Atrioventricular nodal reentrant tachycardia in children: effect of slow pathway ablation on fast pathway function

Prior studies in adults have shown significant shortening of the fast pathway effective refractory period after successful slow pathway ablation. As differences between adults and children exist in other characteristics of AV nodal reentrant tachycardia (AVNRT), we sought to characterize the effect of slow pathway ablation or modification in a multicenter study of pediatric patients.

Data from procedures in pediatric patients were gathered retrospectively from five institutions. Entry criteria were age <21 years, typical AVNRT inducible with/without isoproterenol infusion, and attempted slow pathway ablation or modification. Dual AV nodal pathways were defined as those with > or =50 msec jump in A2-H2 with a 10-msec decrease in A1-A2. Successful ablation was defined as elimination of AVNRT inducibility. A total of 159 patients (age 4.4 to 21 years, mean 13.1) were studied and had attempted slow pathway ablation. AVNRT was inducible in the baseline state in 74 (47%) of 159 patients and with isoproterenol in the remainder. Dual AV nodal pathways were noted in 98 (62%) of 159 patients in the baseline state. Ablation was successful in 154 (97%) of 159 patients. In patients with dual AV nodal pathways and successful slow pathway ablation, the mean fast pathway effective refractory period was 343+/-68 msec before ablation and 263+/-64 msec after ablation. Mean decrease in the fast pathway effective refractory period was 81+/-82 msec (P < 0.0001) and was not explained by changes in autonomic tone, as measured by changes in sinus cycle length during the ablation procedure. Electrophysiologic measurements were correlated with age. Fast pathway effective refractory period was related to age both before (P = 0.0044) and after ablation (P < 0.0001). AV block cycle length was related to age both before (P = 0.0005) and after ablation (P < 0.0001). However, in dual AV nodal pathway patients, the magnitude of change in the fast pathway effective refractory period after ablation was not related to age.

Lack of clear dual AV node physiology is common in pediatric patients with inducible AVNRT (38%). Fast pathway effective refractory period shortens substantially in response to slow pathway ablation. The magnitude of change is large compared with adult reports and is not completely explained by changes in autonomic tone. Prospective studies in children using autonomic blockade are needed.