High-Density Mapping of Ventricular Scar

Abstract

Background-Surviving myocytes within scar may form channels that support ventricular tachycardia (VT) circuits. There are little data on the properties of channels that comprise VT circuits and those that are non-VT supporting channels. Methods and Results-In 22 patients with ischemic cardiomyopathy and VT, high-density mapping was performed with the PentaRay catheter and Ensite NavX system during sinus rhythm. A channel was defined as a series of matching pacemaps with a stimulus (S) to QRS time of ≥40 ms. Sites were determined to be part of a VT channel if there were matching pace-maps to the VT morphology. This was confirmed with entrainment mapping when possible. Of the 238 channels identified, 57 channels corresponded to an inducible VT. Channels that were part of a VT circuit were more commonly located within dense scar than non-VT channels (97% versus 82%; P=0.036). VT supporting channels were of greater length (mean±SEM, 53±5 versus 33±4 mm), had higher longest S-QRS (130±12 versus 82±12 ms), longer conduction time (103±14 versus 43±13 ms), and slower conduction velocity (0.87±0.23 versus 1.39±0.21 m/s) than non-VT channels (P<0.001). Of all the fractionated, late, and very late potentials located in scar, only 21%, 26%, and 29%, respectively, were recorded within VT channels. Conclusions-High-density mapping shows substantial differences among channels in ventricular scar. Channels supporting VT are more commonly located in dense scar, longer than non-VT channels, and have slower conduction velocity. Only a minority of scar-related potentials participate in the VT supporting channels. MethodsThis study was approved by the Human Research Ethics Committee of the Royal Adelaide Hospital and the University of Adelaide. Patient PopulationTwenty-two consecutive patients with ICM with recurrent VT or VT storm (≥3 episodes or implantable cardioverter defibrillator therapies for VT in 24 hours) undergoing a clinically indicated catheter ablation procedure were studied. Patients with a previous VT ablation, acute coronary event within the preceding 1 month, intracardiac thrombus, mechanical prosthetic valve, and severe aortoiliac peripheral vascular disease were excluded. Electrophysiological StudyThe procedure was done in the postabsorptive state under conscious sedation. Briefly, a quadripolar catheter and decapolar catheter were positioned at the right ventricular apex and coronary sinus, respectively. Programmed ventricular stimulation was performed from the right ventricular apex at 2 drive cycle lengths (600 and 400 ms) with ≤3 extrastimuli. All sustained monomorphic VTs induced at baseline, during the course of the study, and after ablation were considered clinical VT. 21 A 20-pole catheter (PentaRay; 2-6-2 mm interelectrode spacing, 1 mm electrodes; Biosense-Webster Inc, Diamond Bar, CA) was introduced either retrogradely using standard sheaths or transeptally using the Agilis NxT steerable introducer (St Jude Medical Inc, St Paul, MN) into the left ventricle (LV) for mapping. Activated clotting time was...

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

“…Entrainment mapping is the yardstick to characterize reentrant arrhythmias, but overestimation and underestimation of true isthmus length can cloud its conclusive performance similar to pace mapping. 38 Nevertheless, for unstable VTs, pace mapping is the best surrogate to approximate central anatomically protected segments, 5,13 and an ultra-high-density pace mapping from small closely spaced bipoles with rigorous matching criteria as was applied in our study reduces underestimation or overestimation of the central isthmus. Despite pace mapping at slower rates, which can reduce the likelihood of lines of functional block, pace map locations matching one of the induced VT morphologies with very long S-QRS intervals were identified in most patients, inclusive for fast VTs, signifying that functional latencies likely had a limited influence on the QRS morphology in the majority of VTs, and not just the exit sites but locations central within a VT channel were established.…”

“…In our recent study, we showed that VT supporting channels have longer protected segments and slower conduction than channels that do not support VT. 13 The complex electrograms expressed from unprotected branched channel segments within the scar have broader voltage distribution compared with electrograms from relatively longer protected channels with paucity of side branches. 18 On the basis of these, we reasoned that the electric information pertinent to the framework of critical segments of VT channels is reflected in their activation time and voltage distribution (=entropy) patterns.…”

“…If the morphology matched to a spontaneous or inducible VT, it was classified as a VT channel. A channel region was drawn by joining matching pace map locations in an orthodromic order of their stimulus to QRS interval (S-QRS), with at least 1 pace map having a S-QRS ≥40 ms. 13,22 Entrainment mapping was performed whenever feasible at sites with abnormal electrograms, long S-QRS latencies, and a paced QRS morphology matching VT. Standard criteria were used to define VT isthmus sites by entrainment mapping. 23 …”

“…[8][9][10] However, the information content of a VT supporting channel remains obscure in this scheme of abnormal electrogram classification, and, in fact, many are innocuous bystanders. [11][12][13] Conversely, only 50% of central, proximal, or exit sites of macroreentry circuits have abnormal electrograms. 14 On the basis of this, and the fact that substrate ablation can be time-consuming in large regions of scar, 6,15 there has been considerable interest into the problem of electric resolution within the scar 16,17 and a more targeted substrate ablation approach.…”

Ventricular Tachycardia Ablation – The Right Approach for the Right Patient

“…Entrance site pacing, however, will frequently yield a "nonmatched" QRS as the stimulus wave front may also exit antidromically in a different manner from the VT. 47 Recently, it has been recognised that an abrupt transition between a paced-QRS that matches the clinical VT (exit site) and a non-matched paced-QRS (entrance site) can identify an isthmus. 48 Typical isthmus sites are located in areas with low EGM voltages (< 1.5 mV EGM), with dimensions ranging from 21-59 mm length by 15-47 mm width.…”