Abstract
Atrial and pulmonary vein (PV) stretch is proarrhythmic, but the mechanical effect of PV ablation scar on atrial fibrillation (AF) arrhythmogenesis is unknown. We hypothesize that discontinuous PV ablation scars are proarrhythmic because they create heterogeneous stretch. To measure local atrial strain and AF inducibility in healthy sheep hearts with and without PV ablation scar. Functional cardiac MRIs acquired in vivo in sheep (n=12) before and 3 months after discontinuous PV ablation by radiofrequency in the right PV (RPV) were analyzed with a feature-tracking algorithm to obtain local strain in the left atrium (LA). Explanted hearts were perfused with 1:4 blood:Tyrode’s solution in a dual-chamber working-heart set-up. Multi-electrode endocardial catheters were positioned in the RPV and left PV (LPV) for premature stimulation during low (∼12mmHg) and high (∼25mmHg) LA pressure. Control hearts (n=12) underwent similar ex vivo investigation. The maximum longitudinal strain of the myocardial wall between the RPV and LPV increased from 20±6 (mean±SD) to 34±16% (pre vs. post-ablation, respectively; p=0.032), whereas the maximum radial motion fraction of the LA septum close to the RPV decreased from 46±10 to 36±7% (pre vs. post, p=0.035). Sustained AF (>30s) was more often induced during stimulation in ablated than in control hearts (22% vs. 9% of induction attempts (n=73 vs. n=87), respectively, p=0.025). In ablated hearts, an increase in LA pressure augmented AF inducibility (11% vs. 34% of induction attempts, n=38 vs. n=35, low vs. high LA pressure, respectively, p=0.024), whereas this was not the case in control hearts (2% vs. 17% of induction attempts (n=45 vs. n=42), low vs. high, p=0.237). Moreover, the diastolic stimulation threshold was higher in ablated than control hearts (90 (60) (median (IQR)) and 75 (40) mA, p=0.007). Local PV ablation scar caused localized disparate mechanical changes and increased inducibility of sustained AF, especially during increased LA pressure. This was associated with decreased tissue excitability. Therefore, ablation scar in a single PV causes an atrial arrhythmogenic substrate. Ablation lesion sets that homogenize atrial mechanics may improve the AF ablation success.
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