A 58-year-old man from Delhi presents with a 3-week history of fever, malaise, and progressive dyspnea. On examination, he has a blood pressure of 165/95 mmHg, a new diastolic murmur, and petechial rash on his lower extremities. Laboratory investigations show elevated ESR (78 mm/h), CRP 12 mg/dL, and urinalysis reveals hematuria with RBC casts. Blood cultures are sterile. Coronary angiography shows no atherosclerotic disease but reveals smooth, tapered narrowing of the left anterior descending coronary artery with involvement of the ostium. What is the most likely diagnosis?