Figure 35-8 Unexpected ventricular tachycardia with antitachycardia pacing (ATP) was found in this patient during her preoperative visit. A 65-year-old woman with a history of ventricular tachycardia (VT) had undergone implantation of a Medtronic single-chamber defibrillator about 8 months earlier. She had no dizziness or syncopal episodes since the implantable cardioverter-defibrillator (ICD) placement. Interrogation of her device in the preoperative center revealed VVE-VVI programming, along with an episode of tachycardia at 150 to 162 beats/min that was detected by the ICD as VT. The ICD delivered a 6-beat burst of antitachycardia pacing at 182 beats/min, which converted the tachycardia back to sinus rhythm. No backup antibradycardia pacing was needed after the VT was terminated. The upper tracing is a digitized ventricular electrogram that was stored in the ICD during the tachycardic event. The lower tracing is the marker channel that reports the interpretation of the ICD for each event. The numbers below the marker channel represent the interval (in milliseconds). The heart rate is calculated by dividing the interval into 60,000 msec/min. TS represents an interval in the VT zone, TD marks the final event that starts therapy, TP is an ATP event, and VS is an intrinsic ventricular depolarization with a rate that is neither too fast (short interval) nor too slow (long interval). This device was set to detect VT as 16 consecutive ventricular events with a rate between 146 and 200 beats/min and to deliver ATP at 84% of the last R-R interval. The last interval was 400 msec, so ATP was delivered at a rate of 182 beats/min (330-msec intervals).