Fast-slow atrioventricular nodal reentrant tachycardia phenotype mimicking the slow-slow type

Abstract Background Fast-slow (F/S-) atrioventricular (AV) nodal reentrant tachycardia (AVNRT) is characterized by a short atrio-His (AH) interval and the earliest site of atrial activation (EAA) in proximal coronary sinus (EAA-CS), while slow-slow (S/S-) AVNRT presents long AH EAA-CS. Those intracardiac appearances are initial indicators for making diagnosis. Purpose To identify an unknown phenotype F/S-AVNRT. Methods Among 46 consecutive patients with F/S-AVNRT, 6 (1 man, age 59±9) had apparent but not typical (pseudo-) S/S-AVNRT during electrophysiologic study. In 2 patients, pseudo-S/S-AVNRT was clinically documented. Results all diagnosis F/S-AVNRT made exclusion findings 1) V-A-V response following ventricular entrainment or 2) termination without capture pacing, AV ventriculoatrial dissociation (so-called QRS transition) zone entrainment. An A-A-V sequence on induction observed 1 patient Wenckebach-type block ongoing developing 3 suggested presence lower common pathway (LCP). Like S/S-AVNRT, induced stimulation after jump double response. However, transited to single cycle and/or from spontaneously triggered contractions. Importantly, these transitions, length (CL) EAA-CS remained unchanged, that is, CL almost identical suggesting essential circuit both tachycardias identical. Actually, were cured ablation at traditional slow (SP). Collectively, diagnosed as another accompanied sustained antegrade conduction via bystander (likely left-sided superior) SP breaking through His bundle owing repetitive LCP occurring linking phenomenon, thus representing When blocked pseudo-S/S-AVNRT, releasing subsequent reach His-bundle fast pathway, returning Conclusions unknown, rare exists apparently mimics also subtype S/S-AVNRT. The this suggests limitation classifying types based HA intervals tachycardia. Understandings can advance atypical multiple phenotypes. Funding Acknowledgement Type funding sources: None.