Atrial flutter is caused by a re-entry circuit in the right atrium, with secondary activation of the left atrium. It can be identified by a number of characteristic findings on the electrocardiogram (ECG).
The changes of atrial flutter are best seen in the inferior leads and in lead V1.
Parameters:
(1) atrial rate
(2) appearance of the "F" (flutter) waves
(3) atrioventricular block and ventricular rate
Atrial rate in atrial flutter:
(1) The atrial rate is regular, with a cycle to cycle atrial variability <= 10 ms.
(2) In the presence of Class IA, IC, or III anti-arrhythmic drugs the rate is 190-350 beats per minute.
(3) In the absence of anti-arrhythmic drugs the atrial rate is 240-350 beats per minute
The characteristic appearance of the "F" wave is a regular "saw tooth" in the baseline of the ECG. This may be obscured in the presence of ventricular tachycardia.
Typically the ventricular rate is regular and about 150 beats per minute. This is due to a 2:1 atrioventricular block.
AV conduction may be:
(1) 1:1 (rare)
(2) 3:1 (most common after 2:1)
(3) 4:1 (rare)
(4) variable
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