The invention described herein was made in the course of work under a grant or award from the Department of Health, Education and Welfare.
A dynamic aortic patch is a device which is permanently surgically implanted in the wall of the aorta to augment the pumping action of the heart. It is sometimes referred to as a mechanical auxiliary ventricle (MAV) or described as a permanently implanted balloon pump.
The device includes a flexible bladder which is inflated and deflated in synchronism with diastole and systole to elevate aortic blood pressure immediately after aortic valve closure. Inflation and deflation of the bladder is accomplished by means of a supply tube connected to the bladder and to a percutaneous access device which is likewise permanently surgically implanted in a patient's body to provide a through-the-skin coupling for connecting the supply tube to an extra-corporeal fluid pressure source. Electrical leads from electrodes implanted in the myocardium are likewise brought out through the skin via a percutaneous access device and the "R" wave of the electrocardiograph is employed to control the fluid pressure source in inflating and deflating the bladder in synchronism with the heart action.
The dynamic aortic patch, as noted above, acts to assist or augment the function of the left ventricle and is best described as an in-series system, as opposed to parallel systems which are capable of taking over the entire function of the left ventricle. While the dynamic aortic patch is restricted in use to patients who have some functioning myocardium, parallel systems require the use of valves. This in turn requires that such parallel systems be operated continuously, because blood clotting can occur if the system is shut down. The dynamic aortic patch, on the other hand, need not be operated full time and in fact is usually operated periodically on a scheduled on-time, off-time regimen. Because the dynamic aortic patch does not require continuous operation, the patient can be at least temporarily independent of the device for periods of one to four hours or more.
The present invention is especially directed to improvements over prior art dynamic aortic patches, an example of which is shown in U.S. Pat. No. 4,051,840. The patch of U.S. Pat. No. 4,051,840 is made up of a generally cigar-shaped external envelope which is permanently sutured in position in an inclusion in the thoracic aorta with one side of the outer envelope exposed at the exterior of the aorta and the other side forming a portion of the interior wall of the aorta. An inflatable bladder is inserted into the interior of this outer envelope after is it sutured in place, and inflation and deflation of the bladder causes the appropriate flexing of the inner wall of the outer envelope in the interior of the aorta.
Experience with the patch of U.S. Pat. No. 4,051,840 has found that there is a slow, but unavoidable, seepage or migration of fluid in the form of plasma and cell fragments through the blood-outer envelope interface into the dead space between the outer envelope and inner bladder. The outer envelope was attached to the wall of the aorta directly, and flexing of the outer envelope during operation of the device occurred closely adjacent the line of juncture between the envelope and aorta wall.
Further, the construction of the device of U.S. Pat. No. 4,051,840 essentially dictates a bladder of elongate tubular shape which in turn imposes practical limitations on the pumping capacity of the patch.
The present invention is directed to improvements in a dynamic aortic patch in which the dead space referred to above is eliminated and in which a more flexible selection of the location of the implanted device--i.e., in the thoracic cavity or in the abdomen--is made possible by a construction in which the pumping capacity may be varied by minor design changes.