Unusual atrial activation recorded near the His bundle during supraventricular tachycardia: What is the mechanism?

F IGURE 1 Intracardiac electrograms during SVT. A, Right ventricular entrainment pacing during the S/F AVNRT. The S/F AVNRTwas changed to the other SVT by entrainment pacing. B, Overdrive pacing from the HRA during S/S AVNRT. Red arrows indicate the unusual atrial activation. AVNRT= atrioventricular nodal reentrant tachycardia; CS= coronary sinus; HBE=His bundle; HRA= high right atrium; RV= right ventricle; S/F= slow-fast; S/S= slow-slow; SVT= supraventricular tachycardia [Color figure can be viewed at wileyonlinelibrary.com] tations. Twelve-leadelectrocardiographyduring sinus rhythmrevealed no significant abnormality. Quadripolar catheters were positioned in the high right atrium (HRA) and right ventricular (RV) apex, an octapolar catheter in the