Accessory mitral valve tissue (AcMVT) is a rare congenital malformation causing left ventricular outflow tract obstruction (LVOTO). The analysis of various published reports reveals 90 patients presenting with AcMVT, ranging in age from newborns to 77 years old. Severe LVOTO is present in most cases, though mild LVOTO was found in 15 patients (16.7%), and 3 other patients (3.3%) presented with no LVOTO. In our practice, we found this anomaly in 5 patients; one presenting with severe LVOTO, two with mild LVOTO, and another who developed moderate LVOTO after a myocardial infarction episode. 68 patients (75.5%) underwent cardiac surgery, with a postoperative mortality of 6 (8.9%). Postoperatively, a residual mild gradient across the left ventricular outflow tract was identified in 9 patients (13.2%). Nine other patients (13.2%) required reoperation due to severe LVOTO. Mild-to-moderate postoperative mitral or aortic valve regurgitation was found in 7 (10.3%) and 5 (7.3%) patients, respectively. Based on reported intraoperative findings, we have classified this anomaly as Type I-FIXED TYPE (A – nodular, B – Membranous), Type II-Mobile type (A – Pedunculated, B – leaflet-like). Type IIB is divided into 1) rudimentary chordae and 2) developed chordae. Based in our own experience and after the analysis of various reports, we conclude that patients with AcMVT causing LVOTO may undergo safe mass excision with acceptable postoperative mortality and morbidity. The removal of the AcMVT should in no way compromise mitral valve function, and its excision should be made subject to careful evaluation of the surrounding structures.

Keywords: Adolescent, Cardiac Surgical Procedures - methods, Child, Preschool, Echocardiography, Transesophageal, Infant, Newborn, Mitral Valve - pathology, Mitral Valve Insufficiency - surgery, Mitral Valve Insufficiency - ultrasonography