A 54-year-old woman with an acute MI develops acute shortness of breath and a new systolic murmur two days later. Which description best matches a mitral regurgitation murmur due to papillary muscle ischemia?

• A. Holosystolic murmur loudest at the apex with radiation to the axilla
• B. Ejection systolic murmur at the left upper sternal border
• C. Diastolic murmur best heard at the apex
• D. Continuous murmur best heard at the left infraclavicular area

Answer: (A)

Papillary muscle ischemia after a myocardial infarction can cause acute mitral regurgitation. The murmur from mitral regurgitation is holosystolic, meaning it spans the entire systole, because blood leaks back into the left atrium throughout systole. It is heard best at the apex, where the mitral valve is located, and it classically radiates toward the axilla due to the direction of the regurgitant jet.

This differs from other murmurs: an ejection systolic murmur at the left upper sternal border points to aortic valve disease, a diastolic murmur at the apex suggests mitral stenosis, and a continuous murmur heard left of the infraclavicular area indicates a PDA or other continuous shunt. Thus, the holosystolic apical murmur with axillary radiation best matches mitral regurgitation from papillary muscle ischemia.