Radiofrequency Lesion Assessment by Cardiac Magnetic Resonance Imaging following Atrial Fibrillation Catheter Ablation
Single ablative therapy for PAF has moderate success and many patients present with recurrent arrhythmia. We propose that the structure of the RF lesion applied during ablation is important in determining recurrences. The nature of the RF lesion was studied using MRI with gadolinium delayed enhanced (DE) imaging and high signal T2 weighted imaging. Levels of DE and T2 were low in pre-procedural scans but rose dramatically immediately following the procedure. Acute DE was greater in patients without recurrences compared to those with recurrences. Conversely T2 levels were lower in patients without recurrences and higher in those with recurrences. On the late scans, T2 reduced to baseline. DE however remained and was greater in patients without recurrences. We therefore propose that acute RF ablation injury is composed of two types of tissue damage. DE infers largely necrotic tissue injury which lasts longer and causes persistent conduction block. T2 is a transitory phenomenon co-existing with DE, causing acute conduction block. We propose that resolution of oedema is associated with recurrences of PV connection and therefore arrhythmia recurrences. Modifications in our ablative techniques to achieve more DE at the acute ablation would potentially be important in conferring better ablation outcomes. The role of DE imaging was utilised to compare left atrial catheter ablation with robotic assisted navigation and standard navigation. A greater circumferential lesion extent by DE was observed in the robotic group . This suggests that catheter stability improves tissue contact permitting the creation of more contiguous durable scar around the PV antrum. We also sought to improve DE imaging sequences to optimise scar visualisation and tested the feasibility of an automatic scar quantification tool to improve reproducibility whilst maintainin accuracy
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