Adjustment of maximum automatic sensitivity (automatic gain control) reduces inappropriate therapies in patients with implantable cardioverter defibrillators.

Abstract

Patients with ICDs might experience oversensing associated with inappropriate shock therapy when paced at low bradycardia rates or if they have a low intrinsic rhythm. The amplifier gain of automatic gain control is maximal at long RR intervals and might lead to oversensing of myopotentials. The hypothesis was that an individual adjustment of the sensitivity floor could reduce inappropriate ICD therapies. Fourteen patients implanted with the VENTAK MINI I/II and III in whom oversensing and/or inappropriate shocks had been documented were included in this evaluation based on stored episodes. Sensitivity was modified in all ICDs by means of noninvasive software downloading that allowed reprogramming of the maximum sensitivity from 0.14 mV in two steps to 0.27 mV ("Normal," "Less," "Least"). Provocation testing (deep inspiration, sit-ups, and abdominal pressing) was conducted at "Nominal" settings (0.14 mV) while the intracardiac electrogram with annotated event marker was running continuously and was repeated at 0.22 mV (Less) and 0.27 mV (Least). All patients evaluated had documented spontaneous episodes due to oversensing before the sensitivity floor was reprogrammed. During provocation testing at Nominal settings, oversensing could be documented in 9 of (64.3%) 14 patients. Provocation testing was repeated after the sensitivity selection was reprogrammed and oversensing could not be provoked in any of the 14 implanted devices. Sensitivity was reprogrammed in all 14 patients to a higher value (5 patients Less, 9 patients Least). After sensitivity adjustment, VF was induced in all patients to verify appropriate arrhythmia detection and termination. Sensitivity reprogramming in patients with documented oversensing eliminates the incidence of inappropriate shock therapy without compromising the ability to detect VF appropriately.