[Accessory pathways of decremential conduction (Mahaim fibers). Treatment by endocavitary ablation; apropos of 8 cases].

Mahaim fibres are rare, right sided accessory pathways comparable with respect to certain properties (slow, decremential conduction) with "accessory atrioventricular node" located on the lateral tricuspid annulus at a distance from the Aschoff-Tawara node. Atriofascicular and atrioventricular fibres may be distinguished, both responsible for wide complex tachycardia (left bundle branch block pattern with left axis deviation). The authors report a series of 8 patients (6 women, 2 men: age: 27 +/- 11 years) without underlying cardiac disease, incapacitated by episodes of antidromic reciprocating tachycardia related to the atriofascicular fibres and justifying the indication of treatment by endocavitary ablation. In all cases, the authors tried to identify a specific potential of the Mahaim fibres on the lateral aspect of the tricuspid annulus. When the potential was recorded (7 out of the 8 cases) ablation was successful (procedure time 160 +/- 11 min; average number of applications: 9). It was not possible to identify a specific Mahaim potential in 1 case and so ablation was performed on the distal right ventricular site of insertion with no criterion of efficacy. In one woman, manipulation of the ablation catheter led to prolonged mechanical block in the Mahaim fibres, so suppressing the usual criteria of evaluation of the initial result of ablation: an early recurrence of tachycardia was observed in this case. No complications occurred during the 8 procedures. These results and those of other published cases, showed that radiofrequency ablation of Mahaim fibres is feasible with a high success rate without any immediate or long-term complications. This reliable and effective technique should form one of the therapeutic options for these invalidating junctional tachycardias.