Ablation of the vanishing PVC, facilitated by quantitative morphology-matching software.

Background: Ablation of cardiac arrhythmias in children and teenagers often necessitates the use of anesthesia, which can suppress ventricular arrhythmias (VAs), making it difficult to map the site of origin using activation time (AT). Pace mapping, a technique employed to assist with VA origin localization, depends on subjective comparison of paced and targeted QRS morphology. We assessed the utility of a quantitative approach to paced QRS to VA morphology matching using the PaSo software (Carto 3, Biosense Webster), to localize the VA site of origin. Methods: Twenty-four patients underwent 26 procedures for frequent VAs, 29 for targeted VA. If AT mapping was precluded due to infrequent VA, pace mapping was executed using the PaSo software, after regionalization based on targeted VA QRS morphology. Results: Subjects were aged 1-32 (mean 14 +/- 6) years; 10 were male. Heart disease was present in six patients. PVC frequency prior to onset of anesthesia was 15 +/- 16/min, decreasing to 0-1 PVC/min in 17 cases prior to ablation. Arrhythmia localization was performed by AT mapping + PaSo (12) or PaSo only (17). Pace mapping exhibited an intraventricular gradient of percent QRS morphology match. Highest achieved QRS match averaged 96 +/- 2%. Successful ablation (>1-month follow-up) was achieved in 24/29 targeted VAs, 11/12 ablated using AT and pace mapping, and 13/17 VA ablated using pace mapping only, P = 0.29. Conclusions: (1) Spontaneous VA frequency was markedly reduced following anesthesia, despite catecholamine administration. (2) Notwithstanding the ability to perform AT mapping, successful ablation can still be performed using pace mapping only, facilitated by the PaSo software.