Characterization of transient atrial rhythm occurring between typical atrial flutter and its termination with class...

The transient atrial rhythm intervened between atrial flutter (AFL) and its termination during class III antiarrhythmic drug therapy for AFL has not been characterized well.

Eighteen patients with typical AFL were included in this study. The transient atrial rhythms converted from AFL with different class III antiarrhythmic drugs, ibutilide (group 1, N = 8) and nifekalant (group 2, N = 10), were determined.

AFL terminated, without any intervened transient atrial rhythms, due to conduction block within the isthmus in three patients in each group. The transient atrial rhythm could be characterized into the following types of rhythm based on the initiating mechanisms. (1) The lower-loop reentry or atrial fibrillation that was triggered by a premature excitation in the lateral right atrium caused by breakdown of a functional barrier predisposed AFL to the termination in three patients in each group. (2) The return excitation that repetitively emerged within the isthmus collided with the antegrade excitation, resulting in the termination in two group 1 patients and in one group 2 patient. In the patients who developed these atrial rhythms, the cycle length (CL) oscillation coincidently increased with emergence of such rhythms and became significantly greater than that in the patients who did not develop such transient rhythms (P < 0.05).

The transient atrial rhythms that emerged with class III drugs are associated with the disruption of the stable AFL reentry that may be triggered by similar electrophysiologic mechanisms with different class III drugs. The increased flutter CL oscillation developing after such drugs might signal the AFL termination.