The porous metal-surfaced heart valve. Long-term study without long-term anticoagulation in mitral position in goats.

On review, all thromboembolic complications in mechanical heart valves start from a thrombus lining that covers the suture ring. The thrombus organizes to a fibrous white sheet over the suture ring, which then can protrude out over the polished surface of the valve ring flange. Pieces of the thrombus can be knocked off by the disc and cause emboli. To diminish thromboembolic complications, one must either prevent this thrombus from protruding into the groove between the suture ring and the valve flange or allow the thrombus to be organized as a thin covering with endothelium-like cells as a continuation from the suture ring over the valve flange. This type of covering was obtained during a short period of anticoagulation by applying a microporous surface to the Björk-Shiley Monostrut mitral valve. These valves were implanted in one set of goats and the conventional Björk-Shiley Monostrut mitral valve, with a polished surface, in another set of goats (control group). The two groups were then compared with regard to the incidence of thromboembolic complications encountered during 1 year's follow-up without anticoagulation. The goats were put to death and examination revealed the following observations: In the control group, (1) a varying amount of thrombus formation was found in the groove between the suture ring and the flange in all nine goats and (2) thrombus formation did not start on the polished struts or discs in any of the nine goats. In the group with the microporous Monostrut mitral valve, 19 animals were put to death and examined: (1) The endothelialized covering over the suture ring, thinner when carbon coated, continued over the microporous flange, tapering off in the center of the orifice in all 19 valves on the ventricular side and in 14 of the 19 valves on the atrial side; (2) the center of the orifice and the struts were never completely covered by endothelialized tissue because of high flow; (3) there was an increased incidence of small thrombus formation on the disc-contacting microporous surface of both inflow and outflow struts. Therefore these surfaces should not be coated but left polished.