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