What are the causes of a pansystolic murmur?

Causes of Pansystolic Murmur

Pansystolic (holosystolic) murmurs are primarily caused by regurgitant flow between cardiac chambers that maintain widely different pressures throughout systole, most commonly involving mitral regurgitation, tricuspid regurgitation, and ventricular septal defects. 1

Pathophysiological Mechanism

Pansystolic murmurs are characterized by:

• Begin with S1 and continue throughout systole until S2 1
• Typically plateau-shaped in configuration 1
• Generated when blood flows between chambers with significant pressure differences throughout systole 1
• Pressure gradient and regurgitant jet begin early in contraction and persist until relaxation is almost complete 1

Specific Causes

1. Mitral Regurgitation

• Backward flow from left ventricle to left atrium due to:
  • Mitral valve prolapse with leaflet malcoaptation 1
  • Rheumatic heart disease affecting valve leaflets 1
  • Papillary muscle dysfunction or rupture (often in acute myocardial infarction) 1
  • Functional MR due to left ventricular dilation and annular enlargement 1
  • Infective endocarditis with leaflet destruction 1
  • Congenital mitral valve abnormalities 1

2. Tricuspid Regurgitation

• Backward flow from right ventricle to right atrium due to:
  • Pulmonary hypertension causing right ventricular dilation 1
  • Right ventricular failure with annular dilation 1
  • Tricuspid valve dysplasia or Ebstein's anomaly 2
  • Infective endocarditis (particularly in injection drug users) 1
  • Rheumatic heart disease 1
  • Carcinoid heart disease 1
  • Trauma to the valve apparatus 3

3. Ventricular Septal Defect (VSD)

• Abnormal communication between left and right ventricles:
  • Congenital VSDs 1
  • Acquired VSDs (post-myocardial infarction) 4
  • Post-surgical complications 1

4. Left Ventricular-Right Atrial Communication

• Rare direct communication between left ventricle and right atrium:
  • Congenital Gerbode defect 1
  • Acquired (post-surgical or post-endocarditis) 3

Clinical Pearls and Differentiation

• Mitral regurgitation murmurs are typically best heard at the apex and radiate to the axilla 1
• Tricuspid regurgitation murmurs are usually loudest at the lower left sternal border and may increase with inspiration 1
• VSD murmurs are typically loudest at the left lower sternal border with little radiation 4
• In neonates, a pansystolic murmur at the lower left sternal border in the first day of life is more likely to be tricuspid regurgitation than VSD 5

Diagnostic Approach

• Echocardiography is the gold standard for confirming the cause of a pansystolic murmur 1
• Dynamic auscultation can help differentiate causes:
  • Right-sided murmurs (tricuspid regurgitation) typically increase with inspiration 1
  • Left-sided murmurs (mitral regurgitation) are usually louder during expiration 1
  • Murmurs of MR and VSD increase with handgrip exercise 1

Clinical Significance

• Unlike midsystolic murmurs, which may be innocent, pansystolic murmurs almost always indicate pathological conditions requiring further evaluation 1, 6
• The presence of a pansystolic murmur should prompt referral for echocardiographic assessment to determine the exact cause and severity 1
• Early identification and management of the underlying cause can prevent complications such as heart failure, pulmonary hypertension, and arrhythmias 1