Response to Letter Regarding Article, “Cardiac Memory in Patients With Wolff-Parkinson-White Syndrome: Noninvasive Imaging of Activation and Repolarization Before and After Catheter Ablation”
We thank Berger and colleagues for their queries about our article.1 Three-dimensional CARTO mapping was not performed because it was not clinically indicated in this pediatric study (it prolongs procedure and fluoroscopy time). The objectives of the study were to guide ablation by noninvasively imaging preexcitation sites before the procedure and then, after the procedure, to study changes in epicardial activation and repolarization. ECG imaging (ECGI) was validated extensively in canine experiments and in humans by direct epicardial mapping during cardiac surgery and by localization of known pacing sites (references1).
Activation recovery interval (ARI), computed from QRS maximum negative derivative to T-wave maximum positive derivative, correlates with action potential duration.2 ARI dispersion imaged by ECGI was shown to quantify dispersion of repolarization.3 The QT interval in the letter by Berger et al is defined from Q-start to T-end. It differs from ARI and does not reflect action potential duration. In fact, it is not uncommon for QT and ARI to change in different directions. Moreover, QT interval of a single electrogram does not reflect spatial properties, and even QT differences between several electrograms are a poor estimate of repolarization dispersion.4
We do not have data for quantification of myocardial damage. Average duration of radiofrequency was 2.3±1.2 minutes and number of lesions 3.1±1.6, with power setting of 50 Watts and temperatures between 50 and 60°C. Three patients (W5, W6, W8) had cryo-ablation (duration 20.6±19.4 minutes, number of lesions 7.6±2.5, temperature −70°C). The lesions were focal, shown to cause significant myocardial injury only in a small percentage of patients.5 ECGI postablation was performed 45 minutes after the procedure end to eliminate any effects of local temperature transients. Moreover, ARI changes were imaged over a much larger epicardial area than the focal lesion size and occurred independently of the ablation method (radiofrequency or cryo).
Dr Rudy chairs the scientific advisory board and holds equity in CardioInsight Technologies. CardioInsight Technologies does not support any research conducted by Dr Rudy, including the research presented here. The remaining authors report no conflicts.
Ghosh S, Rhee EK, Avari JN, Woodard P, Rudy Y. Cardiac memory in patients with Wolff-Parkinson-White syndrome: noninvasive imaging of activation and repolarization before and after catheter ablation. Circulation. 2008; 118: 907–915.
Haws CW, Lux RL. Correlation between in vivo transmembrane action potential durations and activation-recovery intervals from electrograms. Circulation. 1990; 81: 281–288.
Ghanem RN, Burnes JE, Waldo AL, Rudy Y. Imaging dispersion of myocardial repolarization II: noninvasive reconstruction of epicardial measures. Circulation. 2001; 104: 1306–1312.
Fuller MS, Sandor G, Punske B, Taccardi B, MacLeod RS, Ershler PR, Green LS, Lux RL. Estimates of repolarization dispersion from electrocardiographic measurements. Circulation. 2000; 8: 102:685–691.