Head-to-head comparison of Pulsed Field Ablation, very High Power-Short Duration Ablation and conventional Radiofrequency Ablation by LGE-MRI-based ablation lesion assessment

Despite substantial technological and procedural advances that have improved the efficacy and safety of AF ablation in recent years, the long-term durability of ablation lesions is still not satisfactory. Emerging concepts like high power-short duration radiofrequency ablation (HPSD) or pulsed field ablation (PFA) are aiming to optimize the trade-off between efficacy and safety, where more extensive ablation appears to inevitably increase the risk of collateral injury. Preclinical studies suggest a wider and shallower lesion geometry with HPSD that appears ideally suited to create contiguous lesions in the thin-walled atrium. However, clinical confirmation of such favourable features is lacking. The non-thermal PFA on the other hand, promises effective and safe ablation through selectivity for cardiomyocytes and relative resistance of surrounding tissues. However, systematic analyses of redo procedures found relatively low rates of durable PVI after PFA. 

 

Therefore, to systematically investigate lesion characteristics of these novel ablation concepts, we performed a prospective head-to-head comparison between conventional index-guided radiofrequency ablation (RF), HPSD ablation and PFA using late gadolinium enhancement (LGE) MRI.

 

This study prospectively included patients that underwent first-time PVI-only AF ablation - either by ablation index-guided RF ablation, HPSD ablation (QDOT, 90W, 4s, Biosense Webster) or PFA (Farapulse, Boston Scientific).

All patients received an LGE-MRI 3 months post-ablation. Gradient echo MR sequences were acquired in sinus rhythm and 3D-reconstruction of left atrium and PVs performed using ADAS-3D software. LGE was quantified based on the signal intensity ratio of each voxel relative to the blood pool, applying a previously validated threshold of >1.2 to define LGE indicative of ablation-induced scarring. LGE discontinuations of >3 mm were considered as gaps, and complete lesions were defined as LGE covering >90% of the peri-antral circumference of ipsilateral PV pairs.

 

Post-ablation LGE-MRIs from 60 patients were were analysed. The post-ablation LGE-lesions encircling ipsilateral PVs covered 89% (HPSD), 81% and 60% (PFA) of the peri-antral circumference (p<0.01). HPSD ablation resulted in a significantly lower median number of gaps per patient (2 gaps) than conventional RF (3 gaps) and PFA (3 gaps). The proportion of complete circumferential LGE lesions was significantly higher with HPSD than with conventional RF or PFA (68% vs. 50% vs. 21%; p<0.01).

 

As expected large-area ablation with the PFA single-shot device resulted in the widest, albeit inhomogeneous, lesions (12.1 mm). Importantly, HPSD lesions were significantly wider than conventional RF lesions (11.1 mm vs. 8.9 mm; p<0.05).

 

HPSD ablation lesions are wider and more continuous than conventional RF lesions, resulting in a lower number of gaps. This corroborates the concept of a shallower HPSD lesion geometry from experimental studies.

PFA lesions display a more inhomogeneous LGE distribution. While lesions cover larger areas than both, HPSD and conventional RF, PFA resulted in more incomplete lesions and gaps. However, it remains to be determined, to what extent LGE discontinuities in PFA lesions indicate ineffective ablation or only reflect a different kind of remodeling compared to thermal ablation, that may be less detectable by LGE-MRI.