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Figure 1 Electrogram (Atip-Vring EGM) recording (0.5 mv/mm) at a chart speed 25 mm/s, showing a typical episode of dual tachycardia in one patient. Upward markers indicate atrial events; downward markers indicate ventricular events. The short triple atrial markers indicate ongoing atrial fibrillation (AF) detection (FD). Intermediate-height ventricular markers (VS) indicate sensed R-waves (VS); short double ventricular markers indicate ventricular fibrillation (VF) sense (FS); short triple markers indicates VF detection (FD). The vertical arrows show atrial activation complexes during device-defined AF. The short horizontal arrows show R-waves with intrinsic conduction. The ventricular rate accelerates abruptly; at the same time there is a change in the morphology of the ventricular electrogram (long horizontal arrow). The median RR interval of this device-defined VF episode was 260 ms.