Background and aim: To assess safety and efficacy of antazoline for termination of atrial fibrillation (AF) occurring during ablation of accessory pathways (AP).

Methods: We analyzed electrophysiological mechanism of antazoline (changes in A-A interval) and the percentage of pre-excited QRS complexes before and after antazoline administration. The total dose administered and the time from the start of injection to sinus rhythm restoration were also measured.

Results: Out of consecutive 290 patients with Wolff-Parkinson-White syndrome undergoing radiofrequency (RF) ablation, 12 (4.1%) (4 females, mean age 36 ± 20 years) developed sustained AF which did not stop spontaneously within 10 min, and antazoline in 100 mg repeated boluses was administered. In all 12 patients the drug restored sinus rhythm after a mean of 425 ± 365 s (range 43–1245 s) using a mean cumulative dose of 176 ± 114 mg (range 25–400 mg). The drug slightly prolonged R-R intervals during AF (from 383 ± 106 to 410 ± 70 ms) and reduced the percentage of fully pre-excited QRS complexes (from 35% to 26%). Intracardiac recordings showed gradual increase in A-A intervals, as well as regularization and decreasing fractionation of atrial activity following drug injection (mean A-A interval of 162 ± 30 ms at baseline vs. 226 ± 26 ms shortly before sinus rhythm restoration, p < 0.001). AP was not completely blocked in any patient which enabled continuation of ablation.

Conclusions: Antazoline safely and rapidly converts AF into sinus rhythm during ablation of AP. The drug does not block AP completely, enabling continuation of ablation. The drug converting AF into more organized atrial activity (atrial flutter/tachycardia) before sinus rhythm resumption.