Surgery – Specula – Retractor
Reexamination Certificate
1998-05-29
2002-01-15
Smith, Jeffrey A. (Department: 3732)
Surgery
Specula
Retractor
C600S206000, C600S229000, C600S235000
Reexamination Certificate
active
06338712
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the general art of cardiac surgery, and to the particular field of heart retractors used in beating heart surgery.
BACKGROUND OF THE INVENTION
There are as many as 300,000 coronary bypass graft procedures performed annually in the United States. Each of those procedures may include one or more graft vessels. Currently, each graft vessel must be hand sutured. As many as four or more grafts are placed in a procedure. Until recently, coronary artery bypass procedures have been performed with the patient on cardiopulmonary bypass whereby the heart is stopped with cardioplegia and the surgery performed on an exposed and still heart.
Some pioneering surgeons are performing procedures in which the coronary bypass is performed on a beating heart. That is, without heart-lung bypass and cardioplegia. This minimizes the time it takes to perform the procedure and reduces the cost of the operation by eliminating the heart-lung bypass machine.
Coronary Artery Bypass Grafting (CABG) is performed and a new blood supply to the heart muscle is established when coronary arteries are blocked with calcium or plaque. A new blood supply conduit is joined to the diseased coronary, distal to the blockage, thus providing a fresh supply of oxygenated blood to the vessel in question. Today, this is accomplished by hand suturing a graft vessel (the new supply of blood) to the diseased vessel. This junction is called an anastomosis of vessels. Many different types of supply conduits can be used. Examples are cadaver vein, saphenous vein, radial artery, internal mammary artery, and the like.
By way of background, the basic operation of a heart will be briefly discussed. The heart works like a pump. The left and right ventricles are separate but share a common wall (the septum). The left ventricle is thicker and pumps the blood into the systemic circulation. The work it performs is much greater than the right ventricle. The right ventricle pumps blood into the pulmonary circulation, which is a low pressure circuit. The left ventricle wall (a low energy system) is much thinner than the right ventricle.
The left ventricle fills in diastole and ejects in systole. The difference between the diastolic volume (largest) and the systolic volume (smallest) (the stroke volume or amount of blood ejected on each heartbeat) multiplied by heart rate determines the cardiac output of the heart (liters/min. of flow). The heart shortens during systole as the muscle contracts. There are a number of motions during contraction (including a considerable amount of rotation) but for practical purposes the heart can be thought of as a truncated cone. Shortening occurs along its length and also along its diameter. For purposes of this disclosure, the more important of the two motions is the shortening along the diameter since the ejection volume varies as the square vs. along the length which varies with the first power.
The heart functions well whether the person is upright, upside down, prone or supine. It sits inside the pericardium—a sac which limits its motion and spreads the support on the heart so that no matter how a person positions himself, it is not particularly compressed and is able to fill and then eject with each heartbeat. The concept of the pericardium spreading the load is critical, i.e., when lying supine, the posterior pericardium supports the heart over a large surface of the heart just as when the person is lying on his stomach, the front of the pericardium spreads the load.
When the chest is opened by a median sternotomy it is possible to gain access to all chambers and surfaces of the heart. This combined with the fact that this incision is usually less painful than a thoracotomy (rib separation), makes this the preferred surgical approach to the heart.
The coronary vessels are surface vessels, only occasionally dipping into the myocardium making them accessible without opening the heart. Traditionally, bypass surgery is done with the heart arrested. This stops the motion of the heart and allows the arrest of the coronary circulation so the surgeon sews in a bloodless and easy to see field. Since the heart is stopped, the patient would suffer irreversible damage to the brain and other tissues and organs without the use of the heart-lung machine to support the general circulation. Although the heart-lung machine has been refined, it is particularly toxic to older and debilitated patients and it is expensive.
It is possible to perform surgery off bypass, while the heart is beating and the coronaries are under positive blood pressure; however, there may be problems. One problem is that not all vessels are accessible since some vessels are on the posterior or inferior surfaces and that when such vessels are brought into view by lifting the heart, cardiac performance is impaired such that the cardiac output falls and blood pressure drops. A second problem is that the heart moves so that suturing in vessels (12 to 15 stitches in a vessel under 2 mm in diameter) might be inaccurate and a third problem is that there is blood in the field as the coronary circulation is not interrupted. This last problem is now largely solved by snares, which temporarily stop the flow of blood through the targeted arteries. The problem of lifting the heart is not to impair the performance of the heart while at the same time adequately exposing the heart and regionally immobilizing the vessel during beating heart surgery, and this problem is not solved with any prior art system.
For the heart to be effective, it must have adequate biventricular function (both right and left ventricles). The left ventricle pumps into the high resistance systemic circulation and is thicker and generates considerably more energy than the right ventricle. It is primarily circular in cross section. This displacement of blood (and thus heart output) depends on shortening in the short axis (diameter of the cross section) and to a lesser degree on shortening in the long axis (apex to base). There is also rotational motion to the heart as it contracts, thus imparting multiplanar motion to the heart as it beats; still further, the surface of the heart undergoes multiplanar movement during operation of the heart. The right ventricle pumps into the lower resistance pulmonary circulation and is much thinner and its energy generation is much less than that of the left ventricle. Function of both of these ventricles must be maintained during surgical manipulation of a beating heart.
Therefore there is a significant need for a means and a method for moving a beating heart so as not to impair the performance of the heart while at the same time adequately exposing the heart and regionally immobilizing a vessel during beating heart surgery.
Lifting of the heart is deleterious to heart function for several reasons. First, the lifting of the heart impairs the venous return to the heart so that there is less diastolic filling of the heart (this can largely be corrected by putting the head down and the feet up to increase venous return). Second, the heart is distorted. Using a hand or spatula to lift the heart is quite different than simply changing body position when the heart is inside the chest. The force applied by the hand to the heart is localized so that the heart is no longer a truncated cone, but is much flatter. This shape is much less effective for ejection (the circle is the most effective as it has the highest ratio of volume to diameter) and flattening also limits the diastolic volume so that inadequate filling occurs. Third, lifting pressure applied to a beating heart may deleteriously affect valve function of the heart, in particular, the mitral valve function may be adversely affected by such lifting.
In order to perform cardiac surgery on a beating heart, there is a need to lift, support and orient the heart without reducing its ability to function. Therefore, there is a need for a means and method to move and orient a beating heart into position so any vessel of the heart can be accessed with
Ortiz Mark
Spence Paul A.
Williamson IV Warren P.
Bozicevic Field & Francis LLP
Cannon Alan W.
Origin Medsystems Inc.
Priddy Michael B.
Smith Jeffrey A.
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