The main objective was to assess electrophysiological parameters which may be important for effective radiofrequency ablation of accessory atrioventricular pathways. In a group of 66 patients a total of 490 applications of radiofrequency current were made, incl. 68 which led to successful severing of the accessory pathways. The ablations were successful in 65 patients (98.5 %). The potential of the accessory pathways was present in effective ablations in 19 cases of 68 applications (28 %), while in ineffective ablations it was present in 13 cases of 421 applications (3%, p < 0.001).Stability of the electrogram was found in all 68 effective ablations (100%), while in ineffecti- ve ablations a stable electrogram was found in 248 cases of 323 applications (77%, p<0.001).In unstable electrograms the ablation was not effective in any of the patients. The V-delta interval was significantly longer in successful ablations (16 ± 14.2 ms) than in unsuccessful ones (3 ± 19.4 ms, p < 0.001). The ventriculoatrial interval was in successful ablations significantly shorter (57.5 ± 22.5 ms) than in unsuccessful ones (74.5 ± 20.9 ms, p < 0.001). In 90 % applications the ventriculoatrial interval was less than 70 ms. Of 10 evaluated parameters the potential of the accessory pathway, stability of the electrogram,V-delta interval (equal or < 0) and short ventriculoatrial intervals ( equal to or < 70 ms) proved important parameters for successful ablation of accessoray pathways.

        Key words: Radiofrequency ablation - Accessory pathways - Electrophysiological parameters - Effectiveness