Optimized mapping of slow pathway ablation guided by subthreshold stimulation: a randomized prospective study in patients with recurrent atrioventricular nodal re-entrant tachycardia.

OBJECTIVES This randomized prospective study sought to assess the value of slow pathway (SP) mapping and ablation guided by subthreshold stimulation (STS) in comparison with a strategy based on conventional criteria. BACKGROUND Previous studies have demonstrated that STS can be used as a highly specific and sensitive marker for successful SP ablation in the setting of atrioventricular nodal re-entrant tachycardia (AVNRT). Nonetheless, thus far this mapping strategy has not been investigated in contrast with the conventional approach. METHODS One hundred patients with sustained AVNRT were included. Fifty patients (group A) were randomly assigned to endocardial mapping and SP ablation using currently established criteria. In the other 50 patients (group B), SP ablation was guided by STS mapping. In group B patients, only radiofrequency current (RFC) was applied if additionally constant current STS (up to 5 mA) during AVNRT interrupted the tachycardia due to selective block within the SP. RESULTS Termination of AVNRT without apparent capture was observed during STS in 47 of 50 group B patients (94%). In all cases, this effect was indicative for successful subsequent SP ablation. The mean number of RFC pulses required for successful SP ablation was significantly lower in patients assigned to the STS-guided strategy (1.6 +/- 1.3 vs. 3.9 +/- 3.4; p = 0.0003). Similarly, the mean procedure duration was shorter in the STS group (156.9 +/- 33.5 vs. 173.2 +/- 49.7 min; p = 0.0221); the fluoroscopy time was comparable between both groups (14.1 +/- 8.7 vs. 16.9 +/- 10.6 min; p = 0.1278). CONCLUSIONS Subthreshold stimulation is an effective method for detection of target sites for selective SP ablation. This technique helps to minimize the number of RFC pulses without prolongation of the overall procedure and fluoroscopy time required for SP ablation.