disclosed in U.S. Pat. Nos. 5,597,956 and 5,405,363, the entire disclosures of which are herein incorporated by reference.

Differentsubcutaneous electrodes13 of the present invention are illustrated inFIGS. 1-3. Turning toFIG. 1, thelead21 for the subcutaneous electrode is preferably composed of silicone or polyurethane insulation. The electrode is connected to the canister at its proximal end viaconnection port19 which is located on an electricallyinsulated area17 of the canister. The electrode illustrated is a composite electrode with three different electrodes attached to the lead. In the embodiment illustrated, anoptional anchor segment52 is attached at the most distal end of the subcutaneous electrode for anchoring the electrode into soft tissue such that the electrode does not dislodge after implantation.

The most distal electrode on the composite subcutaneous electrode is acoil electrode27 that is used for delivering the high voltage cardioversion/defibrillation energy across the heart. The coil cardioversion/defibrillation electrode is about 5-10 cm in length. Proximal to the coil electrode are two sense electrodes, afirst sense electrode25 is located proximally to the coil electrode and asecond sense electrode23 is located proximally to the first sense electrode. The sense electrodes are spaced far enough apart to be able to have good QRS detection. This spacing can range from 1 to 10 cm with 4 cm being presently preferred. The electrodes may or may not be circumferential with the preferred embodiment. Having the electrodes non-circumferential and positioned outward, toward the skin surface, is a means to minimize muscle artifact and enhance QRS signal quality. The sensing electrodes are electrically isolated from the cardioversion/defibrillation electrode via insulatingareas29. Similar types of cardioversion/defibrillation electrodes are currently commercially available in a transvenous configuration. For example, U.S. Pat. No. 5,534,022, the entire disclosure of which is herein incorporated by reference, disclosures a composite electrode with a coil cardioversion/defibrillation electrode and sense electrodes. Modifications to this arrangement are contemplated within the scope of the invention. One such modification is illustrated inFIG. 2 where the two

sensing electrodes

25 and23 are non-circumferential sensing electrodes and one is located at the distal end, the other is located proximal thereto with the coil electrode located in between the two sensing electrodes. In this embodiment the sense electrodes are spaced about 6 to about 12 cm apart depending on the length of the coil electrode used.FIG. 3 illustrates yet a further embodiment where the two sensing electrodes are located at the distal end to the composite electrode with the coil electrode located proximally thereto. Other possibilities exist and are contemplated within the present invention. For example, having only one sensing electrode, either proximal or distal to the coil cardioversion/defibrillation electrode with the coil serving as both a sensing electrode and a cardioversion/defibrillation electrode.

It is also contemplated within the scope of the invention that the sensing of QRS waves (and transthoracic impedance) can be carried out via sense electrodes on the canister housing or in combination with the cardioversion/defibrillation coil electrode and/or the subcutaneous lead sensing electrode(s). In this way, sensing could be performed via the one coil electrode located on the subcutaneous electrode and the active surface on the canister housing. Another possibility would be to have only one sense electrode located on the subcutaneous electrode and the sensing would be performed by that one electrode and either the coil electrode on the subcutaneous electrode or by the active surface of the canister. The use of sensing electrodes on the canister would eliminate the need for sensing electrodes on the subcutaneous electrode. It is also contemplated that the subcutaneous electrode would be provided with at least one sense electrode, the canister with at least one sense electrode, and if multiple sense electrodes are used on either the subcutaneous electrode and/or the canister, that the best QRS wave detection combination will be identified when the S-ICD is implanted and this combination can be selected, activating the best sensing arrangement from all the existing sensing possibilities. Turning again toFIG. 2, two

sensing electrodes

26 and28 are located on the electricallyactive surface15 with electrical insulator rings30 placed between the sense electrodes and the active surface. These canister sense electrodes could be switched off and electrically insulated during and shortly after defibrillation/cardioversion shock delivery. The canister sense electrodes may also be placed on the electrically inactive surface of the canister. In the embodiment ofFIG. 2, there are actually four sensing electrodes, two on the subcutaneous lead and two on the canister. In the preferred embodiment, the ability to change which electrodes are used for sensing would be a programmable feature of the S-ICD to adapt to changes in the patient physiology and size (in the case of children) over time. The programming could be done via the use of physical switches on the canister, or as presently preferred, via the use of a programming wand or via a wireless connection to program the circuitry within the canister.

The canister could be employed as either a cathode or an anode of the S-ICD cardioversion/defibrillation system. If the canister is the cathode, then the subcutaneous coil electrode would be the anode. Likewise, if the canister is the anode, then the subcutaneous electrode would be the cathode.

The active canister housing will provide energy and voltage intermediate to that available with ICDs and most AEDs. The typical maximum voltage necessary for ICDs using most biphasic waveforms is approximately 750 Volts with an associated maximum energy of approximately 40 Joules. The typical maximum voltage necessary for AEDs is approximately 2000-5000 Volts with an associated maximum energy of approximately 200-360 Joules depending upon the model and waveform used. The S-ICD of the present invention uses maximum voltages in the range of about 700 to about 3150 Volts and is associated with energies of about 40 to about 210 Joules. The capacitance of the S-ICD could range from about 50 to about 200 micro farads.

The sense circuitry contained within the canister is highly sensitive and specific for the presence or absence of life threatening ventricular arrhythmias. Features of the detection algorithm are programmable and the algorithm is focused on the detection of V-Fib and high rate V-Tach (>240 bpm). Although the S-ICD of the present invention may rarely be used for an actual life threatening event, the simplicity of design and implementation allows it to be employed in large populations of patients at modest risk with modest cost by non-cardiac electrophysiologists. Consequently, the S-ICD of the present invention focuses mostly on the detection and therapy of the most malignant rhythm disorders. As part of the detection algorithm's applicability to children, the upper rate range is programmable upward for use in children, known to have rapid supraventricular tachycardias and more rapid ventricular fibrillation. Energy levels also are programmable downward in order to allow treatment of neonates and infants.

Turning now toFIG. 4, the optimal subcutaneous placement of the S-ICD of the present invention is illustrated. As would be evidence to a person skilled in the art, the actual location of the S-ICD is in a subcutaneous space that is developed during the implantation process. The heart is not exposed during this process and the heart is schematically illustrated in the figures only for help in understanding where the canister and coil electrode are three dimensionally located in the left mid-clavicular line approximately at the level of the inframammary crease at approximately the 5th rib. Thelead21 of the subcutaneous electrode traverses in a subcutaneous path around the thorax terminating with its distal electrode end at the posterior axillary line ideally just lateral to the left scapula. This way the canister and subcutaneous cardioversion/defibrillation electrode provide a reasonably good pathway for current delivery to the majority of the ventricular myocardium.

FIG. 5 illustrates a different placement of the present invention. The S-ICD canister with the active housing is located in the left posterior axillary line approximately lateral to the tip of the inferior portion of the scapula. This location is especially useful in children. Thelead21 of the subcutaneous electrode traverses in a subcutaneous path around the thorax terminating with its distal electrode end at the anterior precordial region, ideally in the inframammary crease.FIG. 6 illustrates the embodiment ofFIG. 1 subcutaneously implanted in the thorax with the

proximal sense electrodes

23 and25 located at approximately the left axillary line with the cardioversion/defibrillation electrode just lateral to the tip of the inferior portion of the scapula.

FIG. 7 schematically illustrates the method for implanting the S-ICD of the present invention. Anincision31 is made in the left anterior axillary line approximately at the level of the cardiac apex. This incision location is distinct from that chosen for S-ICD placement and is selected specifically to allow both canister location more medially in the left inframammary crease and lead positioning more posteriorly via the introducer set (described below) around to the left posterior axillary line lateral to the left scapula. That said, the incision can be anywhere on the thorax deemed reasonably by the implanting physician although in the preferred embodiment, the S-ICD of the present invention will be applied in this region. Asubcutaneous pathway33 is then created medially to the inframammary crease for the canister and posteriorly to the left posterior axillary line lateral to the left scapula for the lead.

The S-ICD canister11 is then placed subcutaneously at the location of the incision or medially at the subcutaneous region at the left inframammary crease. Thesubcutaneous electrode13 is placed with a specially designed curved introducer set40 (seeFIG. 8). The introducer set comprises acurved trocar42 and a stiff curved peel awaysheath44. The peel away sheath is curved to allow for placement around the rib cage of the patient in the subcutaneous space created by the trocar. The sheath has to be stiff enough to allow for the placement of the electrodes without the sheath collapsing or bending. Preferably the sheath is made out of a biocompatible plastic material and is perforated along its axial length to allow for it to split apart into two sections. The trocar has aproximal handle41 and acurved shaft43. Thedistal end45 of the trocar is tapered to allow for dissection of asubcutaneous path33 in the patient. Preferably, the trocar is cannulated having acentral Lumen46 and terminating in anopening48 at the distal end. Local anesthetic such as lidocaine can be delivered, if necessary, through the lumen or through a curved and elongated needle designed to anesthetize the path to be used for trocar insertion should general anesthesia not be employed. The curved peel awaysheath44 has aproximal pull tab49 for breaking the sheath into two halves along itsaxial shaft47. The sheath is placed over a guidewire inserted through the trocar after the subcutaneous path has been created. The subcutaneous pathway is then developed until it terminates subcutaneously at a location that, if a straight line were drawn from the canister location to the path termination point the line would intersect a substantial portion of the left ventricular mass of the patient. The guidewire is then removed leaving the peel away sheath. The subcutaneous lead system is then inserted through the sheath until it is in the proper location. Once the subcutaneous lead system is in the proper location, the sheath is split in half using thepull tab49 and removed. If more than one subcutaneous electrode is being used, a new curved peel away sheath can be used for each subcutaneous electrode.

The S-ICD will have prophylactic use in adults where chronic transvenous/epicardial ICD lead systems pose excessive risk or have already resulted in difficulty, such as sepsis or lead fractures. It is also contemplated that a major use of the S-ICD system of the present invention will be for prophylactic use in children who are at risk for having fatal arrhythmias, where chronic transvenous lead systems pose significant management problems. Additionally, with the use of standard transvenous ICDs in children, problems develop during patient growth in that the lead system does not accommodate the growth.FIG. 9 illustrates the placement of the S-ICD subcutaneous lead system such that he problem that growth presents to the lead system is overcome. The distal end of the subcutaneous electrode is placed in the same location as described above providing a good location for the coil cardioversion/defibrillation electrode27 and the

sensing electrodes

23 and25. Theinsulated lead21, however, is no longer placed in a taut configuration. Instead, the lead is serpiginously placed with a specially designed introducer trocar and sheath such that it has numerous waves or bends. As the child grows, the waves or bends will straighten out lengthening the lead system while maintaining proper electrode placement. Although it is expected that fibrous scarring especially around the defibrillation coil will help anchor it into position to maintain its posterior position during growth, a lead system with a distal tine or screwelectrode anchoring system52 can also be incorporated into the distal tip of the lead to facilitate lead stability (seeFIG. 1). Other anchoring systems can also be used such as hooks, sutures, or the like.

FIGS. 10 and 11 illustrate another embodiment of the present S-ICD invention. In this embodiment there are two

subcutaneous electrodes

13 and13′ of opposite polarity to the canister. The additionalsubcutaneous electrode13′ is essentially identical to the previously described electrode. In this embodiment the cardioversion/defibrillation energy is delivered between the active surface of the canister and the two

coil electrodes

27 and27′. Additionally, provided in the canister is means for selecting the optimum sensing arrangement between the four

sense electrodes

23,23′,25, and25′. The two electrodes are subcutaneously placed on the same side of the heart. As illustrated inFIG. 6, onesubcutaneous electrode13 is placed inferiorly and theother electrode13′ is placed superiorly. It is also contemplated with this dual subcutaneous electrode system that the canister and one subcutaneous electrode are the same polarity and the other subcutaneous electrode is the opposite polarity.

Turning now toFIGS. 12 and 13, further embodiments are illustrated where thecanister11 of the S-ICD of the present invention is shaped to be particularly useful in placing subcutaneously adjacent and parallel to a rib of a patient. The canister is long, thin, and curved to conform to the shape of the patient's rib. In the embodiment illustrated inFIG. 12, the canister has a diameter ranging from about 0.5 cm to about 2 cm without 1 cm being presently preferred. Alternatively, instead of having a circular cross sectional area, the canister could have a rectangular or square cross sectional area as illustrated inFIG. 13 without falling outside of the scope of the present invention. The length of the canister can vary depending on the size of the patient's thorax. Currently the canister is about 5 cm to about 15 cm long with about 10 being presently preferred. The canister is curved to conform to the curvature of the ribs of the thorax. The radius of the curvature will vary depending on the size of the patient, with smaller radiuses for smaller patients and larger radiuses for larger patients. The radius of the curvature can range from about 5 cm to about 35 cm depending on the size of the patient. Additionally, the radius of the curvature need not be uniform throughout the canister such that it can be shaped closer to the shape of the ribs. The canister has an active surface,15 that is located on the interior (concave) portion of the curvature and aninactive surface16 that is located on the exterior (convex) portion of the curvature. The leads of these embodiments, which are not illustrated except for theattachment port19 and the proximal end of thelead21, can be any of the leads previously described above, with the lead illustrated inFIG. 1 being presently preferred.

The circuitry of this canister is similar to the circuitry described above. Additionally, the canister can optionally have at least one sense electrode located on either the active surface of the inactive surface and the circuitry within the canister can be programmable as described above to allow for the selection of the best sense electrodes. It is presently preferred that the canister have two

sense electrodes

26 and28 located on the inactive surface of the canisters as illustrated, where the electrodes are spaced from about 1 to about 10 cm apart with a spacing of about 3 cm being presently preferred. However, the sense electrodes can be located on the active surface as described above.

It is envisioned that the embodiment ofFIG. 12 will be subcutaneously implanted adjacent and parallel to the left anterior 5th rib, either between the 4th and 5th ribs or between the 5th and 6th ribs. However other locations can be used.

Another component of the S-ICD of the present invention is a cutaneous test electrode system designed to simulate the subcutaneous high voltage shock electrode system as well as the QRS cardiac rhythm detection system. This test electrode system is comprised of a cutaneous patch electrode of similar surface area and impedance to that of the S-ICD canister itself together with a cutaneous strip electrode comprising a defibrillation strip as well as two button electrodes for sensing of the QRS. Several cutaneous strip electrodes are available to allow for testing various bipole spacings to optimize signal detection comparable to the implantable system.

FIGS. 14-18 depict particular US-ICD embodiments of the present invention. The various sensing, shocking and pacing circuitry, described in detail above with respect to the S-ICD embodiments, may additionally be incorporated into the following US-ICD embodiments. Furthermore, particular aspects of any individual S-ICD embodiment discussed above may be incorporated, in whole or in part, into the US-ICD embodiments depicted in the following figures.

Turning now toFIG. 14, the US-ICD of the present invention is illustrated. The US-ICD consists of acurved housing1211 with a first and second end. Thefirst end1413 is thicker than thesecond end1215. This thicker area houses a battery supply, capacitor and operational circuitry for the US-ICD. The circuitry will be able to monitor cardiac rhythms for tachycardia and fibrillation, and if detected, will initiate charging the capacitor and then delivering cardioversion/defibrillation energy through the two cardioversion/

defibrillating electrodes

1417 and1219 located on the outer surface of the two ends of the housing. The circuitry can provide cardioversion/defibrillation energy in different types of waveforms. In the preferred embodiment, a 100 uF biphasic waveform is used of approximately 10-20 ms total duration and with the initial phase containing approximately ⅔ of the energy, however, any type of waveform can be utilized such as monophasic, biphasic, multiphasic or alternative waveforms as is known in the art.

The housing of the present invention can be made out of titanium alloy or other presently preferred ICD designs. It is contemplated that the housing is also made out of biocompatible plastic materials that electronically insulate the electrodes from each other. However, it is contemplated that a malleable canister that can conform to the curvature of the patient's chest will be preferred. In this way the patient can have a comfortable canister that conforms to the unique shape of the patient's rib cage. Examples of conforming ICD housings are provided in U.S. Pat. No. 5,645,586, the entire disclosure of which is herein incorporated by reference. In the preferred embodiment, the housing is curved in the shape of a 5^thrib of a person. Because there are many different sizes of people, the housing will come in different incremental sizes to allow a good match between the size of the rib cage and the size of the US-ICD. The length of the US-ICD will range from about 15 to about 50 cm. Because of the primary preventative role of the therapy and the need to reach energies over 40 Joules, a feature of the preferred embodiment is that the charge time for the therapy, intentionally be relatively long to allow capacitor charging within the limitations of device size.

The thick end of the housing is currently needed to allow for the placement of the battery supply, operational circuitry, and capacitors. It is contemplated that the thick end will be about 0.5 cm to about 2 cm wide with about 1 cm being presently preferred. As microtechnology advances, the thickness of the housing will become smaller.

The two cardioversion/defibrillation electrodes on the housing are used for delivering the high voltage cardioversion/defibrillation energy across the heart. In the preferred embodiment, the cardioversion/defibrillation electrodes are coil electrodes, however, other cardioversion/defibrillation electrodes could be used such as having electrically isolated active surfaces or platinum alloy electrodes. The coil cardioversion/defibrillation electrodes are about 5-10 cm in length. Located on the housing between the two cardioversion/defibrillation electrodes are two

sense electrodes

1425 and1427. The sense electrodes are spaced far enough apart to be able to have good QRS detection. This spacing can range from 1 to 10 cm with 4 cm being presently preferred. The electrodes may or may not be circumferential with the preferred embodiment. Having the electrodes non-circumferential and positioned outward, toward the skin surface, is a means to minimize muscle artifact and enhance QRS signal quality. The sensing electrodes are electrically isolated from the cardioversion/defibrillation electrode via insulatingareas1423. Analogous types of cardioversion/defibrillation electrodes are currently commercially available in a transvenous configuration. For example, U.S. Pat. No. 5,534,022, the entire disclosure of which is herein incorporated by reference, discloses a composite electrode with a coil cardioversion/defibrillation electrode and sense electrodes. Modifications to this arrangement are contemplated within the scope of the invention. One such modification is to have the sense electrodes at the two ends of the housing and have the cardioversion/defibrillation electrodes located in between the sense electrodes. Another modification is to have three or more sense electrodes spaced throughout the housing and allow for the selection of the two best sensing electrodes. If three or more sensing electrodes are used, then the ability to change which electrodes are used for sensing would be a programmable feature of the US-ICD to adapt to changes in the patient physiology and size over time. The programming could be done via the use of physical switches on the canister, or as presently preferred, via the use of a programming wand or via a wireless connection to program the circuitry within the canister.

Turning now toFIG. 15, the optimal subcutaneous placement of the US-ICD of the present invention is illustrated. As would be evident to a person skilled in the art, the actual location of the US-ICD is in a subcutaneous space that is developed during the implantation process. The heart is not exposed during this process and the heart is schematically illustrated in the figures only for help in understanding where the device and its various electrodes are three dimensionally located in the thorax of the patient. The US-ICD is located between the left mid-clavicular line approximately at the level of the inframammary crease at approximately the 5^thrib and the posterior axillary line, ideally just lateral to the left scapula. This way the US-ICD provides a reasonably good pathway for current delivery to the majority of the ventricular myocardium.

FIG. 16 schematically illustrates the method for implanting the US-ICD of the present invention. Anincision1631 is made in the left anterior axillary line approximately at the level of the cardiac apex. A subcutaneous pathway is then created that extends posteriorly to allow placement of the US-ICD. The incision can be anywhere on the thorax deemed reasonable by the implanting physician although in the preferred embodiment, the US-ICD of the present invention will be applied in this region. The subcutaneous pathway is created medially to the inframammary crease and extends posteriorly to the left posterior axillary line. The pathway is developed with a specially designed curved introducer1742 (seeFIG. 17). The trocar has aproximal handle1641 and acurved shaft1643. Thedistal end1745 of the trocar is tapered to allow for dissection of a subcutaneous path in the patient. Preferably, the trocar is cannulated having acentral lumen1746 and terminating in anopening1748 at the distal end. Local anesthetic such as lidocaine can be delivered, if necessary, through the lumen or through a curved and elongated needle designed to anesthetize the path to be used for trocar insertion should general anesthesia not be employed. Once the subcutaneous pathway is developed, the US-ICD is implanted in the subcutaneous space, the skin incision is closed using standard techniques.

As described previously, the US-ICDs of the present invention vary in length and curvature. The US-ICDs are provided in incremental sizes for subcutaneous implantation in different sized patients. Turning now toFIG. 18, a different embodiment is schematically illustrated in exploded view which provides different sized US-ICDs that are easier to manufacture. The different sized US-ICDs will all have the same sized and shapedthick end1413. The thick end is hollow inside allowing for the insertion of a coreoperational member1853. The core member comprises ahousing1857 which contains the battery supply, capacitor and operational circuitry for the US-ICD. The proximal end of the core member has a plurality of electronic plug connectors.

Plug connectors

1861 and1863 are electronically connected to the sense electrodes via pressure fit connectors (not illustrated) inside the thick end which are standard in the art.

Plug connectors

1865 and1867 are also electronically connected to the cardioverter/defibrillator electrodes via pressure fit connectors inside the thick end. The distal end of the core member comprises anend cap1855, and aribbed fitting1859 which creates a water-tight seal when the core member is inserted intoopening1851 of the thick end of the US-ICD.

The core member of the different sized and shaped US-ICD will all be the same size and shape. That way, during an implantation procedure, multiple sized US-ICDs can be available for implantation, each one without a core member. Once the implantation procedure is being performed, then the correct sized US-ICD can be selected and the core member can be inserted into the US-ICD and then programmed as described above. Another advantage of this configuration is when the battery within the core member needs replacing it can be done without removing the entire US-ICD.

FIGS. 19-26 refer generally to alternative S-ICD/US-ICD canister embodiments. Although the following canister designs, various material constructions, dimensions and curvatures, discussed in detail below, may be incorporated into either S-ICD or US-ICD canister embodiments, hereinafter, these attributes will be discussed solely with respect to S-ICDs.

The canisters illustrated in these Figures possess a configuration that may 1) aid in the initial canister implantation; 2) restrict canister displacement once properly positioned; 3) create a consistently focused array of energy delivered toward the recipient's heart with less disbursement to other areas of the thorax; 4) allow for good signal reception from the heart by an S-ICD system; or 5) provide significant comfort and long-term wearability in a broad spectrum of patients with differing thoracic sizes and shapes. More particularly,FIGS. 19-26 detail various material constructions, dimensions and curvatures that are incorporated within the numerous S-ICD canister designs detailed inFIGS. 19-26C.

Referring now to the particular embodiments,FIG. 19 depicts an S-ICD canister190 of an embodiment of the present invention. The shell of the S-ICD canister190 comprises a hermetically sealedhousing192 that encases the electronics for the S-ICD canister190. As with the previously described S-ICD devices, the electronics of the present embodiment include, at a minimum, a battery supply, a capacitor and operational circuitry.FIG. 19 further depicts alead electrode191 coupled to the shell of the canister through alead193. Adorsal fin197 may be disposed on thelead electrode191 to facilitate the positioning of the lead electrode.

The S-ICD devices of the present invention provide an energy (electric field strength (V/cm), current density (A/cm²), voltage gradient (V/cm) or other measured unit of energy) to a patient's heart. S-ICD devices of the present invention will generally use maximum voltages in the range of 700 V to 3150 V, requiring maximum energies of approximately 40 J to 210 J. These energy requirements will vary, however, depending upon the form of treatment, the proximity of the canister from the patient's heart, the relative relationship of the S-ICD canister's electrode to the lead electrode, the nature of the patient's underlying heart disease, the specific cardiac disorder being treated, and the ability to overcome diversion of the S-ICD electrical output into other thoracic tissues.

Ideally, the emitted energy from the S-ICD device will be directed into the patient's anterior mediastinum, through the majority of the heart, and out to the coupled lead electrode positioned in the posterior, posterolateral and/or lateral thoracic locations. Furthermore, it is desirable that the S-ICD canister190 be capable of delivering this directed energy, as a general rule, at an adequate effective field strength. In the case of a typical biphasic waveform, an effective field strength is about 3-5 V/cm over approximately 90 percent of a patient's ventricular myocardium. This delivered effective field strength should be adequate for defibrillation of the patient's heart—an intended application of an embodiment of the present invention.

Increased energy requirements necessitate larger, or alternatively, additional batteries and capacitors. The latter of these two options is often more desirable in order to reduce the overall depth of the resulting S-ICD canister190. Increasing the number of batteries and capacitors, however, will increase the length and, depending upon number and size, possibly the depth of the S-ICD canister190. Therefore, numerous S-ICD devices of varying depth, widths and lengths are manufactured to accommodate the particular energy needs of a variety of patient recipients. For example, an overweight adult male may require a larger and bulkier S-ICD canister190 than a young child. In particular, the young child is generally smaller, has a relatively lower resistance to current flow, and contains less current diverting body mass than the overweight adult male. As a result, the energy required to deliver an effective therapy to the young child's heart may be considerably less than for the overweight adult male, and therefore, the young child may utilize a smaller and more compact S-ICD canister190. In addition, one may find that individuals, despite equivalent body size, may have different therapy requirements because of differences in their underlying heart disease. This may allow some patients to receive a smaller canister compared to another patient of equal body size but with a different type of heart disease.

The spatial requirements of a resulting S-ICD canister190 are additionally dependent upon the type of operational circuitry used within the device. The S-ICD canister190 may be programmed to monitor cardiac rhythms for tachycardia and fibrillation, and if detected, will initiate charging the capacitor(s) to deliver the appropriate cardioversion/defibrillation energy. Examples of such circuitry are described in U.S. Pat. Nos. 4,693,253 and 5,105,810, and are incorporated herein by reference. The S-ICD canister190 may additionally be provided with operational circuitry for transthoracic cardiac pacing. This optional circuitry monitors the heart for bradycardia and/or tachycardia rhythms. In the event a bradycardia or tachycardia rhythm is detected, the operational circuitry delivers the appropriate pacing energy at the appropriate intervals to treat the disorder.

In additional embodiments, the operational circuitry may be: 1) programmed to deliver low amplitude shocks on the T-wave for induction of ventricular fibrillation for testing the S-ICD canister's performance; 2) programmed for rapid ventricular pacing to either induce a tachyarrhythmia or to terminate one; 3) programmed to detect the presence of atrial fibrillation; and/or 4) programmed to detect ventricular fibrillation or ventricular tachycardia by examining QRS waves, all of which are described in detail above. Additional operational circuitry, being known in the art for sensing, shocking and pacing the heart, are additionally incorporated herein as being within the spirit and scope of the present invention.

The primary function of thecanister housing192 is to provide a protective barrier between the electrical components held within its confines and the surrounding environment. Thecanister housing192, therefore, must possess sufficient hardness to protect its contents. Materials possessing this hardness may include numerous suitable biocompatible materials such as medical grade plastics, ceramics, metals and alloys. Although the materials possessing such hardnesses are generally rigid, in particular embodiments, it is desirable to utilize materials that are pliable or compliant. More specifically, it is desirable that thecanister housing192 be capable of partially yielding in its overall form without fracturing.

Compliant canister housings

192 often provide increased comfort when implanted in patient recipients. S-ICD canisters190 formed from such materials permit limited, but significant, deflection of thecanister housing192 with certain thoracic motions. Examples of permitted deflections are ones that are applied to thecanister housing192 by surrounding muscle tissue. The use of a compliant canister housing is particularly beneficial in canister housing embodiments that extend over a significant portion of a patient's thorax. The compliant material in these embodiments may comprise a portion of the canister housing, or alternatively, may comprise the canister housing in its entirety. The correct material selection (or combination thereof), therefore, is helpful in eliminating patient awareness of the device and in improving the long-term wearability of the implanted device.

Materials selected for thecanister housing192 should further be capable of being sterilized. Often commercial sterilization processes involve exposure to elevated temperatures, pressures or chemical treatments. It is important, therefore, that the materials used in forming the canister housing be capable of withstanding such exposures without degrading or otherwise compromising their overall integrity.

Polymeric materials suitable for thecanister housing192 of the present invention include polyurethanes, polyamides, polyetheretherketones (PEEK), polyether block amides (PEBA), polytetrafluoroethylene (PTFE), silicones, and mixtures thereof. Ceramic materials suitable for thecanister housing192 of the present invention include zirconium ceramics and aluminum-based ceramics. Metallic materials suitable for thecanister housing192 of the present invention include stainless steel, and titanium. Alloys suitable for thecanister housing192 of the present invention include stainless steel alloys and titanium alloys such as nickel titanium. In certain embodiments of the present invention, classes of materials may be combined in forming thecanister housing192. For example, a nonconductive polymeric coating, such as parylene, may be selectively applied over a titaniumalloy canister housing192 surface in order to allow only a specific surface area, such as that at the undersurface of the duckbill distal end, to receive signals and/or apply therapy.

In general, it is desirable to maintain the size of the S-ICD canister housing192 under a total volume of approximately 50 cubic centimeters. In alternative embodiments of the present invention, it is desirable to maintain the size of the S-ICD canister housing192 under a total volume of approximately 100 cubic centimeters. In yet alternative embodiments of the present invention, it is desirable to maintain the size of the S-ICD canister housing192 under a total volume of approximately 120 cubic centimeters.

Moreover, it is additionally desirable to maintain the total weight of the S-ICD canister190, as a whole (including the canister housing, operational circuitry, capacitors and batteries), under approximately 50 grams. In alternative embodiments of the present invention, it is desirable to maintain the total weight of the S-ICD canister190 under approximately 100 grams. In yet alternative embodiments of the present invention, it is desirable to maintain the total weight of the S-ICD canister190 under approximately 150 grams.

Maintaining the weight and size within the above identified parameters is primarily for patient comfort depending upon the shape and location of the device. The implantation of an S-ICD canister190 is a long-term solution to heart dysfunction, and as such, will ideally remain in the patient until the device's batteries need replacement or an alternative therapy eventually leads to its removal. Accordingly, a considerable amount of engineering is devoted to minimizing discomfort associated with the installed device.

Weight and size considerations are particularly important to younger patient recipients. Children possessing ICDs are more likely to be cognitive of any additional weight or bulkiness associated with heavier and/or larger devices. The present invention overcomes these problems by designing an S-ICD canister190 that takes into consideration the concerns of these smaller sized patient recipients. For example, lighter materials may be utilized to minimize discomfort associated with heavier materials. Furthermore, the S-ICD canister190 (length, width and depth) in its entirety, or only a portion thereof, may be modified in order to accommodate a variety of sized patient recipients. For example, the shape of the S-ICD canister housing192 may also be manufactured in a variety of anatomical configurations to better insure comfort and performance in younger children or smaller adults, throughout the life of their S-ICD canisters190. In order to accommodate certain patients, a physician may place thecanister190 posteriorly with the lead electrode positioned anteriorly with the patient's body, the reverse of the canister's190 usual positioning. Thiscanister190 placement is particularly useful when implanted in very small children.Such canister190 placement generally optimizes comfort for these smaller stature recipients. Moreover, the shape of thecanister190 may be altered specifically to conform to a female's thorax, where breast tissue may alter comfort and performance requirements.

Referring now to specific portions of thecanister housing192,FIG. 19 depicts acanister housing192 in accordance with one embodiment of the present invention having atop surface194, abottom surface196 and surroundingsides198 connecting these two surfaces. The S-ICD canister housing192 depicted inFIG. 19 further includes adistal end200 and aproximal end202. In particular canister housing embodiments, thecanister housing192 may lack a proximal end and a distal end.

Thetop surface194 of thecanister housing192 is generally smooth and void of appendages and apertures. The smoothtop surface194 enables the S-ICD canister190 to advance effortlessly through the subcutaneous tissues during an implantation procedure. Smoothing thetop surface194 reduces the coefficient of friction of the S-ICD canister190. Such measures reduce abrasion, and concurrently, also reduce inflammation associated with the device's insertion and advancement. The benefits of a reduction in surface friction also continue on long after implantation through a significant reduction in inflammation and soreness, lending to an overall heightened feeling of wearability and comfort.

In alternative embodiments, thetop surface194 of thecanister housing192 may include one or more apertures, sensors, electrodes, appendages, or a combination thereof. Apertures on thetop surface194 of thecanister housing192 are generally in the form of aconnection port203, or multiple connection ports, for coupling ancillary devices to the canister itself. More specifically, theconnection ports203 couple the operational circuitry housed within the canister to these ancillary devices, as well as to alead electrode191.Connection ports203 may be positioned anywhere along thecanister housing192, however, in particular embodiments, theconnection ports203 are located at thedistal end200 orproximal end202 of thecanister housing192. Theconnection ports203 may additionally be positioned along the canister housing'ssides198 andbottom surface196.

In yet another embodiment,connection ports203 are located at both thedistal end200 and theproximal end202 of thecanister housing192.Positioning connection ports203 at both the canister'sdistal end200 and theproximal end202 may enhance the care provided by the S-ICD canister190. In particular, this canister arrangement allows the operational circuitry in the S-ICD canister190 to utilize multiple electrodes and sensors to best regulate and treat the particular condition experienced by the patient recipient. Examples of ancillary devices suitable for attachment include alead193, such as a lead for sensing, shocking and pacing. Additional ancillary devices suitable for attachment to the S-ICD canister190, being known in the art, (e.g., heart failure monitoring sensors) are additionally incorporated as being within the spirit and scope of the present invention.

Thetop surface194 of thecanister housing192 may additionally include particular appendages. Appendages are especially useful in anchoring thecanister housing192 in a fixed relative position, or alternatively, in advancing thecanister housing192 within the patient recipient. An example of an appendage that may be incorporated into thetop surface194 of thecanister housing192 is an extending fin. A fin-like appendage may extend from thecanister housing192 in order to better direct the S-ICD canister190 during the implantation procedure. In this capacity, the extended fin acts as a rudder preventing the advancing S-ICD canister190 from deviating from its desired path. The extended fin may additionally aid in preventing the S-ICD canister190 from displacing from its original position after implantation—particularly in the direction perpendicular to the fin's length. Extending fins suitable for the present invention may extend the entire length of thecanister housing192, or alternatively, a segment of the length. Additionally, extending fins may be disposed on thebottom surface196 of thecanister housing192 in order to provide similar functions.

Appendages may also aid physicians in advancing the S-ICD canister190 to a desired location within the patient. Motility-enhancing appendages enable the physician to push, pull or otherwise direct the S-ICD canister190 in a particular fashion throughout the patient's body. Such motility-enhancing appendages also may be composed of absorbable material, like mannitol, to allow positioning of the device but without the long term potential for irritation. During the procedure, a physician generally attaches a medical instrument to the motility-enhancing appendage. This attachment step may occur either before or after the S-ICD canister190 has been inserted within the patient. An example of one medical instrument capable of attaching to the motility-enhancing appendage is a hemostat. Other similar medical instruments, known to those skilled in the art, may also be utilized in this attachment step. The physician then advances the hemostat in a desired direction to properly seat the S-ICD canister190 within the patient's body.

The surroundingsides198 of thecanister housing192 are generally smooth and substantially rounded between thetop surface194 and thebottom surface196 of thecanister housing192. Smoothing the side surfaces198 aids in the insertion of the S-ICD canister190 during the implantation procedure. More specifically, smoother side surfaces198 permit the S-ICD canister190, as a whole, to slide easily through the surrounding bodily tissue while minimizing abrasion. In addition, rounded, smooth transition surfaces allow the surrounding tissues to better conform to the presence of the device making the device more comfortable to the patient during chronic implantation.

In contrast, sharp edge formations may have the tendency to ablate, or at a minimum, irritate the surrounding tissue during the implantation process. Subsequent tissue irritation may also occur long after the implantation process. Minor fluctuations in the positioning of a sharp edged canister may cause an inflammatory response in the surrounding tissue. These minor fluctuations are often the result of simple day-to-day movements. Movement of the arms, bending at the waist and rotation of the torso are all daily activities that may cause surrounding bodily tissue to chafe against the installed canister. Smoothing these edges, however, would greatly reduce tissue abrasion, and thereby, reduce the soreness and discomfort associated with the implanted S-ICD canister190.

Referring now toFIG. 20, thebottom surface196 of the S-ICD canister190 ofFIG. 19 is shown. In particular, anelectrode204 possessing an electrically conductive surface is depicted within the confines of, and hermetically sealed within, the S-ICD canister housing192. Although anelectrode204 is specifically illustrated, any sensor capable of receiving physiological information and/or emitting an energy may be similarly situated on thecanister housing192. For example, a sensor may be located on thecanister housing192 that may monitor a patient's blood glucose level, respiration, blood oxygen content, blood pressure and/or cardiac output.

Specifically with reference toFIG. 20, the exposedelectrode204 is electrically coupled to the operational circuitry encased within thecanister housing192. Theelectrode204, therefore, performs many of the functions defined by the operational circuitry's programming. More specifically, theelectrode204 is the vehicle that actually receives the signals being monitored, and/or emits the energy required to pace, shock or otherwise stimulate the heart. Although only asingle electrode204 is shown for illustrative purposes, certain S-ICD canister embodiments190 may be manufactured with multiple electrodes. For these embodiments, the multiple electrodes are often task specific, wherein eachelectrode204 performs a single function. In alternate embodiments, asingle electrode204 may perform both monitoring and shocking functions.

Theelectrodes204 are generally positioned at the

ends

200 and202 of thecanister housing192. In the S-ICD canister190 depicted inFIG. 20, theelectrode204 is placed at thedistal end200 of thecanister housing192. Although theelectrode204 is positioned in close proximity to thedistal end200, theside198 of thecanister housing192 nearest thedistal end200 should generally refrain from exposing any portion of the electrically conductive surface of theelectrode204. Additionally, although the electrode is generally planar, in particular embodiments, the electrode may possess a convex or concave curved shape.

The size of the electrically conductive surface of anelectrode204, in one particular embodiment, is approximately 500 square millimeters in area. In alternate embodiments, it is desirable to maintain the size of the electrically conductive surface between approximately 100 square millimeters and approximately 2000 square millimeters in area. As with the size of thecanister housing192, the size of the electrically conductive surface may vary to accommodate the particular patient recipient. Furthermore, the shape and size of anelectrode204 may vary to accommodate the placement of theelectrode204 on thecanister housing192. The shape and size of an electrode may also be varied to adapt to specified diagnostic and therapeutic functions performed by thecanister190. For example, the electrode's204 size and shape may be altered to minimize energy loss to surrounding bodily tissues, or for minimizing the diversion of current away from the heart.

One factor in minimizing current diversion is in maintaining an equal current density distribution throughout an electrode's204 conductive surface. A controlling factor in an electrode's204 current density distribution is the electrode's204 overall shape.Certain electrode204 shapes draw current to particular areas on the electrode's204 conductive surface (e.g., sharp angles). As a result, theseelectrodes204 create an unequal current density distribution.Electrodes204 possessing sharp corners, for example, may have higher current densities in the regions defined by the sharp corner. This unequal current density distribution results in confined “hot spots”. The formation of hot spots may be desirable and intentional, such as when attempting to increase current density adjacent to the sternum. On the other hand, hot spots may be undesirable as these high current density locations may scorch or singe surrounding tissue during the electrode's204 emission of electrical energy. Moreover,electrodes204 possessing numerous hot spots on the electrode's204 conductive surface consequently generate areas of low current density—or “cold spots”. This unequal distribution may render theelectrode204, as a whole, highly ineffective.

Electrode

204 embodiments of the present invention, in contrast, are substantially rounded. In particular, regions of theelectrode204 traditionally possessing sharp corners are rounded to prevent extreme hot spots. Nevertheless, the distal most segment of theelectrode200 is slightly angulated in order to modestly concentrate current at the tip, and therefore, direct current more through the mediastinum and into the patient's heart.

Another controlling factor in an electrode's204 current density distribution is the electrode's204 overall size. The relatively small conductive surfaces ofelectrodes204 of the present invention, as discussed above, minimize the likelihood of forming either hot or cold spots. Larger electrodes, in contrast, possess large surface areas that may be more prone to generate more regions of unequal current distribution.

As discussed above,electrodes204 may vary in shape and size to accommodate an assortment ofcanister housing192 designs. For illustrative purposes,FIG. 20 andFIGS. 23A-25A show various electrode shapes disposed uponvarious canister housings192. Thecanister housings192 depicted in these figures, however, are not limited to the electrode shape specifically illustrated.

Theelectrode204 depicted inFIG. 20 is “thumbnail” shaped. Thedistal end margin206 of this shapedelectrode204 generally follows the outline of the roundeddistal end200 of thecanister housing192. As theelectrode204 moves proximally along the length of thecanister housing192, the conductive surface terminates. In the thumbnail embodiment, the electrode's conductive surface is generally contained within the rounded portions of thedistal end200 of thecanister housing192. In alternate embodiments, the electrode's conductive surface may extend proximally further within thecanister housing192. In yet another thumbnail shaped electrode embodiment, the margins of the electrode's conductive surface refrain from following the exact rounded contour of thecanister housing192.

A “spade” shapedelectrode236 is depicted inFIG. 23A. The distal end of the spade shaped electrode also generally follows the outline of the roundeddistal end234 of thecanister housing220. As the spade shapedelectrode236 moves proximally along the length of thecanister housing220, the conductive surface terminates in a rounded proximal end. Similar to the thumbnail embodiment described above, the spade shaped electrode's conductive surface is generally contained within thedistal end234 of thecanister housing220. In alternate embodiments, the spade shape electrode's conductive surface may extend proximally further over or within thecanister housing220. In yet another spade shapedelectrode236 embodiment, the margins of the spade shaped electrode's conductive surface refrain from following the exact rounded contour of thecanister housing220, but substantially form a spade shaped configuration.

A circular shapedelectrode238 is illustrated inFIG. 23B.

A rectangular shapedelectrode246 is shown inFIG. 24A. Rectangular shapedelectrodes246 also incorporate electrodes that are substantially rectangular in shape. In particular toFIG. 24A, the corners of the rectangular shapedelectrode246 are rounded. Moreover, one margin of the rectangular shaped electrode's conductive surface generally follows the rounding of thedistal end246 of thecanister housing241.

A triangular shapedelectrode254 is depicted inFIG. 24B. Triangular shapedelectrodes254 also incorporate electrodes that are substantially triangular in shape. In particular toFIG. 24B, the corners of the triangularshaped electrode254 are rounded.

A square shapedelectrode257 is depicted inFIG. 24C. Square shapedelectrodes257 also incorporate electrodes that are substantially square in shape. In particular toFIG. 24C, the corners of the square shapedelectrode257 are rounded.

An ellipsoidal shapedelectrode268 is depicted inFIG. 25A. The distal end of the ellipsoidal shapedelectrode268 generally follows the outline of the roundeddistal end264 of thecanister housing260. As the ellipsoidal shapedelectrode268 moves proximally along the length of thecanister housing260, the conductive surface elongates and then again reduces in length to form a rounded proximal end. Similar to the thumbnail and spade shaped embodiments described above, the ellipsoidal shaped electrode's conductive surface is generally contained within thedistal end264 of thecanister housing260. In alternate embodiments, the ellipsoidal shape electrode's conductive surface may extend proximally further within thecanister housing260. In yet another ellipsoidal shapedelectrode264 embodiment, the margins of the ellipsoidal shaped electrode's conductive surface refrain from following the exact rounded contour of thecanister housing260, but substantially form an ellipsoidal shaped configuration.

Energy emissions from any of the above describedelectrodes204 generally follow a path of least resistance. The intended pathway of the emission, therefore, may not necessarily be the pathway that the emission ultimately travels. This is particularly a problem with emissions made within the human anatomy where tissue conductivities are highly variable and tissue dependent. Obstructing, or low conductivity tissues like bone material, fat, and aerated lung may all redirect released energy away from the heart. Alternatively, surrounding non-cardiac striated muscle tissue, being generally a high conductivity tissue, may divert energy emissions away from the heart. This is a particular concern for the pectoralis, intercostal, and latissimus dorsus musculature, as well as other thoracic, non-cardiac musculature found between the treating electrodes of the S-ICD. Since the S-ICD canister190 of the present invention does not directly contact the heart muscle itself, such low and high conductivity tissues will impede and/or shunt a percentage of the emissions from the present invention'selectrode204—permitting the heart to receive a fraction of the total emitted energy.

The present invention minimizes the effect of impeding and/or obstructing tissues by designing anelectrode204 andcanister housing192 capable of focusing the electrode's field or array of emitted energy. Focusing the electrode's array of energy into a highly concentrated beam enables the resulting beam to be only minimally impeded or shunted away by any surrounding bodily tissue. This focused array, therefore, delivers more of the originally emitted energy directly into the mediastinum, and subsequently, into the intended heart muscle than would otherwise occur if the entire canister, or a majority of the canister, were electrically active—as is the case with standard transvenous ICD systems. The present invention provides anelectrode204 andcanister housing192 design that creates a consistently focused array of energy directed toward the chambers of a recipient's heart.

Generally, it is desirable to have the electrode's longest conductive surface plane positioned perpendicular to the extending ribs within a recipient's rib cage. Aligning theelectrode204 in this manner removes the longest conductive plane from possibly extending directly over any one particular rib. If the longest conductive surface were to extend along the length of a rib, a greater percentage of emitted energy would be distributed through the rib material, and consequently, may fail to reach the heart muscle. When aligned perpendicular to the ribs, only a portion of the conductive surface is directly over any particular rib. This alignment permits only a small percentage of the emitted energy to be obstructed by the impeding rib material. Therefore, in particular S-ICD canister190 embodiments that extend parallel with a recipient's rib cage, thewidth205 of the electrode's conductive surface is approximately greater than or equal to thelength207 of the electrode's conductive surface. Thiselectrode204 sizing is best illustrated with reference toFIG. 20. The conductive surface of the thumbnail-shaped electrode inFIG. 20 is depicted as both shallow and wide. In contrast, S-ICD canister190 embodiments that extend perpendicular with a recipient's rib cage can have their conductive surface'slength207 being greater than their conductive surface'swidth205. The appropriate S-ICD canister190 alignment, and subsequently theappropriate electrode204 alignment, is determined by the style of S-ICD canister190 chosen for the patient recipient.FIGS. 23A-26C illustrate numerous S-ICDcanister housing embodiments192 for properly positioning anelectrode204 over a recipient's heart. The embodiments depicted, however, are for illustrative purposes only, and are not intended to limit the scope of the present invention.

Another solution to the problem of thoracic tissues interfering with energy delivery is by designing acanister housing192 that may be strategically positioned in close proximity to the patient's heart. One embodiment of the present invention possesses acurved canister housing192 that enables the S-ICD canister190 to be advanced just over the patient recipient's ribcage. Moreover, in another embodiment, the curvature of the S-ICD canister190 directly mimics the natural curvature of the ribcage.

Referring now toFIG. 21, the S-ICD canister190 ofFIG. 19 is shown from the side.FIG. 21 shows the S-ICD canister'stop surface194, thebottom surface196 and theside198 of thecanister housing192. In the embodiment depicted, both thetop surface194 and thebottom surface196 of thecanister housing192 are curved. In fact, throughout most of theproximal end202 of thecanister housing192, the curvature is generally similar, and indeed can be identical, between thetop surface194 and thebottom surface196. In alternative embodiments of the present invention, thetop surface194 may be generally planar while thebottom surface196 is curved. In yet another embodiment of the present invention, thetop surface194 may be curved and thebottom surface196 is generally planar.

Referring back to the embodiment depicted inFIG. 21, the curvatures between thetop surface194 and thebottom surface196 are shown differing toward thedistal end200 of thecanister housing192. At the S-ICD canister'sdistal end200, the canister housing'stop surface194 curvature tapers downwardly toward the canister'sbottom surface196. This tapering causes thedistal end200 of thecanister housing192 to be narrower (of a decreased depth) than the canister'sproximal end202. In certain embodiments, this tapering in depth may be gradual throughout the length of the canister'shousing192, or alternatively, the tapering may be confined to a particular area.

Tapering the depth of thecanister housing192 may improve the overall performance of the S-ICD canister190. In particular, a tapereddistal end200 may aid in insertion and advancement of the S-ICD canister190 within the patient recipient's body. A tapereddistal end200 enables the S-ICD canister190 to easily traverse through narrow subcutaneous spaces. In particular, a physician generally tries to create a passageway into the patient's body that is appropriately sized for the canister, especially in regard to positioning the distal segment of the canister with the end containing the electrode in close proximity to the sternum. Tapering the distal end of the canister eliminates unnecessary trauma to the patient in the tight spaces adjacent to the sternum. For larger canisters, however, this tight subcutaneous space is difficult to traverse. Subsequently, these larger canisters cause the physician to undertake extensive sharp and blunt dissection of the patient's tissues in order to place the larger canister in the desired location. Regardless of the extent of the dissection, however, larger non-tapered distal segments may prove extremely uncomfortable if forced into a parasternal position to satisfy the needs of focusing energy through the mediastinum, and subsequently, to the patient's heart.

In contrast, embodiments of the present invention havingnarrow canister housings192 may easily traverse such passageways. Moreover, tapering the S-ICD canister'sdistal end200 further streamlines thecanister housing192, and therefore, enhances the ease of the implantation procedure. Tapering the S-ICD canister'sdistal end200 is particularly important when positioning the distal end of the canister housing as near the left border of a patient's sternum as possible. Thiscanister housing192 placement optimizes energy delivery to the mediastinum, and therefore, to the patient's heart.

The depth of thecanister housing192 is shown as being very narrow as to the canister housing'slength207. The canister's housing depth is less than approximately 15 millimeters. In alternate embodiments, the depth of the canister's housing depth is approximately 5 millimeters to approximately 10 millimeters. At the tapereddistal end200, the canister housing may have a depth of approximately 1-4 millimeters.

In certain embodiments of the present invention, it is desirable to position the S-ICD canister190 in close proximity to the patient recipient's heart, without directly contacting the heart. A favored location for this S-ICD canister190 placement is just over the patient's ribcage. More particularly, in certain embodiments it is favored to place the S-ICD canister190 just to the left of, and adjacent to, the sternum with a segment at thedistal end200 containing theelectrode204 closest to the sternum. FIG.22 depicts the placement of the S-ICD canister190 according to one embodiment of the present invention with the lead electrode traversing the subcutaneous tissues laterally toward the axilla and then posteriorly to “catch” the current as it is emitted fromelectrode204 parasternally and anteriorly toward thelead electrode191 as it receives current exiting the posterior mediastinum and paraspinal tissues.

During the implantation procedure, asingle incision210 is made in the left anterior axillary line approximately at the level of the cardiac apex, or around the fifth to the sixth intercostal space. The location of thissingle incision210 enables the physician to position both the S-ICD canister190 and the canister's ancillary devices (e.g., pacing leads, shocking leads, etc.) from thissingle incision210. Once thisincision210 is made, the physician may insert surgical instruments or a specially designed tool (not shown) through theincision210 to shape a passageway for the S-ICD canister190 to navigate. Although a tool may be utilized in particular embodiments, a tool is not required—standard surgical instruments, together with the general shape of the S-ICD canister190, are sufficient to facilitate proper positioning of the device in the left anterior thorax as adjacent as possible to the sternum.

In particular embodiments, a physician advances both the S-ICD canister190 and thelead electrode191 within the patient to form a depolarization vector with respect to the patient'sheart218. The depolarization vector is a vector having an origin, a first end point and a second end point.

In one embodiment, the origin of the depolarization vector originates approximately within the chambers of the patient'sheart218. Similarly, the first vector end point comprises the S-ICD canister electrode's204 positioning with respect to the patient'sheart218. Finally, the second vector end point comprises the lead electrode's191 positioning with respect to the patient'sheart218. In alternate embodiments, the second vector end point comprises a second canister electrode.

The lead electrode may be positioned at various positions within the body because the length of thelead193 may be varied. For example, S-ICD devices of the present invention may have leads with lengths between 5 centimeters and 55 centimeters. Therefore, the S-ICD canister190 andlead electrode191 of the present invention may create numerous depolarization vectors.

In particular embodiments, a degree of separation of 180 degrees or less exists between the S-ICD canister electrode204 and thelead electrode191. In alternative embodiments, the degree of separation between the S-ICD canister electrode204 and thelead electrode191 is approximately 30 degrees to approximately 180 degrees.

In order to obtain the desired degree of separation for the depolarization vector, generally one device (either the S-ICD canister190 or the lead electrode191) must be advanced anteriorly while the other device is advanced posteriorly from theinitial incision210. Accordingly, when the S-ICD canister190 is advanced subcutaneously and anteriorly from theincision210, thelead electrode191 must be advanced subcutaneously and posteriorly from theincision210. With this particular embodiment, a physician may advance the S-ICD canister190 medially toward the patient's left inframammary crease to a location proximate the patient'ssternum212.

Alternatively, the physician may advance, and subsequently position the S-ICD canister190 within the anterior portion of the patient'sribcage216. This anterior placement may further include the patient's left parasternal region, an anterior placement within the region of the patient's third and the patient'stwelfth rib214, or generally anysubcutaneous ribcage216 placement anterior to the patient'sheart218. In order to complement the S-ICD canister's190 placement and obtain the correct depolarization vector, thelead electrode191 must be advanced posteriorly toward the paraspinal or parascapular region of the patient'sribcage216.

In another embodiment of the present invention, the spatial positioning of the S-ICD canister190 and thelead electrode191, described in detail above, are reversed.

Referring back toFIG. 21, the curvature of particular S-ICD canister embodiments190 may be designed to generally mimic the natural curvature of a patient'sribcage216. These S-ICD canister embodiments190 restrict canister displacement and heighten comfort for the patient implanted with the S-ICD canister190. The anatomical shape of a patient recipient'sribcage216 varies. The present invention includes numerous S-ICD canister housing192 curvatures to accommodate these varying shapes. In particular, the present invention includes S-ICD canisters190 sized and shaped to properly fit children, as well as ones to properly fit fully developed adults.

The curvature of thecanister housing192 is generally arc-shaped. The degree of curvature for any particular embodiment of the present invention is measured through a curvature vector theta (θ). The curvature vector θ is a vector having anorigin199, a first end point and a second end point.

In one embodiment, theorigin199 of the curvature vector θ originates approximately at the center of the S-ICD canister190 (lengthwise). The first vector end point in this embodiment comprises thedistal end200 of the S-ICD canister190 and the second vector end point comprises theproximal end202 of the S-ICD canister190. In particular embodiments, the curvature vector θ possesses a degree of separation between 30 degrees and 180 degrees. For example, acanister housing192 having a degree of separation of 180 degrees is planar. Decreasing the degree of curvature θ causes the canister housing to become more arcuate in shape.

In alternative embodiments, theorigin199 of the curvature vector θ may originate at a point other than the center of the S-ICD canister190.Origins199 shifted from the center of the S-ICD canister190 produce regions of greater curvature, as well as areas of lesser curvature, in the same S-ICD canister190. Similarly, an S-ICD canister190 may possess multiple curvature vectors θ havingorigins199 throughout the length of the S-ICD canister190. Multiple curvature vectors θ produce various non-linear or nonsymmetrical curves that, in certain circumstances, remain generally arc-shaped. Canister housings possessing multiple curvature vectors θ are particularly suitable for S-ICD canister190 placement near the patient's sides (generally in the area under the patient's arms where the thorax has a more marked degree of curvature).Canister housings192 incorporating a nonsymmetrical curvature are generally longer S-ICD canisters190 that span over the front and sides of the patient's ribcage. In particular, these S-ICD canisters190 span areas of theribcage216 that are generally planar (around the patient's sternum212), as well as areas that are highly curved (generally in the area under the patient's arms).

Curved canister housings

192 are generally for S-ICD canisters190 that extend lengthwise, or approximately horizontally, along the length of the ribs in theribcage216. For certain embodiments, however, it is desired to orient the length of the S-ICD canister190 to be perpendicular to the length of the ribs in theribcage216. A perpendicularly orientated S-ICD canister190 generally requires very little, if any, curvature to conform to theribcage216.

FIGS. 23A-26C depict particular S-ICD canister190 designs. In each of these particular S-ICD canister designs, the various material constructions, dimensions and curvatures, discussed in detail above, may be incorporated within each individual S-ICD canister design. Furthermore, particular aspects of any individual S-ICD canister design may be incorporated, in whole or in part, into another depicted S-ICD canister design.

Turning now toFIG. 23A, an S-ICD canister220 having a duckbill-shapedcanister housing222 is shown. The duckbill-shapedcanister housing222 has aproximal end226 and adistal end234. Theproximal end226 of the duckbill-shapedcanister housing222 further includes amain housing member228 and adistal housing member230. Thedistal housing member230 is an elongated segment extending distally from the distal end of themain housing member228. Although the two segments differ in their size and shape, thedistal housing member230 andmain housing member228 are generally contiguously and fluidly attached to one another and may be formed from a single mold. In alternative embodiments, however, thedistal housing member230 may be hinged to themain housing member228. Thedistal housing member230 also generally comprises a material that is similar in composition to that forming themain housing member228. In alternate embodiments, however, thedistal housing member230 may include a material that possesses enhanced electrically insulated characteristics.

Themain housing member228 generally encases the operational circuitry, batteries and capacitors of the duckbill-shaped S-ICD canister220. The width and length of themain housing member228 enable themain housing member228 to accommodate batteries and capacitors for delivering a shocking energy of approximately 50 J of energy, 75 J of energy, 100 J of energy, 125 J of energy, 150 J of energy and 200 J of energy.

Although a specific number of batteries and capacitors are required for delivering these charges, their positioning within thecanister housing222 is highly modifiable. More specifically, the width of themain housing member228 may be altered to accommodate a longer or shorter canister. For example, the width of themain housing member228 may be increased in order to obtain amain canister housing228 of decreased length. Modification of the sizing and orientation of themain housing member228 allow manufacturers to create a variety of differing sized duckbill-shaped S-ICD canisters220. Increased specificity in the canister housing's shape and size enhance the comfort and wearability for the patient recipient.

In general, the width of themain housing member228 is approximately 10 cm wide or less. Likewise, the length of themain housing member228 is approximately 20 cm long or less. In particular embodiments the width of themain housing member228 is 4 cm. In an alternative embodiment, the width of themain housing member228 is 8 cm.

Thedistal housing member230 is an elongated segment of canister housing that possesses a width that differs from that of themain housing member228. The distal housing member's width decreases as thedistal housing member230 extends distally. This tapering in width results in the formation of ashoulder region232. In particular embodiments, the rate with which the width decreases as theproximal housing member230 extends distally is constant. In alternate embodiments, the rate is variable. A variablerate shoulder region232 taper proceeds at a rate of tapering where a unit of tapering width is not directly related to a unit of length in the distal direction. In either of the embodiments, however, bilateral symmetry is maintained throughout the length of thedistal housing member230.

Theshoulder region232 is a generally rounded and smooth region of thecanister housing222. As discussed in detail above, rounding the edges along the canister's surface enhances insertion of the S-ICD canister220. The rounded edges also reduce abrasion and inflammation associated with short-term and long-term wearability.

Extending distally beyond theshoulder region232 is thedistal head224 of thedistal housing member230. Thedistal head224 is the distal termination point of the duckbill-shaped S-ICD canister220. Thedistal head224 includes a generally rounded end. In one embodiment, illustrated inFIG. 23B, thedistal head224 has a width greater than the width at a location within theshoulder region232 of thedistal housing member230. In alternative embodiments, the distal head's width is equal to or less than the width at any point in theshoulder region232 of thedistal housing member230, as illustrated in23A.

The length of the duckbill-shaped S-ICD canister220 may depend highly upon the shape and size of thedistal housing member230. In particular embodiments, the duckbill-shaped S-ICD canister220 is approximately 30 centimeters long or less. In alternative embodiments, the duckbill-shaped S-ICD canister220 is approximately 10 centimeter or less. In particular embodiments, the length of the duckbill-shaped S-ICD canister220 may be curved, or alternatively, or a portion of the length (i.e., theshoulder region232 and distal head224) are curved.

Theelectrode236 for the duckbill-shaped S-ICD canister220 is generally seated within a portion of thedistal housing member230.FIG. 23A diagrams in phantom the approximate location of anelectrode236 on the duckbill-shapedcanister housing222. Although theelectrode236 is depicted as generally circular in shape (inFIG. 23B), the electrode may also be “spade shaped” (depicted inFIG. 23A), thumbnail shaped, square, rectangular, triangular or ellipsoidal. Theelectrode236 is electrically coupled to the operational circuitry within themain housing member228 of the S-ICD canister220.

In certain embodiments of the present invention, an associated feature of theelectrode236 at the distal end is the presence of a margin ofinsulated material237 around theactive electrode236. The margin ofinsulated material237 may aid in directing emitted energy from theelectrode236 inwardly toward the patient's heart instead of dispersing energy outward toward the patient's chest wall. This margin ofinsulated material237 typically ranges from 1-5 mm in width and may extend to the margin of the housing. Moreover, in certain embodiments, the margin ofinsulated material237 comprises a ceramic material or other non-conductive material designed to facilitate focusing of current inward toward the heart.

In certain embodiments of the present invention, the electronic components (e.g., circuitry, batteries and capacitors) of the S-ICD canister220 are generally absent from thedistal housing member230. As such, the depth of thedistal housing member230 may be greatly reduced. In these embodiments, a depth of approximately 1 millimeter may be obtained at thedistal head224 of the duckbill-shaped S-ICD canister220.

The duckbill-shapeddistal housing member230 enhances navigation during canister implantation. Thedistal head224 of thedistal housing member230 is blunt at its end to reduce trauma suffered to surrounding tissue during the S-ICD canister's advancement or during chronic implantation. Similarly, the narrower distal head224 (width-wise and depth-wise) is easier to control during the advancement procedure. The smallerdistal head224 also enables a physician to navigate the smaller and more compact tissues adjacent to the sternum, which a larger head might otherwise find unobtainable. Moreover, the narrowerdistal head224 may be advanced to a location in close proximity to the patient recipient'sheart218 without concern of distorting or stressing the skin in the left parasternal region.

The closer theelectrode236 is to the patient'sheart218, the less energy is required to achieve an adequate electric field or current density to defibrillate the heart. A desirable anatomical position for reducing this energy requirement is just lateral to thesternum212 of the patient. The area surrounding the patient'ssternum212 generally lacks a considerable accumulation of bodily tissue. Thus, subcutaneous S-ICD canister190 positioning over thesternum212, or some other location just over therib cage216, provides a significant lessening of the required energy due to proximity to theheart218 and a reduction in impeding surrounding tissue. Positioning an ICD canister of normal contour in this area has proven difficult, however, and is additionally aesthetically displeasing. The reduced profile of the duckbill-shaped S-ICD canister220, however, provides suchoptimal electrode236 placement in a more aesthetically and less physically obtrusive manner.

Structurally, a reduction in the energy requirement frees space within thecanister housing222. This space was previously occupied by batteries and capacitors needed for the higher energy requirements. This space, however, is no longer required. The duckbill-shaped S-ICD canister220, therefore, can be smaller in length, width and depth. Eliminating batteries and capacitors and most circuitry in this space also reduces the weight of the present invention. As described in detail above, reducing the weight of the S-ICD canister enhances patient recipient comfort.

FIG. 24A illustrates another embodiment of an S-ICD canister having a generally rectangular-shapedcanister housing240. The rectangular-shapedcanister housing240 includes atop surface241, a bottom surface (not shown) and surroundingsides248 connecting these two surfaces. The rectangular-shapedcanister housing240 further includes adistal end242 and aproximal end244. Theelectrode246, shown in phantom, is generally positioned at either thedistal end242 or theproximal end244 of thecanister housing240. In alternative embodiments, the rectangular-shapedcanister housing240 may include two ormore electrodes246. When two electrodes are utilized, one electrode is positioned at thedistal end242 of thecanister housing240 while the second electrode is positioned at theproximal end244 of thecanister housing240.

The length of the rectangular-shapedcanister housing240 is approximately 30 centimeters long. In alternative embodiments, the rectangular-shapedcanister housing240 is approximately 10 centimeter long or less. The width of the rectangular-shapedcanister housing240 is approximately 3 centimeters to approximately 10 centimeter wide.

FIGS. 24B and 24C depict additional embodiments of an S-ICD canister having a generally square-shapedcanister housing250. The square-shapedcanister housing250 includes atop surface251, a bottom surface (not shown) and surroundingsides252 connecting these two surfaces. Thesides252 of the square-shaped canister housing are generally of the same length. Theelectrode254, shown in phantom, is generally positioned in the center and to one side of the square-shapedcanister housing250. A triangular shapedelectrode254 is specifically illustrated at the corner of the square-shapedcanister housing250 inFIG. 24B. In alternate embodiments, however, theelectrode254 may be positioned toward the center of one of thesides252 of the square-shapedcanister housing250, or at the center of the square-shapedcanister housing250, or rotated more. A square shapedelectrode257 is specifically illustrated at the side of thecanister housing250 inFIG. 24C.

The length and width of the square-shapedcanister housing250 is approximately 6 centimeters to approximately 8 centimeter long and wide.

FIG. 25A depicts yet another embodiment of an S-ICD canister having a “tongue depressor-shaped”canister housing260. The tongue depressor-shapedcanister housing260 includes atop surface261, a bottom surface (not shown) and surroundingsides262 connecting these two surfaces. The tongue depressor-shapedcanister housing260 further includes adistal end264 and aproximal end266. Thedistal end264 and theproximal end266 of the tongue depressor-shapedcanister housing260, however, are rounded. In one embodiment, the rounded ends extend outwardly away from thecanister housing260 in either the corresponding distal or proximal direction. The rounded ends generally are circular arc-shaped curves. However, the rounded ends may also be elliptical or nonsymmetrical arc-shaped curves.

Theelectrode268, shown in phantom, is generally positioned at either thedistal end264 or theproximal end266 of thecanister housing260. In alternative embodiments, the tongue depressor-shapedcanister housing260 may include two ormore electrodes268. When two electrodes are utilized, one electrode is positioned at thedistal end264 of thecanister housing260 while the second electrode is positioned at theproximal end266 of thecanister housing260.

The length of the tongue depressor-shapedcanister housing260 is approximately 30 centimeters long or less. In alternative embodiments, the tongue depressor-shapedcanister housing260 is approximately 15 centimeter long or less. The width of the tongue depressor-shapedcanister housing260 is approximately 3 centimeters to approximately 10 centimeters wide.

Referring now toFIG. 25B, where a modified tongue depressor-shapedcanister housing270 is shown. The modified tongue depressor-shapedcanister housing270 is similar to the tongue depressor-shaped S-ICD canister260 depicted inFIG. 25A, however, the modified tongue depressor-shapedcanister housing270 comprises only has a single roundeddistal end272. Theproximal end274 of the modified tongue depressor-shapedcanister housing270 is generally square.

FIGS. 26A-26C illustrate another embodiment of an S-ICD canister having amulti-segment canister housing280. Themulti-segment canister housing280 includes at least two canister housing segments that are coupled together. The S-ICD canister depicted inFIGS. 26A, 26B and26C specifically have adistal segment282 and aproximal segment284 hinged, or otherwise coupled, together.

Thedistal segment282 includes atop surface292, a bottom surface (not shown) and surroundingsides286 connecting these two surfaces. The distalmost end288 of thedistal segment282 comprises a rounded region. Anelectrode290 is disposed within this rounded region of the distal segment282 (shown in phantom). Theelectrode290 generally follows the outline of the rounded region of the distalmost end288 of the canister housing, however, theelectrode290 may comprise of other shapes and sizes.

In an embodiment of themulti-segment canister housing280, both theelectrode290 and the electronics are disposed within thedistal segment282. In alternative embodiments, theelectrode290 is disposed within thedistal segment282 and the electronics are located within theproximal segment284 of themulti-segment canister housing280.

FIG. 26B shows thedistal segment282 of themulti-segment canister housing280 being curved to mimic the anatomical shape of a patient recipient'sribcage216. In the embodiment depicted, both thetop surface292 and thebottom surface294 of theproximal segment282 are curved. The curvature, however, differs at the distalmost end288 of thedistal segment282. At the distal segment's distalmost end288, the distal segment'stop surface292 tapers downwardly toward the distal segment'sbottom surface294. This tapering causes the distalmost end288 of thedistal segment282 to be narrower than the distal segment'sdistal end296. In certain embodiments, this tapering in depth may be gradual throughout the length of thedistal segment282, or alternatively, the tapering may be confined to a particular area.

Theproximal segment284 also includes atop surface298, abottom surface300 and surroundingsides302 connecting these two surfaces. Theproximal segment284 depicted inFIG. 26B, however, is generally planar. In alternative embodiments, depicted inFIG. 26C, theproximal segment284 may also be curved and may also be of a different curvature to that of the distal segment.

The length of themulti-segment canister housing280 is approximately 30 centimeters long or less. In alternative embodiments, themulti-segment canister housing280 is approximately 20 centimeters or less. In yet another embodiment, themulti-segment canister housing280 is approximately 12 centimeters or less. The width ofmulti-segment canister housing280 is approximately 3 centimeters to approximately 10 centimeters wide.

Referring now toFIG. 27, a plan view of an alternative Unitary Subcutaneous Implantable Cardioverter-Defibrillator (“US-ICD”) canister made of ceramic materials according to an embodiment of the present invention is illustrated. The US-ICD canister400 comprises ahousing410 having adistal end405 and aproximal end407. Adistal electrode412 is integrally disposed at thedistal end405 of thehousing410, and aproximal electrode414 is integrally disposed at theproximal end407 of thehousing410 for sensing and shocking. In an embodiment, thedistal electrode412 and theproximal electrode414 are directly fused on to thehousing410.

Although a “tongue-depressor-shaped” S-ICD canister housing is illustrated, it should be noted that the shape and size of the electrodes, and the shape, size and weight of the housing may vary as described in relation to particular embodiments above. In addition, though not shown, the integration of an electrode into a housing in the present invention can also apply to the US-ICD.

In an embodiment, thehousing410 can comprise any suitable ceramic material such as zirconia, stabilized zirconia, partially stabilized zirconia, tetragonal zirconia, zirconia stabilized with yttria, magnesia, ceria, calcia or combinations thereof, alumina, silicon nitride, silicon carbide, titanium carbide, tungsten carbide, titanium nitride, silicon-aluminum oxy-nitride (sialon), graphite, titanium di-boride, boron carbide, zirconia toughened alumina, and molybdenum disilicide. These materials and materials having similar properties are collectively referred to as “ceramic materials” in this specification and the appended claims.

Because of its inherent nonconductive properties, a housing made of ceramic materials allows an electrode to be integrally disposed therein as described above. Fusing of an electrode to the housing can be accomplished via known processes involving a combination of temperature and pressure. For example, one such process is described in U.S. Pat. No. 6,221,513 entitled “Methods for Hermetically Sealing Ceramic to Metallic Surfaces and Assemblies Incorporating Such Seals.”

The use of only ceramic materials may cause the housing to appear white in color. In an embodiment, titanium can be mixed with the ceramic materials to cause the housing to appear darker in color and makes the ceramics stronger and more aesthetically pleasing to the implanting physician. The relatively small amount of titanium that may be used for coloring does not significantly and clinically alter housing conductivity.

FIG. 28 illustrates an alternative S-ICD canister according to an embodiment of the present invention. S-ICD canister500 comprises a housing divided into adistal segment510 and aproximal segment512. Adistal electrode514 is integrally disposed on thedistal housing segment510 and aproximal electrode516 is integrally disposed on theproximal housing segment516. In an embodiment, thedistal electrode514 and theproximal electrode516 are used for both sensing and shocking purposes. In an embodiment, the

housing segments

510 and512 can comprise a mixture of titanium and ceramic materials. Because of the inherent conductive properties of titanium,

housing segments

510 and512, which have

integral electrodes

514 and516 disposed therein, are insulated from each other by a distal insulating wall orplate518. The insulatingplate518 is disposed at an end of thedistal housing segment510 opposite thedistal electrode514. In an embodiment, the insulatingplate518 can comprise a ceramic material. A distal conductive wall orplate520 is disposed abutting the distal insulatingplate518. In an embodiment, theconductive wall520 comprises titanium or other metals such as stainless steel, or cobalt chromium alloys. A proximal insulating wall orplate524 is disposed at an end of thehousing segment512 opposite theproximal electrode516 and a proximal conductive wall orplate522 is disposed abutting the proximal insulatingplate524. In an embodiment, proximalconductive plate522 also comprises titanium or other suitable metals such as stainless steel, or cobalt chromium alloys. Proximal insulatingplate524 can comprise a ceramic material. In an embodiment,

conductive plates

522 and520 are coupled to each other. Therefore, the two electrodes may be disposed on the same housing and used as part of a unitary device. It should be noted that according to alternative embodiments of the present invention, an S-ICD canister may have a housing comprising a titanium mixture masked with paralene or another material suitable for applications in implantable devices with a single electrode integrally disposed at one end.

Numerous characteristics and advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many aspects, only illustrative. Changes may be made in details, particularly in matters of shape, size and arrangement of parts without exceeding the scope of the invention. The invention's scope is defined in the language in which the appended claims are expressed.

Claims

1. An implantable cardioverter-defibrillator comprising:

a housing comprising a mixture of conductive and non-conductive materials;

an electrode disposed on the housing; and

a cardioversion-defibrillation circuitry located within the housing and coupled to the electrode.

2. The implantable cardioverter-defibrillator ofclaim 1, wherein the housing comprises a mixture of ceramic materials and titanium.

3. The implantable cardioverter-defibrillator ofclaim 1, wherein the electrode is integrally positioned on a portion of the housing.

4. The implantable cardioverter-defibrillator ofclaim 1, wherein at least a portion of the housing is curved.

5. The implantable cardioverter-defibrillator ofclaim 1, wherein the electrode is a subcutaneous electrode that is adapted to emit energy for treating the patient's heart from a subcutaneous position within the patient.

6. The implantable cardioverter-defibrillator ofclaim 5 wherein the electrode is further adapted to receive sensory information.

7. The implantable cardioverter-defibrillator ofclaim 1, wherein the electrode is adapted to receive sensory information.

8. The implantable cardioverter-defibrillator ofclaim 1, wherein the implantable cardioverter-defibrillator is adapted for subcutaneous positioning between the third rib and the twelfth rib within a patient.

9. An implantable cardioverter-defibrillator comprising:

a housing for subcutaneous implantation within a patient, the housing comprising a mixture of conductive and nonconductive materials;

a subcutaneous electrode disposed on the housing; and

cardioversion-defibrillation circuitry located within the housing and coupled to the subcutaneous electrode.

10. The implantable cardioverter-defibrillator ofclaim 9, wherein the housing comprises a mixture of ceramic materials and titanium.

11. The implantable cardioverter-defibrillator ofclaim 9, wherein the housing is sized and shaped for subcutaneous positioning between the third rib and the twelfth rib within the patient.

12. The implantable cardioverter-defibrillator ofclaim 9, wherein the subcutaneous electrode is positioned on the housing such that when the housing is subcutaneously implanted within the patient, the electrode is maintained in a predetermined subcutaneous position relative to the patient's heart.

13. The implantable cardioverter-defibrillator ofclaim 9, wherein the subcutaneous electrode is adapted to emit energy for treating a patient's heart from a subcutaneous position within the patient.

14. The implantable cardioverter-defibrillator ofclaim 13, wherein the electrode is further adapted to receive sensory information.

15. The implantable cardioverter-defibrillator ofclaim 9, wherein the subcutaneous electrode receives sensory information.

16. The implantable cardioverter-defibrillator ofclaim 9, wherein the subcutaneous electrode is integrally positioned on a portion of the housing.

17. An implantable cardioverter-defibrillator comprising:

a housing comprising a mixture composition including both conductive and nonconductive materials;

an electrical circuit located within the housing; and

an electrode disposed on a portion of the housing, wherein the electrode couples to the electrical circuit.

18. The cardioverter-defibrillator ofclaim 17, wherein the mixture composition comprises a mixture of ceramic and titanium.

19. A method of making an implantable cardioverter-defibrillator, the method comprising:

providing a housing comprising a mixture of conductive and non-conductive materials;

disposing an electrode on the housing;

disposing a cardioversion-defibrillation circuitry within the housing; and

coupling the cardioversion-defibrillation circuitry to the electrode.

20. The method ofclaim 19, wherein providing a housing includes providing a housing for subcutaneous implantation within a patient, and wherein the electrode is a subcutaneous electrode.

21. The method ofclaim 19, wherein disposing the electrode includes integrally positioning the electrode on a portion of the housing.

22. A method of providing therapy to a patient, the method comprising:

providing a subcutaneously implantable cardioverter-defibrillator, the implantable cardioverter-defibrillator including a housing comprising a mixture of conductive and non-conductive materials, a subcutaneous electrode disposed on the housing, and a cardioversion-defibrillation circuitry disposed within the housing and coupled to the electrode; and

subcutaneously implanting the housing between the third rib and the twelfth rib within the patient such that the electrode is maintained in a predetermined subcutaneous position relative to the patient's heart.