[Unidirectional block and longitudinal dissociation in an accessory pathway induced by radiofrequency]

This report describes an unusual arrhythmia due to partial damage of an accessory pathway by radiofrequency energy delivered during a catheter ablation procedure. The following phenomena were observed after the first radiofrequency current application: a) manifest anterograde conduction over the Kent bundle was abolished, so that preexcitation disappeared; b) concealed anterograde conduction over the accessory pathway was interrupted, resulting in initiation of orthodromic re-entrant tachycardia by any sinus impulse; c) retrograde conduction through the accessory pathway was impaired, but still present, and a pattern of longitudinal dissociation manifested; this was suggested by alternation of the R-P intervals, that during orthodromic tachycardia were alternatively long and short. Following a second radiofrequency application, the R-P interval during orthodromic tachycardia became markedly prolonged (0.36 sec), to the extent that the pattern mimicked a form of atrial or sinus tachycardia. Retrograde accessory pathway conduction was totally interrupted following a third radiofrequency energy application.