Normalization of increasing shocking coil impedance with full output synchronized shock

Impedance is a crucial parameter in cardiovascular implantable electronic devices (CIEDs). Clinically, most CIEDs measure impedance using low voltage sub-threshold measurement (LVSM). Although the LVSM of shock impedance (LVSM-SI) is generally comparable with high voltage shock impedance (HVSI), LVSM-SI might be inaccurate if peri-lead tissue degeneration occurs.

We present a case of elevated LVSM-SI occurring 8 years post-lead implantation, possibly attributed to encapsulation of the right ventricular lead coil. After 0.1 J shock was delivered, a full output synchronized shock was administered to measure HVSI, revealing a normal value. Furthermore, LVSM-SI was normalized and maintained within the normal range during long-term follow-up.

Our findings suggest conducting a full-output synchronized shock test to assess HVSI when abnormal LVSM-SI is detected in the remote phase post-ICD implantation, which may be considered to help normalize LVSM shock impedance.