Cor triatriatrum or divided left atrium presenting as mitral stenosis in an adult patient.

A 26-year-old male patient presented to the hospital with a 2-month history of progressive dyspnoea. He denied chest pain, coughing, orthopnoea, paroxysmal nocturnal dyspnoea, syncope or pre-syncope. He had no other significant comorbidities and he was not on any chronic medication. His cardiovascular examination revealed an undisplaced apex beat with a parasternal heave and a loud second heart sound (P2) suggestive of pulmonary hypertension. On auscultation, the first heart sound was normal with a loud second heart sound and a diastolic rumble. Given these findings, a clinical diagnosis of severe mitral stenosis with pulmonary hypertension was made. ECG was atypical for mitral stenosis, it revealed a dilated LA with left axis deviation due to a left anterior hemiblock. No features of right ventricular hypertrophy was noted. To our surprise, echocardiographic evaluation (Figs 1 and 2) revealed a primum ASD with the normal function of the left and right atrioventricular (AV) valve. A left-sided supra-valvular ridge or divided left atrium was identified with peak and mean gradients of 43/21 mmHg, respectively (Fig. 3). Video 1 is an apical four-chamber view of the defect, pre-operatively. -20-0016 ID: 20-0016