Review Question - QID 210497

A 49-year-old man is referred to a cardiologist by his primary care provider (PCP) for a new heart murmur. He otherwise feels well and has no complaints. He had not seen a doctor in the last 15 years but finally went to his PCP for a check-up at the urging of his girlfriend. His past medical history is notable for gastroesophageal reflux disease, hypertension, and hepatitis B. He takes omeprazole and lisinopril. He has a prior history of intravenous drug abuse and a 50-pack-year smoking history. He has had many prior sexual partners and uses protection intermittently. He reports that he may have had a sore on his penis many years ago, but it went away without treatment. His temperature is 99°F (37.2°C), blood pressure is 141/91 mmHg, pulse is 89/min, and respirations are 18/min. On exam, S1 is normal and S2 has a tambour-like quality. There is a visible and palpable pulsation in the suprasternal notch and a diastolic decrescendo murmur over the right upper sternal border. A chest radiograph demonstrates calcification of the aortic root. Which of the following is the most likely cause of this patient's condition?