title: Analysis of amplitude spectral area and slope to predict defibrillation in out of hospital cardiac arrest due to ventricular fibrillation (VF) according to VF type: recurrent versus shock-resistant.
abstract: BACKGROUND
  In out-of-hospital cardiac arrest (OHCA) due to ventricular fibrillation (VF), VF may recur during resuscitation (recurrent VF) or fail to defibrillate (shock-resistant VF). While retrospective studies have suggested that amplitude spectral area (AMSA) and slope predict defibrillation, it is unknown whether the predictive power is influenced by VF type. We hypothesized that in witnessed OHCA with initial rhythm of VF that the utility for AMSA and slope to predict defibrillation would differ between shock-resistant and recurrent VF.
  
  
  METHODS
  AMSA and slope were measured immediately prior to each shock. For second or later shocks, VF was classified as recurrent or shock-resistant. Cardiac arrest was classified according to whether the majority of shocks were for recurrent VF or shock-resistant VF.
  
  
  RESULTS
  44 patients received 98 shocks for recurrent VF and 96 shocks for shock-resistant VF; 24 patients achieved ROSC in the field. AMSA and slope were higher in recurrent VF compared to shock-resistant VF (AMSA: 28.8±13.1 vs 15.2±8.6 mVHz, P<0.001, and slope: 2.9±1.4 vs 1.4±1.0 mVs(-1), P=0.001). Recurrent VF was more likely to defibrillate than shock-resistant VF (P<0.001). AMSA and slope predicted defibrillation in shock-resistant VF (P<0.001 for both AMSA and slope) but not in recurrent VF. Recurrent VF predominated in 79% of patients that achieved ROSC compared to 55% that did not (P=0.10).
  
  
  CONCLUSIONS
  In witnessed OHCA with VF as initial rhythm, recurrent VF is associated with higher values of AMSA and slope and is likely to re-defibrillate. However, when VF is shock-resistant, AMSA and slope are highly predictive of defibrillation.
authors.affiliation: The Sarver Heart Center at the University of Arizona College of Medicine, Tucson, AZ 85724-5037, United States. msundaram@shc.arizona.edu
authors.forename: Madhan
authors.initials: M
authors.lastname: Shanmugasundaram
authors.forename: Amanda
authors.initials: A
authors.lastname: Valles
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kellum
authors.forename: Gordon A
authors.initials: GA
authors.lastname: Ewy
authors.forename: Julia H
authors.initials: JH
authors.lastname: Indik
mesh_terms: D000368:Aged; D004554:Electric Countershock; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D058687:Out-of-Hospital Cardiac Arrest / Q000209:etiology*; D011237:Predictive Value of Tests; D012008:Recurrence; D012189:Retrospective Studies; D014693:Ventricular Fibrillation / Q000145:classification / Q000150:complications* / Q000628:therapy