Background: Rapid anterograde conduction in the setting of ventricular preexcitation is associated with an increased risk of sudden cardiac death. The effect of isoproterenol in this setting is unclear, particularly in younger anesthetized patients. The aim of this study was to determine the effect of isoproterenol on accessory-pathway conduction in children undergoing general anesthesia and its role in the risk-stratification process.
Methods and results: The records of 151 pediatric patients with preexcitation undergoing electrophysiologic study under propofol anesthesia during a 5-year period were reviewed. Data included accessory-pathway effective refractory period, minimum 1:1 accessory pathway conduction with atrial pacing, and shortest preexcited R-R interval in atrial fibrillation. Measurements were repeated after administration of low-dose isoproterenol (mean, 0.013 μg/kg per min; range, 0.003 to 0.027). All accessory-pathway characteristics were significantly shortened with isoproterenol (P<0.001). Accessory-pathway effective refractory period increased modestly with age, both in the baseline state (r=0.172, P=0.04) and with isoproterenol (r=0.267, P<0.01) as did minimum 1:1 accessory pathway conduction with atrial pacing (r=0.178, P=0.034, and r=0.175, P<0.01, respectively). Accessory-pathway effective refractory period ≤250 ms was observed in only 5% of patients at baseline vs 25% after isoproterenol, and Shortest preexcited R-R interval in atrial fibrillation ≤250 ms was noted in 16% vs 41%. Tachycardia was induced in 48 of 151 patients before and in 102 of 151 after isoproterenol.
Conclusions: In anesthetized children with ventricular preexcitation, accessory pathways display shorter conduction properties at younger ages and important adrenergic sensitivity at all ages. Use of low-dose isoproterenol resulted in a substantial increase in the number of patients who would otherwise meet typical criteria for ablation.