Haemodynamic and echocardiographic characteristics of a stentless allograft mitral prosthesis: an in vitro study

Poor long-term durability and impaired haemodynamic performance are known disadvantages of bioprosthetic heart valves when compared to valve replacement using aortic allografts. A new stentless allograft mitral implant was developed and tested in vitro in a left ventricular model and pulsatile flow system to evaluate hydrodynamic function. Mitral valves were excised from sheep hearts and the mitral annulus reinforced by a strip of ovine pericardium. A patch of expanded polytetrafluoroethylene (ePTFE) was placed above the tips of the remaining papillary muscles. For in vitro evaluation of a total of five valves were investigated in a pulse duplicator. Transvalvular pressure gradients (delta P) were measured over a flow range corresponding to a cardiac output of 5l/min, at a heart rate of 70 beats/min, with a systole accounting for approximately 35% of the cardiac cycle. The systolic ejection period and diastolic filling period in this model were 350 and 510 ms, respectively, and aortic pressure was 120/80 mmHg. The effective orifice area was calculated from measurements of mean pressure drop and root mean square flow. Additionally, valve performance was evaluated by Doppler echocardiography. Results of in vitro studies of a 25 mm stentless allograft mitral implant, which is similar to the valves implanted in a chronic weaning sheep model, revealed a mean(s.d.) delta P of 2.0(1.6) mmHg (range 1.0-4.9 mmHg). The mean calculated effective orifice area was 3.38(0.52) cm(2) (range 2.5-3.8 cm(2)). Doppler echocardiography showed excellent performance of the mitral valve components and valve competence could be achieved. During the in vitro studies no failure caused by tissue rupture was detected. The results of the in vitro studies revealed data for delta P and effective orifice area superior to data obtained for standard 25 mm porcine bioprostheses.