Predictors of decremental conduction after extrastimulus in post-infarction ventricular tachycardia substrate maps

Ventricular tachycardia (VT) substrate ablation techniques attempt to identify areas of decremental conduction (DC) within the scar, given their close relationship with VT isthmuses. DC identification requires the systematic use of extrastimuli during substrate mapping. This can be time consuming and induce ventricular arrhythmias during mapping.

This study aims to identify predictors of decremental response after extastimulus that allow recognizing areas with higher probability of DC conduction in order to focus functional mapping of the substrate on them.

Sixteen consecutive ischemic patients (93.8% male, 66.3±12.4 years) undergoing VT substrate ablation were included. A detailed substrate map during right ventricular (RV) pacing was obtained in all of them. Systematic analysis of electrograms (EGMs) recorded from the infarct area was performed during RV pacing at 600-500 ms, and during a short-coupled RV extrastimulus. Electrograms during RV pacing exhibiting decremental evoked conduction delay after an extrastimulus (DECD-AE) were compared to those not showing DECD-AE.

Mean low voltage (<1.5 mV) area was 45±18.6 cm2. A total of 1744 EGMs were analyzed. Of them, 453 (26%) showed DECD-AE. Bipolar EGMs showing DECD-AE exhibited a higher number of deflections [4(interquartile range 3-5) vs 2(1-3); p<0.0001], a higher amplitude [0.52(0.27-1) vs 0.3(0.14-0.7) mV; p=0.003] and similar duration [114(102-135) vs 117(100-133 ms); p=0.492] compared to EGMs without DECD-AE. The area under curve was 0.64 for bipolar voltage and 0.8 for number of bipolar deflections. The presence of <3 bipolar deflections excluded DECD-AE with a negative predictive value of 98.5%.

In areas of myocardial scar, bipolar EGMs with <3 deflections are unlikely to present DECD-AE. Focusing functional mapping on signals with ≥3 deflections could simplify procedures and save time.