Reliability of ECG monitoring with a gel pad/paddle combination after defibrillation

Recent warnings have highlighted the possibility of unreliable monitoring through gel pads and paddles when using manual defibrillators. Occasionally, this causes an apparent asystole to be displayed when the true rhythm is ventricular fibrillation. We investigated this phenomenon in the laboratory using defibrillator-testing devices with two different impedances and with two defibrillators (Physio-Control LIFEPAK 9 and Hewlett Packard XL). After delivery of a 200 J shock, the time taken for the original ECG test signal to return to the defibrillator monitor was measured. Measurements were made after each of a series of ten shocks delivered with each defibrillator and gel pad/ testing device combination. Additional measurements were made using self-adhesive combination defibrillator electrodes. When using a low-impedance testing device with gel pads, on all occasions the initial rhythm reappeared immediately. When using the high-impedance testing device, the post shock rhythm was initially displayed as 'no signal' (Hewlett Packard XL) or 'asystole' (Physio-Control LIFEPAK 9). Over the series of ten shocks, the time to return of the original signal ranged between 24 and 154 s with the Hewlett Packard and 17-61 s with the Physio-Control LIFEPAK 9. The time for return of the signal increased with successive shocks. When using Fast-Patch electrodes, the original test signal always returned immediately. We conclude that after the delivery of a shock, monitoring through gel pads may result in the display of spurious asystole being displayed. This is more likely to occur in the presence of high chest impedance and with an increasing number of shocks delivered through the same gel pads. If defibrillator paddles and gel pads have been used for 'quick-look' monitoring, and 'asystole' is displayed after delivery of a shock, the rhythm should be confirmed immediately with monitoring leads.