Implantable Defibrillator Timing Windows

We present the case of a 68-year-old man with dilated cardiomyopathy who had an implantable cardioverter defibrillator implanted for primary prevention (Unify Assura with a Durata 7122Q ventricular lead, St. Jude Medical). The device was programmed DDDR 60–110 beats per minute and Table shows more specific programming parameters.View this table:Table. Programming Parameters for Bradycardia and Tachycardia Therapies From the Patient’s DefibrillatorSee Editor’s Perspective by Asirvatham and Stevenson Six months after implantation, routine device interrogation revealed many asymptomatic episodes logged as nonsustained lead noise (NSLN). The electrograms from one of these episodes are shown in Figure 1A. What is the differential diagnosis?Figure 1. , A stored electrogram from the patients implantable cardioverter defibrillator that was classified as nonsustained right ventricular lead noise. Respective electrograms and marker channels are labeled and are consistent for each panel. Numbered arrows indicate key points in the tracing for discussion. Intervals annotated with a (−) on the ventricular marker channel indicate that the current interval is within the tachycardia zone, however, the interval average (average of the current interval and the previous 3 intervals) is not. These beats do not count toward tachycardia detection. B , Electrograms in sinus rhythm for comparison. C and D , Tachycardias recorded on different occasions. AP indicates atrial pace; F, beat in the ventricular fibrillation zone; NSLN, nonsustained lead noise; SIR, sensor-indicated rate; VP, ventricular pace; VS, ventricular sense; and VSP, ventricular safety pace.A rhythm strip showing sinus rhythm is shown for comparison in Figure 1B and similar episodes of tachycardia are shown in Figure 1C and 1D from subsequent interrogation. These subsequent figures assist in clarifying the rhythm diagnosis; however, further questions arise as to the behavior of …