Regurgitation and Haemolysis in Artificial Heart Valves: An Experimental Study of Overlapping and Non-overlapping Closing Mechanisms and of Paraprosthetic Leakage

Abstract

Overlapping and non-overlapping prosthetic closing mechanisms were evaluated in respect of regurgitation and haemolysis. The test chamber, which is described in this paper, permitted an almost physiological valve function in a minimal volume of human whole blood. A non-overlapping closing mechanism was represented by the Björk-Shiley tilting disc valve and an overlapping one by the Lillehei-Kaster pivoting disc prosthesis. Regurgitation after closure of the Björk-Shiley prosthesis, when the non-overlapping disc was seated, increased linearly with the mean diastolic pressure difference. The slope of this line increased with the size of the tissue diameter of the prosthesis and was steepest for valve size 29 mm. Converted to in vivo conditions, this regurgitation corresponded to 2% of an average forward stroke volume of 80 ml at rest in patients with 21 or 23 mm valves. With 25, 27 and 29 mm valves, the corresponding values were 3%, 3% and 5%, respectively. Regurgitation would diminish with the haemodynamic changes from rest to exercise. Regurgitation with this prosthesis in the mitral position would be less at rest than during exercise. Haemolysis was significantly lower with a non-overlapping disc than with an overlapping one on closure. The magnitude of red cells destroyed in 70 ml of blood/hour was 0.24% and 0.50%, respectively. Moderate paraprosthetic leakage involved an increase in haemolysis of maximally 0.58%. Assuming a linear progress with time in haemolysis, this erythrocyte destruction can be extrapolated to in vivo conditions. In postoperative prosthetic valve patients, the blood volume amounted to 4 800 ml in average. The magnitude of red cells destroyed in 4 800 ml of blood/24 hours corresponded to 0.08% with a non-overlapping closing mechanism, 0.18% with an overlapping one and 0.20% with paraprosthetic leakage. Mechanical crushing and shearing stress were considered as determinants of red cell destruction associated with prosthetic cardiac valve replacement.