Question: Cardiovascular System
A 24-year-old man is referred for evaluation of a heart murmur found on a routine examination. He is asymptomatic. On auscultation there is a fixed splitting of the second heart sound that does not vary with respiration, along with a soft mid-systolic murmur at the left upper sternal border and a soft mid-diastolic rumble at the lower left sternal border. There is a right ventricular heave. Which of the following is the most likely diagnosis?
Choose one answer.
Explanation
Correct answer: B. Atrial septal defect
Wide, fixed splitting of S2 that does not change with respiration is the classic sign of an atrial septal defect, because the left-to-right shunt keeps right-sided volume and pulmonary flow elevated throughout the respiratory cycle. The increased flow produces a pulmonic mid-systolic murmur and, when large, a tricuspid diastolic rumble. Aortic and pulmonic stenosis cause ejection murmurs without fixed splitting; mitral stenosis gives a loud S1 with an opening snap; mitral valve prolapse gives a mid-systolic click.
Learning objective: Recognize fixed splitting of S2 as the hallmark of an atrial septal defect.
Want this back right before you'd forget it?
Ebb Deck brings back 1,500 USMLE Step 1 questions like this one with spaced repetition, on the web and on iPhone. Your first 100 are free.