Atrial flutter classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Overview
There are two types of atrial flutter, the common type I and rarer type II. Most individuals with atrial flutter will manifest only one of these. Rarely someone may manifest both types; however, they can only manifest one type at a time.
Classifications
- Type I atrial flutter, also known as common atrial flutter or typical atrial flutter, has an atrial rate of 240 to 350 beats/minute. However, this rate may be slowed by antiarrhythmic agents. The re-entrant loop circles the right atrium, passing through the isthmus - a body of fibrous tissue in the lower atrium between the inferior vena cava, and the tricuspid valve.
Type I flutter is further divided into two subtypes, known as counterclockwise atrial flutter and clockwise atrial flutter depending on the direction of current passing through the loop. Counterclockwise atrial flutter (known as cephalad-directed atrial flutter) is more commonly seen. The flutter waves in this rhythm are inverted in ECG leads II, III, and aVF. The re-entry loop cycles in the opposite direction in clockwise atrial flutter, thus the flutter waves are upright in II, III, and aVF.
- Type II flutter, also known as atypical flutter, follows a significantly different re-entry pathway to type I flutter, and is typically faster, usually 340–430 beats/minute.