Mechanism of development of atrial fibrillation in valvular heart disease

Electrical activity of heart in atrial fibrillation
  • Progressive fibrosis of the atria is the underlying pathologic change that results in atrial fibrillation
  • Fibrosis of atria can occur due to:
    • Atrial dilatation (most common)
    • Inflammation
    • Genetic causes
  • In valvular heart diseases that cause increase in atrial pressure (mitral stenosis, mitral regurgitation, tricuspid regurgitation), there is progressive dilatation of the atria
  • Dilatation can also occur due to hypertension or heart failure

How atrial dilatation causes atrial fibrosis?

  • Atrial dilatation results in activation of Renin Angiotensin Aldosterone system
  • This induces rise in matrix metalloproteinases and disintegrin, which promotes atrial remodelling and fibrosis

How fibrosis of atria results in atrial fibrillation?

  • Fibrosis not only involves the muscle mass of the atria, but also involves the conduction system of the heart
  • SA node and AV node are affected
  • The conduction speed is decreased and multiple foci of electrical activity occur in the atria
  • Multiple re-entry loops are setup which results in irregular activation of atrial musculature and atrial fibrillation

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