Safety Margins for Sensing and Detection: Programming Tradeoffs

FOR DEFIBRILLATION energy, at least a 10 J safety margin between the estimate of the defibrillation threshold for a patient and the programmed shock energy is a widely accepted requirement for proper ICD function. Safety margins for sensing and for rate detection are also critical requirements but they are not as widely considered and evaluated during implant testing and followup. Sensing of an event occurs at the instant in time when the processed electrogram signal exceeds a reference threshold. Detection classifies each sensed event and analyzes the recent series of events with algorithms to initiate therapy. A sensing safety margin is needed to compensate for variability in electrogram amplitudes, whereas a detection safety margin is required to compensate for cycle length variability during an episode or between episodes. This chapter describes these sensing and detection safety margins; offers practical methods for their estimation; and discusses implications for programming ICD sensing and detection parameters.