FURTHER OBSERVATIONS OF LINKING OF ATRIAL EXCITATION DURING CLINICAL ATRIAL-FIBRILLATION

The objective of this article was to look for evidence of nonrandom be havior during atrial fibrillation by examining long (> 15 minutes) rec ordings. We have previously reported transient ''linking'' of atrial a ctivation during atrial fibrillation, and showed that activation was n ot entirely random. Over the few episodes of linking seen during 1 min ute, activation directions apparently repeated, indicating a possible anatomical or physiological constraint. In the present study, we exami ned atrial fibrillation over longer time periods to see if this consta ncy of direction was stable. Endocardial recordings were made from 12 patients with atrial fibrillation using a catheter with three orthogon al bipoles, allowing measurements of local activation directions in th ree dimensions. The direction was calculated using Pipberger's half-ar ea method, and episodes of transient linking were identified. An avera ge direction for each episode of linking was calculated and plotted in two dimensions using spherical coordinates (altitude and azimuth). In addition, the nature of initiation and termination of linking was exa mined. Of the twelve patients, 611 episodes of linking (range 1 to 169 per patient, mean 51) were identified. The episodes for most patients clustered closely in direction. In contrast, directions measured for all activations (i.e., linked and not linked) filled up the entire ava ilable range. Linking in most cases subjectively appeared to initiate and terminate suddenly. The results indicate that the local anatomy, p athology, or physiology of the atrium has a strong constraining effect on the electrical activations occurring during atrial fibrillation, a nd revises our perception of activation during atrial fibrillation as ''random.'' The demonstration that local properties greatly influence conduction during fibrillation has important implications for ablation or pacing therapy.