title: Dynamic nature of electrocardiographic waveform predicts rescue shock outcome in porcine ventricular fibrillation.
abstract: OBJECTIVE
  Survival decreases with duration of ventricular fibrillation, and it is possible that failed rescue shocks increase myocardial damage. Structure in the ECG signal during ventricular fibrillation can be quantified by using the scaling exponent, a dimensionless measure that correlates with ventricular fibrillation duration. This study examined whether the scaling exponent could predict rescue shock success and whether unsuccessful rescue shocks altered the structure of the ventricular fibrillation waveform and the responsiveness to subsequent rescue shocks.
  
  
  METHODS
  Ventricular fibrillation was electrically induced in 44 anesthetized swine, which were randomly assigned to receive 70-J biphasic rescue shocks at 2, 4, 6, 8, or 10 minutes. If rescue shocks failed, up to 2 subsequent rescue shocks were performed at 2-minute intervals. The scaling exponent was calculated at 1-second intervals from ECG to quantify the organization of the ventricular fibrillation waveform.
  
  
  RESULTS
  A total of 92 rescue shocks were delivered, of which 23 successfully converted ventricular fibrillation to an organized rhythm (immediate success). After these 23 rescue shocks, 14 swine sustained organized rhythms for more than 30 seconds (sustained success). Lower scaling exponent values were associated with increased probability of successful rescue shocks. Receiver operating characteristic curves had an area under the curve of 0.86 for immediate rescue shock success and 0.93 for sustained rescue shock success. Failed rescue shocks increased the rate of scaling exponent increase over time but did not appear to affect subsequent rescue shock success when the scaling exponent was taken into account.
  
  
  CONCLUSIONS
  Highly deterministic ventricular fibrillation, reflected by a low scaling exponent, predicted rescue shock success regardless of antecedent failed rescue shocks. In addition, unsuccessful rescue shocks might decrease post-rescue shock ventricular fibrillation waveform organization.
authors.affiliation: Department of Emergency Medicine, Center for Emergency Medicine of Western Pennsylvania, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Lightfoot
authors.lastname: Nremt-P
authors.forename: Clifton W
authors.initials: CW
authors.lastname: Callaway
authors.forename: Margaret
authors.initials: M
authors.lastname: Hsieh
authors.forename: Kristofer C
authors.initials: KC
authors.lastname: Fertig
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Sherman
authors.forename: James J
authors.initials: JJ
authors.lastname: Menegazzi
mesh_terms: D000818:Animals; D016887:Cardiopulmonary Resuscitation / Q000009:adverse effects / Q000379:methods; D002985:Clinical Protocols; D003627:Data Interpretation, Statistical; D016002:Discriminant Analysis; D004195:Disease Models, Animal; D004554:Electric Countershock / Q000009:adverse effects / Q000379:methods; D004562:Electrocardiography / Q000379:methods / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012372:ROC Curve; D011897:Random Allocation; D012044:Regression Analysis; D016019:Survival Analysis; D013552:Swine; D013997:Time Factors; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000175:diagnosis* / Q000401:mortality / Q000628:therapy*