Introduction.  M-mode in bedside point-of-care ultrasound (POCUS) transthoracic echocardiography (TTE) remains an important tool for emergency physicians.  M-mode of the mitral valve is used to assess ejection fraction (EF) during assessment of E-point septal separation (EPSS).  Anterior mitral leaflet fluttering visualized on M-mode echocardiography is a known sequelae of aortic regurgitation.  Although not reported in the Emergency Medicine literature, anterior mitral leaflet fluttering also occurs with atrial fibrillation.

Case Report. We present the first case in peer-reviewed Emergency Medicine literature of anterior mitral leaflet fluttering observed on M-mode echocardiography caused by atrial fibrillation.  Our patient was a 54-year-old male with chest pain who was evaluated in the Emergency Department with a point-of-care ultrasound transthoracic echocardiogram that showed anterior mitral leaflet fluttering on E-point septal separation.  Subsequent inpatient workup confirmed the diagnosis of symptomatic atrial fibrillation without ischemia or clinically-significant aortic regurgitation.

Conclusion.  Emergency physicians must rapidly assess and risk-stratify undifferentiated patients presenting with chest pain.  Understanding that anterior mitral leaflet fluttering on M-mode during EPSS may signal atrial fibrillation augments efficient and appropriate disposition of these patients.

Keywords. POCUS, point-of-care ultrasound, transthoracic echocardiogram, TTE, M-mode, aortic regurgitation, atrial fibrillation, anterior mitral leaflet flutter, case report