title: Preshock cardiopulmonary resuscitation worsens outcome from circulatory phase ventricular fibrillation with acute coronary artery obstruction in swine.
abstract: BACKGROUND
  Some clinical studies have suggested that chest compressions before defibrillation improve survival in cardiac arrest because of prolonged ventricular fibrillation (VF; ie, within the circulatory phase). Animal data have also supported this conclusion, and we have previously demonstrated that preshock chest compressions increase the VF median frequency and improve the likelihood of a return of spontaneous circulation in normal swine. We hypothesized that chest compressions before defibrillation in a swine model of acute myocardial ischemia would also increase VF median frequency and improve resuscitation outcome.
  
  
  RESULTS
  Twenty-six swine were subjected to balloon occlusion of the left anterior descending coronary artery for 2 hours. The balloon was removed and VF was induced and untreated for 8 minutes. Swine were then treated with up to 3 stacked defibrillation shocks (n=13, shock-first group) or 3 minutes of chest compressions before shock (n=13, preshock cardiopulmonary resuscitation group). In the preshock cardiopulmonary resuscitation group, median frequency was increased from 7.0+/-0.8 to 13.9+/-1.6 Hz after chest compressions (P=0.002). Despite the improved median frequency in the preshock cardiopulmonary resuscitation group, 24-hour survival with favorable neurological status was significantly worse in the preshock cardiopulmonary resuscitation group (1/13) compared with the shock-first group (8/13, P=0.01).
  
  
  CONCLUSIONS
  In a swine model of prolonged VF in acute myocardial ischemia, 24-hour survival with favorable neurological status was more likely when defibrillation was performed first without preceding chest compressions. Myocardial substrate is an important factor in determining the optimal resuscitation strategy.
authors.affiliation: Sarver Heart Center, Department of Medicine, University of Arizona College of Medicine, Tucson, Arizona 85724-5037, USA. jindik@email.arizona.edu
authors.forename: Julia H
authors.initials: JH
authors.lastname: Indik
authors.forename: Ronald W
authors.initials: RW
authors.lastname: Hilwig
authors.forename: Mathias
authors.initials: M
authors.lastname: Zuercher
authors.forename: Karl B
authors.initials: KB
authors.lastname: Kern
authors.forename: Marc D
authors.initials: MD
authors.lastname: Berg
authors.forename: Robert A
authors.initials: RA
authors.lastname: Berg
mesh_terms: D000208:Acute Disease; D000818:Animals; D016887:Cardiopulmonary Resuscitation / Q000009:adverse effects* / Q000379:methods; D003326:Coronary Circulation; D023921:Coronary Stenosis / Q000628:therapy; D004195:Disease Models, Animal; D004554:Electric Countershock / Q000379:methods*; D005260:Female; D017202:Myocardial Ischemia / Q000628:therapy*; D034421:Sus scrofa; D014693:Ventricular Fibrillation / Q000628:therapy*