USMLE Step 3 - Question 32

A 68 year old female with a history of hypertension and diabetes presents with chest pains intermittently for 4 days and now significantly worse and acute onset shortness of breath. Her temperature is 37.1, blood pressure 85/65, heart rate 110, respirations 24, and oxygen saturation 79% on room air. Physical examination reveals diffuse pulmonary rales, a II/VI holosystolic murmur at the cardiac apex radiating to the axilla, and elevated jugular venous pressure. A Swan-Ganz catheter is inserted and the pulmonary capillary wedge pressure tracing shows large V waves. Her ECG shows significant ST segment elevation. Which of the following coronary arteries is the most likely culprit?

A. Left main coronary artery

B. Left anterior descending coronary artery

C. Left circumflex coronary artery

D. Right coronary artery

This patient has acute mitral valve regurgitation resulting in pulmonary edema and cardiogenic shock. Remember that the posteromedial palpillary muscle receives its sole blood supply from the right coronary artery, thus thrombosis of this vessel can completely disrupt this papillary muscle’s function resulting in severe mitral regurgitation and even palpillary muscle rupture (as in our case which occurs a few days after the infarction). Treatment is emergent surgical repair. The anteromedial palpillary muscle has dual blood supply from the left anterior descending and left circumflex coronary artery, thus thrombosis of those vessels do not result in mitral regurgitation. The large V waves on the pulmonary capillary wedge tracing (which represents left atrial pressure) indicates backflow of blood from the left ventricle to the atrium. The murmur that our patient has is also typical for mitral regurgitation.

Note other right heart catheterization findings frequently asked on board exams include an "oxygen step-up" from one cardiac chamber to another after a MI indicating an acute ventricular septal defect and "elevation and equalization" of cardiac pressures indicating cardiac tamponade from left ventricular free wall rupture.