Abstract 174: Current-Based Defibrillation: The Relationship Between Peak Current and Defibrillation Shock Success in Out-of-Hospital Cardiac Arrest
Background: Success of a shock depends on the transcardiac current; all the myocardium must get a pulse of current of sufficient magnitude for the chosen pulse duration and waveform. This transcardiac current is a small, unknown fraction of the transthoracic current, determined by electrode location, patient anatomy and other factors. External defibrillators today adjust waveform characteristics for impedance while maintaining a similar delivered energy for all impedances. As a result, they deliver much less transthoracic current to high-impedance patients than low-impedance patients. As an alternative to today’s “energy-based” defibrillators, “current-based defibrillation” has been proposed, with the goal of delivering the same transthoracic current to every patient. If efficacy of energy-based shocks is low for high-impedance patients (who receive the least transthoracic current), current-based defibrillation might help. We tested the hypothesis that patients receiving less transthoracic current have lower defibrillation shock success.
Methods: We analyzed data from biphasic energy-based defibrillation of 681 patients with out-of-hospital cardiac arrest to determine transthoracic current and VF termination success of each shock. We sorted shocks by peak current, divided them into 10 bins, and compared shock success across these deciles.
Results: There was wide variation in first shock impedance (range 24 to 248 ohms, median 95) and peak current (figure). First shock VF termination success did not vary significantly across peak current deciles (Chi-square for linear trend, p=0.80).
Conclusion: First shock defibrillation success did not vary despite a wide range of delivered transthoracic current. This shows that, across out-of-hospital cardiac arrest patients, current-based defibrillation would not have helped, and suggests that transcardiac current from energy-based shocks is not primarily determined by transthoracic impedance.
- © 2013 by American Heart Association, Inc.