Loss of pace capture on the ablation line: a new marker for complete radiofrequency lesions to achieve pulmonary vein isolation.

BACKGROUND: Catheter ablation procedures for atrial fibrillation (AF) often involve circumferential antral isolation of pulmonary veins (PV). Inability to reliably identify conduction gaps on the ablation line necessitates placing additional lesions within the intended lesion set.
OBJECTIVE: This pilot study investigated the relationship between loss of pace capture directly along the ablation line and electrogram criteria for PV isolation (PVI).
METHODS: Using a 3-dimensional anatomic mapping system and irrigated-tip radiofrequency (RF) ablation catheter, lesions were placed in the PV antra to encircle ipsilateral vein pairs until pace capture at 10 mA/2 ms no longer occurred along the line. During ablation, a circular mapping catheter was placed in an ipsilateral PV, but the electrograms were not revealed until loss-of-pace capture. The procedural end point was PVI (entrance and exit block).
RESULTS: Thirty patients (57 +/- 12 years; 15 male [50%]) undergoing PVI in 2 centers (3 primary operators) were included (left atrial diameter 40 +/- 4 mm, left ventricular ejection fraction 60 +/- 7%). All patients reached the end points of complete PVI and loss of pace capture. When PV electrograms were revealed after loss of pace capture along the line, PVI was present in 57 of 60 (95%) vein pairs. In the remaining 3 of 60 (5%) PV pairs, further RF applications achieved PVI. The procedure duration was 237 +/- 46 minutes, with a fluoroscopy time of 23 +/- 9 minutes. Analysis of the blinded PV electrograms revealed that even after PVI was achieved, additional sites of pace capture were present on the ablation line in 30 of 60 (50%) of the PV pairs; 10 +/- 4 additional RF lesions were necessary to fully achieve loss of pace capture. After ablation, the electrogram amplitude was lower at unexcitable sites (0.25 +/- 0.15 mV vs. 0.42 +/- 0.32 mV, P < .001), but there was substantial overlap with pace capture sites, suggesting that electrogram amplitude lacks specificity for identifying pace capture sites.
CONCLUSION: Complete loss of pace capture directly along the circumferential ablation line correlates with entrance block in 95% of vein pairs and can be achieved without circular mapping catheter guidance. Thus, pace capture along the ablation line can be used to identify conduction gaps. Interestingly, more RF ablation energy was required to achieve loss of pace capture along the ablation line than for entrance block into PVs. Further study is warranted to determine whether this method results in more durable ablation lesions that reduce recurrence of AF. Copyright 2010 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.