Rise in ICD shock impedance: lead fracture or death?

Background: Remote monitoring allows for interrogation and extensive data retrieval of implantable cardioverter-defibrillators (ICDs). Data on ICD parameters at the time of death and afterwards are limited. The purpose of this retrospective study was to examine the changes in lead impedances of ICDs at the time of death and afterwards.

Methods: A total of 37 Biotronik (SE & CO. KG, Berlin, Germany) ICDs (20 ICD-cardiac resynchronization therapy, 16 dual-chamber ICDs, and one single-chamber ICD), retrieved after death, were interrogated. Stored intracardiac electrograms were analyzed to determine the cause of death. Impedance trend curves of shock and pacing lead impedances were analyzed and correlated retrospectively with the reported time of death. The influence of cold exposure on lead impedances was tested in three other single-chamber Biotronik ICDs.

Results: Of 37 patients, the cause of death was due to ventricular tachyarrhythmias in 21 patients. In 12 patients, death was not arrhythmia-related. In four patients, the cause of death could not be determined due to overwriting of the episodes at the time of death. A significant increase of shock and pacing lead impedances was observed in the postmortem days (P < 0.001 for all lead impedances). All lead impedance values increased significantly within the first postmortem day (P < 0.001 for all lead impedances). Cold exposure decreased shock lead impedance but did not affect pacing lead impedance.

Conclusion: Postmortem analysis of ICDs allows tracking of lead impedance changes, which correlate with the day of death. The rise in postmortem impedances should not be interpreted as contributing to the mode of death.