Doppler color flow evaluation of prosthetic mitral valves: Experimental epicardial studies

Abstract More than 300 epicardial Doppler color flow mapping studies on 23 different types of clinical and preclinical valves were performed after implantation in the mitral position in sheep. The transducers were placed directly on the heart to obtain the greatest possible resolution. Studies were performed in each animal under different hemodynamic conditions by varying heart rate and cardiac output. Eighty-six valves were studied late (20 to 52 weeks), whereas the remainder were studied early (0 to 10 days) after operation. The valves included 3 types of ball and cage valves, 3 types of disc and cage valves, 7 types of tilting disc valves, 1 type of bileaflet hemidisc mechanical valve, 13 types of porcine aortic valves and 5 types of bovine pericardial valves. The results of these studies were compared with those obtained in 40 studies of 20 native mitral valves. Doppler color velocity/flow profiles were imaged in real time with simultaneous electrocardiographic gating; the aortic flow was also displayed for the timing of velocity/flow events. Native normal mitral valves had no in-orifice flow disturbances and laminar low velocity/flow directed toward the left ventricular apex. Ball and cage and disc and cage valves had high velocity peripheral jets and vortices of velocity/flow reversals distal to the occluders. Tilting disc valves had differing velocity/flow patterns determined by their orientation in the mitral anulus. Bileaflet hemidisc valves had three jets, which decayed 1.5 cm downstream. Porcine aortic and bovine pericardial bioprosthetic valves had high velocity, turbulent, nonaxisymmetric jets (more severe for the latter). These observations are similar and complementary to those obtained by in vitro flow visualization techniques and those obtained by laser Doppler anemometry. As such, they provide an important interface between the in vitro assessment of prosthetic valve function and the clinical utility of Doppler color velocity flow imaging technology.