Cardiac radiologic landmarksDownloads

A 52-year-old man presents to a medical clinic to establish care. He has no known chronic illnesses but has not seen a physician in over 20 years. He generally feels well but occasionally has shortness of breath when he jogs and exercises. He smokes 2-5 cigarettes per day and uses IV heroin “now and then.” Physical exam is unremarkable. ECG shows prominent QRS voltage and left axis deviation. Trans-thoracic echocardiogram shows mild concentric left ventricular hypertrophy but is otherwise normal. Which of the following is the most likely etiology of the echocardiogram findings?

A 42-year-old woman comes to the physician because of 2 episodes of loss of consciousness over the past week. She recovered immediately and was not confused following the episodes. During the past 5 months, she has also had increased shortness of breath and palpitations. She has been unable to carry out her daily activities. She also reports some chest tightness that resolves with rest. She has no history of serious illness and takes no medications. She immigrated with her family from India 10 years ago. Her temperature is 37.3°C (99.1°F), pulse is 115/min and irregular, and blood pressure is 108/70 mm Hg. Examination shows jugular venous distention and pitting edema below the knees. Bilateral crackles are heard at the lung bases. Cardiac examination shows an accentuated and split S2. There is an opening snap followed by a low-pitched diastolic murmur in the fifth left intercostal space at the midclavicular line. An ECG shows atrial fibrillation and right axis deviation. Which of the following is the most likely underlying mechanism of these findings?