Congenital Heart Disease USMLE Step 1 Practice Question

A 6-year-old girl presents to clinic for a routine physical examination. She reports mild dyspnea with vigorous play but denies chest pain, syncope, or orthopnea. Her parents note a family history of bicuspid aortic valve in a maternal uncle who required valve replacement at age 42. Vital signs are normal with SpO2 98% on room air. Cardiac examination reveals a systolic ejection murmur best heard at the right upper sternal border with normal S2 splitting. Transthoracic echocardiography shows a bicuspid aortic valve with mild stenosis (peak gradient 32 mmHg) and normal left ventricular function. Which of the following represents the most important long-term complication to monitor in this patient?