Atrial Septal Defect
A 26-year-old woman is referred with 6 months of exertional dyspnea and palpitations. There is a grade 2/6 systolic ejection murmur at the left upper sternal border and a soft mid-diastolic rumble at the lower left sternal border. Electrocardiography shows right axis deviation with incomplete right bundle branch block. Echocardiography demonstrates a 15 mm secundum atrial septal defect with left-to-right shunting. Which auscultatory finding is characteristic of this lesion?
- A.Third heart sound gallop at the cardiac apex
- B.Mid-systolic click at the cardiac apex
- C.Opening snap following the second heart sound
- D.Wide fixed splitting of the second heart soundCorrect
Explanation
Wide and fixed splitting of the second heart sound is the auscultatory hallmark of an atrial septal defect. Normally the split between aortic and pulmonic closure widens on inspiration because increased venous return delays pulmonic valve closure. With an atrial septal defect the two atria are in continuity, so any inspiratory increase in systemic venous return is offset by a reciprocal decrease in the left-to-right shunt, and right ventricular filling therefore stays constant through the respiratory cycle; the split is wide because of chronic right ventricular volume overload and delayed pulmonic closure, and it is fixed because it no longer varies with respiration. The associated pulmonary flow murmur at the left upper sternal border and the tricuspid diastolic rumble both reflect increased flow across normal valves rather than valvular disease. A mid-systolic click indicates mitral valve prolapse, an opening snap indicates a pliable stenotic mitral valve in rheumatic mitral stenosis, and a third heart sound reflects rapid early ventricular filling in volume overload states such as heart failure or severe mitral regurgitation, and is normal in children and young adults. A hemodynamically significant defect, defined by a shunt ratio above 1.5 to 1 with right heart enlargement, warrants closure, usually by percutaneous device for secundum defects with adequate rims. Untreated large shunts can progress to pulmonary vascular disease and Eisenmenger physiology with shunt reversal and cyanosis.
Why each option
- A.
- An S3 reflects rapid early diastolic filling in volume-overloaded ventricles, as in heart failure or severe mitral regurgitation.
- B.
- A mid-systolic click, often with a late systolic murmur, indicates mitral valve prolapse.
- C.
- An opening snap after S2 is heard in rheumatic mitral stenosis and reflects a pliable stenotic mitral valve.
- D.
- Correct. Constant right ventricular filling across the respiratory cycle produces the wide, fixed splitting of S2 that characterizes an atrial septal defect.
Reference: Braunwald's Heart Disease, 12th ed., 2022; AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease, 2018
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