Opening characteristics of three-cusp tissue heart valves

Abstract

Since April 1969, frame-mounted three-cusp fascia lata and pericardial valves have been used in over 200 patients for heart valve replacement. Six autologous fascia lata valves have been removed from the mitral position because of regurgitation produced by shrinkage of one or two cusps. To elucidate the cause and mechanism of graft failure the opening characteristics of fascia lata and Silastic valves were studied in a steady state flow rig. In virtually all valves examined the cusps opened in sequence and the order in which the cusps of a particular valve opened was maintained irrespective of its position in the testing apparatus. Under the conditions prevailing in this experiment the sequential opening of the cusps seems to be inherent in the design of the valve. Inequalities in the size and shape of the cusps or in the physical properties of the material accentuated this phenomenon. Fully open valves were geometrically similar and the relationship between pressure gradient, flow rate, and valve diameter has the form: pd⁴=4,600 Q². This formula will apply to all such valves tested in water, irrespective of material or size, provided that they are fully open. The experiment has shown that the pressure gradient across the valve increases rapidly as the diameter of the valve is reduced and that with reduction in valve diameter a decreased flow rate is required for complete valve opening. It is postulated that in patients with postoperative low cardiac output, large grafts in the mitral position may not open fully and consequently the cusp or cusps with little or no mobility may undergo structural changes leading to fibrosis with thickening or atrophy.