Accessory mitral valve tissue with mitral complex structural abnormality

A 64-year-old Japanese man was referred to our hospital because of palpitation. An electrocardiogram revealed firstdegree atrioventricular block without ST-T change. An echocardiography showed structural abnormality into the left ventricular outflow tract (LVOT), mitral valve leaflet cleft without mitral regurgitation, and single papillary muscle (loss of posterior papillary muscle) (Figs. 1, 2). A structural abnormality was attached between the base of the intraventricular septum and anterior mitral leaflet, which was mobile in the cardiac cycle. Peak velocity of LVOT was 1.7 m/s. Cardiac systolic function was normal. We diagnosed accessory mitral valve tissue (AMVT) with mitral complex structural abnormality (mitral valve leaflet cleft and single papillary muscle). AMVT is a rare congenital cardiac malformation. The age of AMVT diagnosis ranged from newborns to 77 years [1]. It was reported that the incidence of AMVT in adults was 1/26,000 echocardiogram [2]. Although the exact embryologicmechanism of AMVT formation is not clear, it may stem from the abnormal or incomplete separation of the mitral valve from the endocardial cushions [3]. AMVT is associated with other congenital intracardiac and vascular malformations such as ventricular septal defect [4]. In this case, we found AMVT with a combination of mitral valve leaflet cleft and single papillary muscle (loss of posterior papillary muscle). To our knowledge, this is the first reported case of AMVT with a combination of mitral valve leaflet cleft and single papillary muscle. An echocardiography can be considered the gold standard modality for the diagnosis of AMVT with other cardiac abnormality. Although single papillary muscle usually combined the parachute mitral valve, the parachute mitral valve was not observed in this case. The majority of patients with AMVT have no symptoms, such as chest pain, palpitation, and syncope [5–7]. However, this patient was referred to our hospital because of palpitation. No arrhythmia was observed in electrocardiogram monitoring.