Marfan Syndrome — Arachnodactyly and Wrist/Thumb Signs

A 19-year-old man presents to the cardiology clinic for evaluation of a new early diastolic murmur detected on routine sports screening. He is noted to be unusually tall and thin with long, slender fingers. On examination, when he flexes his thumb into a closed fist, the tip of the thumb protrudes beyond the ulnar border of his hand—the structure marked **B** in the diagram. His father died suddenly at age 39 from suspected aortic dissection. Slit-lamp examination reveals bilateral superotemporal ectopia lentis, and echocardiography shows aortic root dilatation (5.1 cm, Z-score > 3) with aortic regurgitation and mitral valve prolapse. Which of the following is the most appropriate next step in management of this patient?