Chasing Conduction Gaps Across the Roof Line: Nearby and Overlap Better Than Appendage Pacing.

Background: Blocking a line depends not only on the ablation but also on the validation technique. We sought to compare the performance of different pacing modes for roof line validation.

Methods: Fifty consecutive patients underwent atrial fibrillation ablation, which included a roof line and a floor line. Floor line block was mandatory for clear evaluation of the roof line, the block of which was demonstrated by a box isolation of the dome. Before floor line creation, first-pass roof line evaluation was based on high-density mapping while pacing from either: (1) the left appendage; (2) just above the line; or (3) with an overlapping multispline catheter.

Results: Roof line mapping was feasible in all patients (100%) during left appendage and nearby pacing, and in 45 (90%) patients during overlap pacing. Left appendage pacing sensitivity for true gaps was significantly lower than nearby (48% versus 97%; P<0.001) and overlap (48% versus 93%; P<0.001) pacing. Left appendage pacing negative predictive value for true block was significantly lower than nearby (50% versus 94%; P=0.001) and overlap (50% versus 89%; P=0.004) pacing. Double potentials during left appendage pacing were shorter than during nearby pacing (63±20 ms versus 103±22 ms; P<0.001). In 1 patient, a slow conduction gap was unmasked only after floor line block. Final box isolation of the dome was achieved in 47 (94%) patients.

Conclusions: The longer the activation delay from one side of a line to the other, the greater the chance to unmask a slow conduction gap across the line. Nearby pacing thus better identifies roof line gaps than left appendage pacing. Overlap pacing offers a simple and fast alternative with similar performance.