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Atrial Fibrillation
Atrial fibrillation occurs when the atria depolarize repeatedly and in an irregular uncontrolled manner
usually at at atrial rate greater than 350 beats per minute. As a result, there is no concerted
contraction of the atria. No P-waves are observed in the EKG due to the chaotic atrial depolarization.
The chaotic atrial depolarization waves penetrate the AV node in an irregular manner, resulting in
irregular ventricular contractions. The QRS complexes have normal shape, due to normal ventricular
conduction. However the RR intervals vary from beat to beat. The ventricular rate may increase to
greater than 150 beats per minute if uncontrolled.
The irregular ventricular contractions cause the systolic arterial pressure to vary from beat to beat as
ventricular filling time changes. The pulse pressure also may vary from beat to beat because the
diastolic runoff time varies from beat to beat.
Atrial fibrillation often involves microreentry. Atrial fibrillation is most common in individuals with
atrial enlargement, often associated with valve diseases, sick sinus syndrome, pericarditis, lung
disease and congenital heart defects. The incidents of atrial fibrillation increase with age and are
slightly more frequent in men than women.