Is S1 (first heart sound) loud in mitral regurgitation?

Heart Sound Characteristics in Mitral Regurgitation

In mitral regurgitation, S1 (first heart sound) is typically soft or diminished in intensity, not loud.

Pathophysiological Basis for Diminished S1

The intensity of S1 in mitral regurgitation is determined by several key factors:

1. Valve Closure Dynamics:

   • In mitral regurgitation, the mitral valve leaflets are often already partially closed at the onset of systole due to regurgitant flow 1
   • This reduces the excursion of the valve leaflets during closure, resulting in a softer S1

2. Severity Correlation:

   • The more severe the mitral regurgitation, the softer S1 typically becomes
   • In severe mitral regurgitation, S1 may be barely audible or completely absent

3. Clinical Manifestation:

   • Patients with severe mitral regurgitation often present with a soft S1, a holosystolic murmur at the apex, and frequently a third heart sound (S3) 1
   • The combination of a holosystolic murmur, S3, and a diastolic flow rumble is highly suggestive of significant regurgitant volume 1

Auscultatory Features of Mitral Regurgitation

• Murmur Characteristics:

  • Holosystolic murmur that begins with S1 and continues throughout systole until S2 2
  • Best heard at the apex
  • Typically radiates to the axilla
  • Maintains relatively constant intensity throughout systole

• Associated Findings:

  • S3 gallop (third heart sound) is often present in severe MR 1
  • Diastolic filling complex (S3 plus short diastolic murmur) usually indicates significant regurgitant volume 1

Diagnostic Implications

The physical examination findings in mitral regurgitation should be correlated with imaging studies:

• When a patient presents with a soft S1, holosystolic murmur, and S3, this suggests severe mitral regurgitation that warrants further evaluation with echocardiography 1

• Discrepancies between physical examination and echocardiographic findings should prompt careful review of both:

  • A patient with clear physical signs of severe MR (soft S1, holosystolic murmur, S3) but an echocardiogram showing only mild MR may have an eccentric jet that is underestimated by conventional measurements 1

Clinical Pearls

• The intensity of S1 can help differentiate mitral regurgitation from other valvular conditions:

  • Mitral stenosis typically has a loud S1
  • Mitral regurgitation typically has a soft S1

• Dynamic changes in the murmur with different maneuvers can help confirm the diagnosis:

  • Handgrip increases the intensity of mitral regurgitation murmurs 2
  • Valsalva maneuver typically decreases the intensity of MR murmurs 2

Remember that a comprehensive cardiac examination should include careful auscultation of all cardiac areas, with attention to both heart sounds and murmurs, to accurately identify and characterize mitral regurgitation.