[Etiology of left ventricular rupture following mitral valve replacement].

Two uncommon cases of left ventricular rupture that occurred during cardiac surgery were treated successfully. These cases may be useful in understanding the etiology of common left ventricular rupture following mitral valve replacement. One case occurred during coronary bypass surgery. The myocardium which is already abnormal seems to be weak to trauma such as bending, traction and torsion. In the other case, who underwent mitral valve replacement with preservation of the posterior leaflet with its attached chordae, the disruption was localized in the epicardial side of the left ventricular posterior wall, though direct injury by some instrument was excluded as a possibility, with a depth of half the thickness of the wall. In experiments using dogs, shape and movement of the mitral annulus were examined. The length of the annulus attached to the posterior leaflet in end-systole was shortened to 89.0 +/- 4.6% of that in late diastole. Furthermore, the annulus was distorted by the elevation of the heart. We approve of Cobbs' "untethered ventricle theory" and consider moreover as follows: In general, whether with or without preservation of the mitral loop, the mitral annulus and the left ventricular posterior wall after mitral valve replacement are severely constricted by the rigid prosthetic ring and become tense, which limits movement in both circular and longitudinal directions. Then even slight stress may cause a primary tear on the posterior wall of the left ventricle, resulting in rupture. In order to treat the rift, the prosthesis must be removed before the apex of the heart is lifted, to avoid excessive ventricular wall tension.