Accessory Mitral Valve Leaflet Causing Severe Left Ventricular Outflow Tract Obstruction in a Preterm Neonate with a Partial Atrioventricular Septal Defect

Abstract

A trioventricular septal defects (AVSDs) are characterized by deficiency of the atrioventricular (AV) septum, abnormalities of the AV valves, and a predisposition to progressive left ventricular outflow tract (LVOT) obstruction. This progressive obstruction is caused by an elongated "gooseneck" LVOT deformity that displaces the aortic valve anteriorly. Left ventricular outflow tract obstruction occurs most often when 2 distinct AV valve orifices are present, as in partial AVSD; and also in complete AVSD when the superior bridging leaflet attaches to the crest of the interventricular septum (creating 2 orifices and further elongating the LVOT). Abnormal left-AV-valve chordal attachments, septal hypertrophy, and abnormally oriented papillary muscles can further exacerbate subaortic narrowing.1 Accessory mitral valve tissue (AMVT), a rare congenital malformation, can result in LVOT obstruction and is associated with other congenital cardiac anomalies. Accessory mitral valve (MV) leaflet, the typical form of AMVT, has been reported only once before in association with AVSD. 2 We describe the case of a very small, premature neonate who underwent partial-AVSD repair and accessory MV (or left-AV-valve) leaflet resection to correct severe LVOT obstruction. Case ReportIn May 2014, a 6-day-old preterm male neonate was transferred to our institution from another hospital. The diagnosis was severe aortic stenosis. His mother's pregnancy was notable for dizygotic twins, well-controlled gestational diabetes mellitus, and delivery by cesarean section because of placenta previa and premature membrane rupture. The infant's birth weight of 1,790 g was appropriate for his estimated gestational age of 31 weeks. At birth, he needed continuous positive airway pressure support but overall appeared clinically well; however, a murmur prompted echocardiographic testing, the results of which raised concerns about severe aortic stenosis. His twin brother was concurrently diagnosed with a membranous ventricular septal defect. There was no other known family history of congenital heart disease.Prostaglandin E 1 therapy had been initiated before the infant's transport to our hospital. Physical examination revealed a nondysmorphic premature neonate. Auscultation yielded a gallop, a harsh grade 4/6 systolic murmur best heard along the mid right sternal border, and a palpable thrill across the sternum. A chest radiograph showed Case Reports