Simultaneous occurrence of atrial fibrillation and atrial flutter

Introduction: Early reports suggested that some patients with "atrial fibri llation/flutter" might have atrial fibrillation in one atrium and atrial bu tter in the other, However, more recent conceptions of atrial fibrillation/ flutter postulate that the pattern is due to a relatively organized (type I ) form of atrial fibrillation, We report the occurrence and ECG manifestati ons of simultaneous atrial fibrillation and butter in patients undergoing a ttempted catheter ablation of atrial flutter. Methods and Results: In patients undergoing radiofrequency ablation for atr ial flutter, an attempt was made to entrain atrial flutter by pacing in the right atrium, The arrhythmias observed occurred following attempts at entr ainment, or spontaneously in one case, Twelve transient episodes of simulta neous atrial fibrillation and flutter were observed in five patients. The a trial fibrillation was localized to all or a portion of one atrium, during which the other atrium maintained atrial flutter, In each case, the surface 12-lead ECG reflected the right atrial activation pattern. No patients had interatrial or intra-atrial conduction block during sinus rhythm, suggesti ng functional intra-atrial block as a mechanism for simultaneous atrial fib rillation/flutter. Conclusion: In certain patients, the occurrence of transient, simultaneous atrial fibrillation and flutter is possible. In contrast to prior studies i n which it was suggested that left atrial or septal activation determines P wave morphology, the results of the present study show that P wave morphol ogy is determined by right atrial activation. Functional interatrial block appears to be a likely mechanism for this phenomenon.