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

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.

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.

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.

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.