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 h aving mitral valve repair, in some cases requiring further surgery to relieve the obstruction, but the mechanism and the geometry involved a re not certain. Methods and Results. We studied 14 patients who develo ped systolic anterior motion and left ventricular outflow tract obstru ction, 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 echocar diography was recorded before pump, after failed repair during left ve ntricular outflow tract obstruction, and after a corrective second pum p run to relieve the systolic anterior motion. Systolic anterior motio n occurred when the mitral valve coaptation to septum distance was red uced (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 coaptati on to posterior mitral annulus distance was greater (before, 18.9+/-3. 4; during systolic anterior motion, 22.2+/-4.6 versus after second pum p, 17.4+/-3.6 mm), both P<.01. Comparing dimensions before pump, durin g systolic anterior motion, and after the second pump, there were no d ifferences in left ventricular cavity diameter in systole or diastole, the septum to posterior annulus distance, or the angle between the ao rtic and mitral annular planes. Conclusions. After mitral repair, left ventricular outflow tract obstruction occurs when the mitral coaptati on line is displaced anteriorly. When systolic anterior motion occurs, reduction of the amount of annuloplasty or use of the posterior leafl et sliding procedure may eliminate this problem. Understanding the geo metry 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 tech nique to avoid the problem of outflow tract obstruction after mitral v alve repair.