Mitral valvar grafts.

While prosthetic valves are acceptable in the subcoronary position, their use for mitral or tricuspid replacement is less satisfactory. Introduced by Ross in I962, aortic homografts for aortic valve replacement have found a definite place in the modem surgical armamentarium and have paved the way towards heart valve grafting. Naturally, for an improved mitral valve substitute, attention was directed towards the use of biological tissues. The geometry of the aortic valve is known and partly understood, while the functional anatomy of the complex mitral valve has still to be elucidated. There are several facts that complicate grafting of the mitral valve. There is a greater pressure differential between atrium and ventricle than between ventricle and aorta, and the closure pressure of the mitral valve is higher than that of the aortic valve. The great majority of patients requiring mitral valve replacement are in atrial fibrillation with an enlarged left atrium and consequent propensity to thrombus formation, and they may also have a raised pulmonary vascular resistance. To add to the complexity of the problem the continuously moving mitral annulus has an elliptical shape and is connected with the ventricle by chordae tendineae and papillary muscles. It is self-evident that a prosthetic device could not produce ideal results in the mitral position and that the construction of a tissue valve similar in function to the normal mitral valve is a great surgical challenge.