Mechanism of outflow tract obstruction causing failed mitral valve repair. Anterior displacement of leaflet coaptation.

Background: Systolic anterior motion of the mitral valve causing left ventricular outflow tract obstruction occurs in 1% to 2% of patients having mitral valve repair, in some cases requiring further surgery to relieve the obstruction, but the mechanism and the geometry involved are not certain.
Methods and Results: We studied 14 patients who developed systolic anterior motion and left ventricular outflow tract obstruction, all after posterior leaflet resection and annuloplasty, in whom a second repair eliminated systolic anterior motion by complete (n = 6) or partial (n = 8) ring removal. Intraoperative transesophageal echocardiography was recorded before pump, after failed repair during left ventricular outflow tract obstruction, and after a corrective second pump run to relieve the systolic anterior motion. Systolic anterior motion occurred when the mitral valve coaptation to septum distance was reduced (before, 26.5 +/- 4.3; during systolic anterior motion, 17.4 +/- 4.4 versus after second pump, 23.4 +/- 6.9 mm) and the mitral valve coaptation to posterior mitral annulus distance was greater (before, 18.9 +/- 3.4; during systolic anterior motion, 22.2 +/- 4.6 versus after second pump, 17.4 +/- 3.6 mm), both P < .01. Comparing dimensions before pump, during systolic anterior motion, and after the second pump, there were no differences in left ventricular cavity diameter in systole or diastole, the septum to posterior annulus distance, or the angle between the aortic and mitral annular planes.
Conclusions: After mitral repair, left ventricular outflow tract obstruction occurs when the mitral coaptation line is displaced anteriorly. When systolic anterior motion occurs, reduction of the amount of annuloplasty or use of the posterior leaflet sliding procedure may eliminate this problem. Understanding the geometry of this phenomenon may facilitate preoperative echo selection of high-risk patients (those with large redundant posterior leaflets and relatively normal ventricular size) and modification of surgical technique to avoid the problem of outflow tract obstruction after mitral valve repair.