In new-onset atrial fibrillation, the presence of a diastolic opening snap and an accentuated first heart sound most strongly suggests which valve lesion?

• A. MR
• B. MS
• C. AR
• D. AS

Answer: (B)

Opening snap after S2 with an accentuated S1 points most clearly to mitral stenosis. In rheumatic mitral stenosis the mitral leaflets become thickened and immobilized, so diastolic opening requires a sudden tensing of the valve as LA pressure exceeds LV pressure. That abrupt opening produces the diastolic opening snap. The S1 is often loud in this setting because the thickened leaflets close with force at the start of systole. In new-onset atrial fibrillation, the lack of organized atrial contraction reduces the presystolic—or pre-systolic—accentuation of the murmur, but the opening snap and loud S1 remain characteristic clues for mitral stenosis. Other valve lesions don’t produce this combination: mitral regurgitation causes a systolic murmur, aortic regurgitation a early diastolic decrescendo murmur, and aortic stenosis a systolic ejection murmur with a softer S2.