Atrial fibrillation propagates through gaps in ablation lines: implications for ablative treatment of atrial fibrillation

Abstract

Background: It has been hypothesized that atrial lesions must be transmural to successfully cure atrial fibrillation (AF). However, ablation lines often do not extend completely across the atrial wall.

Objective: The purpose of this study was to determine the effect of residual gaps on conduction properties of atrial tissue.

Methods: Canine right atria (n = 13) were isolated, perfused, and mounted on a 250-lead electrode plaque. The atria were divided with a bipolar radiofrequency ablation clamp, leaving a gap that was progressively narrowed. Conduction velocities at varying pacing rates and AF frequencies were measured before and after ablations. AF was induced with an extra stimulus and acetylcholine.

Results: Gap widths from 11.2 to 1.1 mm were examined. Conduction velocities through gaps were dependent cycle length (P = .002) and gap size (P <.001). Overall, 253 (97%) of a total of 260 gaps allowed paced propagation; 51 (91%) of 56 gaps 1-3 mm in width permitted paced propagation, as did 202 (99%) of 204 gaps >or=3.0 mm. Similarly, 253 (97%) of a total of 260 gaps allowed propagation of AF. For AF, 51 (93%) of 55 gaps 1-3 mm allowed AF to pass through, as did 202 (99%) of 205 gaps >or=3.0 mm. Gaps as small as 1.1 mm conducted paced and AF impulses.

Conclusions: Conduction velocities were slowed through residual gaps. However, propagation of wave fronts during pacing and AF occurred through the majority of residual gaps, down to sizes as small as 1.1 mm. Leaving viable tissue in ablation lines for the treatment of AF could account for failures.

Figures

Figure 1

Isolated right atrial preparation, mounted to 250-lead electrode plaque in the bath, epicardial surface down. a. superior pacing electrode; b: inferior pacing electrode; c. 16-gauge perfusion catheter inserted in the origin of the right coronary artery; d. ablation lines created by bipolar radiofrequency clamp; e. gap measured between ablation lines.

Figure 2

Electrograms are presented from recordings near the pacing sites. (a) NSR. (b) Initiation of AF in the entire preparation. (c) NSR in the preparation after complete closure of the gap. (d) Initiation of AF in one half of the preparation after closure of the gap. “i” and “ii” represent recordings near the superior pacing electrode, “iii” and “iv” represent recordings near the inferior pacing electrode.

Figure 3

Effect of gap size on paced conduction velocity (shown as percent of control), with pacing from the upper pole of the atrium. Error bars show standard error of the mean. The conduction velocity was slower with decreasing gap sizes (p

Figure 4

The dependence of velocity on PCL (paced cycle length) and gap size greater than 10 mm vs less than 10mm is shown.

Figure 5

Percentage of impulses that successfully pass through remaining gap. AF, atrial fibrillation.

Figure 6

Electrograms are presented from recordings near the pacing sites; the top two represent recordings near the superior pacing electrode, the bottom two represent recordings near the inferior pacing electrode. Atrial fibrillation was initiated at the superior pacing electrode, propagated through a gap to the inferior portion of the atrium and was sustained at a 2:1 ratio.