Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis
Reexamination Certificate
1999-06-07
2002-09-24
Isabella, David J. (Department: 3728)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Reexamination Certificate
active
06454794
ABSTRACT:
II. BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and apparatus for performing a coronary artery bypass procedure. More particularly, the present invention performs a coronary artery bypass by providing a direct flow path from a heart chamber to the coronary artery. The present invention is suitable for a number of approaches including an open-chest approach (with and without cardiopulmonary bypass), a closed-chest approach under direct viewing and/or indirect thoracoscopic viewing (with and without cardiopulmonary bypass), and an internal approach through catheterization of the heart and a coronary arterial vasculature without direct or indirect viewing (with and without cardiopulmonary bypass).
2. Description of the Prior Art
A. Coronary Artery Disease
Coronary artery disease is the leading cause of premature death in industrialized societies. The mortality statistics tell only a portion of the story. Many who survive face prolonged suffering and disability.
Arteriosclerosis is “a group of diseases characterized by thickening and loss of elasticity of arterial walls.” DORLAND'S ILLUSTRATED MEDICAL DICTIONARY 137 (27th ed. 1988). Arteriosclerosis “comprises three distinct forms: atherosclerosis, Monckeberg's arteriosclerosis, and arteriolosclerosis.” Id.
Coronary artery disease has been treated by a number of means. Early in this century, the treatment for arteriosclerotic heart disease was largely limited to medical measures of symptomatic control. Evolving methods of diagnosis, coupled with improving techniques of post-operative support, now allow the precise localization of the blocked site or sites and either their surgical re-opening or bypass.
B. Angioplasty
The re-opening of the stenosed or occluded site can be accomplished by several techniques. Angioplasty, the expansion of areas of narrowing of a blood vessel, is most often accomplished by the intravascular introduction of a balloon-equipped catheter. Inflation of the balloon causes mechanical compression of the arteriosclerotic plaque against the vessel wall.
Alternative intravascular procedures to relieve vessel occlusion include atherectomy, which results in the physical desolution of plaque by a catheter equipped with a removal tool (e.g., a cutting blade or high-speed rotating tip). Any of these techniques may or may not be followed by the placement of a mechanical support (i.e., a stent) which physically holds open the artery.
Angioplasty, and the other above-described techniques (although less invasive than coronary artery bypass grafting) are fraught with a correspondingly greater failure rate due to intimal proliferation. Contemporary reports suggest re-stenosis is realized in as many as 25 to 55 percent of cases within 6 months of successful angioplasty. See Bojan Cercek et al., 68 AM. J. CARDIOL. 24C-33C (Nov. 4, 1991). It is presently believed stenting can reduce the re-stenosis rate.
A variety of approaches to delay or prevent re-blockage have evolved. One is to stent the site at the time of balloon angioplasty. Another is pyroplasty, where the balloon itself is heated during inflation. As these alternative techniques are relatively recent innovations, it is too early to tell just how successful they will be-in the long term. However, because re-blockage necessitates the performance of another procedure, there has been renewed interest in the clearly longer-lasting bypass operations.
C. Coronary Artery Bypass Grafting
i. Outline of Procedure
The traditional open-chest procedure for coronary artery bypass grafting requires an incision of the skin anteriorly from nearly the neck to the navel, the sawing of the sternum in half longitudinally, and the spreading of the ribcage with a mechanical device to afford prolonged exposure of the heart cavity. If the heart chamber or a vessel is opened, a heart-lung, or cardiopulmonary bypass, procedure is usually necessary.
Depending upon the degree and number of coronary vessel occlusions, a single, double, triple, or even greater number of bypass procedures may be necessary. Often each bypass is accomplished by the surgical formation of a separate conduit from the aorta to the stenosed or obstructed coronary artery at a location distal to the diseased site.
ii. Limited Number of Available Grafts
The major obstacles to coronary artery bypass grafting include both the limited number of vessels that are available to serve as conduits and the skill required to effect complicated multiple vessel repair. Potential conduits include the two saphenous veins of the lower extremities, the two internal thoracic (mammary) arteries under the sternum, and the single gastroepiploic artery in the upper abdomen.
Newer procedures using a single vessel to bypass multiple sites have evolved. This technique has its own inherent hazards. When a single vessel is-used to perform multiple bypasses, physical stress (e.g., torsion) on the conduit vessel can result. Such torsion is particularly detrimental when this vessel is an artery. Unfortunately, attempts at using artificial vessels or vessels from other species (xenografts), or other non-related humans (homografts) have been largely unsuccessful. See LUDWIG K. VON SEGESSER, ARTERIAL GRAFTING FOR MYOCARDIAL REVASCULARIZATION: INDICATIONS, SURGICAL TECHNIQUES AND RESULTS 38-39 (1990)
While experimental procedures transplanting alternative vessels continue to be performed, in general clinical practice, there are five vessels available to use in this procedure over the life of a particular patient. Once these vessels have been sacrificed or affected by disease, there is little or nothing that modern medicine can offer. It is unquestionable that new methods, not limited by the availability of such conduit vessels, are needed.
iii. Trauma of Open Chest Surgery
In the past, the normal contractions of the heart have usually been stopped during suturing of the bypass vasculature. This can be accomplished by either electrical stimulation which induces ventricular fibrillation, or through the use of certain solutions, called cardioplegia, which chemically alter the electrolyte milieu surrounding cardiac muscles and arrest heart activity.
Stoppage of the heart enhances visualization of the coronary vessels and eliminates movement of the heart while removing the need for blood flow through the coronary arteries during the procedure. This provides the surgeon with a “dry field” in which to operate and create a functional anastomosis.
After the coronary artery bypass procedure is completed, cardioplegia is reversed, and the heart electrically stimulated if necessary. As the heart resumes the systemic pumping of blood, the cardiopulmonary bypass is gradually withdrawn. The separated sternal sections are then re-joined, and the overlying skin and saphenous donor site or sites (if opened) are sutured closed.
The above-described procedure is highly traumatic. Immediate post-operative complications include infection, bleeding, renal failure, pulmonary edema and cardiac failure. The patient must remain intubated and under intensive post-operative care. Narcotic analgesia is necessary to alleviate the pain and discomfort.
iv. Post-Operative Complications
Once the immediate post-surgical period has passed, the most troubling complication is bypass vessel re-occlusion. This has been a particular problem with bypass grafting of the left anterior descending coronary artery when the saphenous vein is employed.
Grafting with the internal thoracic (internal mammary) artery results in a long-term patency rate superior to saphenous vein grafts. This is particularly the case when the left anterior descending coronary artery is bypassed. Despite this finding, some cardiothoracic surgeons continue to utilize the saphenous vein because the internal thoracic artery is smaller in diameter and more fragile to manipulation. This makes the bypass more complex, time-consuming, and technically difficult. Additionally, there are physiological characteristics of an artery (such as a tendency to constrict) which
Giese William L.
Knudson Mark B.
HeartStent Corporation
Isabella David J.
Merchant & Gould P.C.
LandOfFree
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