Not All Elevated Transaortic Gradients Are Valvular: Triple Discrete Subaortic Membranes Mimicking Severe Aortic Stenosis

Subaortic fibrous membranes are a rare but significant source of fixed left ventricular outflow tract obstruction. Although it is typically diagnosed in childhood, the membrane can remain clinically silent for years and present in adulthood, most likely due to secondary aortic valve failure. We report a case of a 48-year-old obese woman known to have recently diagnosed hypertension, who presented for progressive dyspnea on minimal exertion over the past four months. Serial echocardiograms revealed inconsistent findings but mainly suggested moderate to severe calcified aortic stenosis except for one report of possible subaortic membrane with minimal aortic regurgitation. Surgical exploration revealed three discrete subaortic fibrous membranes within the left ventricular outflow tract, which to our knowledge, is exceedingly rare, localized calcification and moderate to severe aortic regurgitation. Complete membranectomy and mechanical aortic valve replacement were performed, and the post-operative course was satisfactory. This case highlights the diagnostic difficulty of distinguishing valvular from subvalvular obstruction in adults with increased transaortic gradients. It also emphasizes the importance of repeat imaging and careful intraoperative assessment when there is a discrepancy from preoperative imaging findings.