Radiofrequency transcatheter ablation of a bidirectional decremental accessory atrioventricular pathway in the coronary sinus

We report the case of a 63-year-old patient who underwent radiofrequency catheter ablation of an atrioventricular accessory pathway with bidirectional decremental conduction properties. The successful ablation site was the distal end of a wedge-shaped dilation of the first tract of the coronary sinus. Atrioventricular accessory pathways with anterograde decremental conduction properties was thought to belong to fibers with Mahaim type electrophysiological properties. They rarely show decremental retrograde conduction properties. Most Mahaim type atrioventricular pathways are right-sided with atrial insertion points at various sites along the tricuspid ring. On the other hand, left-sided decrementally conducting accessory pathways are very rare. Mahaim type atrioventricular pathways were never found in the coronary sinus. The bidirectional decremental conduction properties and in particular the anatomic site of the atrioventricular accessory pathway we describe in the present report are both very interesting findings.