Atrial fibrillation is caused by multiple re-entry circuits in the atrial myocardium. It can be identified by a number of characteristic findings on the electrocardiogram (ECG).



(1) atrial rate

(2) P waves

(3) appearance of the "f" fibrillation waves

(4) ventricular rate and rhythm


Atrial rate: 350 to 600 beats per minute, which may be impossible to count manually


P waves are often absent. If present they do not show a regular pattern.


The "f" waves give the ECG baseline a wavy, irregular appearance. The amplitude of the waves is variable and may range from barely perceptible to coarse.


The atrioventicular conduction is variable, resulting in an irregular ventricular rhythm ("irregularly irregular"). The R-R interval is irregular. The ventricular rate usually ranges from 100-180 beats per minute.


A slower ventricular rate may occur with higher degrees of AV block or with medications such as digoxin.


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