Atrial flutter pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
Atrial flutter is a type of atrial tachycardia characterized by an atrial rate ranging from 240 to 400 beats per minute. It is caused by a reentrant rhythm in either the right or left atrium. Some degree of atrioventricular block is associated with atrial flutter.
Pathophysiology
Typically initiated by a premature electrical impulse arising in the atria, atrial flutter is propogated due to differences in refractory periods of atrial tissue. This creates a self perpetuating loop of electrical activity moving around the atrium.
The impact and symptoms of atrial flutter depend on the heart rate of the patient. Heart rate is a measure of the ventricular rather than atrial activity. Impulses from the atria are conducted to the ventricles through the atrio-ventricular node. Due primarily to its longer refractory period, the AV node exerts a protective effect on heart rate by blocking atrial impulses in excess of about 180 beats/minute (This block is dependent on the age of the patient, and can be calculated roughly by subtracting patient age from 220). If the flutter rate is 300/minute only half of these impulses will be conducted, giving a ventricular rate of 150/minute, ie. 2:1 block. The addition of rate-controlling drugs or conduction system disease can increase this block substantially (see image below).