Substrate Mapping for Ventricular Tachycardia: Assumptions and Misconceptions

Substrate mapping was developed to treat poorly tolerated infarct-related ventricular tachycardias (VTs). This concept was based on 30-year-old data derived from surgical and percutaneous mapping during sinus rhythm and VT that demonstrated specific electrograms (EGMs) that characterized the "arrhythmogenic substrate" of VT. Electrogram characteristics of the arrhythmogenic VT substrate during sinus rhythm included low-voltage, fractionation, long duration, split signals, and isolated late potentials as well as EGMs demonstrating adjacent early and late activation. Introduction of electroanatomical mapping (EAM) systems during the mid-1990s has allowed investigators to record electrograms in 3 dimensions and to identify sites assumed to represent the central common pathway ("isthmus") during re-entrant VTs. However, several important assumptions and misconceptions make currently used "substrate mapping" techniques inaccurate. These include: 1) re-entrant circuits are produced by fixed barriers of immutable "inexcitable" scar; 2) low voltage amplitude (≤0.5 mV) implies dense "inexcitable" scar; 3) isthmuses identified in patients with tolerated VTs using entrainment mapping are both valid and provide an accurate depiction of isthmuses in less hemodynamically tolerated VTs; and 4) current mapping tools and methods can delineate specific electrophysiologic features that will determine the barriers forming channels during re-entrant VTs. None of these assumptions has been validated and recent experimental and human data using higher resolution mapping with very small electrodes cast doubt on their validity. These data call for re-evaluation of substrate-mapping techniques to characterize the arrhythmogenic substrate of post-infarction VT. Standardization of recording techniques including electrode size, interelectrode spacing, tissue contact, catheter orientation, and wavefront activation must be taken into consideration.