ATRIAL ELECTROGRAMS AND ACTIVATION SEQUENCES IN THE TRANSITION BETWEEN ATRIAL-FIBRILLATION AND ATRIAL-FLUTTER

Introduction: The electrophysiologic mechanism of atrial fibrillation (AF) has a wide spectrum, and it seems that some atrial regions are es sential for the occurrence of a particular type of AF. We focused on o ne type of AF: AF associated with typical atrial flutter (AFL), which was right atrial (RA) arrhythmia, and sought to investigate intra-atri al electrograms and activation sequences in the transition between AF and AFL. Methods and Results: Intra-atrial electrograms and activation sequences in the RA free wall and the septum were evaluated in the tr ansition between AF and AFL in seven patients without organic heart di sease (all men; mean age 57 +/- 11 years). In five episodes of the con version of AFL into AF, the AFL cycle length was shortened (from 211 /- 6 msec in stable AFL to 190 +/- 15 msec before the conversion, P, 0 .001). Interruption of the AFL wavefront and an abrupt activation sequ ential change induced by a premature atrial impulse resulted in fracti onation and disorganization of the septal electrograms. During sustain ed AF, septal electrograms were persistently fractionated with disorga nized activation sequences. However, the RA free-wall electrograms wer e organized, and the activation sequence was predominantly craniocauda l rather than caudocranial throughout AF. In 12 episodes of the conver sion of AF into AFL, the AF cycle length measured in the RA free wall increased (from 165 +/- 26 msec at the onset of AF to 180 +/- 24 msec before the conversion, P, 0.001). AFL resumed when fractionated septal electrograms were separated and organized to the caudocranial directi on, despite the RA free-wall electrograms remaining discrete and sharp with an isoelectric line. Conclusion: Changes of the electrogram and activation sequence in the atrial septum played an important role in t he transition between AF and AFL.