A pregnant woman at 28 weeks with signs suggestive of rheumatic heart disease shows an opening snap and a diastolic rumble best heard at the apex in the left lateral decubitus position. Which lesion is most likely on echocardiogram?

• A. Tricuspid regurgitation
• B. Atrial septal defect
• C. Mitral stenosis
• D. Aortic regurgitation

Answer: (C)

The opening snap with a diastolic rumble heard best at the apex in the left lateral position is the hallmark of mitral stenosis caused by rheumatic heart disease. The stiff, narrowed mitral valve leaflets snap open after S2 (opening snap) and the rapid, turbulent filling through the constricted orifice produces the low-pitched diastolic rumble.

Echocardiography would most likely show a narrowed mitral valve orifice with thickened, restricted leaflets and possibly fused commissures. You’d also expect a reduced mitral valve area on planimetry and a diastolic gradient across the valve, reflecting the obstruction to flow. Chronic pressure overload from the stenotic valve typically leads to left atrial enlargement.

Why the other lesions don’t fit: tricuspid regurgitation would give a holosystolic murmur at the left lower sternal border, not an opening snap or diastolic rumble. Atrial septal defect produces a fixed split S2 with a systolic ejection murmur, not the diastolic murmur described. Aortic regurgitation causes an early diastolic decrescendo murmur along the left sternal border and pulse abnormalities, not the apical diastolic murmur with an opening snap.