Epidemiology and pathophysiology of atrial fibrillation. Atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia worldwide. Its incidence and prevalence (currently 1 to 4% of the world population) are increasing. Most of the cardiovascular risk factors increase the risk of developing AF. AF is associated with a doubling risk of total mortality; it increases also the risk of stroke by 4-5 fold and therefore represents a public health problem. Mechanistically, the anarchic electrical activity recorded in the atrium in AF can be triggered by arrhythmogenic foci located in the pulmonary veins. In persistent AF, deep alterations in cellular electrophysiology, calcium metabolism, and extracellular matrix are observed, which tend to perpetuate the arrhythmia.