Characterization of atrial flutter. Studies in man after open heart surgery using fixed atrial electrodes.

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Abstract
Studies were performed using bipolar atrial wire electrodes to record atrial electrograms and to pace the atria in 27 patients who developed atrial flutter after open heart surgery. Two types of atrial flutter, classic or type I atrial flutter and type II atrial flutter, were identified. Both types of atrial flutter were charaterized by uniformity of the beat-to-beat atrial cycle length, morphology, polarity and amplitude of the recorded bipolar atrial electrogram. Both types sometimes manifested a beat-to-beat electrical alternans, which was sometimes associated with an alternans in beat-to-beat cycle length. The initial basis of separation of types I and II atrial flutter was that type I atrial flutter was influenced by rapid atrial pacing from the high right atrium; type II atrial flutter was not. Two additional observations suggested that types I and II atrial flutter were different, although related, rhythms. In 4 patients, type II atrial flutter was present after termination of rapid atrial pacing used to treat type I atrial flutter, in 2 patients, type II atrial flutter changed to type I atrial flutter in a 1-step fashion. The range of rates of the 2 types of atrial flutter were different: type I atraial flutter was slower (rang 240-338 beats/min) than type II (range 340-433 beats/min). Apparently type II atrial flutter is a distinct rhythm which may be intermediate between classic, or type I, atrial flutter and atrial fibrillation.