Dynamic mild subaortic left ventricular obstruction caused by an accessory mitral valve attached to the anterior mitral valve in a young pregnant woman.

Accessory mitral valve tissue is an extremely rare congenital cardiac anomaly of embryologic development of the endocardial cushion. This anomaly is often associated with left ventricular outflow tract obstruction (LVOTO). A 26-year-old pregnant female was referred to our Department of Cardiology with exertional shortness of breath and tachycardia. Transthoracic and transesophageal echocardiography revealed a flexible circular (1.3 x 1.4 cm), mobile structure attached to the ventricular side of anterior mitral valve leaflet, with chordal attachments structure from anterior papillary muscle. This picture is compatible with a parachute-like accessory mitral valve tissue. We performed an echocardiographic exercise test that shows a systolic flow turbulence starting immediately proximal to this structure, resulting in a small increase in left ventricular outflow tract (LVOT) gradient (30 mmHg). Therefore we started low dose of beta-blocker therapy in order to decrease heart frequency and reduce the future risk of a worsening of an LVOT dynamic obstruction. Transthoracic and transesophageal echocardiography is critical for the differential diagnosis of LVOT and in the management of accessory mitral valve tissue. In patients without rest and only an exertional mild LVOTO and no other cardiac malformations, prophylactic removal of mitral accessory tissue excision is not required; antibiotic prophylaxis for endocarditis can be indicated and a regular follow-up is recommended to identify any progression in LVOTO entity.