Unipolar Electrogram Morphology to Assess Lesion Formation During Catheter Ablation of Atrial Fibrillation

The past decade has seen a significant increase in catheter ablation procedures for atrial fibrillation (AF)1; however, data on the efficacy of pulmonary vein (PV) isolation (PVI) are soberingly modest, with single and multiple procedure success rates of 54% and 79% for paroxysmal AF, respectively, during long-term follow-up (≥3 years).2 The main mechanism of AF recurrence after catheter ablation is resumption of PV-left atrial (LA) conduction.3 The time-dependent inevitability of recovery of PV conduction has been consistently demonstrated in acute studies showing PV conduction in ≤93% of patients during an intraprocedural waiting period of 60 minutes after PVI.4 Furthermore, late recurrence of AF is associated with conduction recovery in ≥1 PV in >97% of patients who are having a redo procedure.2 Thus, durable PVI is critical if we are to make inroads toward enhancing procedural efficacy.Article see p 1095 Gaps in the ablation line5 and failure to produce transmural lesions6 are implicated in recovery of PV conduction. PVI can be achieved after partial completion of a circumferential ring of lesions around the PVs, irrespective of intervening gaps. This is thought to result from a combination of irreversible and reversible atrial injury.7 Reversible atrial injury may stem from incomplete lesion formation that causes temporary electric uncoupling but not cell death ≤3.5 mm away from the lesion boundary, dependent on tissue temperature and tissue geometry.8 With time, tissue at the boundary of the transmural lesion recovers normal conduction during the course of 1 to 4 weeks.8 Thus, lesion gaps that exhibit conduction block frequently go undetected during the index procedure, and block persists for up to several weeks or months thereafter until tissue injury heals. Conduction block may occur in tissue with normal conductivity despite a gap of ≤1.4 mm …