Body surface potentials during discharge of the implantable cardioverter defibrillator

Little is known about the hazard for persons in contact with patients experiencing a high-voltage discharge of their implantable cardioverter defibrillator (ICD). Compared to epicardial systems, this risk may be increased with transvenous electrode systems and particularly in active can configurations.

In 23 patients with a transvenous active can ICD system, body surface potentials Vs and current through an external resistance were measured during 35 discharges. Vs was detected using skin electrodes positioned over the left subpectorally implanted pulse generator [C], apex of the heart [A], and the right pectoral region [RP]. Mean Vs during discharges without an external shunt resistance ranged between 13 and 63.8 V [C to A] and 12.5 to 47.3 V [C to RP] (ICD peak stored/output voltage Vcap = 183 to 606 V, n = 20). Mean current flow [C to A] was 8.2 to 46.8 mA (Vcap = 288 to 633 V, n = 10) and 42 to 120.7 mA (Vcap = 447 to 579 V, n = 5) across a resistance of 1,696 and 797 omega, respectively.

During high-output shocks, a considerable potential difference is present on the body surface of ICD patients that, according to the literature, may induce a single cardiac response in a bystander. Analogous to spontaneous extrasystoles, there is only a minimal chance of triggering a tachyarrhythmia by this stimulated extra beat. Direct induction of ventricular fibrillation is unlikely, since reported fibrillation threshold values are much higher than the observed magnitudes of current and voltage.