Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients

Objective: Following out-of-hospital defibrillation attempts, electrocardio graphic instability challenges accurate assessment of defibrillation effica cy and post-shock rhythm. Presently, there is no precise definition of defi brillation efficacy in the out-of-hospital setting that is consistently use d. The objective of this study was to characterize out-of-hospital cardiac arrest rhythms following low-energy biphasic and high-energy monophasic sho cks in order to precisely define defibrillation efficacy and establish unif orm criteria for the evaluation of shock performance. Methods: Automatic ex ternal defibrillators (AEDs) delivering 150 J impedance-compensating biphas ic or 200-360 J monophasic damped sine waveform shocks were observed in a c ombined police and paramedic program. ECGs from 29 biphasic patients and 87 monophasic patients were classified as organized, asystole or VF at post-s hock times of 3, 5, 10, 20 and 60 s. Results: Post-shock time (P < 0.0001) and shock waveform type (P = 0.02) affected the classification of post-shoc k rhythm. At each analysis time, there were more patients in VF following h igh-energy monophasic shocks than following 150 J biphasic shocks (P < 0.00 01). The percentage of patients in VF increased with post-shock time. The r ate of VF recurrence was not a function of shock type, indicating that refi brillation is largely a function of the patient's underlying cardiac diseas e. Conclusion: Defibrillation should uniformly be defined as termination of VF for a minimum of 5-s after shock delivery. Rhythms should be reported a t 5-s after shock delivery to assess early effects of the defibrillation sh ock and at 60-s after shock delivery to assess the interaction of the defib rillation therapy and factors such as post-shock myocardial dysfunction and the patient's underlying cardiac disease. (C) 1999 Elsevier Science Irelan d Ltd. All rights reserved.