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 EKG on the top shows normal sinus rhythm. The EKG at the bottom shows atrial fibrillation
- The irregular ventricular contractions cause the systolic atrial 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.