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

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BACKGROUND: Radiofrequency and pulsed-field ablation are mechanistically distinct, yet no validated noninvasive imaging method has directly quantified how they differentially alter atrial tissue biomechanics in vivo or over time. OBJECTIVE: This study aimed to compare acute and chronic atrial lesion stiffness after focal radiofrequency ablation (F-RFA) and focal monopolar pulsed-field ablation (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 seconds), F-PFA (25 A, 10 pulse trains), or both. MMRE-derived shear wave speed, a surrogate of tissue stiffness, was measured in vivo ∼3 hours after ablation (acute, n = 17) and at 6 weeks (chronic, n = 8). Acute ex vivo tabletop magnetic resonance elastography 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: tabletop magnetic resonance elastography 6.40 m/s vs 3.65 m/s (P = .008) and in vivo MMRE 2.23 m/s vs 1.90 m/s (P = .041). By 6 weeks, neither of the groups demonstrated a significant temporal change in stiffness; however, a strong trend toward higher shear wave speed in F-RFA lesions than F-PFA lesions persisted (2.29 m/s vs 1.79 m/s; P = .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, noninvasive longitudinal quantification of atrial lesion stiffness in a large animal, providing a translational platform for energy selection and lesion maturation.

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