Radiofrequency ablation produces stiffer atrial lesions than pulsed-field ablation: in vivo and ex vivo MR elastography in pigs

BACKGROUND: Radiofrequency (RFA) and pulsed-field ablation (PFA) are mechanistically distinct, yet no validated non-invasive imaging method has directly quantified how they differentially alter atrial tissue biomechanics in vivo or over time. OBJECTIVES: To compare acute and chronic atrial lesion stiffness following focal RFA (F-RFA) and focal monopolar PFA (F-PFA) using a novel multifrequency magnetic resonance elastography (MMRE) technique in a porcine model. METHODS: Linear posterior intercaval right atrial lesions were created in 25 pigs (⁓50 kg), using F-RFA (25 W, 30 s), or F-PFA (25 A, 10 pulse trains) or both. MMRE-derived shear wave speed (SWS), a surrogate of tissue stiffness, was measured in vivo ∼3 hours post-ablation (acute, n=17) and at 6 weeks (chronic, n=8). Acute ex vivo tabletop MRE (ttMRE) on excised lesion samples served as an independent mechanical reference. RESULTS: Acutely, transmural F-RFA lesions were stiffer than transmural F-PFA lesions by both methods: ttMRE 6.40 m/s vs 3.65 m/s (p = 0.008) and in vivo MMRE 2.23 m/s vs 1.90 m/s (p = 0.041). By 6 weeks, neither of the groups demonstrated a significant temporal change in stiffness; however, a strong trend toward higher SWS in F-RFA lesions compared to F-PFA lesions persisted (2.29 m/s vs 1.79 m/s, p = 0.057). CONCLUSION: In this porcine model, F-RFA produced acutely stiffer atrial lesions than F-PFA, with this trend persisting over 6 weeks. The novel in vivo MMRE technique enables, for the first time, non-invasive longitudinal quantification of atrial lesion stiffness in a large animal, providing a translational platform for energy-selection and lesion-maturation.