Abstract 301: Does Refibrillation Occur in High-Impedance Patients Who Have Received Shocks Using Biphasic Waveforms with Longer Pulse Durations?
The electrical impedance between defibrillator pads has a significant effect on the ability of defibrillators to deliver a therapeutic shock. A variety of technologies are used to deliver the chosen therapeutic shocks safely yet effectively across a wide range of patient impedances.
Defibrillators will not deliver a shock above pre-set impedance. We assessed the hypothesis that devices which have pulse durations over 20ms may predispose the patient to spontaneous re-fibrillation after a successful shock.
Two defibrillators were tested. Device A (A) limited the current delivered and in high impedance patients would extend the pulse duration as needed to deliver the selected energy while staying below the current limit. Device B (B) would truncate the shock to restrict the pulse duration but operated with higher currents. A high impedance porcine model of ventricular fibrillation (VF) was created. Following pilot work we were unable to demonstrate any relationship between pig mass and impedance. Therefore to create high impedance it was necessary to place resistors in series with the pig between the defibrillator under test and the pads.
From the pilot studies we determined that an impedance of approximately 95ohms resulted in a pulse duration of 20ms when device A delivered a 200J shock. A total of 5 anaesthetised pigs weighing 17-20kg (18.8kg) where used with 168 episodes of VF where impedance was greater than 100 ohms are included in the results. Two energies were tested for A (150 and 200J). B only delivers shocks at a single energy (150J). No re-fibrillation was observed in any patient after any shock.
This study failed to show any evidence of re-fibrillation even at pulse durations longer than 20ms with either device.
- Arrhythmias, treatment of
- Ventricular defibrillation
- Ventricular fibrillation
- Cardiac arrest
- Emergency care
- © 2012 by American Heart Association, Inc.