Development of Time- and Voltage-Domain Mapping (V-T-Mapping) to Localize Ventricular Tachycardia Channels During Sinus Rhythm

Abstract

Background-In ventricular scar, impulse spread is slow because it traverses split and zigzag channels of surviving muscle.We aimed to evaluate scar electrograms to determine their local delay (activation time) and inequality in voltage splitting (entropy), and their relationship to channels. We reasoned that unlike innocuous channels, which are often short with multiple side branches, ventricular tachycardia (VT) supporting channels have very slow impulse spread and possess low entropy because of their longer protected length and relative lack of side-branching. Methods and Results-Patients with ischemic cardiomyopathy and multiple VT were studied. In initial mapping stage (16 patients and 58 VTs), left ventricular endocardial mapping was performed in sinus rhythm. Detailed pace mapping was used to identify VT channels and confirmed, when feasible, by entrainment. Scar electrograms were analyzed in time and voltage domains to determine mean activation time, dispersion in activation time, and entropy. Predictive performances of these properties to detect VT channels were tested. In the application stage (7 patients and 20 VTs), these properties were prospectively tested to guide catheter ablation. A mean number of 763±203 sampling points were taken. From 1770 pace maps, 47 channels corresponded to VTs. A combination of scar electrograms with the latest mean activation time and minimum entropy, in a high activation dispersion region, accurately recognized regions containing VT channels (κ=0.89, sensitivity=86%, specificity=100%, positive predictive value=93%, and negative predictive value=100%). Finally, focused ablation within 5-mm rim of the prospective channel regions eliminated 18 of 20 inducible VTs. Conclusions-Activation time and entropy mapping in the scar accurately identify VT channels during sinus rhythm. The method integrates principles of reentry formation to recognize VT channels without pace mapping or mapping during VT. (Circ Arrhythm Electrophysiol. 2016;9:e004050.

Mapping of ventricular tachycardia in patients with ischemic cardiomyopathy: Current approaches and future perspectives

“…Moreover, even the sites of functional barriers present only during VT could be identified in sinus rhythm by cardiac MRI. In fact, functional block during VT occurs at the lateral isthmus boundaries, where there is a sharp change from the thinnest to the thickest infarct border zone . As previously discussed, this sharp thin‐to‐thick transition can also result in critical wavefront curvature and impedance or source‐sink mismatch, causing functional conduction block .…”

“…27 3. sites showing long Effective refractory period (ERP), long total recovery time, a wide refractoriness dispersion 35,36 or a high vulnerability to reentry (see below). A recent paper by Nayyar et al 42 where there is a sharp change from the thinnest to the thickest infarct border zone. 42 As previously discussed, this sharp thin-to-thick transition can also result in critical wavefront curvature and impedance or source-sink mismatch, causing functional conduction block.…”

“…A recent paper by Nayyar et al 42 where there is a sharp change from the thinnest to the thickest infarct border zone. 42 As previously discussed, this sharp thin-to-thick transition can also result in critical wavefront curvature and impedance or source-sink mismatch, causing functional conduction block. 37 Therefore, if we acquire high-resolution cardiac MRI images (at the moment not available for human use) regions with significant thinnest-tothickest geometry could be detected and located finally.…”

“…Regarding the third point, it could be of paramount importance to identify, in sinus or paced rhythms, the morphological electrogram features, the EPS characteristics and the specific structural anatomic and geometric hallmarks of a site that will become the functional barrier or the isthmus of a functional re‐entrant circuit. Recent studies suggest that such sites, and therefore possible new targets for ablation, could be: sites where recorded electrograms show lateness, low Shannon entropy and low SD in the activation time of their components sites that show sudden thin‐to‐thick transition on high‐resolution Magnetic Resonance Imaging (MRI) …”

“…A recent paper by Nayyar et al reported that sinus rhythm electrograms residing within the location where the isthmus forms during VT are often characterized by multiple deflections, late mean activation time of the deflections, greater disparity in the time of deflections and lesser value of Shannon entropy (narrow voltage distribution). Ablating the regions with these electrogram criteria enabled the authors to eliminate many of the clinical VT that were inducible in each patient.…”