Transmural unipolar electrogram change occurs within 7 s at the left atrial posterior wall during pulmonary vein isolation.

Background: To assess occurrence of a histologically validated measure of transmural (TM) atrial ablation-pure R unipolar electrogram (UE) morphology change-at first-ablated left atrial posterior wall (LAPW) sites during contact force (CF)-guided pulmonary vein isolation (PVI).

Methods: Objectively annotated VISITAG™ Module and CARTOREPLAY™ (Biosense Webster Inc., Diamond Bar, CA, USA) UE morphology data were retrospectively analyzed in 23 consecutive patients undergoing PVI under general anesthesia.

Results: PVI without spontaneous/dormant recovery was achieved in all, employing 16.3 (3.2) min of radiofrequency (RF; 30 W) energy. All first-ablated LAPW sites demonstrated RS UE morphology preablation, with RF-induced pure R UE morphology change in 98%. Time to pure R UE morphology was significantly shorter at left-sided LAPW sites (4.9 [2.1] vs 6.7 [2.5] s; P = .02), with significantly greater impedance drop (median 13.5 vs 9.9 Ω; P = .003). Importantly, neither first-site RF duration (14.9 vs 15.0 s) nor maximum ablation catheter tip distance moved (during RF) was significantly different, yet the mean CF was significantly higher at right-sided sites (16.5 vs 11.2 g; P = .002). Concurrent impedance and objectively annotated bipolar electrogram (BE) data demonstrated ∼6-8 Ω impedance drop and ∼30% BE decrease at the time of first pure R UE morphology change.

Conclusions: Using objective ablation site annotation, UE morphology evidence of TM RF effect was demonstrated far sooner than considered biologically possible according to the "conventional" 20-40 s RF per-site approach, with significantly greater ablative effect evident at left-sided sites. This novel methodology represents a scientifically more rigorous foundation toward future research into the biological effects of RF ablation in vivo.