US20140094647A1 - Heart wall tension reduction apparatus and method - Google Patents

Abstract

Devices and methods for treatment of a failing heart by reducing the heart wall stress. The device can be one which reduces wall stress throughout the cardiac cycle or only a portion of the cardiac cycle.

Description

RELATED APPLICATIONS
• This application is a continuation of U.S. application Ser. No. 13/609,585, entitled Heart Wall Tension Reduction Apparatus and Method, filed Sep. 11, 2012, which is a divisional of U.S. application Ser. No. 12/832,507, entitled Heart Wall Tension Reduction Apparatus and Method, filed Jul. 8, 2010, now U.S. Pat. No. 8,267,852, which is a continuation of U.S. application Ser. No. 10/127,731 (“the '731 application”) of Cyril J. Schweich Jr. et al., entitled Heart Wall Tension Reduction Apparatus and Method, filed on Apr. 23, 2002, now U.S. Pat. No. 7,883,539, which is a continuation-in-part of U.S. application Ser. No. 09/985,361, entitled Heart Wall Tension Reduction Apparatus and Method, filed Nov. 2, 2001, now U.S. Pat. No. 6,589,160, which is a continuation of U.S. application Ser. No. 09/697,597, filed Oct. 27, 2000, now U.S. Pat. No. 6,332,864, which is a continuation of application Ser. No. 09/492,777, filed Jan. 28, 2000, now U.S. Pat. No. 6,162,168, which is a continuation of application Ser. No. 08/778,277, filed Jan. 2, 1997, now U.S. Pat. No. 6,050,936.
• The '731 application also is a continuation-in-part of U.S. application Ser. No. 09/843,078 of Todd J. Mortier et al. for Stress Reduction Apparatus and Method, filed Apr. 27, 2001, now U.S. Pat. No. 6,402,680, which is a continuation of application Ser. No. 09/522,068, filed Mar. 9, 2000, now U.S. Pat. No. 6,264,602, which is a continuation of application Ser. No. 09/124,321, filed Jul. 29, 1998, now U.S. Pat. No. 6,077,214. The entirety of each of the above applications is incorporated herein by reference.
FIELD OF THE INVENTION
• The present invention pertains to the field of apparatus for treatment of a failing heart. In particular, the apparatus of the present invention is directed toward reducing the wall stress in the failing heart.
BACKGROUND OF THE INVENTION
• The syndrome of heart failure is a common course for the progression of many forms of heart disease. Heart failure may be considered to be the condition in which an abnormality of cardiac function is responsible for the inability of the heart to pump blood at a rate commensurate with the requirements of the metabolizing tissues, or can do so only at an abnormally elevated filling pressure. There are many specific disease processes that can lead to heart failure with a resulting difference in pathophysiology of the failing heart, such as the dilatation of the left ventricular chamber. Etiologies that can lead to this form of failure include idiopathic cardiomyopathy, viral cardiomyopathy, and ischemic cardiomyopathy.
• The process of ventricular dilatation is generally the result of chronic volume overload or specific damage to the myocardium. In a normal heart that is exposed to long term increased cardiac output requirements, for example, that of an athlete, there is an adaptive process of slight ventricular dilation and muscle myocyte hypertrophy. In this way, the heart fully compensates for the increased cardiac output requirements. With damage to the myocardium or chronic volume overload, however, there are increased requirements put on the contracting myocardium to such a level that this compensated state is never achieved and the heart continues to dilate.
• The basic problem with a large dilated left ventricle is that there is a significant increase in wall tension and/or stress both during diastolic filling and during systolic contraction. In a normal heart, the adaptation of muscle hypertrophy (thickening) and ventricular dilatation maintain a fairly constant wall tension for systolic contraction. However, in a failing heart, the ongoing dilatation is greater than the hypertrophy and the result is a rising wall tension requirement for systolic contraction. This is felt to be an ongoing insult to the muscle myocyte resulting in further muscle damage. The increase in wall stress is also true for diastolic filling. Additionally, because of the lack of cardiac output, there is generally a rise in ventricular filling pressure from several physiologic mechanisms. Moreover, in diastole there is both a diameter increase and a pressure increase over normal, both contributing to higher wall stress levels. The increase in diastolic wall stress is felt to be the primary contributor to ongoing dilatation of the chamber.
• Prior art treatments for heart failure fall into three generally categories. The first being pharmacological. for example, diuretics. The second being assist systems, for example, pumps. Finally, surgical treatments have been experimented with, which are described in more detail below.
• With respect to pharmacological treatments, diuretics have been used to reduce the workload of the heart by reducing blood volume and preload. Clinically, preload is defined in several ways including left ventricular end diastolic pressure (LVEDP), or left ventricular end diastolic volume (LVEDV). Physiologically, the preferred definition is the length of stretch of the sarcomere at end diastole. Diuretics reduce extra cellular fluid which builds in congestive heart failure patients increasing preload conditions. Nitrates, arteriolar vasodilators, angiotensin converting enzyme inhibitors have been used to treat heart failure through the reduction of cardiac workload through the reduction of afterload. Afterload may be defined as the tension or stress required in the wall of the ventricle during ejection. Inotropes like digoxin are cardiac glycosides and function to increase cardiac output by increasing the force and speed of cardiac muscle contraction. These drug therapies offer some beneficial effects but do not stop the progression of the disease.
• Assist devices include mechanical pumps and electrical stimulators. Mechanical pumps reduce the load on the heart by performing all or part of the pumping function normally done by the heart. Currently, mechanical pumps are used to sustain the patient while a donor heart for transplantation becomes available for the patient. Electrical stimulation such as bi-ventricular pacing have been investigated for the treatment of patients with dilated cardiomyopathy.
• There are at least three surgical procedures for treatment of heart failure: 1) heart transplant; 2) dynamic cardiomyoplasty; and 3) the Batista partial left ventriculectomy. Heart transplantation has serious limitations including restricted availability of organs and adverse effects of immunosuppressive therapies required following heart transplantation. Cardiomyoplasty includes wrapping the heart with skeletal muscle and electrically stimulating the muscle to contract synchronously with the heart in order to help the pumping function of the heart. The Batista partial left ventriculectomy includes surgically remodeling the left ventricle by removing a segment of the muscular wall. This procedure reduces the diameter of the dilated heart, which in turn reduces the loading of the heart. However, this extremely invasive procedure reduces muscle mass of the heart.
SUMMARY OF THE INVENTION
• The present invention pertains to a non-pharmacological, passive apparatus for the treatment of a failing heart. The device is configured to reduce the tension in the heart wall. It is believed to reverse, stop or slow the disease process of a failing heart as it reduces the energy consumption of the failing heart, decrease in isovolumetric contraction, increases sarcomere shortening during contraction and an increase in isotonic shortening in turn increases stroke volume. In embodiments, the device reduces wall tension during diastole (preload) and systole.
• In an embodiment, the apparatus includes a compression member for drawing at least two walls of a heart chamber toward each other to reduce the radius or area of the heart chamber in at least one cross sectional plane. In one embodiment of the apparatus, a frame is provided for supporting the compression member.
• Yet another embodiment of the invention includes a clamp having two ends biased toward one another for drawing at least two walls of a heart chamber toward each other. The clamp includes at least two ends having atraumatic anchoring member disposed thereon for engagement with the heart or chamber wall.
• The present invention also pertains to a device and method for reducing mechanical heart wall muscle stress. Heart muscle stress is a stimulus for the initiation and progressive enlargement of the left ventricle in heart failure. Reduction of heart wall stress with the devices and methods disclosed herein is anticipated to substantially slow, stop or reverse the heart failure disease process. Although the primary focus of the discussion of the devices and methods of the present invention herein relates to heart failure and the left ventricle, these devices and method could be used to reduce stress in the heart's other chambers .
• The devices and methods of the present invention can reduce heart wall stress throughout the cardiac cycle including end diastole and end systole. Alternatively, they can be used to reduce wall stress during the portions of the cardiac cycle not including end systole. Those devices which operate throughout the cardiac cycle are referred to herein as “full cycle splints”. Those devices which do not operate to reduce wall stress during end stage systole are referred to as “restrictive devices”. Restrictive devices include both “restrictive splints” which alter the geometric shape of the left ventricle, and “wraps” which merely limit the magnitude of the expansion of the left ventricle during diastolic filling without a substantial shape change.
• While it is desirable to reduce wall stress for the treatment of heart failure, to slow or reverse the disease process and to increase heart wall muscle shortening and pumping efficiency, it is also desirable to maintain or improve stroke volume and allow for variable preload.
• Improving muscle shortening both total length change and extent at end systole, is particularly important in symptomatic heart failure wherein the heart has decreased left ventricle function and has enlarged. Full cycle splinting can be used to obtain a substantial increase in muscle shortening. Improved shortening will lead to an increase in pump function, and chronically may result in muscle strengthening and reversal of the disease because of increased pumping efficiency. The increase in shortening should be balanced against a reduction in chamber volume.
• In asymptomatic, early stage heart failure, it may be possible to use only a restrictive device or method as elevated wall stress is considered to be an initiator of muscle damage and chamber enlargement. Restrictive devices and methods acting during diastole will reduce the maximum wall stress experienced during end diastole and early systole. It should be understood that restrictive devices and methods can be used in combination with full cycle splinting to more precisely control or manipulate stress reduction throughout the cardiac cycle. control or manipulate stress reduction throughout the cardiac cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a vertical side view of a heart including a transventricular splint and band splint;
• FIG. 2 is a horizontal cross section of the heart, splint and band splint ofFIG. 1;
• FIG. 3 is a graph showing the relationship between stress and strain for the sarcomeres of the left ventricle for a normal and failing heart throughout the cardiac cycle;
• FIG. 4 is an idealized horizontal cross section of a left ventricle splinted to form two lobes;
• FIG. 5 is an idealized horizontal cross sectional left ventricle splinted to for three lobes;
• FIG. 6 is a vertical view of a heart including two transventricular splints and two bands splints;
• FIG. 7 is a cross sectional view of the heart, a band splint and a splint ofFIG. 6;
• FIG. 8 is a vertical view of a heart including a transventricular splint and a partial band splint;
• FIG. 9 is a horizontal cross sectional view of the heart, splint and band splint ofFIG. 8;
• FIG. 10 is a horizontal cross section of a heart including a splint having full cycle and restrictive elements at the beginning of diastolic filling;
• FIG. 11 is a view of the splint ofFIG. 10 at end diastole;
• FIG. 12 is a vertical view of the heart in phantom line including a band splint;
• FIG. 13 is an alternate embodiment of the bank splint ofFIG. 12;
• FIG. 14 is an alternate embodiment of the bank splint ofFIG. 12;
• FIG. 15 is an alternate embodiment of the bank splint ofFIG. 12;
• FIG. 16 is a vertical view of a heart including a partial circumferential strap;
• FIG. 17 is a horizontal cross sectional view of the heart and strap ofFIG. 16;
• FIG. 18 is a vertical view of a heart in phantom line including a single element wrap including longitudinal axis securing points;
• FIG. 19 is an alternate embodiment of the wrap ofFIG. 18;
• FIG. 20 is an alternate embodiment of the wrap ofFIG. 18;
• FIG. 21 is an alternate embodiment of the wrap ofFIG. 18;
• FIG. 22 is a vertical view of the heart including a mesh wrap;
• FIG. 23 is a cross sectional view of a patient's torso and heart showing a band splint anchored to the patient's ribs;
• FIG. 24 is a partial vertical view of the heart and band splint ofFIG. 23;
• FIG. 25 is a partial vertical view of a failing heart;
• FIG. 26 is a cross sectional view of the heart ofFIG. 25;
• FIG. 27 is a vertical view of the heart for decreasing the horizontal radius of the ventricles and increasing their vertical length;
• FIG. 28 is an exaggerated vertical view of the heart ofFIG. 25 elongated by the device ofFIG. 27;
• FIG. 29 is a view of the cross section ofFIG. 26 showing the decrease in radius of the ventricles;
• FIG. 30 is a horizontal cross sectional view of the left and right ventricles including reinforcement loops;
• FIG. 31 is an alternate embodiment of the reinforcing loops ofFIG. 30;
• FIG. 32 shows a vertical view of the heart including the reinforcement loops ofFIG. 31 and a rigid shape changing member;
• FIG. 33 is a transverse cross-section of the left and right ventricles of a human heart showing the placement of an external compression frame structure in accordance with the present invention;
• FIG. 34 is a transverse cross-section of the left and right ventricles of a human heart showing a clamp in accordance with the present invention;
• FIG. 35 is a idealized cylindrical model of a left ventricle of a human heart;
• FIG. 36 is a splinted model of the left ventricle ofFIG. 35;
• FIG. 37 is a transverse cross-sectional view ofFIG. 36 showing various modeling parameters;
• FIG. 38 is a transverse cross-section of the splinted left ventricle ofFIG. 36 showing a hypothetical force distribution; and
• FIG. 39 is a second transverse cross-sectional view of the model left ventricle ofFIG. 36 showing a hypothetical force distribution.
DESCRIPTION OF THE EMBODIMENTS
• The present invention is directed at reducing wall stress in a failing heart. Diastolic wall stress is considered to be an initiator of muscle damage and chamber enlargement. For this reason, it is desirable to reduce diastolic wall stress to prevent the progression of the disease. The significant impact of stress occurs at all stages and functional levels of heart failure, however, independent of the original causes. For example, in asymptomatic early stages of heart failure, mechanical stress can lead to symptomatic heart failure marked by an enlarged heart with decreased left ventricle function. As the heart enlarges, mechanical stress on the heart wall increases proportionally to the increasing radius of the heart in accordance with LaPlace's Law. It can thus be appreciated that as stress increases in symptomatic heart failure, those factors that contributed to increasing stress also increase. Thus, the progression of the disease accelerates to late stage heart failure, end stage heart failure and death unless the disease is treated.
• Three parameters influence mechanical stress on the muscle. These are: (1) muscle mass, i.e., as reflected by the thickness of the muscle; (2) pressure in the chamber which is a function of the resistance to blood flow of the patient's vasculature and the volume of blood within the patient; and (3) chamber geometry. The present invention pertains to devices and methods for directly and passively changing chamber geometry to lower wall stress. In addition to treatment of heart failure, the devices and methods of the present invention also lend themselves to application in the case of a decrease in cardiac function caused by, for example, acute myocardial infarction.
• The devices disclosed herein for changing chamber geometry are referred to as “splints”. In addition to splints, wraps which can be placed around the heart can limit muscle stress without the chamber shape change. When a wrap is used, wall stress is merely transferred to the wrap, while the generally globular shape of the heart is maintained. A wrap could be used in conjunction with a splint to modulate heart wall stress reduction at various stages of the cardiac cycle.
• The present invention includes a number of splint embodiments. Splints and wraps can be classified by where in the cardiac cycle they engage the heart wall, i.e., mechanically limit the size of the left ventricle in the case of wraps and change the geometry of the ventricle in the case of splints. If a splint or wrap only begins to engage during diastolic filling, the splint can be termed a “restrictive splint”. If the splint or wrap is engaged throughout the cardiac cycle, both during diastolic filling and systolic contraction and ejection, the splint can be termed a “full cycle splint”. The wrap will generally be a restrictive device which begins to engage during diastolic filling to increase the elastance (reduces compliance) of the chamber. If a wrap is made from elastic material it may engage full cycle, but the force required to elongate the wrap will increase as diastolic filling progresses, preload strain will be reduced without an improvement in systolic contraction.
• FIG. 1 is a view of a heart A in a normal, generally vertical orientation. Awrap11 surrounds heart A and atransventricular splint12 extends through the heart and includes an anchor oranchor pad13 disposed on opposite sides of the heart.FIG. 2 is a horizontal cross sectional view of heart A taken throughwrap11 andsplint12.Splint12 includes atension member15 extending through left ventricleB. Anchor pads13 are disposed at each end oftension member15. Right ventricle C is to the left of left ventricle B.
• InFIG. 1, wrap11 andsplint12 are shown engaged with heart A. InFIG. 2, heart A is shown spaced fromwrap11 except atanchor pads13. InFIG. 2, heart A is thus at a point in the cardiac cycle where the muscles are shortening during systole, or have yet to stretch sufficiently during diastolic expansion to reachwrap11. Accordingly, wrap11 can be considered a restrictive device as it does not engage the heart full cycle. Althoughwrap11 is in contact with heart A atpads13, only the splint is providing a compressive force to change the shape of the heart and limiting the stress of the heart inFIG. 2.
• If heart A, as shown inFIG. 2 is at end systole,transventricular splint12 is a full cycle device as the cross section of left ventricle B does not have the generally circular unsplinted shape. Alternately, wrap11 could be secured to heart A by sutures or other means thansplint12, in which case wrap11 would be merely a restrictive device. It should be noted that unlesswrap11 extends vertically along heart A a sufficient amount, as heart A expands and engages wrap11, the portion of left ventricle B disposed above or belowwrap11 could expand substantially further than that portion of the left ventricle wall restrained bywrap11. In such a case, left ventricle B could have a bi-lobed shape in a vertical cross section. As such, thewrap11 would not be merely limiting the size of the left ventricle, but rather inducing a shape change in the left ventricle. In such a case, theelement11 would not be a wrap, but rather a splint which could be referred to as a “band splint”.
• Each of the splints, wraps and other devices disclosed in this application preferably do not substantially deform during the cardiac cycle such that the magnitude of the resistance to the expansion or contraction of the heart provided by these devices is reduced by substantial deflection. It is, however, contemplated that devices which deflect or elongate elastically under load are within the scope of the present invention, though not preferred. The materials from which each device are formed must be biocompatible and are preferably configured to be substantially atraumatic.
• The distinction between restrictive devices, such as restrictive splints and wraps, and full cycle splints and wraps, can be better understood by reference toFIG. 3.FIG. 3 is a plot of sarcomere, i.e., heart wall muscle, stress in (g/cm²) versus strain throughout a normal cardiac cycle N, and a failing heart cardiac cycle F. The cardiac cycles or loops shown onFIG. 3 are bounded by the normal contractility curve N_cand failing heart contractility curve F_cabove and to the left, and thediastolic filling curve12 toward the bottom and right. Contractility is a measure of muscle stress at an attainable systolic stress at a given elongation or strain. It can be appreciated that the muscle contractility N_cof normal muscle tissue is greater than the contractility F_cof the muscle tissue of a failing heart. Thediastolic filling curve12 is a plot of the stress in the muscle tissue at a given elongation or strain when the muscle is at rest.
• An arbitrary beginning of the normal cardiac cycle N can be chosen atend diastole14, where the left ventricle is full, the aortic valve is closed. Just afterend diastole14, systole begins, the sarcomere muscles become active and the mitral valve closes, increasing muscle stress without substantially shortening (sometimes referred to as “isovolumic contraction”). Stress increases until the aortic valve opens at16. Isotonic shortening begins and stress decreases and the muscles shorten until end systole18, where the blood has been ejected from the left ventricle and the aortic valve closes. After end systole18, diastole begins, the muscles relax without elongating until diastolic filling begins when the mitral valve opens at20. The muscles then elongate while the mitral valve remains open during diastolic filling untilend diastole14. The total muscle shortening and lengthening during the normal cycle N is N_s.
• An analogous cycle F also occurs in a failing heart. As the left ventricle has dilated, in accordance with LaPlace's Law, the larger radius of a dilated left ventricle causes stress to increase at a given blood pressure. Consequently, a failing heart must compensate to maintain the blood pressure. The compensation for the increased stress is reflected in the shift to the right of failing heart cardiac cycle F relative to the normal cycle N. The stress, atend diastole22 is elevated over the stress atend diastole14 of the normal heart. A similar increase can be seen for the point at which the aortic valve opens24,end systole26 and the beginning of diastolic filling28 relative to the analogous points for the normal cycle N. Muscle shortening and elongation F_sthroughout the cycle is also reduced in view of the relative steepening of thediastolic curve12 to the right and the flatter contractility curve F_crelative to the normal contractility N_c.
• By reference to the heart cycle stress strain graph ofFIG. 3, the effect on mechanical muscle stress and strain caused by the use of the devices and methods of the present invention can be illustrated. Restrictive devices begin to engage during diastolic filling, which in the case of a failing heart occurs alongdiastolic filling curve12 betweenpoint28 and22. Restrictive devices do not engage atend systole26. Thus, the acute effect of placement of a restrictive device is to reduce muscle stress at end diastole relative to the stress atpoint22, and shift the line22-24 to the left reducing muscle shortening and elongation F_s. Acutely, the cardiac cycle will still operate between the failing heart contractility curve F_cand thediastolic filling curve12. If chronic muscle contractility increases such that the muscle contractility curve F_cshifts back toward the normal heart contractility curve N_cas a consequence of the stress reduction, the stress/strain curve F of the cardiac cycle will shift to the left reducing mechanical stress still further.
• The effect on the stress/strain relationship of a full cycle splint will acutely shift the entire stress/strain curve F for the cycle to the left. That is, stress is reduced at bothend diastole22 andend systole26. Muscle shortening and elongation F_swill increase acutely. If, as in the case of a restrictive splint, muscle contractility F_cimproves, the entire cardiac cycle curve F will shift further to the left reducing mechanical stress still further.
• The type and magnitude of shape change are important factors in determining the effectiveness of splinting. There are several types of lower stress cardiac geometries that can be created from an enlarged globular left ventricular chamber typically associate with heart failure. They include lobed, disc-like, narrowed elongate, and multiple vertically stacked bulbs.
• FIG. 4 shows an idealized horizontal cross section of aleft ventricle30 subdivided into twosymmetrical lobes32 and34 having an arc passing through an angle θ>π, and aradius R lobes32 and34 can be formed using a splint, such astransventricular splint12 shown inFIGS. 1 and 2.Lobes32 and34 are joined atpoints36 and38.Points36 and38 are separated by a distance l.
• FIG. 5 is an idealized horizontal cross section of aleft ventricle40 subdivided into three generally equalsized lobes42,44 and46. Each lobe has an equal radius and has an arc passing through an angle less than π. Adjacent ends of thelobes48,50 and52 are separated by a distance l. A plurality of transventricular splints such assplint12 as shown inFIGS. 1 and 2 could be extended between adjacent ends48,50 and52 to formlobes42,44 and46.
• For a restrictive splint, thehorizontal cross sections30 and40 will have a generally circular shape, i.e., a non-splinted shape at end systole. As diastolic filling proceeds, the radius of the circular shape will continue to increase until the splint engages. At the point the splint engages, the lobed shape will begin to form. In the case of the two lobe splinting ofFIG. 4, the radius will continue to increase as diastolic filling proceeds. In the case of the three or more lobed shape, such as the three lobed configuration ofFIG. 5, radius R will decrease as diastolic filling proceeds. The radius will continue to decrease unless or until the pressure in the heart causes tile heart to expand such that the arc of the lobe passes through an angle θ greater than π.
• In the case of a full cycle splint, at end systole, the splint will already be engaged. Thus, for a full cycle splint at end systole, the horizontal cross section of the chamber will not have the normal generally circular shape. Rather, at end systole, thehorizontal cross sections30 and40 will have a lobed shape such as shown inFIGS. 4 and 5. Subsequent shape change during diastolic filling for a full cycle splint will be similar to that described with respect to restrictive splints.
• In view of LaPlace's Law which states that stress is directly proportional to radius of curvature, it can be appreciated that whether the radius is increasing or decreasing during diastolic filling, will have an impact on heart pumping performance. Where R is increasing during diastolic filling, wall stress will increase more rapidly than where R is decreasing. The number of lobes that are created can significantly influence the level of end diastolic muscle stress reduction achieved through splinting. Eventually adding additional lobes forms a configuration which approaches a behavior similar to a wrap. If a wrap is substantially inelastic, or of sufficient size, a wrap will only engage the heart wall at some stage of diastolic filling. If the wrap is substantially inelastic, as pressure increases in the chamber during diastolic filling, stress in the heart wall muscle will increase until the wrap fully engages and substantially all additional muscle elongating load created by increased chamber pressure will be shifted to the wrap. No further elongation of the chamber muscles disposed in a horizontal cross section through the wrap and the chamber will occur. Thus, inelastic wraps will halt additional preload muscle strain (end diastolic muscle stretch).
• The type of shape change illustrated inFIGS. 4 and 5 is of substantial significance for restrictive splints. It is undesirable in the case of restrictive splints, to excessively limit preload muscle strain. The Frank-Starling Curve demonstrates the dependence and need for variable preload muscle strain on overall heart pumping performance. During a person's normal activities, their body may need increased blood perfusion, for example, during exertion. In response to increased blood perfusion through a person's tissue, the heart will compensate for the additional demand by increasing stroke volume and/or heart rate. When stroke volume is increased, the patient's normal preload strain is also increased. That is, the lines14-16 and22-24 of the normal and failing hearts, respectively, will shift to the right. An inelastic wrap will, at engagement, substantially stop this shift. In the case of the bi-lobed shape change ofFIG. 4 or a multiple lobed change having a small number of lobes ofFIG. 5, significant stress reduction can be achieved while allowing for variable preload strain. If the number of lobes is increased substantially, however, variable preload will decrease as the multi-lobed configuration approaches the performance of an inelastic wrap.
• The magnitude of shape change in the case of full cycle splinting becomes very important as full cycle splinting generally reduces chamber volume more than restrictive splinting. Although as with restrictive devices, the type of shape change is also important to allow for variable preload strain. Both restrictive device and full cycle splints reduce chamber volume as they reduce the cross sectional area of the chamber during the cardiac cycle. The magnitude of the shape change can vary from very slight at end diastole, such that chamber volume is only slightly reduced from the unsplinted end diastolic volume, to an extreme reduction in volume, for example, complete bifurcation by transventricular splint. The magnitude of the shape change, for example, as measured by the ratio of splint length to nonsplinted ventricular diameter, is preferably modulated to reduce muscle stress while not overly reducing chamber volume. For full cycle splint, the reduction of chamber volume is compensated for by increased contractile shortening, which in turn leads to an increased ejection fraction, i.e., the ratio of the stroke volume to chamber volume. For given stress/volume and stress/shortening relationships, there will be a theoretical optimum maximal stroke volume. Clinically, 20% to 30% stress reduction is expected to be attainable through full cycle bi-lobe splinting. See U.S. Pat. No. 5,961,440 and the discussion further herein for calculation of stress reduction for idealized bi-lobe splinting.
• When using the full cycle and restrictive devices described herein, caution should be .exercised to limit the pressure on the coronary vasculature. In the case of transventricular splints, valve structure, electrical pathways and coronary vasculature should be avoided.
• FIG. 6 is a vertical view of a heart A similar to that shown inFIG. 1. Rather than having a single band splint surrounding heart A, there are twoband splints51 affixed to the heart by two transventricular splints52.Splints52 include oppositely disposed anchors oranchor pads53.FIG. 7 is a horizontal cross sectional view of heart A ofFIG. 6, wraps51 andsplint52.Splints52 include atension member54 disposed through leftventricle B. Pads53 are disposed on the opposite ends oftension members54. Right ventricle C is shown to the left of left ventricle B.
• Splints52 can be restrictive or full cycle splints.Band Splints51 are shown as restrictive band splints as inFIG. 6, heart A is shown engaged with the band splints51, whereas inFIG. 7, heart A has contracted to move away from band splints51.Wraps51 andsplints52 should be made from biocompatible materials. Band splints51 are preferably made from a pliable fabric or other material which resists elongation under normal operating loads. Band splints51 can, however, be made from an elastic material which elongates during the cardiac cycle.Tension members54 also preferably resist elongation under normal operating loads.Tension members54 can, however, be made from an elastic material which elongates during the cardiac cycle.
• FIG. 8 is a vertical view of heart A,partial wrap61 andtransventricular splint62.Transventricular splint62 includesanchor pads63.FIG. 9 is a horizontal cross sectional view of heart A,partial band splint61 andsplint62.Splint62 is essentially similar to wrap orband splint12 shown inFIGS. 1 and 2.Partial band splint61 is also essentially similar to wrap orband splint11 shown inFIGS. 1 and 2 except thatband splint61 only surrounds a portion of heart A. This portion is shown inFIGS. 8 and 9 to the left including a portion of left ventricle B.
• FIG. 10 is a horizontal cross sectional view of left ventricle B and right ventricle C of heart A taken at a similar elevation as that shown inFIG. 2. Asplint70 is shown disposed onheart A. Splint70 includes a frame having two heart engaging anchors orpads72 disposed at its opposite ends. A thirdheart engaging pad73 is disposed alongframe70 approximately midway betweenpads72.
• Pads72 are shown engaged with heart A to change the shape of ventricle B inFIG. 10.Pads73 are not engaged with heart A inFIG. 10.FIG. 11 is the same horizontal cross sectional view asFIG. 10 except that heart A has to contactpad73 to create a further shape change of left ventricle B.
• Frame70 is preferably rigid enough thatpads72 could be disposed on the heart for full cycle splinting and sufficiently adjustable thatpads72 could be spaced further apart for restrictive splinting.Pad73 accomplishes restrictive splinting.Frame71,pads72 and73 ofsplint70 are made of a biocompatible material.Pads72 and73 are preferably substantially atraumatic.
• FIG. 12 is a vertical view of heart A shown in phantom line. Shown disposed about the ventricles of heart A is a basket-like band splint100.Band splint100 includes a horizontalencircling band101 around an upper region of the ventricles and fourbands102 which extend downward toward the apex of heart A. It can be appreciated thatbands102 can act as splints to form four lobes in heart A in a horizontal plane. Depending on the placement ofbands102 around heart A, lobes could be created only in the left ventricle or in the left ventricle and/or other chambers of the heart.Band102 is joined at the apex.Band101 andband102 can be made from a webbing, fabric or other biocompatible material.
• Ifband splint100 substantially elongated elastically under normal operating loads, it could be friction fit to heart A and act full cycle, limiting muscle stress at end diastole as well end systole.Band splint100 could be sutured into place or otherwise held on heart A and act as a restrictive device. Ifband101 were securely fastened to heart A,bands102 could limit the vertical elongation of heart A during diastolic filling.
• FIG. 13 is analternate embodiment110 of the band splint ofFIG. 12.Band splint110 includes a horizontallyheart encircling band111 and fourbands113 extending downward fromband111.Bands113, however, unlikebands102 ofband splint100 do not extend to the apex of heart A, but rather to a second horizontallyheart encircling band112.
• Band splint110 could be made of the same materials asband splint100.Band splint110 can also be used in a manner similar toband splint100 except thatband splint110 would limit the vertical elongation of the ventricles less thanband splint100.
• FIG. 14 is yet anotheralternate embodiment120 of the wrap ofFIG. 12.Band splint120 closely resemblesalternate embodiment110 ofFIG. 13, except that rather than having four vertically extending web members,band splint120 includes two substantiallyrigid members123 interconnecting two horizontally encirclingweb members121 and122.
• FIG. 15 is yet anotheralternate embodiment130 of the band splint ofFIG. 12. Like the wrap ofFIG. 12,band splint130 includes a horizontally encirclingmember131 and four downwardly extendingmembers132. At a location proximate of the apex of heart A,members132 are joined by aring133.Members132 extend throughring133.Ring133 can be used to adjust the length ofmembers132 betweenband131 andring133.Ring133 can be formed from metallic material and crimped inwardly to fix its position alongmembers132. Other means of holdingring133 in position would be readily apparent to those skilled in the art.
• FIG. 16 is a vertical view of heart A including apartial band splint140 secured around a substantial portion of left ventricleB. Band splint140 includes a vertically elongatinganchor member141 which sutures142 can encircle to anchormember141 to heart A. Aband143 extends generally horizontally fromanchor member141 to anopposite anchor141.
• The length ofband143 can be seen in its entirety inFIG. 17 which is a horizontal cross sectional view of heart A throughband143, left ventricle B and right ventricle C. InFIG. 16, heart A is shown engaged withband143, however, InFIG. 17,band143 is shown spaced from heart A. Thus, in this configuration, wrap140 would be acting as a restrictive device. Ifband splint140 were made from a material that substantially deforms elastically under normal loads,band splint140 could also be secured sufficiently snuggly to heart A to act as a full cycle device. Preferably. however,band143 ofband splint140 is formed from a webbing or substantially inelastic fabric.
• FIG. 18 is a vertical view of heart A including awrap160. Wrap160 can include a single thread orline161 encircling the heart several times. Afterline161 encircles heart A,line161 can be threaded through abar162, including a plurality ofeyelets163 spaced along its length in pairs.Bar162 is preferably rigid enough to substantially maintain the distance betweeneyelets163 under normal operating loads.
• Whenline161 is placed in heart A, one end ofline161 can be tied to bar162 at164.Line161 can then encircle the heart and be drawn througheyelet162 adjacent the beginning ofline161 at164.Line161 can then be drawn through oneeyelet163 of a lower pair of eyelets to encircle the heart again. This process continues untilline161 is tied to aneyelet163 at165. It can be appreciated thatwrap160 could be used as a restrictive or full cycle device depending on the diameter of loop formed byline161.
• FIG. 19 is analternate embodiment170 of the wrap ofFIG. 18.Wrap170, however, includes two vertically extendingbars172 havingeyelets173 through whichline171 is threaded.Line171 can be tied to one of thebars172 at174 and175.
• FIG. 20 is a vertical view of heart A including yet anotherembodiment180 of the wrap ofFIG. 18.Wrap180 includes aline181 encircling heart A a plurality of times. Rather than having a single vertically extendingbar162 to positionline180 on heart A, wrap180 includes a plurality ofhorizontal bars182 including a pair ofeyelets183. One end ofline181 is tied to anupper bar182 at184 and the opposite end ofline181 is tied to alower bar182 at185. Between184 and185,line181 is threaded througheyelets182 to form the heart encircling pattern shown inFIG. 20.
• FIG. 21 is a vertical view of heart A including yet anotheralternate embodiment190 of the wrap ofFIG. 18.Wrap190 closely resembles180 ofFIG. 20.Line181 has, however, been threaded througheyelets183 ofbars182 in a pattern which unlike that ofFIG. 20,bars182 are disposed at various selected locations around the circumference of heart A.
• FIG. 22 is a vertical view of heart A including awrap200.Wrap200 is substantially similar to wrap11 ofFIGS. 1 and 2, except thatwrap200 extends vertically a greater distance thanwrap11.Wrap200 is not shown with a transventricular splint. It can be appreciated thatwrap200 could be used as restrictive or full cycle device.
• FIG. 23 is a horizontal cross section of a human torso including heart A, left ventricle B, right ventricle C, lungs E and ribs G. Awrap210 is shown partially encircling heart A. Opposite ends ofwrap210 are anchored at211 to ribs G. At211, wrap210 can be anchored to ribs G by bone screw, knot or other means of fastening. It can be appreciated thatband splint210 could be used as a restrictive or full cycle device.
• FIG. 25 is a vertical view of heart A having a horizontal width W₁.FIG. 26 is an idealized horizontal cross sectional view of heart A ofFIG. 25. Heart A includes left ventricle B and right ventricle C. Left ventricle B has a radius R₁.
• FIG. 27 is a view of adevice220.Device220 includes a horizontally encirclingband222 which can be affixed to heart A by sutures, other attachment means or friction fit. Extending fromband222 is a substantially rigidelongate member224.Member224 extends to the apex ofheart A. Pin226 extends into left ventricle B of the apex. An anchor orpad228 is disposed within left ventricle B to anchor the apex of heart A to elongatemember224.Elongate member224 can be made of sufficient length such that heart A is vertically elongate full cycle, or alternately not at end diastole.
• FIG. 28 is a vertical view of an elongate heart A having a horizontal width W₂less than W₁.FIG. 29 is a horizontal cross section of the heart A ofFIG. 28 including left ventricle B and right ventricle C. InFIG. 29, the radius R₂of left ventricle B is less than R₁ofFIG. 26. Assuming that the hearts ofFIGS. 25 and 28 are at the same point in the cardiac cycle, it can be appreciated that the wall stress in heart A is less inFIG. 29 as R₂is shorter R.
• Ifelongate bar224 is sized such thatdevice220 does not engage at end diastole, but rather anchor pad228 first engages during systolic contraction,device220 can fall into a third class of device neither full cycle nor restrictive. Such a device would reduce wall stress during a portion of systolic contraction including end systole, but not reduce wall stress during end diastole, thus maintaining maximum preload.
• Band222 ofdevice220 is preferably formed from a web material or other fabric.Band220 is preferably does not elongate substantially during diastolic filling.Members224,226 and228 are formed from materials which remain substantially rigid under the influences of the forces encountered during the cardiac cycle.
• FIG. 30 is a horizontal cross sectional view of heart A including left ventricle B and right ventricleC. A device260 including a thread orline261 is disposed transventricularly and transmyocardially through heart A. A portion ofline261 is disposed outside of heart A. Opposite ends ofline261 are connected at262. Those portions ofline261 outside heartA form loops263. The size ofloops263 are exaggerated for purposes of illustration. It is assumed that heart A in the process of diastolic filling inFIG. 30, andloops263 are sufficiently small, eventually heart A will engageloops263. In such a configuration,device260 is used as a restrictive device.Loops263 could be sized, however, such that they engage full cycle.
• Line261 is preferably made from atraumatic biocompatible material. The diameter ofline261 is preferably sufficiently great that cutting of heart A does not occur during diastolic filling.
• FIG. 31 is a horizontal cross sectional view of heart A including left ventricle B and right ventricle C and analternate embodiment270 of the device ofFIG. 30.Device270 includes aline271 which does not extend transventricularly but extends through the myocardium of heart A to form fourloops273.
• Device270 can be formed from material similar to that used to formdevice260. Additionally,device270 can be made to function as a restrictive device or full cycle device in a manner similar to that ofdevice260.
• Line261 and line267 could be disposed within a tube to avoid cheese cutting of the myocardium. The tube may be highly flexible, yet durable enough to prevent the line from cheese cutting through the myocardium of the heart.Devices260 and270 could extend through the septum or right ventricle to avoid forming lobes in right ventricle C.
• FIG. 32 is a vertical view of heart A including threedevices270 disposed at three spaced elevations. An elongate generallyrigid bar274 is disposed throughloops273 to distribute the load on heart A fromloops273 across a larger area thanlines271 can alone.
• It should be understood that although devices disclosed herein are described in relation to the left ventricle of a human heart, these devices could also be used to reduce the radius or cross-sectional area of the other chambers of a human heart in transverse or vertical directions, or at an angle between the transverse and vertical.
• FIG. 33 shows a transverse cross-section of a left ventricle10′ and aright ventricle12′ of ahuman heart14′.FIG. 33 also shows an embodiment of the present invention deployed with respect to left ventricle10′ ofhuman heart14′. Here acompression frame structure300 is engaged withheart14′ atatraumatic anchor pads310. Acompression member312 having anatraumatic surface314 presses against a wall of left ventricle10′ to reduce the radius or cross-sectional area thereof.
• FIG. 34 is a transverse cross-sectional view ofhuman heart14′ showing yet another embodiment of the present invention. In this case aclamp400 havingatraumatic anchor pads410 biased toward each other is shown disposed on a wall of left ventricle10′. Here the radius or cross-sectional area of left ventricle10′ is reduced by clamping off the portion of the wall betweenpads410.Pads410 can be biased toward each other and/or can be held together by a locking device.
• Each of the various embodiments of the present invention can be made from materials which can remain implanted in the human body indefinitely. Such biocompatible materials are well-known to those skilled in the art of clinical medical devices.
• In use, the various embodiments of the present invention are placed in or adjacent the human heart to reduce the radius or cross-section area of at least one chamber of the heart. This is done to reduce wall stress or tension in the heart or chamber wall to slow, stop or reverse failure of the heart.
• To discuss further the stress reduction associated with splinting,FIG. 35 is a view of a cylinder oridealized heart chamber48′ which is used to illustrate the reduction of wall stress in a heart chamber as a result of deployment of the splint in accordance with the present invention. The model used herein and the calculations related to this model are, intended merely to illustrate the mechanism by which wall stress is reduced In the heart chamber. No effort is made herein to quantify the actual reduction which would be realized in any particular in vivo application.
• FIG. 36 is a view of theidealized heart chamber48′ ofFIG. 35 wherein the chamber has been splinted along its length L such that a “figure eight” cross-section has been formed along the length thereof. It should be noted that the perimeter of the circular transverse cross-section of the chamber inFIG. 35 is equal to the perimeter of the figure eight transverse cross-section ofFIG. 36. For purposes of this model, opposite lobes of the figure in cross-section are assumed to be minor images.
• FIG. 37 shows various parameters of the figure eight cross-section of the splinted idealized heart chamber ofFIG. 36. Where l is the length of the splint between opposite walls of the chamber, R₂is the radius of each lobe, θ is the angle between the two radii of one lobe which extends to opposite ends of the portion of the splint withinchamber48′ and h is the height of the triangle formed by the two radii and the portion of the splint within thechamber48′ (R₁is the radius of the cylinder ofFIG. 35). These various parameters are related as follows:
• 
  h=R₂COS(θ/2)
• 
  l=2R₂SIN(θ/2)
• 
  R₂=R₁n/(2π−θ)
• From these relationships, the area of the figure eight cross-section can be calculated by:
• 
  A₂=2π (R₂)²(l−θ/2π)+h1
• Wherechamber48′ is unsplinted as shown inFIG. 35, A₁, the original cross-sectional area of the cylinder, is equal to A₂where θ=180°, h=O and l=2R₂. Volume equals A₂times length L and circumferential wall tension equals pressure within the chamber times R₂times the length L of the chamber.
• Thus, for example, with an original cylindrical radius of four centimeters and a pressure within the chamber of 140 mm of mercury, the wall tension T in the walls of the cylinder is 104.4 newtons. When a 3.84 cm splint is placed as shown inFIGS. 36 and 37 such that l=3.84 cm, the wall tension T is 77.33 newtons.
• FIGS. 38 and 39 show a hypothetical distribution of wall tension T and pressure P for the figure eight cross-section. As θ goes from 180° to 0°, tension T_θin the splint goes from 0 to a 2T load where the chamber walls carry a T load.
• 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 respects, only illustrative. Changes may be made in details, particularly in matters of shape, size and ordering of steps without exceeding the scope of the invention. The invention's scope is defined in the language of the claims.

Claims (16)

What is claimed is:

1. A method for improving the function of a heart, the method comprising:

positioning a passive device relative to an external heart wall, the device including a wrap and at least one elongated band secured to the wrap, wherein the wrap has sufficient length to encircle a portion of the heart, and wherein the band extends in a direction substantially perpendicular to the length of the wrap;

encircling a portion of the heart with the wrap of the device;

securing the device to an epicardial surface of the heart; and

exerting a force on the external heart wall with the device during a portion of a cardiac cycle.

2. The method ofclaim 1, wherein the band includes a plurality of bands.

3. The method ofclaim 2, wherein the plurality of bands are secured to one another.

4. The method ofclaim 1, wherein the device includes a predetermined size adapted to not encompass an apex of the heart, and wherein encircling a portion of the heart with the wrap of the device comprises leaving the apex of the heart uncovered by the wrap.

5. The method ofclaim 1, wherein exerting a force on the external heart wall comprises altering a geometric configuration of the heart.

6. The method ofclaim 5, wherein the geometric configuration is a shape of a heart chamber.

7. The method ofclaim 6, wherein the heart chamber is a left ventricle of the heart.

8. The method ofclaim 1, wherein encircling a portion of the heart with the device comprises fully encircling the heart.

9. The method ofclaim 1, wherein the wrap is substantially elastic.

10. The method ofclaim 1, wherein the wrap is substantially inelastic.

11. A device for improving the function of a heart, the device comprising:

a wrap having sufficient length to encircle at least a portion of the heart but not encompass an apex of the heart; and

a plurality of bands disposed along the length of the wrap, wherein each of the bands extends transversely to the length of the wrap, and wherein the device is a passive device.

12. The device ofclaim 11, wherein the plurality of bands are configured to be secured to one another.

13. The device ofclaim 11, wherein the wrap is configured to completely encircle the heart.

14. The device ofclaim 11, wherein each of the plurality of bands is substantially rigid.

15. The method ofclaim 11, wherein the wrap is substantially elastic.

16. The method ofclaim 11, wherein the wrap is substantially inelastic.

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