title: Prehospital cardiac arrest treated by urban first-responders: profile of patient response and prediction of outcome by ventricular fibrillation waveform.
abstract: OBJECTIVE
  To determine the speed and characteristics of patient response to urban first-responder defibrillation and to determine whether amplitude of ventricular fibrillation (VF) can predict outcome in these patients.
  
  
  METHODS
  All adult patients in prehospital VF treated by fire department first-responders (265).
  
  
  METHODS
  A prospective observational study occurring between February 1, 1989, and January 1, 1991. Patients were defibrillated according to advanced cardiac life support and first-responder protocols. ECG and time data were recorded digitally.
  
  
  RESULTS
  Sixty-five percent of patients converted from VF to a more stable rhythm at least once during first-responder monitoring. Fifty-four percent of converted patients refibrillated at least once, and 42% of all stable conversions occurred after at least one episode of refibrillation. Seventy percent of all refibrillations occurred less than six minutes after the defibrillator was turned on, and 23% occurred after more than ten minutes. The proportion of stable conversions decreased from 30% on first conversion to 2% on fourth conversion. With each successive conversion the interval to refibrillation grew shorter, and development of a pulse or blood pressure became less likely. Presence of blood pressure or pulse after conversion had a sensitivity for hospital discharge of 54% and a specificity of 98%. Maximum VF amplitude before countershock was highly predictive of postshock rhythm, stable conversion in the field, time interval before refibrillation, inpatient admission, and hospital discharge. VF amplitude was unrelated to response interval or interval to defibrillation but was positively related to bystander CPR. Logistic regression identified VF amplitude as the most important predictor of hospital discharge; traditional variables such as response interval and bystander CPR were not predictive once amplitude had been accounted for. Changes in VF amplitude during the course of resuscitation efforts were frequent and also predictive of outcome.
  
  
  CONCLUSIONS
  Patients in VF who were treated by early countershock refibrillated much more frequently than previously reported. Refibrillations occur both early and late. Initial VF maximum amplitude is strongly predictive of outcome. Future reports of VF cardiac arrest should control for this previously neglected variable. Increased amplitude of VF during repeated refibrillation episodes is associated with increased hospital discharge, so future studies of advanced cardiac life support interventions should explore changes in VF amplitude as an outcome variable.
authors.affiliation: Division of Emergency Medicine, University of California, San Francisco.
authors.forename: M
authors.initials: M
authors.lastname: Callaham
authors.forename: O
authors.initials: O
authors.lastname: Braun
authors.forename: W
authors.initials: W
authors.lastname: Valentine
authors.forename: D M
authors.initials: DM
authors.lastname: Clark
authors.forename: C
authors.initials: C
authors.lastname: Zegans
mesh_terms: D000368:Aged; D001794:Blood Pressure; D004554:Electric Countershock; D004632:Emergency Medical Services; D005260:Female; D006339:Heart Rate; D006801:Humans; D007902:Length of Stay; D008020:Life Support Care; D008297:Male; D011379:Prognosis; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000503:physiopathology*