This invention relates to apparatus for assisting circulation of blood and more particularly to a device for providing circulatory assistance to patients in ventricular failure whose hearts cannot maintain a blood circulation adequate to sustain life or to patients with acute coronary occlusion to reduce workload of the heart and limit the damage while collateral circulation develops.
The need for devices to provide mechanical assistance for failing blood circulatory systems has been recognized for several years and a number of blood pumps have been developed and tested. One clinically accepted method of assistance is use of an intraaortic balloon pump, an inflatable balloon attached to the end of a catheter and positioned in the thoracic aorta of a patient. The balloon pump is operated in a counterpulsation mode wherein the balloon is inflated with a gas immediately following left ventricular ejection and deflated just prior to the next ventricular ejection, thus imparting a pumping force to the blood and reducing the load on the left ventricle. Balloon pumps, though helpful, are limited to support of the left ventricle only, typically operate only synchronously with the heartbeat of the patient, and can provide support for only a small fraction of the total workload of the left ventricle. Other drawbacks of these devices include possible blockage of arterial branches to major organs during inflation or removal/insertion of the balloon, particularly with children, and the creation of emboli during their insertion or use by fragmenting plaque in the blood vessels.
Another assist device which has been tested clinically is a left ventricular assist device (LVAD) which includes an implantable pump which may be connected between the left ventricle and aorta of a person such as a patient in acute left ventricular failure following open-heart surgery. This pump, which is similar to that described in U.S. Pat. No. 4,104,005 issued in the name of V. L. Poirier, has a flexible bladder which fills from the left ventricle through an inlet valve. Pneumatic pulses, either synchronous with the heartbeat or asynchronous at a fixed rate, apply pressure to collapse the bladder and eject blood through an outlet valve into the aorta. The LVAD, like the balloon pump, is designed to assist the left ventricle only but in contrast thereto may assume total workload of the left ventricle. However, because of the size of the LVAD pump and a requirement that it be implanted, use of the LVAD is restricted to adults. Also the LVAD pump is considerably more invasive than the balloon pump and usually requires a second rather extensive surgical procedure for removal at the end of its period of use of from about one day to two weeks.
A third apparatus for mechanically assisting circulation of blood is shown in U.S. Pat. No. 4,034,742 issued to H. Thoma. The apparatus described in this patent comprises an implantable pumping chamber connectable to the aorta by a conduit through which blood flows to and from the aorta, and an inflatable balloon which is positioned in the aorta downstream of the conduit connection point. In operation, the balloon is inflated during ejection of blood by the left ventricle (systole), blocking the aorta, and blood is sucked into the pumping chamber. This is followed by deflation of the balloon and application of a pneumatic pulse to the pumping chamber during the period of rest of the heart (diastole), which forces blood through the aorta and cardiovascular system of the patient. This apparatus operates in synchronism with the heartbeat and, like the above-described devices, is usable only with the left ventricle and is ill-suited for use with children. Possible imposition of back pressure on the heart by the balloon during filling of the pumping chamber is a further drawback of this apparatus.
Accordingly, it is an object of this invention to provide improved apparatus for assisting circulation of blood in a patient.
It is also an object of the invention to provide a ventricular assist device suitable for supporting the right or left side of the heart.
A further object of the invention is to provide apparatus for assisting circulation of blood which is suited for use with children as well as adults.
Another object of the invention is to provide apparatus for assisting circulation of blood which is simple to implant and remove and which does not impede normal blood flow within blood vessels of a patient.
It is an additional object of the invention to provide apparatus which in addition to fulfilling the above objectives, is operable synchronously or asynchronously with the heartbeat.