High Density Isochronal Repolarisation Mapping (iREM) and Reentry Vulnerability Estimation for Scar-related VT Ablation: Mechanistic Basis, Clinical Application and Challenges.

Alterations in repolarisation gradients and increased heterogeneity are key electrophysiological determinants of ventricular arrhythmogenesis across a variety of aetiologies with and without structural heart disease. High-density repolarisation mapping to localise these repolarisation abnormalities could improve characterisation of the individual arrhythmogenic substrate and inform more targeted ablation. Yet, due to challenges posed by intrinsic features of human cardiac repolarisation itself as well as technical and practical limitations, they are not routinely assessed, and traditional substrate mapping techniques remain strictly limited to determining conduction abnormalities. Here, we provide an overview of the mechanistic role of repolarisation alterations in ventricular re-entry arrhythmias followed by a description of a clinical workflow that enables high-density repolarisation mapping during VT ablations using existing clinical tools. We describe step-by-step guidance of how-to set-up and generate repolarisation maps illustrating the approach in case examples of structural normal and abnormal hearts. Furthermore, we discuss how repolarisation mapping could be combined with existing substrate mapping approaches, including isochronal late activation mapping, to delineate sites of increased re-entry vulnerability, that may represent targets for ablation without the requirement for VT induction. Finally, we review challenges and pitfalls and ongoing controversies in relation to repolarisation mapping and discuss the need for future technical and analytical improvements in repolarisation mapping to integrate into ventricular substrate mapping strategies. Repolarisation mapping remains investigational and future research efforts need to be focused on prospective trials to establish the additional diagnostic value and its role in clinical ablation procedures.