Accessory mitral valve--an unexpected intra-operative TEE finding causing left ventricular outflow tract obstruction in an adult.

There is a long-standing debate between proponents of routine intra-operative echo and those who want it restricted to selected groups of patients (such as those undergoing valve repair or correction of congenital abnormalities). We present a case where routine transesophageal echocardiography (TEE) identified completely unexpected pathology, with implications for the postoperative follow-up and for patient outcomes. A 64-year-old male, with a history of surgical repair of coarctation of the aorta in childhood, was admitted for elective valve replacement for severe aortic stenosis (AS). Previous transthoracic echocardiography had not identified any other pathology apart from AS, but routine intra-operative TEE picked up severe turbulence in the left ventricular outflow tract (LVOT). On further analysis this was due to 2 mechanisms: a localized subaortic membrane and a "cystic" mass attached to the anterior mitral leaflet, protruding into the LVOT in systole. Multiplane imaging of the mass disclosed an accessory mitral valve (MV), a rare congenital abnormality. The patient had excision of the stenosed aortic valve and of the subaortic membrane, while the accessory MV was spared, as the surgeon judged its removal might distort the mitral apparatus. Postoperative recovery was unremarkable and the patient went home with symptomatic improvement. This case illustrates the fact that even "standard" cardiac procedures can benefit from intra-operative TEE which, in our view, should be available for all patients who undergo heart surgery.