Assessment of acute and chronic atrial lesion stiffness after radiofrequency and pulsed-field ablation using multifrequency magnetic resonance elastography

Extensive catheter ablation beyond pulmonary vein isolation may increase atrial tissue stiffness, potentially depending on the energy source.

This study aimed to compare the acute and chronic effects of radiofrequency ablation (RFA) and pulsed field ablation (PFA) on atrial tissue stiffness using a non-invasive novel in vivo multifrequency magnetic resonance elastography (MMRE) approach in a porcine model.

Ablation lines were created between the superior and inferior vena cava in 19 pigs (11 acute, 8 chronic, ∼50 kg and ∼16 weeks old) using either focal RFA (25 W, 30 s) or focal monopolar biphasic PFA (CENTAURI PFA generator, 25 A, 10 pulse trains). Acute lesions were assessed ∼3 hours post-ablation using a novel in vivo MMRE protocol to derive shear wave speed (SWS) as a surrogate for tissue stiffness, and cross-validated by ex vivo tabletop MRE (ttMRE). In chronic animals, MMRE was repeated 6 weeks post-ablation.

In vivo MMRE revealed significantly higher stiffness for the acute RFA ablation zone (RFA-A) than the acute PFA ablation zone (PFA-A) (RFA-A mean: 2.40±0.3 m/s; PFA-A mean: 2.10±0.3 m/s; p=0.03). Ex vivo ttMRE confirmed these findings (RFA-A mean: 6.49±1.0 m/s; PFA-A mean: 3.50±0.6 m/s; p=0.008). At 6 weeks, both lesion types exhibited stiffness reduction with a greater decline for PFA than RFA (PFA: 16% vs RFA: 10%; p=0.11) (Figure 1).

RFA produces acutely stiffer atrial lesions than PFA in pigs, consistent across in vivo and ex vivo MRE. However, over the course of six weeks, stiffness differences diminished, suggesting divergent remodeling dynamics between thermal and electroporative injury. Novel MMRE enables noninvasive characterization of atrial lesion stiffness in vivo and may inform energy selection and lesion durability assessment in future ablation strategies.