Roles of the left atrial roof and pulmonary veins in the anatomic substrate for persistent atrial fibrillation and ablation in a canine model

Objectives: the aim of this study was to establish the electrophysiological consequences of pulmonary vein encircling ablation (PVEA) and linear left atrial roof ablation (LARA) for the atrial fibrillation (AF) substrate in an experimental model.

Background: sequential application of ablation lesions is often used in the management of AF, almost always incorporating PVEA and LARA.

Methods: Atrial tachypacing (400 beats/min, 5 weeks) was used to create an AF substrate in 13 dogs. PVEA and LARA were applied in randomized order. Regional atrial refractoriness, AF vulnerability, AF duration, and activation during AF were assessed before and after applying ablation lesion sets.

Results: PVEA failed to terminate AF or affect AF duration (742 ± 242 s before vs. 627 ± 227 s after PVEA) but decreased AF vulnerability to single extrastimuli from 91 ± 4% to 59 ± 5% (p < 0.001) by increasing effective refractory periods at sites with suppressed AF induction (from 78 ± 4 ms to 102 ± 8 ms, p < 0.01). LARA terminated AF in 67% of dogs (p < 0.05 vs. PVEA) and reduced AF duration (from 934 ± 232 s to 322 ± 183 s, p < 0.01) without affecting AF vulnerability. Baseline AF mapping showed left atrial (LA)-dominant complex reactivations (LA 9.4 ± 0.9 vs. right atrial 1.1 ± 0.3 reactivations/500-ms window, p < 0.001), with the LA roof frequently involved in re-entry circuits (44 ± 9% of LA reactivations). LARA terminated AF by interrupting LA roof reactivation circuits. In 5 of 13 cases, macro-re-entrant tachycardias (usually perimitral) occurred after LARA eliminated persistent AF.

Conclusions: both PVEA and LARA had beneficial but limited actions in this canine model. LARA suppressed AF perpetuation by interrupting LA roof reactivation, without affecting AF vulnerability. PVEA suppressed AF initiation by prolonging regional effective refractory period but failed to affect the AF-perpetuating substrate. These findings indicate the need to systematically study individual stepwise components to refine AF ablation procedures.