High-Rate Pacing Reduces Variability of Repolarization and Prevents Repolarization-Dependent Arrhythmias in Dogs With Chronic AV Block.

Introduction: High-rate pacing may have an inhibitory effect on the initiation of Torsade de Pointes arrhythmias (TdP). However, permanent pacing is only indicated in high-risk patients. We performed a proof of concept study into automatic overdrive pacing for prevention of drug-induced TdP, using short-term variability of repolarization (STV) as a feedback parameter of arrhythmic risk. Methods and Results: The minimal signal sampling frequency required for measuring STV was determined through computer simulation. Arrhythmogenic response to dofetilide (25 μg/kg/5minutes) was tested at two different paced heart rates (60-65 bpm vs 100-110 bpm) in 7 dogs with chronic atrioventricular block, while recording right and left ventricular (LV) monophasic action potential (MAP) and LV electrogram (EGM). Simulations showed a sampling frequency of 500 Hz is sufficient to capture relevant STV values. High-rate pacing prevented dofetilide-induced TdP seen at the low rate (low: 6/7 vs high: 1/7). At the low rate, STV from LV MAP duration increased before occurrence of spontaneous, ectopic activity and TdP (1.7 ± 0.6-3.0 ± 1.8 ms, P < 0.05), but at the high-rate STV did not change significantly (0.9 ± 0.2-1.5 ± 1.4 ms, NS). Regression analysis showed a close relation between STV calculated from LV MAP and from LV EGM (R= 0.71). Conclusions: High-rate pacing increases repolarization reserve in dogs with chronic atrioventricular block, preventing dofetilide-induced TdP. Changes in repolarization reserve are reflected in values of STV. (J Cardiovasc Electrophysiol, Vol. 21, pp. 1384-1391, December 2010) [ABSTRACT FROM AUTHOR]