Surgery – Cardiac augmentation
Reexamination Certificate
2000-10-03
2004-10-26
Getzow, Scott M. (Department: 3762)
Surgery
Cardiac augmentation
C600S037000
Reexamination Certificate
active
06808483
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to devices used to physically support the heart and, alternatively, also actively assist the pumping action of the heart.
BACKGROUND OF THE INVENTION
The treatment of heart failure over the long term is a difficult problem. At the same time, weak cardiac muscle function is becoming an increasing problem. Patients are surviving longer and more patients are surviving myocardial infarcts leading to a large pool of patients who are inadequately served by current medical practice. Drug treatment to increase the strength of mycardial contraction has been unsuccessful over the long term. Recently, biventricular pacing (rather than the usual univentricular pacing) has been tried and this offers some promise in selected patients but is unlikely to solve the problem.
Devices will therefore remain the mainstay of treatment for terminal heart failure. Conventional methods have been unable to inject adequate energy into the cardiovascular system. Past attempts with the Jarvic heart or other replacement systems have met with problems such as failure due to thromboembolism. The patient is typically connected to a bulky internal or external controller and power supply for the heart replacement system. The inside of the artificial heart exposes a large artificial surface area to the flow of blood and clots develop as a result. These clots eventually break off and lodge in the brain leading to strokes or resulting in ischemic injury to other body organs. It has also been postulated that long-term exposure of blood to large artificial surfaces sets up a chronic inflammatory reaction which may predispose the patient to infection.
Currently, there are two major areas of development. A simplified system involves cannulation of the left ventricle or atrium with a tube-like structure and pumping of blood from this source into the aorta. A blood propeller system is located within the tubing of this system. A drive system powers the pump. The drive system can be located outside the patient, or can be implanted within the patient. If implanted, energy may be transmitted by induction coils from outside the body to the device. This device requires considerable residual cardiac function to operate. The heart must beat adequately to perform some function and usually only the left ventricle is supported by the device. Thus, right ventricular function must be adequate for survival.
The second and more complex pump is a totally implantable heart. The patient's heart is entirely removed or both ventricles are cannulated and artificial left and right ventricles are attached by a surgeon. The patient has a large surface exposed to the flow of blood as the blood comes in contact with the artificial ventricles, the connection tubes and the valves. Blood clotting, hemolysis and degradation of blood become problems in this situation.
For an entire generation, attempts have been made to create a heart assist device which leaves the native heart in place and squeezes the native heart. The blood is thus exposed only to the patient's natural tissue. Clotting on natural tissue is extremely rare. Pneumatically and electrically driven devices have been evaluated, but these devices have not reached clinical application. These devices have wrapped around the entire heart and squeezed both the left and right ventricles. Unfortunately, this does not mimic the way the heart contracts.
U.S. Pat. No. 4,925,443 illustrates a heart assist device including a tension band which is surgically placed within an interventricular muscle wall in order to compensate for weakness of the interventricular muscle wall or septum. An operating mechanism then opens and closes a pair of pressure plates to compress the left ventricle. The drawback to this device, however, is that the interventricular wall or septum experiences significant trauma due to the surgical implantation of the band within the wall or septum itself. Especially in cases in which the interventricular wall is already weakened, such trauma could severely damage the heart.
Another proposed device is disclosed in U.S. Pat. No. 5,119,804. With this device, the heart is placed within a cup having a vacuum source connected to hold the cup in position around the heart and having a pulsed pressure system to alternately apply relatively high positive and negative pressures to provide systolic and diastolic effects on the heart. This system, however, squeezes the entire heart muscle at one time and will tend to cause weaker portions of the heart to bulge outward while stronger portions of the heart muscle retain a normal shape. Therefore, the contraction applied to the heart muscle is not a natural one, but one that is dictated by the particular heart problems of the patient.
Another ventricular assist device is disclosed in U.S. Pat. No. 4,685,446. This device utilizes an inflatable balloon secured to the end of a catheter and inserted into the left ventricle. The balloon is inflated during left ventricular systole and then deflated in a repeating manner. Unfortunately, this device will also tend to cause weakened portions of the heart muscle to bulge around the left ventricle rather than causing the intended function of expelling blood from the ventricle. Thus, the ejection fraction of blood can be deficient with this device as well.
Despite the intuitively attractive nature of heart assist devices, no device has ever been clinically proven. Attention to some physiologic details will make the difference. The left ventricle is a thick-walled structure which propels blood into the systemic circulation at high pressure. The left ventricle is shaped as a truncated cone. During systole (contraction) this cone shortens along its length and narrows around its circumference. By this narrowing and shortening action, the internal volume of the left ventricular cavity decreases and blood is expelled. In a healthy heart, 60% to 70% of the blood volume (that is, the ejection fraction) is expelled on each beat. As the heart fails, the cavity enlarges, the heart wall thins and progressively smaller fractions of blood are expelled on each beat. In other words, the heart shortens and narrows much less during each beat.
The right ventricle has been described as a bellows pump. It wraps around and attaches to the circumference of the outside of the left ventricular wall. The outside wall of the right ventricle is considerably thinner than the wall of the left ventricle and also contracts against a lower pressure. The energy consumption of the right ventricle is therefore much lower than that of the left ventricle. The right ventricle expels blood when the muscle shortens and reduces the diameter of the crescent shaped cavity which is located between the outside wall the interventricular wall or septum shared with the left ventricle.
It is not surprising that merely squeezing the left and right ventricles with a device wrapped around both ventricles has not been successful. With previous devices, the left ventricle does not shorten from base to apex. There is also limited short axis shortening because the device does not squeeze the left ventricle in isolation, but with the right ventricle. To be effective the left ventricle requires more controlled compression. Generally, blood must be expelled from the ventricle in a more controlled and complete manner.
SUMMARY OF THE INVENTION
The present invention is generally directed toward heart support and assist devices including fully passive restraints, combinations of passive and active devices and fully active devices for assisting with heart contractions. Passive restraints generally include an external support member, which may be a strap, web or mesh, sheathing or other member configured to extend around the outside of the heart coupled with an internal support member extending within at least one of the ventricles and against one side of the interventricular septum. This type of passive restraining system can assist the heart muscle by supporting those portions of the muscle necessary
Ortiz Mark
Spence Paul A.
Getzow Scott M.
Spence Paul A.
Wood Herron & Evans L.L.P.
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