The automaticity of Mahaim fibre and its response to effective ablation.

BACKGROUND: Typical accessory pathways (APs) of Wolf-Parkinson-White syndrome have been widely discussed in recent decades. However, the characteristics of the special AP, Mahaim fibre, are not so clear. It is known that these fibres have antegrade conduction only, long conduction time, decremental node-like conduction and automaticity properties. This study was to elucidate the automaticity of Mahaim fibre and its response to effective ablation. METHODS: Thirteen patients with Mahaim fibre (ten atrioventricular and three atriofascicular accessory pathways) were subjected to electrophysiological study and radiofrequency ablation via catheter. The incidence and characteristics of anautomatic rhythm originating from Mahaim fibre were observed during the whole procedure, especially during radiofrequency current delivery. RESULTS: Repetitive and short-run automatic rhythm (rate: 65-72 beats per minute), with a QRS morphology similar to that of clinical pre-excited atrioventricular re-entrant tachycardia (AVRT), occurred in two patients during sinus rhythm. Conduction via Mahaim fibre was successfully eliminated by radiofrequency current. Fourteen applications of RF were associated with irregularly accelerated automatic tachycardia of Mahaim fibre (with a sensitivity of 78%), lasting for 1.2-14 seconds. However, such automatic tachycardia of Mahaim fibre did not occur during 54 failed applications of radiofrequency current. CONCLUSIONS: Mahaim fibre has the function of automaticity. The accelerated automatic tachycardia of Mahaim fibre occur red during radiofrequency catheter ablation can be used as a predictor for successful procedure.