title: Development of the probability of return of spontaneous circulation in intervals without chest compressions during out-of-hospital cardiac arrest: an observational study.
abstract: BACKGROUND
  One of the factors that limits survival from out-of-hospital cardiac arrest is the interruption of chest compressions. During ventricular fibrillation and tachycardia the electrocardiogram reflects the probability of return of spontaneous circulation associated with defibrillation. We have used this in the current study to quantify in detail the effects of interrupting chest compressions.
  
  
  METHODS
  From an electrocardiogram database we identified all intervals without chest compressions that followed an interval with compressions, and where the patients had ventricular fibrillation or tachycardia. By calculating the mean-slope (a predictor of the return of spontaneous circulation) of the electrocardiogram for each 2-second window, and using a linear mixed-effects statistical model, we quantified the decline of mean-slope with time. Further, a mapping from mean-slope to probability of return of spontaneous circulation was obtained from a second dataset and using this we were able to estimate the expected development of the probability of return of spontaneous circulation for cases at different levels.
  
  
  RESULTS
  From 911 intervals without chest compressions, 5138 analysis windows were identified. The results show that cases with the probability of return of spontaneous circulation values 0.35, 0.1 and 0.05, 3 seconds into an interval in the mean will have probability of return of spontaneous circulation values 0.26 (0.24-0.29), 0.077 (0.070-0.085) and 0.040(0.036-0.045), respectively, 27 seconds into the interval (95% confidence intervals in parenthesis).
  
  
  CONCLUSIONS
  During pre-shock pauses in chest compressions mean probability of return of spontaneous circulation decreases in a steady manner for cases at all initial levels. Regardless of initial level there is a relative decrease in the probability of return of spontaneous circulation of about 23% from 3 to 27 seconds into such a pause.
authors.affiliation: Department of Electrical and Computing Engineering, University of Stavanger, Stavanger, Norway. kenneth.gundersen@uis.no
authors.forename: Kenneth
authors.initials: K
authors.lastname: Gundersen
authors.forename: Jan Terje
authors.initials: JT
authors.lastname: Kvaløy
authors.forename: Jo
authors.initials: J
authors.lastname: Kramer-Johansen
authors.forename: Petter Andreas
authors.initials: PA
authors.lastname: Steen
authors.forename: Trygve
authors.initials: T
authors.lastname: Eftestøl
mesh_terms: D016887:Cardiopulmonary Resuscitation / Q000379:methods*; D004562:Electrocardiography / Q000706:statistics & numerical data; D006323:Heart Arrest / Q000473:pathology* / Q000628:therapy*; D006801:Humans; D016019:Survival Analysis; D013610:Tachycardia; D014693:Ventricular Fibrillation