Slow potentials and catheter ablation for AVNRT.

A functional discordance of conductive and refractile properties within atrionodal and AV nodal tissues is thought to be the basis for AV nodal reentrant tachycardia (AVNRT). Contemporary therapy aimed at curing AVNRT without materially damaging normal AV conduction began with surgical AV node modification.' Catheter based techniques with DC shocks and later with radiofrequency energy have been shown to be equally effective. The recognition of the posteriorly placed usual exit site of the slow pathway then led to the evolution of techniques of selective slow pathway ablation aimed at reducing the risk of complete AV block.2-5 One approach to slow pathway ablation has therefore been anatomical, with radiofrequency energy sequentially applied to the posteroinferior interatrial septum and, later, if required, to the mid-septum. Published data show that the success rates usually achieved (> 90%) require a high number of radiofrequency energy applications (range of medians 4-14).34 The electrophysiological approach on the other hand uses either retrograde slow pathway mapping or recognition of pathway potentials to guide ablation.5-'7 As retrograde slow pathway conduction is elicitable only in a minority of patients such mapping is not commonly used in spite of its reported specificity.4