Abstract 2240: When Have You Burned Enough? Transmural Atrial Ablation Lesions Can Be Identified By Higher Pacing Thresholds.
Background: Nontransmural lesions may contribute to recurrences of atrial arrhythmias after ablation, while excessive ablation may injure extracardiac structures. We hypothesized that atrial ablation lesion size and transmurality could be assessed from pacing threshold or electrogram amplitude.
Methods: In 6 anesthetized swine (43 ± 2 kg) 3D Electroanatomic mapping of the RA and LA was performed with a 4 mm tip catheter. Temperature controlled RF (56 ± 8°C, range 45–75°C) was delivered for 69 ± 45 (range 8 – 120) seconds to create a range of lesion sizes. Electrogram amplitude and 3 unipolar pacing threshold checks were obtained before and after each lesion. Lesions were excised, fixed and digitally imaged for quantitative assessment.
Results: 40 lesions were created with length 8 ± 3 mm and endocardial surface area 39 ± 31 mm2; 59% were transmural. Bipolar electrogram amplitude decreased from 3.0 ± 1.7 to 1.2 ± 0.9 mV post-ablation (p<0.001), while unipolar signal amplitude diminished from 3.8 ± 1.7 to 2.3 ± 1.1 mV. Pacing threshold rose from 2.6 ± 2.0 to 7.8 ± 3.4 mA (at 2 mS pulse width) post-ablation (p<0.001). Change in threshold and absolute post-ablation threshold correlated with lesion area (R=.54, p<.001 and R=.38, p=0.01 respectively). Transmural lesions had higher post-ablation thresholds (See Figure⇓, 6.1 ± 3.3 vs 9.4 ± 3.6 mA, p=0.035). Lesions with >2.5 mA rises in pacing threshold were 4-fold more likely to be transmural (p<0.05). Electrogram amplitude correlated poorly with lesion size (Unipolar amplitude R=0.04; Bipolar amplitude R=0.06).
Conclusions: Pacing threshold can assess atrial ablation lesion size and transmurality, and may serve as an endpoint for RF delivery.