A 32-year-old woman with rheumatic mitral stenosis has an opening snap audible after S2. As her stenosis worsens over years, what happens to the A2 to opening snap (A2-OS) interval?

• A It widens because left atrial pressure falls relative to aortic pressure
• B It disappears only when atrial fibrillation develops
• C It remains fixed at 120 ms regardless of severity
• D It shortens because higher left atrial pressure snaps the valve open earlier in diastole ✓

Explanation

The opening snap occurs when the stenosed but pliable mitral valve domes open under the left atrial to left ventricular pressure gradient at the start of diastole. The more severe the stenosis, the higher the LA pressure, so the gradient equilibrates earlier and the OS moves closer to A2, shortening the A2-OS interval below about 60 to 70 ms in critical MS. The snap disappears with heavy calcification or immobility of the leaflets, not only with AF.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.