In vitro closing behavior of the St. Jude Medical heart valve in the pulmonary position. Valve incompetence originating in the prosthesis itself.

We examined the in vitro closing behavior of the St. Jude Medical heart valve, simulating (1) a low-pressure system, (2) the anatomic peculiarity of the right ventricular outflow tract and the main pulmonary artery, and (3) disturbed diastolic compliance of the right ventricle. The variables in the experiment were the load impedance to the pump and the valve orientation. The results were as follows. The sequence of closure of the two semidiscs was based on the valve orientation; reduction in impedance caused the semidisc that closed last to remain open, while the other semidisc continued its open-close motion; further reduction in impedance prevented the semidisc, which continued its open-close motion, from closing completely. These results highlight the forces involved in semidisc closure and the existence of a threshold of force for completion of semidisc closure. Further, the results demonstrate that under certain circumstances the threshold cannot be exceeded via those forces. Therefore this incompetence must originate in the prosthesis itself. In this regard, we suggest an urgent need to reconsider the indications for St. Jude Medical heart valve pulmonic implantation. Finally, we advocate the necessity for an in vitro assessment of valve prostheses in a low-pressure system, to evaluate the safety of right-sided placement.