Experience with Vascular Grafts in total Artificial Heart Replacement

In total artificial heart replacement the pumps are attached to the vascular system with the help of connectors. These consist of a woven Dacron vessel graft to which a short silastic segment is vulcanized. In 36 calves surviving total artificial heart replacement between one and seven months (average 85 days) the morphological alterations due to interfacial reactions were studied: thrombus formation and neointimal fibrous hyperplasia at the anastomoses.

In 15 calves (41.7%) thrombus growth within the outflow tract led to anastomotic stenosis: pulmonary artery 14 (93.3%), aorta-anastomosis 1 (2.8%), both vessels 1 (2.8%), in combination with pannus growth in atrial location 13 (86.7%). In 73.3% the pannus consisted of infected organized thrombus imitating the course of septic vegetative endocarditis. Two calves were reoperated in order to remove the vegetative thrombi, one successfully. In five animals pulmonary stenosis was the main cause of death. The presence and location of excessive tissue growth and thrombus formation within the outflow tract are also inherent to the fluid mechanical design of the valve. Neointimal fibrous hyperplasia at the anastomoses of the grafts seems to be a reparative process started up by platelet-induced subendothelial cell proliferation in response to intimal injuries.

Mechanisms causing the death of 8 calves surviving with implanted artificial heart from 31 to 173 days

Causes of the death of four animals from the total of eight were technical failures (diaphragm perforations, disconnection of the quick-connector, and a failure of the supply of electric current which could not be prevented). Causes of the death of the remaining four animals were embolisation in the brain stem, embolisation in the superior mesenteric artery leading to diffuse peritonitis, ruptures of aorta and hemocoagulation disorder causing fatal gastrointestinal bleeding.

Twin calves, total artificial heart, cardiac transplantation

Numerous laboratories throughout the world are successful in sustaining life in calves, sheep, and goats implanted with total artificial hearts for 4-8 months. Very good reliability has been demonstrated with some of these devices, and all of the more successful devices are pneumatically driven. These pneumatic controllers are, for the most part, large and nonportable, and thus are criticized when considered for permanent tethering to a human recipient. The artificial hearts, however, have been developed to a stage where they could sustain the circulation for indeterminate periods of time, for 2-3 years. The pneumatic total artificial heart was used for a few weeks in calves, and then followed with cardiac transplantation. This format has been suggested for human application.