A2-Opening Snap Interval
The normal A2-opening snap (A2-OS) interval ranges from 0.04 to 0.12 seconds (40-120 milliseconds), with shorter intervals indicating more severe mitral stenosis. 1
Understanding the A2-OS Interval Components
The A2-OS interval consists of two distinct physiologic components that are clinically important to understand 1:
- Isovolumic relaxation period: The time from aortic valve closure (A2) to actual mitral valve opening 1
- Mitral valve excursion time: The time required for the mitral leaflets to move from closed to fully open position 1
Clinical Significance and Severity Assessment
The duration of the A2-OS interval inversely correlates with the severity of mitral stenosis - the shorter the interval, the more severe the stenosis 1:
- Severe mitral stenosis: A2-OS interval approaches 0.04 seconds (40 ms) 1
- Mild mitral stenosis: A2-OS interval extends toward 0.12 seconds (120 ms) 1
- The isovolumic relaxation period specifically correlates with stenosis severity, while the excursion time is influenced by valve calcification 1
Important Clinical Context
When Opening Snap is Present vs Absent
The opening snap occurs in mitral stenosis but has specific requirements 2:
- Present: When the mitral valve body remains pliable enough to arch anteriorly in early diastole, even with tip calcification 3
- Absent: When heavy calcification involves both the tip and body of the valve, eliminating leaflet mobility 3
- Never present: In isolated aortic regurgitation (Austin-Flint murmur has no opening snap) 2
Critical Distinction from A2 Itself
The question asks about "A2 opening snap gap," which refers to the interval between the aortic component of the second heart sound (A2) and the mitral opening snap - not an "aortic opening snap" which does not exist 2. The aortic valve does not produce an opening snap; only stenotic atrioventricular valves (mitral or tricuspid) produce opening snaps 2.
Practical Auscultatory Considerations
Physical examination findings that help identify the opening snap 2:
- Timing: Occurs after S2 (specifically after A2), creating the characteristic "snap" sound 2
- Location: Best heard at the apex or left sternal border 2
- Quality: High-pitched, sharp sound distinct from S2 2
- Associated findings: Usually accompanied by a mid-diastolic rumble at the apex in mitral stenosis 2