Pre-ablation staging identified 2 subgroups of AF patients with either an excellent (minimal fibrosis) or a poor (extensive fibrosis) prognosis following ablation. In addition, postablation assessment of the PV antral region scarring demonstrated that catheter ablation targeting acute electrical isolation does not correlate with PV antral circumferential scarring at 3 months, as seen using DE-MRI. We also demonstrate circumferential PV scarring to be an important predictor of arrhythmia recurrence in the subgroup of patients with mild fibrosis (Utah stage 2), as opposed to the moderate fibrosis group (Utah stage 3), where overall LA scarring, specifically LA posterior wall and septum, is shown to be the most important determinant of procedural failure.
Most approaches to ablation for AF aim at isolation of PV triggers.11, 12
This is accomplished by encircling the PV antral region with ablation lesions and achieving electrical isolation, which is an accepted acute endpoint.12, 17
Some operators advocate for additional ablation aimed at “substrate modification” for patients with longstanding or persistent arrhythmia.11, 13–15
This study examines the anatomical correlate of electrical isolation by examining scarring in the PV antral region as well as the overall scarring in the LA. We show that even though electrical isolation is achieved acutely, this does not translate to persistent circumferential scarring around the PVs at 3 months. This indicates that either (1) electrical isolation does not require complete encirclement of the PVs or (2) that initial ablation is ineffective at creating irreversible scarring, i.e., there is recovery from the initial injury. The first scenario is less likely as operators currently ablate away from the true ostia of the PVs to avoid PV stenosis. Lesions therefore target continuous left atrial tissue rather than muscle sleeves inside the PVs. The second scenario is more likely especially when it is suspected that electrical reconnection of the PVs to the main left atrial musculature has occurred in the majority of recurrent cases.18–21
Our study also shows that PV encirclement with scar correlates with the overall scarring in the LA 3 months postablation. Patients with fewer veins encircled with scarring have a lower overall left atrial scar burden at 3 months. This is seen despite the fact that all patients were ablated using the same approach and achieved the same endpoints at the end of the procedure. This indicates that the mechanism leading to ineffective lesion formation or tissue recovery following ablation is the same in the antral region and throughout the LA.
PV antrum encirclement with ablation scar and overall ablation scar in the LA predicted recurrence independently in patients with mild and moderate fibrosis/SRM subgroups, respectively. This is in line with other publications suggesting that isolation of PV triggers may be acceptable in paroxysmal AF, whereas patients with more clinically advanced AF are likely to have a better long-term outcome with more extensive ablation. Variable success rates have been reported with adding linear lesions to PV circumferential isolation,14, 22
targeting areas of complex fractionated electrograms (CFAEs)13
and dominant frequency,23
as well as disrupting ganglionated plexi connections to the atrium.24
The common denominator to all these approaches helping improve outcomes following ablation is that, especially in patients with more advanced clinical AF, there is more left atrial tissue involved in creating the AF substrate than the triggers in the PVs and that going outside the PV antral region to modify this substrate leads to improved ablation outcomes. Our study offers an insight onto this AF substrate by quantifying the extent of LA remodeling and fibrosis associated with it, which we demonstrate to require more extensive ablation in order to overcome and achieve better long-term success.