Electrophysiologic Study
After giving informed written consent, patients underwent electrophysiologic studies (EPS). Atrial overdrive and extrastimulus were delivered to induce supraventricular tachycardia. Isoproterenol infusion was used to facilitate sustained tachycardia if needed. In order to demonstrate that the mechanism of this tachycardia is the typical slow-fast AVNRT, not automaticity (i.e., JT) or ventricular dependent reentry, AOD, AES, or ventricular overdrive (VOD) pacing were delivered during tachycardia. AVNRT was diagnosed using criteria as follows; 1) evidence of dual AV nodal physiology at the initiation of tachycardia, 2) tachycardia initiation by atrial drive train with A-H-A response, 3) septal ventriculoatrial (VA) time < 70 ms, and 4) ventricular-atrial-ventricular (V-A-V) response to ventricular overdrive (VOD) pacing with post pacing interval minus tachycardia cycle length (PPI-TCL) > 115ms. 5) Demonstration that both the slow pathway (SP) and fast pathway (FP) are capable of conducting faster than the TCL during entrainment. 6) During atrial entrainment via the SP, atrial septal PPI-TCL is less than 50 ms. 7) Advancement or termination of the tachycardia was demonstrated by AOD or AES3,4. These maneuvers also serve to exclude concealed nodoventricular or nodofascivular pathways.
From the EPS, the following data were also investigated; tachycardia cycle length (TCL), atrial-His (AH) interval during tachycardia, His-ventricular (HV) interval during tachycardia, AH interval during sinus.