Slow-fast Form of Atrioventricular Nodal Reentrant Tachycardia with Unusual Retrograde Activation in the Right Atrium —Possible Conduction Disturbance across the Tendon of Todaro Related to the Genesis of Positive Component of Biphasic Retrograde P Wave—

We report a rare case of slow-fast form of atrioventricular nodal reentrant tachycardia with delayed activation in the low septal right atrium (His bundle area). During supraventricular tachycardia (SVT), electrocardiogram showed “pseudo-positive P waves” in II, III, and aVF leads. SVT was induced by atrial extrastimulus with marked AH prolongation (i.e., jump phenomenon). Ventricular pacing showed a decremental retrograde conduction without jump phenomenon. Double atrial potentials were observed in the His bundle area during SVT and during ventricular pacing. The first electrogram of these split potentials, which was the earliest activation during SVT and during ventricular pacing, showed a dull and small deflection, whereas the second electrogram was sharp and clear. The interval of these discrete potentials was 70 msec during SVT. After a standard slow pathway ablation, SVT could never be induced by any programmed stimuli. It was concluded that in this case, the conduction disturbance across the tendon of Todaro was likely to cause the delayed atrial activation in the His bundle area, which created the pseudo-positive (biphasic. retrograde P wave.