Is the activation potential of Mahaim pathway always a fast potential? Implication for radiofrequency catheter ablation.

INTRODUCTION

Accessory pathways (AP) exhibiting Mahaim physiology are amenable to radiofrequency (RF) catheter ablation. The recording of an AP potential is an excellent guide for selection of ablation site. The purpose of this study is to determine whether the pathway potential is always a fast potential.

METHODS

Ten patients (six females, mean age, 30 +/- 12 years) with preexcited tachycardias involving a Mahaim pathway underwent electrophysiological study and subsequent attempts at RF ablation. Mahaim potentials (M-potential) recorded at the site of successful ablation were reviewed and classified by at least two reviewers.

RESULTS

In all patients, Mahaim pathways were characterized as atriofascicular types. The M-potential was fast in seven patients (group one), and slow in the remaining patients (group two). All group two patients had a history of prior failed ablation. Atrial electrograms were recorded closer to the QRS onset in group one. Atrium to fast M-potential (42 +/- 15 ms) was shorter than atrium to slow M-potential (83 +/- 12 ms, P = 0.03) but M-potentials were recorded with similar distance before local ventricular electrogram (P = NS). Ablation was successful in all patients with mean of 2.9 +/- 1.4 RF applications per patient. Ablation data were similar between the two groups (P = NS). No complications occurred. During 12 months of follow-up, no recurrence was observed.

CONCLUSION

Our results illustrated that the activation potential of Mahaim pathways is not always a fast potential. One-third of Mahaim pathways can be mapped and ablated when the slow type of M-potential was used as a target for ablation. We also confirmed high efficacy of catheter ablation of Mahaim pathways guided by activation potentials.