What is the pathophysiology of atrial fibrillation?

Atrial fibrillation can be caused by atrial fibrosis, and lost of atrial muscle mass.  This fibrosis would occur as result of aging, chamber dilatation, inflammatory processes, and genetic causes. Dilatation of the atria activates several molecular pathways, including the renin - aldosterone - angiotensin- system. Angiotensin II is upregulated in response to stretch leading to increase in matrix metaloproteinases and disintegrin, which leads to atrial remodeling and fibrosis, with loss of atrial muscle mass.

Atrial fibrillation is thought to be caused by atrial fibrosis, and lost of atrial muscle mass.  This fibrosis would occur as result of aging, chamber dilatation, inflammatory processes, and genetic causes.  Dilatation of the atria can be due to any structural abnormalities of the heart that cause a rise in the intra-cardiac pressures.  This includes valvular heart disease (such as mitral stenosis, mitral and tricuspid regurgitation), hypertension, and congestive heart failure.  Inflammatory processes such as sarcoidosis, and other autoimmune disorders will also result in similar cardiac remodeling.  Finally, mutation of the lamin AC gene has also been associated with fibrosis of the atria and seen in familial cases

it is single or multiiple reentry circuit