Time dependent changes in duration of ventricular repolarization after AV node ablation: Insights into the possible mechanism of postprocedural sudden death

Although effective, there is a disturbing incidence of sudden death after A V node ablation. The mechanism may be related to proarrhythmia associated w ith prolongation in ventricular repolarization from the sudden decrease in heart rate. To examine this issue, we studied 15 patients undergoing comple te radiofrequency ablation of the AV node for rapid atrial arrhythmias. Twe lve-lead ECGs of paced rhythms at rates of 60, 80, 100, and 120 beats/min w ere recorded at time points of 30 minutes, 24 hours, 1 week, and 1 month af ter ablation. The QT interval was measured in the limb and precordial leads with the best T wave offset. The change in the QT interval (Delta QT) rela tive to the measurement at 30-minute postablation was calculated. For compa rison, a similar procedure was performed on patients receiving pacemakers f or primary bradycardia (n = 5). The mean QT interval at 60 beats/min, 30-mi nutes postablation was significantly longer than at time points thereafter (482 +/- 39 vs 446 +/- 28 ms at 1 month, limb leads, for example, P < 0.05) . Analysis of <Delta>QT revealed a significant shortening of the QT interva l at nearly every paced rate at every time point relative to the value at 3 0-minute postablation. The QT intervals shortened and stabilized after 24 h ours. Neither the QT interval nor Delta QT changed significantly in patient s paced for primary bradycardia. We conclude that there is a relative incre ase in the duration of ventricular repolarization after AV node ablation, w hich then decreases and stabilizes after 24 hours. Such changes are not see n in patients being paced for primary bradycardia. This data is consistent with the hypothesis that sudden death after AV node ablation may be related to proarrhythmia from prolonged ventricular repolarization.