Electrophysiology study and radiofrequency catheter ablation of atriofascicular tracts with decremental properties (Mahaim fibre) at the tricuspid annulus

AIMS: The aim was to study the common mapping methods for Mahaim fibre and their role in radiofrequency (RF) ablation. METHODS AND RESULTS: Fifteen patients having Mahaim fibre tachycardia underwent electrophysiological study. Mahaim fibre mapping methods like (i) Mahaim potential (M), (ii) shortest atrial stimulus-to-pre-excitation (STP), and (iii) mechanical trauma induced loss of conduction were studied. Accessory pathway mapping was performed by M potential in 10 patients (67%), shortest atrial STP in 3 patients (20%), and mechanical trauma in 2 patients (13%). Mahaim fibre was localized at right atrial freewall of tricuspid annulus (8-10 o'clock) in 13 patients (87%), at 6.30 o'clock in one patient, and at 5 o'clock in 1 patient. Fourteen patients underwent RF ablation. Thirteen patients had complete loss of conduction over accessory pathway and one had partial modification with a conduction delay. Radiofrequency ablation was not performed in one patient (shortest STP group) due to its closeness to the compact atrioventricular node. Mahaim junctional acceleration during RF ablation was observed in all patients of M potential, 1 patient of mechanical trauma, and none of the atrial STP group. One patient (M potential group) had tachycardia recurrence during follow-up. CONCLUSION: Mahaim fibre is commonly located between 8 and 10 o'clock at tricuspid annulus. M potential guides to successful RF ablation in most patients. Mahaim junctional acceleration is commonly seen during RF ablation guided by M potential map.