Role of Magnetic Resonance Imaging in Electrophysiology

Cardiac magnetic resonance imaging (MRI) is a highly accurate non-invasive method for assessing myocardial scar by delayed enhancement imaging. Attempts to correlate electrogram voltage characteristics obtained by catheter-based point mapping to scar detected by MRI suggest that conventional substrate mapping techniques have limitations that could hinder ablative efficacy. This chapter discusses the role of cardiac MRI in the substrate-based ablation of unstable, reentrant ventricular tachycardias prior to ablation, during ablation and after ablation. Prior to ablation, the presence of delayed enhancement and its patterns can provide clues about the potential for reentrant circuits and regions where substrate may be present. During ablation, the integration of MRI-based scar maps with voltage-based scar maps within electroanatomical mapping systems has an emerging role, and may help identify residual channels ofconduction embedded within regions of heterogeneous scar. After ablation, particularly in the case of failed ablations, MRI can be used to detect the size and location of previous ablationlesions. While much of this chapter focuses on ventricular substrate detection, the emerging role of MRI for the detection of fibrosis and lesion formation in the thin-walled atria is addressed in the context of atrial fibrillation ablation as well. This edition first published 2013