US 20060137697 A1
Apparatuses and methods are provided to reconstruct an enlarged left ventricle of a human heart, using a shaper, having a size and shape substantially equal to the size and shape of an appropriate left ventricle, wherein the shaper is adapted to be temporarily placed into the enlarged left ventricle during a surgical procedure. Another aspect of one embodiment comprises a ventricular patch adapted for placement into the left ventricle of a heart made from a sheet of biocompatible material, and having a plurality of markings coupled to the sheet, wherein the markings are configured in distinct patterns for post operatively evaluating movement of the patch. In another aspect of one embodiment, a device is presented, comprising of a handle and a sizing template adapted to be coupled to the handle. Such components are also presented as a kit for use during ventricular restoration surgery.
29. A method for reshaping an enlarged left ventricle of a human heart, comprising:
positioning a shaper in the left ventricle, wherein the left ventricle has a first shape;
using the shaper as a model to reshape at least a portion of the left ventricle such that the reshaped left ventricle has a second shape; and
removing the shaper from the left ventricle.
30. The method of
31. The method of
32. The method of
33. The method of
34. The method of
35. The method of
36. The method of
37. The method of
engaging a wall of the left ventricle of a beating heart to sense tactile feedback; and
determining a demarcation line between non-viable tissue and viable tissue of the left ventricle.
38. The method of
39. The method of
determining a demarcation line between non-viable tissue and viable tissue of the left ventricle; and
excluding at least some of the non-viable tissue;
placing at least one suture along at least a portion of the demarcation line; and
pulling the suture such that the left ventricle is pulled around the shaper.
40. The method of
41. The method of
42. The method of
43. A method for reshaping a left ventricle of a human heart, comprising:
positioning a shaper in the left ventricle; and
reshaping at least a portion of the left ventricle about the shaper such that at least a portion of the left ventricle substantially conforms to a predetermined shape of the shaper.
44. The method of
determining a demarcation line between non-viable tissue and viable tissue;
excluding at least some of the non-viable tissue;
placing at least one suture along at least a portion of the demarcation line; and
pulling the suture such that the left ventricle is pulled around the shaper.
45. The method of
46. The method of
47. The method of
48. The method of
This invention claims the benefit of U.S. Provisional Patent Application Ser. No. 60/272,073 filed on Feb. 28, 2001.
This invention relates generally to surgical methods and apparatus for addressing cardiomyopathy, and more specifically to methods and apparatus for restoring the architecture and normal function of a mammalian heart.
The function of a heart in an animal is primarily to deliver life-supporting oxygenated blood to tissue throughout the body. This function is accomplished in four stages, each relating to a particular chamber of the heart. Initially deoxygenated blood is received in the right auricle of the heart. This deoxygenated blood is pumped by the right ventricle of the heart to the lungs where the blood is oxygenated. The oxygenated blood is initially received in the left auricle of the heart and ultimately pumped by the left ventricle of the heart throughout the body. It can be seen that the left ventricular chamber of the heart is of particular importance in this process as it is relied upon to pump the oxygenated blood initially through an aortic valve into and ultimately throughout the entire vascular system.
The amount of blood pumped from the left ventricle divided by the amount of blood available to be pumped is referred to as the ejection fraction of the heart. Generally, a healthier heart has a higher ejection fraction. A normal heart, for example may have a total volume of one hundred milliliters and an ejection fraction of 60 percent. Under these circumstances, 60 milliliters of blood are pumped with each beat of the heart. It is this volume in the normal heart of this example that is pumped with each beat to provide nutrients including oxygen to the muscles and other tissues of the body.
The heart is part of the body tissue, and the heart muscle also requires oxygenated blood. Its normal function is greatly upset by clotting or closure of the coronary arteries. When the coronary arteries are blocked, an associate portion of the heart muscle becomes oxygen-starved and begins to die. This is clinically referred to as a heart attack. Ischemic cardiomyopathy typically occurs as the rest of the heart dilates in an attempt to maintain the heart's output to the body.
As the ischemia progresses through its various stages, the affected myocardium dies losing its ability to contribute to the pumping action of the heart. The ischemic muscle is no longer capable of contracting so it cannot contribute to either squeezing or twisting motion required to pump blood. This non-contracting tissue is said to be “akinetic.” In severe cases the akinetic tissue, which is not capable of contracting, is elastic so that blood pressure tends to develop a bulge or expansion of the chamber. In this situation, this muscle tissue is not only akinetic, in that it does not contribute to the pumping function, but it is in fact “dyskinetic,” in that it detracts from the pumping function. This situation is particularly detrimental as the heart loses even more of its energy due to pumping the blood to the bulge instead of through the aorta.
After a heart attack, the body seems to realize that with a reduced pumping capacity, the ejection fraction of the heart is automatically reduced. For example, the ejection fraction may drop from a normal 60 percent to 20 percent. Realizing that the body still requires the same volume of blood for oxygen and nutrition, the body causes its heart to dilate or enlarge in size so that the smaller ejection fraction pumps about the same amount of blood. As noted, a normal heart with a blood capacity of seventy milliliters and an ejection fraction of 60 percent would pump approximately 42 milliliters per beat. The body seems to appreciate that this same volume per beat can be maintained by an ejection fraction of only 30 percent if the ventricle enlarges to a capacity of 140 milliliters. This increase in volume, commonly referred to as “remodeling”, not only changes the volume of the left ventricle, but also its shape. The heart becomes greatly enlarged. An enlarged heart will tend to change its architecture from the normal conical or apical shape, to a generally spherical shape.
On the level of the muscle fibers, it has been noted that enlargement or dilation of the heart causes the fibers to reorient themselves so that they are directed away from the inner heart chamber containing the blood. As a consequence, the fibers are poorly oriented to accomplish even the squeezing action, as the lines of force become less perpendicular to the heart wall. This change in fiber orientation occurs as the heart dilates and moves from its normal elliptical shape to its dilated spherical shape. The spherical shape further reduces pumping efficiency since the fibers which normally encircle the apex to facilitate writhing are changed to a more flattened formation as a result of these spherical configurations. The resulting orientation of these fibers produces lines of force, which are also directed laterally of the ventricle chamber. Thus, the dilation and resulting spherical configuration greatly reduces contraction efficiency.
Perhaps the most notable symptom of ischemic cardiomyopathy is the reduction in the ejection fraction which may diminish, for example, from a normal 60 percent to only 20 percent. This results clinically in fatigue and in an inability to do stressful activities that require an increase in output of blood from the heart. The output of blood by the enlarged heart at rest is kept normal, but the capacity to increase output of blood during stress (i.e., exercise, walking) is significantly reduced. Of course, the change in architecture has a dramatic effect on wall thickness, radius, and stress on the heart wall. In particular, it will be noted that absent the normal conical shape, the twisting motion of the heart, which can account for as much as one half of the pumping action, is lost. As a consequence, the more spherical architecture must rely almost totally on the lateral squeezing action to pump blood. This lateral squeezing action is inefficient and very different from the more efficient twisting action of the heart. The change in architecture of the heart will also typically change the structure and ability of the mitral valve to perform its function in the pumping process. Valvular insufficiency can also occur due to dilatation.
Although the dilated heart may be capable of sustaining life, it is significantly stressed and rapidly approaches a stage where it can no longer pump blood effectively. In this stage, commonly referred to as congestive heart failure, the heart becomes distended and is generally incapable of pumping blood returning from the lungs. This further results in lung congestion and fatigue. Congestive heart failure is a major cause of death and disability in the United States with approximately 400,000 new cases annually.
Following coronary occlusion, successful acute reprefusion by thrombolysis, (clot dissolution) percutaneous angioplasty, or urgent surgery can decrease early mortality by reducing arrhythmias and cardiogenic shock. It is also known that addressing ischemic cardiomyopathy in the acute phase, for example with reperfusion, may salvage the epicardial surface. Although the myocardium may be rendered akinetic, at least it is not dyskinetic. Post-infarction surgical re-vascularation can be directed at remote viable muscle to reduce ischemia. However, it does not address the anatomical consequences of the akinetic region of the heart that is scarred. Despite these techniques for monitoring ischemia, cardiac dilation and subsequent heart failure continue to occur in approximately 50 percent of post-infraction patients discharged from the hospital.
Various surgical approaches have been tried to treat the dilation of the ventricle by primarily reducing the ventricular volume. Some of these procedures involve removing or excluding dyskinetic and akinetic regions of the heart, then surgically joining the viable portions of the myocardial walls, typically with the use of a patch surgically placed in the walls using a Fontan stitch.
Typically, the exact placement of the patch has been visually determined using only a visual indication where the typically white scar tissue meets the typically red normal tissue. Location of the patch has been facilitated in a further procedure where a continuous suture has been placed around the ventricular wall to define a neck for receiving the patch. The neck has been formed in the white scar tissue rather than the soft viable muscle. This procedure has relied on cardioplegia methods to stop the beating of the heart and to aid in suture placement.
These surgical procedures have been met with some success as the ejection fraction has been increased, for example, from 24 percent to 42 percent. However, despite this level of success, it is often difficult for the surgeon to reconstruct the shape and size of the left ventricle. If the reconstructed ventricle is too small, the patient will not be able to pump enough oxygenated blood. If the reconstructed ventricle is too large, the ejection fraction may diminish. In addition to the size, the shape of the reconstructed ventricle is also important. If the left ventricle is reconstructed in a spherical shape, a twisting motion of the heart about its apex, which can account for as much as one half of the pumping action, is lost. As a consequence, the spherical shaped reconstructed ventricle must rely almost totally on the lateral squeezing action to pump blood. This lateral squeezing action is inefficient and very different from the more efficient twisting action of the heart. What is needed, therefore is a reliable method and apparatus to allow a surgeon to reconstruct the left ventricle to the appropriate shape, size and contour.
In response to these and other problems, an improved apparatus and method is provided for restoring the geometry of the left ventricle to counteract the effects of cardiac remodeling. One embodiment of the present invention provides an apparatus and method to reconstruct an enlarged left ventricle of a human heart, using a shaper, having a size and shape substantially equal to the size and shape of an appropriate left ventricle, wherein the shaper is adapted to be temporarily placed into the enlarged left ventricle during a surgical procedure. Another aspect of one embodiment comprises a ventricular patch adapted for placement into the left ventricle of a heart made from a sheet of biocompatible material, and having a plurality of markings coupled to the sheet, wherein the markings are configured in distinct patterns for post operatively evaluating movement of the patch. In another aspect of one embodiment, a device is presented, comprising of a handle and a sizing template adapted to be coupled to the handle. Such components are also presented as a kit for use during ventricular restoration surgery.
An overview method of one embodiment is presented which introduces the primary components of one embodiment. A detailed discussion of these components then follows. Finally, a method of using the components is discussed in detail.
Description of Components:
The Shaping Device:
The shape of the normal heart is of particular interest as it dramatically affects the way that the blood is pumped. The left ventricle which is the primary pumping chamber, is somewhat conical or apical in shape in that it is longer (long axis longest portion from aortic valve to apex) than it is wide (short axis widest portion from ventricle wall to septum) and descends from a base with a decreasing cross-sectional circumference to a point or apex. The left ventricle is further defined by a lateral and posterior ventricle wall and a septum, which extends between the auricles and the ventricles. The pumping of the blood from the left ventricle is accomplished by two types of motion. One of these motions is a simple squeezing motion, which occurs between the lateral wall and the septum. The squeezing motion occurs as a result of a thickening of the muscle fibers in the myocardium. This compresses the blood in the ventricle chamber and ejects it into the body. The thickness changes as the ventricle contracts. This is seen easily by echocardiogram and can be routinely measured.
The other type of motion is a twisting or writhing motion, which begins at the apex and rises toward the base. The rising writhing motion occurs because the heart muscle fibers run in a circular or spiral direction around the heart. When these fibers constrict, they cause the heart to twist initially at the small area of the apex, but progressively and ultimately to the wide area of the base. These squeezing and twisting motions are equally important, as they are each responsible for moving approximately one-half of the blood pumped. Turning now to
The shaping device may be of an “appropriate shape” for a patient. In other words, the shaping device may be of a shape similar to the shape of the left ventricle. In one embodiment, the shaping device 200 may be a generally conical shaped object composed of portions of spherical elements having different radii. Referring back to
At a line “E-E”, a width W3 of the shaping device 200 is 0.435*L. Between the line C-C and the line E-E, the side surfaces 204 a and 204 b have a radius of 0.945 L. The shaping device 200 narrows from the line designated “E-E” through a line designated as “F-F” to a vertex 206 at point “G”. It is important to note that the above discussion is illustrative of only one embodiment of the present invention and is not meant to limit the invention to the above ratios or shapes.
In some embodiments, such as illustrated in
The fluid pressure inside the balloon 201 may also be monitored by a pressure transducer, such as a piezoelectric transducer (not shown) coupled to the filler tube 208 with a y-connection (not shown). In other words, one lead of the y-connection would be coupled to a pressure monitor and the other lead would be coupled to the fluid source. Alternatively, the pressure monitor could be coupled to a three way stopcock (not shown), which would monitor the pressure on the filler tube side of the three way stopcock.
The fluid used to fill the balloon 201 may be any one of a number of fluids, such as saline solution or distilled water. Alternatively, another embodiment could use a sealed balloon containing a silicone gel, such as a liquid methyl silicone resin capable of being vulcanized blended with a dimethyl silicone fluid. Such gels are available from Applied Silicon Inc. (Ventura, Calif.). An embodiment using a sealed balloon would not need an external fluid reservoir, such as syringe 210.
The balloon 201 may be conventionally formed on a mandrel (not shown) having dimensions corresponding to the shape, contour and size of the shaping device. As is known in the art, the mandrel can be made of metal, glass or a hardened gelatin. To form the balloon 201, the mandrel is dipped into a polymer solution, which leaves a thin polymer coating on the mandrel surface. After the polymer has cured, the balloon 201 is removed by peeling the thin coating off the mandrel or by flushing mandrel material out of the shaping device.
Shaping Device—Other Embodiments:
The shaping device of the present invention may be made out of a variety of materials in a number of configurations creating a number of embodiments. For instance if the shaping device is molded from a thermoplastic polymer such as PVC or polyethylene or a similar material, the balloon may be “non-expandable” when inflated. In other words, once the balloon is inflated, the balloon 201 will not significantly expand beyond the original shape. To illustrate, several shaping devices might have volumes ranging from 100 cc to 150 cc at 10 cc increments. If a surgeon predetermines that a patient's pre-enlarged left ventricle was 128 cc., then the surgeon might select a non-expandable balloon having a volume of 130 cc. A surgeon could also request a custom non-expandable balloon with a volume specifically sized for an individual patient.
In contrast, if the balloon 201 is made from an elastomeric material, the balloon 201 may significantly expand. Such elastomeric materials may include latex, polyurethane, silicone, and other elastomers sold under the trade names KRATON (Shell Chemical, New York, N.Y.), C-FLEX (Concept Polymer, Largo, Fla.) and SANTOPRENE (Monsanto, St. Louis, Mo.) Once the balloon is substantially inflated, the influx of additional fluid causes additional expansion of the balloon. Using this embodiment, the surgeon would simply inflate the balloon to a specific volume. The original shape of the balloon may be maintained during this expansion by selectively thickening the walls of the balloon.
In another embodiment, the shaping device could have walls that are relatively thick and are coupled to foam spacers or thermoplastic polymer pads surrounding the exterior of the balloon. Turning now to
In yet another embodiment, the shaping device could be a balloon within a balloon.
The shaping device is not limited to polymeric balloon embodiments.
The shaping device 280 illustrated in
As will be explained in greater detail below, a patch is often used in the ventricle reconstruction procedure. A patch is made from sheet material and may be a variety of shapes, including circular, elliptical, or triangular, preferably sized and configured with a shape similar to a Fontan neck, as discussed below. As illustrated in
The sheet material for the patch 300 may be formed from a biocompatible synthetic material, for example, from polyester, Dacron (Hemoshield) manufactured by the DuPont Corporation, or polytetrafluoroethylene (Gortex). The sheet material may also be autologous pericardium, or some other fixed mammalium tissue such as bovine pericardium or porcine tissue. The biocompatible synthetic material patch may be collagen impregnated to assist in hemostasis, or it may be sprayed with a hemostatic sealant to achieve better and instantaneous hemostasis.
The patch may have markings that enable the movement and position of the patch to be post-operatively observed and analyzed under imaging systems, such as Magnetic Resonance Imaging (“MRI”), x-ray machines, fluoroscopy or other external visualization methods, for post-operative clinical evaluation. Such markings will allow identification of the patch and allow for analysis of the heart's contractility in future post-operative evaluations.
The markings may be radiopaque. Radiopaque markings are made from material that are impenetrable to radiation such as x-rays. Radiopaque markings may be applied to the patch material in a wide variety of methods. For instance, if the patch material is from a woven fabric, then radiopaque threads could be woven into the fabric at regular intervals. Such radiopaque threads could be metal and made from alloys of gold, nitinol, platinum, or stainless steel. Radiopaque threads could also be made of a biocompatible polymeric material mixed with a metal powder, such as barium sulfate. Radiopaque markings could also be imprinted onto the fabric with radiopaque ink. Such ink is available from Creative Imprints Inc., (Norton, Mass.).
Other techniques for marking the patch 300 might include chemical vapor deposition, physical vapor deposition, electroplating and ion-beam assisted deposition. In ion-beam assisted deposition, an electron beam evaporator is used to create a vapor of atoms that coats the surface of the material.
Radiopaque threads might interfere with MRI scans because MRI is extremely sensitive to metal and metal can substantially mask MRI signals. However, if metal markings are made sufficiently small, they will show as bands in an MRI scan. Using metal fibers 0.1 mm to 0.05 mm to create the grid or pattern by weaving into the patch can make a patch MRI sensitive. Also, the metal can be applied to the patch by ion deposition which could deposit a layer of metal 0.01 mm thick onto the patch material. Small tubular strands filled with fatty acids could also be used as be used as MRI sensitive markings. Such strands could be woven into the patch material.
The markings may be Positron Emission Tomography (“PET”) sensitive by making the markings slightly radioactive. However, such markings would probably only be useful for a relatively short time frame after the procedure because of radioactive decay.
The markings may also be attached to the material by a variety of mechanical means such as sewing or weaving the markings into patch material or using microclips. Similarly, the markings such as metal threads may also be attached to the material by adhesive means, such as a bio-compatible glue. Such bio-compatible glues are available from Bioglue, Cryolife Inc. (Kennesaw, Ga.) or Cyanoacrylate, by Loc Tite Corp.
In order to be useful, the markings must be arranged in a pattern that allows post operative evaluation. One such pattern is a series of equally spaced substantially parallel lines as illustrated in
Turning now to
Turning now to
In another embodiment, the sizers may have a cutting edge which can be used to cut the patch 300 to the appropriate shape. Turning now to
A set of cutting dies could also be provided which corresponds to the set of sizers. In other words, for each sizer provided in a set of sizers, there would be a corresponding cutting die, sized to be slightly larger than the sizer. Once a surgeon has determined the correct sizer, he could then select the corresponding cutting die and use the cutting die to cut the patch material to the appropriate size. Alternatively, a set of pre-cut patches could be provided, each pre-cut patch corresponding to a particular sizer in the set of sizers. The use of pre-cut patches would eliminate the need to cut the patch material to the required shape. The pre-cut patches may also have pre-printed suture lines which may be used as a guide for the surgeon when attaching the patch to the heart.
Turning now to
Turning now to
In yet another embodiment of the present invention, a kit 600 for surgically reshaping the left ventricle of the heart is illustrated in
With the primary purpose of restoring the ventricle's size, shape and contour, the intent of the procedure initially is to remove that portion of the wall, which is not capable of contracting. Such portions include the scarred dyskinetic segments, which are easy to see visually, and may also include akinetic segments, which do not contract.
Referring now to
In step 706, the patient's chest cavity is opened up in a conventional manner. In step 708, an incision is cut into the myocardial wall of the dilated heart. If the surrounding tissue is dyskinetic, it will typically be formed entirely of thin, elastic scar tissue. It is the elasticity of this scar tissue, which causes the detrimental ballooning, or bulging effects previously discussed.
In step 710, a determination as to where the akinetic portions of the tissue begin and end must be made. The determination between viable and non viable tissue can be made by multiple methods, including: visual inspection, electrical methods, marking with dyes, echocardiography, radionuclear imaging, and palpation of a beating heart.
The electrical methods might include the use of an electromyogram which detects electrical impulses from active tissue to distinguish between the akinetic and viable tissue. Positron Emission Tomography (PET) scanning, Single Proton Emissions Computer Tomography and Electrical Mapping Electrophysiology are all other examples of a method to determine viable tissue from akinetic tissue with by electrical means. With Electrical Mapping Electrophysiology, a catheter is inserted into the heart to find areas void of electrical activity.
Marking with dyes can be accomplished by staining the myocardium tissue with a dye that adheres to viable tissue and does not adhere to scar tissue. Triphenyltetrazolium chloride, Tropinin I or T, and Creatine Kinase are all examples of dyes that perform this marking function.
Once the extent of the non-viable areas are determined, in step 712, the portion of the tissue in the ventricle and septal walls may be excised from the epicardium from the incision to the borderline separating akinetic tissue from viable tissue. This border between akinetic and viable tissue becomes the preferred location of the patch and forms an imaginary circumferential line between the non viable areas and viable areas of the myocardium.
In step 714, the preferred location of the patch 300 is been determined relative to the circumferential line. In step 716, a continuous Fontan stitch may be placed in proximity to the line, along the long axis of the heart. The Fontan stitch produces an annular protrusion, which forms a neck relative to the circumferential line. The annular protrusion may be further defined by placing a rim support around its perimeter. This neck initially may have a round circular configuration. A second Fontan stitch may be placed 90 degrees from the initial stitch along the short axis of the heart. Other stitches may be placed as needed to form the heart to the shaping device. The stitch will serve to shape the heart along the short axis of the heart if needed.
In step 718, the shaping device 200 may then be inserted into the ventricle. The shaping device 200 is then inflated or expanded, the volume of which is equivalent to the appropriate volume of the ventricle for the patient. The shaping device 200 provides the model upon which the ventricle can be shaped and contoured through the use of the Fontan suture in step 720. The Fontan suture may then tightened with the aid of the suture hook 520, in step 722. As the suture or sutures are tightened, the musculature of the myocardium will form the physiologically correct volume, shape and contour over the shaping device. The appropriately oval-shaped opening in the neck defines the area where the patch will be placed. Once the suture is tightened down, the shaping device 200 may be collapsed and removed in step 724.
The size of the opening in the neck formed by the Fontan stitch will vary from patient to patient. If the patch 300 is used to close the ventricle, the surgeon should determine the size of the patch to be used (step 726). To determine the appropriate size of the patch, the surgeon may connect any of the sizers 402 a-402 d to the handle 404 to measure the size of the opening, and thus, the size patch 300 that is needed to fit into the neck formed by the Fontan stitch or stitches. In step 728, the surgeon may then construct a patch. In embodiments with different sizers, once the proper sizer has been selected, the sizer can be placed on the patch and be used as a template to cut the patch 300 to the appropriate size. Alternatively, a surgeon may select a precut patch.
In a preferred method for placing the patch, continuous or interrupted sutures can be threaded through the rim covered annular protrusion. The rim covering acts as a large continuous pledget along the perimeter. After the patch has been moved into position on the neck, the sutures can be tied, in step 730.
Alternatively, in cases of extensive nonfibrotic trabecular tissue on the lateral ventricle, another suture method can be placement of mattressed braided sutures over a pericardial strip from outside the ventricle to its interior through the inner oval of the patch. This procedure can be done in conjunction with other procedures such as: Mitral valve repair, ablation of ventricular arrhythmias for treatment of refractory ischemic ventricular tachycardia.
With the patch, suitably placed, in step 732, the suture line can be sprayed with a hemostatic agent or an agent can be applied to achieve better and instantaneous hemostasis. In step 734, the operative site can be closed by joining or folding over the myocardial walls. Care should be taken not to distort the right ventricle by folding the septum wall over the ventricular wall. Alternatively, the lateral wall can be disposed interiorly of the septum wall so a majority of the force on the patch is diverted to the lateral wall. These walls can be overlapped in close proximity to the patch in order to avoid creating any cavity between the patch and the walls.
When air evacuation is confirmed by transesophageal echo, the patient can be weaned off bypass usually with minimal, if any inotropic support. Decannulasation may be accomplished with conventional methods (step 736).
As is well known, the human heart contains an electrical conduction system which sends electrical impulses to spark the heart muscle into regular cycles of contraction. This conduction system includes a Sinoatrial node (SA node), Atrioventricular Node (AV node), and Purkinie Fibers which act as conduits for the electrical pulses. The SA node is located in the right atrium. The electrical impulse leaves the SA node and travels to the right and left Atria, causing them to contract together. This takes 0.04 seconds. There is now a natural delay to allow the Atria to contract and the Ventricles to fill up with blood. The electrical impulse has now traveled to the Atrioventricular Node (AV node). The electrical impulse now goes to the Bundle of His, then it divides into the Right and Left Bundle Branches where it rapidly spreads using Purkinje Fibers to the muscles of the Right and Left Ventricle, causing them to contract at the same time.
Because ventricular restoration may compromise the conduction system due to the fact that a ventricle portion has been severed or excluded, the pacing or rhythm of the impulses between the right and left ventricles of the heart may get out of synchronization after ventricular restoration. This asynchronous pacing contributes to a reduced output by the left ventricle. Thus, restoring or assuring synchronization would assist the reconstructed left ventricle to maximize the output of the left ventricle. Synchronization may be restored or controlled by implanting a pacemaker or a Biventricular pacing device (“BVP”) before closing the chest cavity.
A pacemaker comprises: (1) an implantable controller that sets the heart rate to the desired interval, and (2) two leads that deliver electrical impulses to specific regions of the heart (i.e., one lead is placed in the right atrium and the second lead in right ventricle) to artificially cause contractions of the ventricle at the appropriate time and synchronization. In contrast, BVPs have a third lead designed to conduct signals directly into the left ventricle. When using a BVP, one lead is placed in the right atrium, the second lead in right ventricle, and third lead is placed to pace the left ventricle (i.e., in a tributary of the coronary sinus in the left ventricle). Thus, with a BVP, simultaneous electrical impulses are given to both left and right ventricles so the time delay in traveling of electrical impulse is significantly reduced which aids in restoring the normal physiology of the heart and improves the pumping action of the heart.
Pacemakers and biventricular pacing devices are available from Medtronic, Inc. (Minneapolis, Minn.), Guidant Corporation (Menlo Park, Calif.), and St. Jude Medical Inc. (St. Paul, Minn.).
The mortality associated with ventricular restoration is primarily from sudden death caused from extremely fast arrthymias. The higher risk of arrthymias may be caused from the removal of a portion of the left ventricle. This risk may be prevented by implanting a defibrillator at the time of the ventricle restoration. The automatic implantable cardioverter/defibrillator is commonly referred to as an AICD. The AICD is a device that is similar to a pacemaker, but continuously monitors the heart rhythm. If the AICD detects an abnormally fast or slow heart rhythm, it either electrically paces the heart very fast or delivers a small electrical shock to the heart to convert the heart rhythm back to normal.
Some BVP devices have defibrillators built into the circuitry that controls the pacing. Implanting a bi-ventricular pacing device with defibrillator after surgical ventricular restoration will not only optimize the output of the ventricle but also prevent many sudden deaths.
After a BVP has been installed in step 738, closure of the chest cavity may be accomplished in step 740 by conventional methods.
It is further understood that other modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the disclosure will be employed without corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.