Diastolic Murmurs: Timing in Relation to Heart Sounds
Diastolic murmurs characteristically begin with the onset of the S2 heart sound and terminate with or before the S1 heart sound. This is the defining temporal characteristic that distinguishes diastolic from systolic murmurs.
Timing and Classification
According to the ACC/AHA guidelines, diastolic murmurs are categorized based on their precise timing within diastole 1:
Early Diastolic Murmurs
- Begin with or shortly after S2 when ventricular pressure drops below aortic or pulmonary artery pressure
- High-pitched, decrescendo murmurs typical of:
- Aortic regurgitation (AR)
- Pulmonic regurgitation with pulmonary hypertension
- The murmur onset coincides with semilunar valve closure (S2) 1
Middiastolic Murmurs
- Occur during early ventricular filling
- Originate from mitral or tricuspid valves
- Typically due to:
- Mitral or tricuspid stenosis
- Increased diastolic flow across normal valves
- Austin-Flint murmur in severe chronic AR 1
Presystolic Murmurs
- Begin during ventricular filling after atrial contraction
- Require sinus rhythm to be present
- Usually indicate mitral or tricuspid stenosis 1
Key Distinguishing Features
All diastolic murmurs share the common feature of occurring between S2 and S1 - this is the diastolic period of the cardiac cycle 1. This timing is fundamentally different from systolic murmurs, which occur between S1 and S2.
Common Pitfalls to Avoid
- S3 heart sounds are NOT always present with diastolic murmurs - they represent a separate finding related to ventricular filling and are not a characteristic feature of diastolic murmurs
- Diastolic murmurs are NOT typically functional or innocent - most innocent murmurs in children and young adults are midsystolic, not diastolic 1
- The physical examination remains critical even in the echocardiography era, as imaging can underestimate or overestimate severity depending on technical factors 2, 3
Clinical Recognition
The "inching" technique helps accurately time murmurs: keep S2 as your reference point and move the stethoscope from aortic area to apex. If a murmur appears after S2, it is diastolic; if before S2, it is systolic 4.
In summary: Diastolic murmurs begin at or shortly after S2 and end at or before S1, spanning the diastolic phase of the cardiac cycle. This temporal relationship is the fundamental characteristic that defines these murmurs and guides their clinical interpretation.