US20070255270A1 - Intraluminal guidance system using bioelectric impedance - Google Patents

Abstract

A system using bioelectric impedance to guide a flexible elongate transluminal device through an occlusion in a vessel. The device can be a guidewire or a device for performing an atherectomy, discectomy, ablation or similar technique. The device includes a first electrode disposed on a distal portion of the device. A second electrode is disposed in electric contact with the patient separate from the first electrode. An electric current is supplied between the first and second electrodes and a voltage drop is measured between the first and second electrodes. The voltage drop is converted to bioelectric impedance. Based on the impedance measurement, a clinician can determine if the device is approaching the vessel wall, permitting the clinician to redirect the device away from the vessel wall.

Description

FIELD OF THE INVENTION
• The disclosure relates generally to a guidance system for use in a patient's vessel, and more particularly, to a system for guiding an intra-luminal device through an arterial chronic total occlusion (CTO) using bioelectric impedance.
BACKGROUND OF THE INVENTION
• Stenotic lesions may comprise a hard, calcified substance and/or a softer thrombus material, each of which forms on the lumen walls of a blood vessel and restricts blood flow there through. Intra-luminal treatments, such as balloon angioplasty, stent deployment, atherectomy, and thrombectomy are well known and have proven effective in the treatment of such stenotic lesions. These treatments often involve the insertion of a therapy catheter into a patient's vasculature, which may be torturous and may have numerous stenoses of varying degrees throughout its length. In order to place the distal, treatment portion of a catheter within the treatment site, a steerable guidewire is typically introduced and tracked from an incision, through the vessels, and across the lesion. Then, a catheter, e.g., a balloon catheter, perhaps carrying a stent, can be tracked over the guidewire to the treatment site. Ordinarily, the distal end of the guidewire is quite flexible so that as it is directed, or steered through the lumen, it can find its way through the turns of the typically irregular passageway without perforating or otherwise damaging the vessel wall.
• In some instances, the extent of occlusion of the lumen is so severe that the lumen is completely or nearly completely obstructed, leaving virtually no passageway for the guidewire. Such a condition may be described as a total occlusion. If this occlusion persists for a long period of time, the lesion is referred to as a chronic total occlusion or CTO. Furthermore, in the case of diseased blood vessels, the lining of the vessels may be characterized by the prevalence of atheromatous plaque, which may form total occlusions. The extensive plaque formation of a chronic total occlusion typically has a fibrous cap surrounding softer plaque material. This fibrous cap may present a surface that is difficult to penetrate with a conventional guidewire, and the typically flexible distal tip of the guidewire may be unable to cross the lesion.
• Thus, for treatment of total occlusions, guidewire having stiffer distal tips have been employed to recanalize a total occlusion. However, blood vessels are not straight and fluoroscopic visualization of the natural path through an occlusion is poor because there is little or no flow of radiographic contrast through the occlusion. Therefore, simply using a stiffer guidewire to push through an occlusion increases the risk that the guidewire tip will penetrate the vessel wall.
• Atherectomy is another established treatment for occlusions. Atherectomy procedures typically involve inserting a cutting or ablating device through the access artery, e.g. the femoral artery or the radial artery, and advancing it through the vascular system to the occluded region, and rotating the device at high speed via a drive shaft to cut through or ablate the plaque over the wire. The removed plaque or material can then be suctioned out of the vessel or be of such fine diameter that it is cleared by the reticuloendothelial system. Atherectomy devices also present the danger of unwanted perforation of a vessel wall by the material removal device. This can occur when the material removal device improperly engages the vessel wall, for example when the material removal device is not oriented substantially parallel to the axis of the vessel. In this situation, the material removal device, e.g. cutter or abrasive ablator, may improperly engage the vessel wall and cause unwanted damage thereto. Other ablation and discectomy devices also present the danger of damage to a vessel wall.
• Thus, there is a need for a device and method to reduce the risk of damage to a vessel wall when a guidewire or a device for performing an atherectomy, discectomy, ablation or similar procedure is crossing an occlusion.
• Electrical impedance is the opposition to the flow of an alternating current, which is the vector sum of ohmic resistance plus additional resistance, if any, due to induction, to capacitance, or to both. Bioelectric impedance is known, e.g., for use in measuring body fat composition. For example, bathroom scales may include means to measure body fat composition using bioelectric impedance. According to this technique, a person's body fat is measured by determining the impedance of the person's body to electrical signals, and calculating the percent body fat based upon the measured impedance and other variables, such as height, weight, age, and sex.
• Bioelectric impedance is typically determined by supplying a harmless electric current through at least two separated electrodes that contact portions of a body, and measuring a voltage across the body portion. This voltage is measured either (1) via the same electrodes through which current is supplied, or (2) via one or more distinct pairs of voltage-measuring electrodes. The bioelectric impedance is then readily calculated from the current and the measured voltage. The calculated bioelectric impedance may be compared to an expected value or range of common or known values, or it may be compared to one or more bioelectric impedance values previously measured in, and calculated for the same patient.
BRIEF SUMMARY OF THE INVENTION
• The present disclosure is a system that uses bioelectric impedance to guide an elongate intraluminal device through an occlusion in a vessel. The device can be a medical guidewire or a therapeutic catheter for performing an angioplasty, atherectomy, discectomy, ablation or similar procedure. The device includes an electrode disposed on a distal portion of the device. A second electrode is disposed separately of the first electrode, either on the same device or on a separate device. For example, the second electrode may be mounted on a skin electrode or on a balloon of a catheter. The system provides an electric power source and an impedance monitor for connection to the first and second electrodes.
• During use of the above system to guide an elongate device through a vessel occlusion in a patient, a first electrode is disposed adjacent the occlusion targeted for crossing. A second electrode is spaced apart from the first electrode and disposed in electrical contact with the patient's tissue, e.g., against the wall of the occluded or another vessel. The second electrode may be a skin electrode in contact with the patient's skin. As the elongate device is advanced through the occlusion, an electric current is supplied between the first and second electrodes and a voltage drop is measured between the first and second electrodes. The voltage drop is converted arithmetically to a calculated bioelectric impedance. By comparing the measured/calculated bioelectric impedance to a known, e.g., expected standard or previously measured impedance, a clinician can determine whether the device is approaching the vessel wall and posing a risk of perforating the wall. With this information, the clinician can halt advancement of the device, and possibly redirect the device away from the vessel wall.
BRIEF DESCRIPTION OF DRAWINGS
• The foregoing and other features and advantages of the disclosure will be apparent from the following description of the disclosure as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art to make and use the disclosure. The drawings are not to scale.
• FIG. 1 is a partial cut-away view of a vessel including an occlusion and illustrating a system in accordance with an embodiment of the present disclosure.
• FIG. 2 illustrates the system as shown inFIG. 1, with the introduction of a microcatheter.
• FIG. 3 illustrates the system as shown inFIG. 2, with the introduction of a guidewire.
• FIG. 4 illustrates the system as shown inFIG. 3, with the guidewire advanced into the occlusion.
• FIG. 5 is a partial cut-away view of the system ofFIGS. 1-4 illustrating a schematic representation of equipment outside of the vessel.
• FIG. 6 is a side view of a steerable guidewire of the present disclosure.
• FIG. 7 is a partial cut-away view of a vessel including an occlusion and illustrating another embodiment in accordance with the present disclosure.
• FIG. 8 is a cross-section of a vessel including an occlusion and showing another embodiment in accordance with the present disclosure.
• FIG. 9 is a plan view of a patient illustrating another embodiment in accordance with the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
• Specific embodiments of the present disclosure are now described with reference to the figures, where like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician.
• The present disclosure is directed to a system and method for guiding an elongate medical device, such as a guidewire or catheter for performing an angioplasty, atherectomy, dissection, or ablation, through an occlusion in a patient's vessel. Although the present description relates to crossing an occlusion in a blood vessel, such as an arterial stenosis, the invention is not so limited, and may be applicable for providing guidance during crossing of other blockages in other passageways in a patient. Ablood vessel10 with anocclusion12 blocking blood flow through it is shown inFIGS. 1-4. Aballoon catheter14 with aballoon16 near its distal end is advanced through the vasculature to a position proximal toocclusion12, as shown inFIG. 1.Catheter14 andballoon16 can be made of materials known to those skilled in the art. In an embodiment of the present disclosure,balloon16 includes a second,ring electrode18 disposed about its periphery. Optionally, a micro-catheter20 is advanced throughcatheter14 such that a distal portion ofmicro-catheter20 extends from a distal end ofcatheter14, as shown inFIGS. 2 and 3. Aguidewire22 may be advanced throughballoon catheter14 and optional micro-catheter20 and extends intoocclusion12, as shown inFIGS. 3 and 4. AlthoughFIG. 1 showsballoon16 inflated for clarity of the illustration,balloon16 is typically advanced throughblood vessel10 in an uninflated condition.Balloon16 is inflated prior to advancing guidewire throughocclusion12. Thus,balloon16 need not be inflated until after the step shown inFIG. 3, although it can be inflated at anytime after being advanced throughblood vessel10 to the position shown inFIG. 1. Further, althoughFIGS. 1-4show balloon16 withring electrode18, any suitable device can be equipped with an electrode, provided that the electrode can be maintained in electrical contact with the wall of the vessel during crossing of the occlusion. For example, a second guidewire could be used with an electrode disposed thereon and placed against the wall of the vessel. Alternatively, the second electrode may be positionable in electrical contact with the patient's tissue in a different vessel, or outside of the patient's vascular system, or outside the patient's body, viz. a skin electrode as will be discussed below with respect toelectrode50.
• Referring toFIG. 6, guidewire22 includes atip24 with afirst electrode26 disposed thereon.Guidewire22 inFIG. 6 is shown as a steerable guidewire. Any guidewire suitable for crossing an occlusion may be used, as would be apparent to those skilled in the art.Guidewire22 can be fabricated from materials as known to those skilled in the art.Electrode26 may be an electrically conducting electrode and can be fabricated from a variety of conductive materials known in the art, including stainless steel, copper, silver, gold, platinum and alloys and combinations thereof.
• Referring toFIG. 5, an electricallyconductive lead28 communicates withelectrode26, as by an insulated wire (not shown) withinguidewire22, and lead28 extends outside of the body to anelectric power source32. An electricallyconductive lead30 communicates withring electrode18, as by an insulated or otherwise electrically isolated wire (not shown) withincatheter14, and lead30 extends outside the body to an electrical impedance monitor34.Power source32 and impedance monitor34 are connected together externally or they may be combined in an integral device.Power source32 and impedance monitor34, in conjunction withleads28,30 andelectrodes18,26 form a complete electrical circuit that includes a portion of a patient's body extending betweenelectrodes18,26. The materials that define the portion of a patient's body in the electrical circuit will be discussed in detail below.
• Power source32 generates a harmless electric current throughlead28 betweenelectrodes26 and30. The current may be a pulsed and/or alternating current and the selected alternating frequency may be in the range of 1 kHz to 500 kHz or other suitable frequencies known to those of skill in the art of bioelectric impedance.Ring electrode18 may be fabricated from a variety of conductive materials known in the art, including stainless steel, copper, silver, gold, platinum and alloys and combinations thereof. In an alternative embodiment of the disclosure, a smaller, viz., non-ring shaped electrode or a plurality of electrodes may be disposed onballoon16, provided such that that the electrode(s) may be brought into electrical contact with the wall ofvessel10, as by inflatingballoon16 into apposition with the vessel wall.
• In practice, asguidewire22 is advanced throughocclusion12,power source32 generates an electric current through leads28,30 and through the patient's tissue betweenelectrodes18,26. The current can be pulsed in a suitable range of pulse frequencies as may be determined by those of skill in the art of bioelectric impedance. While current is flowing throughelectrodes18,26, a corresponding resistance or voltage drop is measured betweenelectrodes18,26. The voltage drop is arithmetically converted to an impedance measurement atimpedance monitor34. Impedance monitor34 may include logic resources, such as a microprocessor, and/or memory resources, such as a RAM or DRAM chip, configured to analyze, store and display bioelectric information derived fromelectrodes18,26. For example, impedance monitor34 may include a voltage-current converting circuit, an amplifying circuit, an A/D converting circuit, and an impedance arithmetic operation section. Impedance monitor34 may further include, or may be coupled to, adisplay device34d, such as a cathode ray tube, liquid crystal display, plasma display, flat panel display or the like.
• Occlusions14 are generally made of atherosclerotic plaques. Although atherosclerotic plaques may vary, they contain many cells; mostly these are derived from cells of the wall that have divided wildly and have grown into the surface layer of the blood vessel, creating a mass lesion. Plaques also contain cholesterol and cholesterol esters, commonly referred to as fat, that lie freely in the space between the cells and within the cells themselves. A large amount of collagen is present in the plaques, particularly in advanced plaques of the type which cause clinical problems. Additionally, human plaques contain calcium to varying degrees, hemorrhagic material including clot and grumous material composed of dead cells, fat and other debris. Plaques also contain about 10-20% water. This general composition of atherosclerotic plaques results in a relatively high electrical resistance (and correspondingly high bioelectric impedance), as compared to more lean body tissue, such asvessel wall10.
• Thus, whenelectrode26 located ontip24 ofguidewire22 is disposed generally at the center ofocclusion12, the electric current frompower source32 passes through the relatively high resistance atherosclerotic plaque ofocclusion12 before reaching the relatively lower resistance wall ofvessel10. The current then travels through the wall ofvessel10 to ringelectrode18. Iftip24 ofguidewire22 goes off-course such that it becomes closer to the wall ofvessel10, then the current travels a shorter distance through less thickness of the relatively high resistance atherosclerotic plaque ofocclusion12 before reaching the wall ofvessel10. Ultimately, iftip24 approaches the wall ofvessel10, the current passes through very little of the relatively high resistance atherosclerotic plaque ofocclusion12 before reachingvessel10. Thus, the impedance detected betweenelectrodes18,26 and displayed at impedance monitor34 will decrease iftip24 approaches the wall ofvessel10.
• A clinician may stop the advancement of, and/or attempt to redirectguidewire22 away from the wall ofvessel10 when the bioelectric impedance drops below a certain threshold value. Such a threshold value may be measured and calculated by measuring bioelectric impedance in undiseased vessel tissueadjacent target occlusion12, using the system of the disclosure prior to advancingguidewire22 intoocclusion12. Alternatively, a bioelectric impedance threshold value for comparison during crossing ofocclusion12 may be a value that may be predicted by an experienced clinician, or a value that a large number of similar patients are known to have in common, or a value that is otherwise available, e.g., from a printed or electronic reference source. The clinician's reaction to the bioelectric impedance reaching a low limit may preventtip24 ofguidewire22 from piercingvessel10. Impedance monitor34 may further include analarm34asuch that when the impedance reaches a predetermined limit, the alarm is activated, thereby alerting the clinician that the impedance has reached the predetermined limit.
• FIG. 7 shows another embodiment of the present disclosure which is similar to the embodiment shown inFIGS. 1-6 except that anatherectomy device36 is advanced throughballoon catheter14 intoocclusion12.Atherectomy device36 includes a cuttinghead38 that is rotated at high speed, e.g., via a drive shaft to cut or ablate a passageway through the plaque ofocclusion12. The removed plaque or material may be suctioned out of the vessel as is known to those skilled in the art. Afirst electrode44 is disposed on cuttinghead38. An electric current is provided throughelectrodes18,44 and a voltage drop is measured betweenelectrodes18,44, in the same manner as described above with respect to the embodiment ofFIGS. 1-6 (the power source, impedance monitor, and leads are not shown). The measured voltage drop is converted to impedance by the impedance monitor. Based on the calculated impedance, it can be determined if cuttinghead38 is too close to the wall ofvessel10. In such a case, advancement ofatherectomy device36 may be halted and/or cuttinghead38 may be redirected away from the wall ofvessel10. In any of the embodiments wherein the device for crossingocclusion12 is power-assisted, impedance monitor34 may further include a shut-off switch34ssuch that when the impedance reaches a predetermined low limit, power to the device is shut-off. For example, power to atherectomydevice36 may be shut-off byswitch34ssuch that cuttinghead38 stops rotating, thereby preventing cuttinghead38 from damagingvessel10.
• FIG. 8 is an alternative embodiment ofatherectomy device36 shown inFIG. 7. Anatherectomy device36aofFIG. 8 includes aguidewire40 disposed through and extending slightly beyond a cuttinghead38a. Afirst electrode42 is disposed at the distal tip ofguidewire40.Atherectomy device36afunctions in the same manner as the device ofFIG. 7, except that the electrode is disposed in a different position.
• In an alternative to the embodiments described with respect toFIGS. 1-8,balloon16 withring electrode18 is not required. Instead, a second,skin electrode50 may be placed externally on the patient's chest, as shown inFIG. 9. In this embodiment, if one offirst electrodes26,42 or44 is inocclusion12, not near the wall ofvessel10, then the impedance betweenfirst electrodes26,42 or44 andskin electrode50 may be safely above the bioelectric impedance threshold low limit and the clinician can continue advancingguidewire22,atherectomy device36,36a, or a device for performing laser ablation, discectomy, or other similar procedures. When guidewire22,atherectomy device36,36a, or a device for performing laser ablation, discectomy, or other similar procedures approaches the wall ofvessel10, the impedance betweenfirst electrodes26,42 or44 andskin electrode50 may approach the bioelectric impedance threshold low limit, and optionally providing an audible or visual signal to the clinician. When a signal is detected, the clinician may be alerted, for example, byimpedance monitor34, to indicate that thedevice crossing occlusion12 may need to be redirected away from the wall ofvessel10. Upon examination, the clinician may determine that the device has safely passed throughocclusion12 andelectrode26,42, or44 may have contacted the wall ofvessel10 distal toocclusion12.
• Impedance monitor34 may includedisplay device34d, alarm34a, and shut-off switch34s, as described with respect to the embodiment shown inFIG. 5. While the embodiment withskin electrode50 is described in conjunction with the detection of any bioelectric impedance value indicating to the clinician that the device may be approaching the vessel wall, the embodiments may be interchangeable. For example, when usingring electrode18 onballoon16, a low value of impedance may not be detected betweenelectrode26,42, or44 andring electrode18 whenguidewire22 is near the center ofocclusion12. Factors such as the frequency of the current provided bypower source32 and the location ofring electrode18, for example, may be adjusted so that the device functions in the “go/no-go” manner. Similarly,skin electrode50 may be used in the embodiments described inFIGS. 1-8 such that changes in the measured bioelectric impedance may apprise the clinician of the anatomical location of the device in the patient, instead of providing information regarding the distance of the device from a surrounding vessel wall.
• While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the disclosure. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.

Claims (25)

1. A guidance system for crossing an occlusion in a patient's vessel, the system comprising:

a first flexible elongate element adapted for transluminally approaching and crossing the occlusion, the first elongate element having a first electrode disposed adjacent a distal end thereof, the first electrode electrically connectable to the patient;

a second electrode electrically connectable to the patient, wherein the second electrode is a skin electrode or the second electrode is disposed on a balloon, the balloon mounted on a flexible elongate catheter adapted for transluminal insertion into the vessel;

an electric power source connectable to the first and second electrodes and adapted to provide an electric current thereto; and

an impedance monitor connectable to the first and second electrodes and adapted to determine a bioelectric impedance there between.

2-4. (canceled)

5. The system ofclaim 1, wherein the first elongate element is a guidewire

6. The system ofclaim 1, wherein the first elongate element is an ablation device.

7. The system ofclaim 6, wherein the power source provides power to the ablation device.

8. The system oftclaim 7, wherein the impedance monitor is coupled to a shut-off switch that shuts off power to the ablation device when the impedance drops below a predetermined value.

9. The system ofclaim 1, wherein the current provided by, the power source is an alternating current with a frequency in the range of 1 kHz to 500 kHz.

10. The system ofclaim 1, wherein the impedance monitor is coupled to an alarm that sounds when the impedance drops below, a predetermined value.

11. The system oftclaim 1, wherein the first elongate element is an atherectomy device comprising a rotatable cutting head wherein the first electrode is disposed on the cutting head.

12. The system ofclaim 11, wherein the impedance monitor is coupled to a shut-off switch that stops the cutting head frown rotating when the impedance drops below a predetermined value.

13. The system ofclaim 1, wherein the first elongate element is an atherectomy device comprising a rotatable cutting head, further comprising a guidewire disposed within the cutting head, wherein tire first electrode is disposed on the guidewire.

14. A method for guiding a device through an occlusion in a patient's vessel, the method comprising the steps of:

delivering a flexible elongate element transluminally to the occlusion, wherein a first electrode is disposed on a distal portion of the elongate element;

advancing the elongate element into the occlusion;

providing a second electrode separate from the first electrode and in electrical contact with the patient, wherein the second electrode is a skin electrode or the second electrode is disposed on a balloon, the balloon mounted on a flexible elongate catheter adapted for transluminal insertion into the vessel;

providing an electric power source coupled to the first and second electrodes;

activating the power source to provide an electric current between the first and second electrodes;

measuring a voltage drop between the first and second electrodes; and

calculating a bioelectric impedance based on the voltage drop between the first and second electrodes.

15-17. (canceled)

18. The method ofclaim 14, wherein the step of activating the power source to provide a current between the first and second electrodes takes place in a pulsed sequence.

19. The method ofclaim 18, wherein the impedance is calculated each time a current is provided between the first and second electrodes.

20. The method ofclaim 14, further comprising the step of advancing the elongate element through the occlusion as the current is applied between the first and second electrodes.

21. The method ofclaim 14, further comprising, prior to advancing the elongate element into the occlusion, the steps of:

positioning the first electrode in electrical contact with the vessel adjacent the occlusion;

measuring a voltage drop between the first electrode and the second electrode; and

calculating a predetermined bioelectric impedance value based on the voltage drop between the first second electrodes.

22. The method ofclaim 14, further comprising the step of directing the elongate element away from the vessel wall when the calculated impedance reaches a predetermined bioelectric impedance value.

23. The method ofclaim 14, wherein an alarm is triggered when the calculated impedance reaches a predetermined bioelectric impedance value.

24. The method ofclaim 14, wherein the elongate element is a guidewire.

25. The method ofclaim 14, wherein the elongate element is an atherectomy device.

26. The method ofclaim 25, wherein the atherectomy device includes a cutting head that rotates as the atherectomy device is advanced through the occlusion.

27. The method ofclaim 26, wherein a shut-off switch stops the rotation of the cutting head when the impedance reaches a predetermined level.

28. The method ofclaim 14, wherein the elongate element is a laser ablation device.

29. The method ofclaim 23, wherein the power source provides power to the laser ablation device, and wherein a shut-off switch off power to the laser ablation device when the impedance reaches a predetermined level.

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