ACCESSORY PATHWAYS OF DECREMENTIAL CONDUC TION (MAHAIM FIBERS) - TREATMENT BY ENDOCAVITARY ABLATION - RESULTS IN 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 a nnulus at a distance from the Aschoff-Tawara node. Atriofascicular and atrioventricular fibres may be distinguished, both responsible fcr wi de complex tachycardia (left bundle branch block pattern with left axi s deviation). The authors report a series of 8 patients (6 women, 2 me n; age: 27 +/- 11 years) without underlying cardiac disease, incapacit ated by episodes of antidromic reciprocating tachycardia related to th e 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 t ricuspid annulus. When the potential was recorded (7 out of the 8 case s) ablation was successful (procedure time 160 +/- 11 min; average num ber of applications : 9). It was not possible to identify a specific M ahaim 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 mech anical block in the Mahaim fibres, so suppressing the usual criteria o f evaluation of the initial result of ablation : an early recurrence o f tachycardia was observed in this case. No complications occurred dur ing the 8 procedures. These results and those of other published cases , showed that radiofrequency ablation of Mahaim fibres is feasible wit h a high success rate without any immediate or long-term complications . This reliable and effective technique should form one of the therape utic options for these invalidating junctional tachycardias.