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Figure 1 Real-time telemetered data from implanted device. An atrial cardioversion shock (arrow) is delivered, resulting in termination of atrial fibrillation (AF). However, AF recurrence is swift, occurring well within the five consecutive ventricular beats required for device determination of success. Had this been an ambulatory event, the device would have characterized it as a failed shock. As such events were not stored by the device, the incidence of this phenomenon is unknown. Aegm = atrial electrogram; EKG = surface electrocardiogram; MC = marker channel.