Atypical retrograde atrial activation in 'typical' atrioventricular nodal reentrant tachycardia.

Atrioventricular nodal reentrant tachycardia (AVNRT) can be cured by radiofrequency catheter ablation by selective ablation of the slow or the fast pathway. Retrograde fast pathway ablation is performed anterosuperiorly at the apex of Koch's triangle, whereas slow pathway ablation is performed at the base of Koch's triangle near the coronary sinus ostium. A patient with otherwise typical slow-fast AVNRT who demonstrated earliest retrograde atrial activation at the proximal coronary sinus rather than the usual His bundle recording position is described. Loss of retrograde fast pathway conduction occurred after radiofrequency ablation at the base of Koch's triangle, suggesting an atypical location of the fast pathway. This supports recent evidence that the retrograde fast pathway may be located near the coronary sinus ostium in some patients with otherwise typical AVNRT.