[Efficacy criteria in the fulguration of the bundle of His]

The authors have endeavoured to determine which of the parameters commonly used for His bundle ablation are likely to predict that ablation will be effective in altering the atrioventricular (AV) conduction system durability. His bundle ablation was performed in 18 patients (9 men, 9 women; mean age 47 years) presenting with supraventricular tachycardia refractory to all medical treatments. A total of 29 shocks were delivered with an Odam fulgurator, using a distal electrode connected to the positive pole of a selected catheter. Fifteen shocks were effective, resulting in a complete and permanent AV block (group I); the remaining 14 shocks failed to modify permanently the AV conduction system (group II). The parameters which differed between these two groups were the amplitude and the stability of the His bundle potential, the energy per kg bodyweight delivered with the shock and the possibility to shock the potential with the greatest amplitude in case of instability. A discriminant linear analysis showed that 3 interrelated criteria could be used to classify 83% of the shocks into one or the other group. In order of importance these criteria were: (1) amplitude of the His bundle potential; (2)energy delivered per kg bodyweight, and (3) stability of the potential. The corresponding discriminant values for successful results were more than 300 mV for parameter 1, more than 3 J/kg bodyweight for parameter 2 and very good stability of His bundle potential.