Why can the murmur of mitral stenosis be heard during systole?

Why Mitral Stenosis Murmur Can Be Heard During Systole

The murmur of mitral stenosis can be heard during systole in specific circumstances, particularly in patients with atrial fibrillation where the diastolic murmur appears augmented during early systole before the mitral valve closure sound. 1

Physiological Explanation

The classic mitral stenosis murmur is primarily a diastolic murmur, but can be heard during systolic phases in certain conditions:

1. In Atrial Fibrillation:

   • When critically timed short cardiac cycles occur in atrial fibrillation, the diastolic murmur of mitral stenosis can appear to continue into early systole 1
   • This occurs before the mitral valve closure sound and is related to initial muscular contraction of an underfilled ventricle

2. Presystolic Augmentation:

   • The phenomenon involves either:
     • The ventricular contraction itself producing sound
     • Sudden deceleration of rapidly moving blood across the stenotic mitral valve orifice

Associated Conditions That May Cause Systolic Murmurs in Mitral Stenosis

Patients with mitral stenosis may have concurrent conditions that produce systolic murmurs:

• Concurrent Mitral Regurgitation: Many patients with mitral stenosis (97 out of 184 in one study) have associated mitral regurgitation that produces a systolic murmur 2

• Secondary Cardiac Changes:

  • Relative tricuspid valve incompetence
  • Functional pulmonary artery stenosis
  • Concomitant aortic stenosis
  • These can all produce systolic murmurs in patients with mitral stenosis 2

Distinguishing Features

When evaluating a patient with suspected mitral stenosis who has a systolic murmur:

• Timing is crucial:

  • True mitral stenosis murmurs are primarily diastolic, but may have presystolic augmentation
  • Holosystolic murmurs (beginning with S1 and continuing throughout systole) suggest mitral regurgitation rather than stenosis 3

• Response to maneuvers:

  • Left-sided murmurs (including mitral) are typically louder during expiration 3
  • Right-sided murmurs increase with inspiration

Clinical Implications

Understanding why mitral stenosis can sometimes be heard during systole is important because:

• It prevents misdiagnosis of concurrent valve lesions
• It helps distinguish between pure mitral stenosis and mixed mitral valve disease
• It aids in determining appropriate intervention strategies (commissurotomy vs. valve replacement) 4

Diagnostic Approach

When a systolic component is heard in a patient with suspected mitral stenosis:

• Echocardiography is essential to determine the exact cause and severity of the valve pathology 3
• Careful auscultation at different cardiac areas can help distinguish between mitral stenosis with presystolic augmentation and true systolic murmurs of other origins

Remember that the presence of a systolic murmur in a patient with mitral stenosis doesn't necessarily indicate mitral regurgitation, as demonstrated in studies where pure mitral stenosis was confirmed during surgery despite the presence of systolic murmurs 2.