Abstract 11336: Different Mechanisms of Torsade de Pointes Arrhythmias in the Drug-induced Chronic AV Block Dog

Abstract

Introduction: The arrhythmia Torsade de Pointes (TdP) is responsible for >5% of all sudden cardiac deaths. However, the mechanism(s) underlying the TdPs is under debate. Clinical and experimental data suggest that TdP may be driven either by focal sources or by moving reentry. One way to study the mechanisms of TdP is to use the electrically remodeled canine heart after chronic AV block (CAVB), which has a high susceptibility for drug-induced TdPs. Methods: Five TdP-sensitive CAVB dogs were studied. In all animals, 66 needle electrodes were evenly distributed transmurally to record 240 unipolar local electrograms simultaneously. If the TdP was non-terminating after 10s, it was defibrillated. Software was developed to automatically detect activation times during the dofetilide-induced TdPs and to create 3D visualisations of the arrhythmia. For each episode of TdP, directed graphs of the wave propagation were created and loops were detected by using an iterative depth first search algorithm(Johnson). Interbeat intervals were computed by taking the average of the time intervals of activation for each electrode. Results: In total we analysed 53 TdPs: from those 9 were non-terminating (> 50 beats) and 44 self terminating. In all non-terminating TdPs reentry loops were identified. In the 44 self terminating TdPs reentry loops were found only in 6 (20±10 beats) cases, while in the 38 (7±4 beats) other cases TdP was driven by focal sources. Secondly, during reentry, excitation fronts were constantly present in the heart, while during ectopic TdP there was always a pause between the end of the previous wave and the beginning of the next wave (121±51 ms) during which excitation fronts were absent. Thirdly, we found that the interbeat intervals were significantly smaller for the cases where reentry loops were detected, then in the cases of the ectopic TdPs (221±21 versus 310±96 ms). Finally, in all cases where reentry loops were detected, the signal of certain electrodes had significantly smaller amplitude than the average amplitude under normal pacing, which via computer simulations could be related to the cores of the reentry loops. Conclusions: In the non-terminating TdPs reentry is always present, while paroxysmal TdP was in most of the cases based on ectopic activity (86%).