Automatic Impedance Monitoring and Patient Alert Feature in Implantable Cardioverter Defibrillators:

Abstract

Recent advances in implantable cardioverter defibrillator (ICD) technology have enabled implementation of an automatic monitoring feature in ICDs that provides daily measurements of several technical parameters such as battery status, pacing, and high-voltage impedance. The system alerts the patient with an audible alarm to contact the physician in case the measured parameters are not within normal limits. Early detection of intermittent and potentially serious complications justifies routine use of this feature. This report describes a patient with an ICD who died suddenly due to ventricular fibrillation, which was not appropriately treated by the device. The cause of device malfunction was most likely an intermittent lead fracture that was not detected by the automatic impedance monitoring and alert feature of this device. Based on these data, potential benefits and theoretical pitfalls of automatic impedance monitoring and alert features are discussed.

Implementation of Lead Safety Recommendations

“…Becker et al reported that standard impedance‐measurement‐based patient alerts in ICDs are useful additional tools for early detection of lead failure 12 . However, these impedance measurements alone seemed to be insufficient for inappropriate therapy prevention 13,14 . Accordingly, the research focus shifted to the combined use of impedance measurements with quantitative measures of oversensing resulting in a better and earlier lead failure detection 15,16 .…”

Failure of impedance monitoring to prevent adverse clinical events caused by fracture of a recalled high-voltage implantable cardioverter-defibrillator lead

“…One failure was signaled by an impedance change and the other by noise on the shocking coil in the presence of a normal shocking impedance. Although failure of high-voltage conductor impedance monitoring has been reported, 14 additional studies are needed to determine whether impedance monitoring or electrogram analysis can prevent adverse events caused by high-voltage conductor failure.…”

Fatal Inappropriate ICD Shock

“…No inappropriate therapy was delivered until the day of admission, although recurrent episodes of nonsustained ventricular fibrillation were detected a few days before the fatal event. Alarm systems in the defibrillators may help to detect lead malfunction early 13,14 . In the present case, the defibrillator implanted was equipped with a patient alert system, which alarms if the impedances of the pace/sense lead or the high‐voltage lead exceed predefined ranges.…”

“…Alarm systems in the defibrillators may help to detect lead malfunction early. 13,14 In the present case, the defibrillator implanted was equipped with a patient alert system, which alarms if the impedances of the pace/sense lead or the high-voltage lead exceed predefined ranges. The patient alert was activated, but did not alarm because values for impedances were within the normal range, although the lead was dislodged.…”