"In situ" evaluation of the aortic pivoting disc valve prosthesis.

An index of the "in situ" forward flow characteristics of an aortic valve prosthesis is suggested. The effective area index, Ia, is defined as the ratio between the effective orifice area, Aeff, and the area occupied by the valve in the aortic root. Aeff is calculated from a hydraulic formula using peroperative measurements of instantaneous ascending aortic flow, Fao, and the pressure gradient, deltaP. Ia was found to be 0.29 +/- 0.33 (S.D.) for Lillehei-Kaster valves and 0.32 +/- 0.059 (S.D.) for Björk-Shiley valves. The variations in valve performance among the Björk-Shiley valves may partly be due to differences in valve orientation in the aortic root. Attention should therefore be given to the choice of the opening direction of the disc in order to optimize valve performance in the patient.