A 38-year-old Asian immigrant presents for the evaluation of exertional dyspnea with minimal activity. His past medical history is significant for acute rheumatic fever. He denies any fever, chest pain, cough, malaise or weight loss. His PR: 70/min and regular; BP: 126/76mmHg; Temperature: 37.2C(99F). His apex beat is tapping and non-displaced. Auscultation of his lungs shows crepitations in both lower lung fields. Auscultation of heart reveals a loud first heart sound, mid-diastolic rumbling and a low-pitched murmur at the apex with an opening snap. The murmur is accentuated by mild exercise. Chest X-ray shows straightening of the left border of the heart and presence of Kerley B lines. EKG shows left atrial enlargement. Which of the following findings is a hallmark of the suspected disease?
a. Left atrial enlargement
b. Elevated left atrioventricular pressure gradient
c. Wide pulse pressure
d. Elevated left ventricular diastolic pressure
e. Atrial fibrillation