A 52-year-old man with a prosthetic aortic valve (mechanical, inserted 3 years ago for aortic stenosis) presents with fever, malaise, and new-onset heart failure. He has been compliant with anticoagulation (INR 2.5–3.5). On examination: temperature 39.2°C, new early diastolic murmur at the left sternal border, and signs of acute pulmonary edema. Blood cultures (before antibiotics) are pending. Transthoracic echocardiography is suboptimal due to acoustic shadowing from the prosthesis. Transesophageal echocardiography shows a 6 mm vegetation at the prosthetic valve-tissue interface with paravalvular aortic regurgitation. What is the most appropriate next step in management?