A 38-year-old woman presents to the primary care clinic with progressive shortness of breath on exertion over the past several weeks. She reports episodes of chest pain, nonproductive cough, fatigue, and lightheadedness. She works as a teacher in a middle school. Physical examination reveals: Oxygen saturation: 92% on room air Loud P2 and right ventricular heave Jugular venous distention and lower extremity edema An ECG shows: Right axis deviation Tall R waves in the right precordial leads R-to-S wave ratio >1 in lead V1 Atrial fibrillation Right heart catheterization demonstrates a pulmonary artery pressure of 32 mm Hg. Which of the following is the most likely cause of this patient’s symptoms?
