Late-Presenting Congenital Subaortic Membrane With Aortic Regurgitation Presenting as Dyspnoea: A Case Report and Review of the Literature.

Subaortic membrane (SAM) is a rare congenital cause of left ventricular outflow tract (LVOT) obstruction. While often diagnosed in childhood, it can remain clinically silent until adolescence or adulthood, presenting diagnostic and management challenges due to its indolent progression and lack of adult-specific guidelines. SAM is frequently associated with progressive aortic valve pathology, including aortic regurgitation (AR). We report the case of an 18-year-old male with a previously unrecognised congenital subaortic membrane presenting with exertional dyspnoea and dizziness. Transthoracic echocardiography revealed a discrete 0.5 cm subaortic membrane, a peak left ventricular outflow tract (LVOT) gradient of 45 mmHg, and mild-to-moderate central AR. Cardiac computed tomography (CT) confirmed the lesion with no coronary anomalies. The patient underwent successful surgical resection of the membrane, resulting in a reduced post-operative LVOT gradient (peak 1.68 m/s, mean gradient (MG) 6 mmHg) and resolution of symptoms. Follow-up echocardiography at three months confirmed persistence of only mild AR with no residual LVOT gradient, and the patient reported full return to premorbid functional status (New York Heart Association (NYHA) I), highlighting favourable short-term outcomes. This case highlights the importance of recognising late-presenting congenital SAM in symptomatic adolescents and young adults. Early diagnosis, appropriate imaging, and timely surgical intervention are essential. The case underscores the need for standardised long-term surveillance and the development of adult-specific management strategies, especially considering the high risk of recurrence after surgery.