Development of the Philadelphia Heart System

A new pneumatic artificial heart system has been developed. The design criteria have been to produce an integrated series of blood pumps and drive systems that would reduce blood trauma and reactivity, while incorporating industrial, mass-production techniques. The system attempts to reproduce the natural heart's pressure and flow waveforms and allows the prosthetic valves to be installed in a manner consistent with their design. The system's ventricles are constructed entirely of polyurethane by a combination of vacuum-forming and solution-casting techniques. The atrial cuffs and arterial grafts are permanently attached to the pumps and do not incorporate a quick connect system. The prosthetic valves are sewn into the inflow and outflow tracts using their clinical sewing rings. Besides eliminating the crevices normally found in quick connect systems, this method mounts the valves in an extremely compliant housing to increase shock absorption. The drive system produces a systolic air flow with a variable pressure rise (dP/dt) to reduce mitral valve closing velocity. This system has been implanted into 25 calves to date, of which 17 were chronic experiments. In 14 animals, St. Jude bileaflet valves were used and these animals had a mean survival of 39 days. Six of these animals survived over 30 days, with the longest being 129 days. All of the animals showed the characteristic postoperative drop in red blood cell count and hematocrit that returned to near preoperative values in about 3 weeks. The plasma free hemoglobin values generally remained below 5 mg/dl. The necropsies performed on several of the earlier animals revealed renal infarcts. However, in two of the later experiments, no kidney damage was found. The blood contacting surfaces of the atrial cuffs from the animals surviving over 100 days were covered with a fibroproliferative pseudoneointimal growth that extended from the sewing rings to the natural atrial tissue. Grossly, this appears to be the same type of tissue response seen when only a valve is implanted in a natural calf heart.