title: Electrocardiographic evaluation of defibrillation shocks delivered to out-of-hospital sudden cardiac arrest patients.
abstract: OBJECTIVE
  Following out-of-hospital defibrillation attempts, electrocardiographic instability challenges accurate assessment of defibrillation efficacy and post-shock rhythm. Presently, there is no precise definition of defibrillation efficacy in the out-of-hospital setting that is consistently used. The objective of this study was to characterize out-of-hospital cardiac arrest rhythms following low-energy biphasic and high-energy monophasic shocks in order to precisely define defibrillation efficacy and establish uniform criteria for the evaluation of shock performance.
  
  
  METHODS
  Automatic external defibrillators (AEDs) delivering 150 J impedance-compensating biphasic or 200-360 J monophasic damped sine waveform shocks were observed in a combined police and paramedic program. ECGs from 29 biphasic patients and 87 monophasic patients were classified as organized, asystole or VF at post-shock 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-shock rhythm. At each analysis time, there were more patients in VF following high-energy monophasic shocks than following 150 J biphasic shocks (P<0.0001). The percentage of patients in VF increased with post-shock time. The rate of VF recurrence was not a function of shock type, indicating that refibrillation is largely a function of the patient's underlying cardiac disease.
  
  
  CONCLUSIONS
  Defibrillation should uniformly be defined as termination of VF for a minimum of 5-s after shock delivery. Rhythms should be reported at 5-s after shock delivery to assess early effects of the defibrillation shock and at 60-s after shock delivery to assess the interaction of the defibrillation therapy and factors such as post-shock myocardial dysfunction and the patient's underlying cardiac disease.
authors.affiliation: HP Heartstream, Seattle, WA 98121, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Gliner
authors.forename: R D
authors.initials: RD
authors.lastname: White
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D016009:Chi-Square Distribution; D002648:Child; D016001:Confidence Intervals; D004554:Electric Countershock / Q000379:methods*; D004562:Electrocardiography; D004632:Emergency Medical Services; D005069:Evaluation Studies as Topic; D005260:Female; D006323:Heart Arrest / Q000150:complications / Q000175:diagnosis / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000150:complications / Q000175:diagnosis*