title: Quadriphasic waveforms are superior to triphasic waveforms for transthoracic defibrillation in a cardiac arrest swine model with high impedance.
abstract: BACKGROUND
  We have demonstrated previously that triphasic waveform shocks were superior to biphasic waveform shocks for transthoracic defibrillation. Our purpose was to compare the efficacy and safety of quadriphasic versus triphasic shocks for transthoracic defibrillation in a porcine model.
  
  
  METHODS
  Sixteen adult swine (19-25 kg, mean: 21.5 kg) were deeply anesthetized and intubated. To simulate impedance of the human chest, fixed electrical resistors (25 or 50 ohms) was placed in series with the defibrillator and the chest of each pig. After 30 s of electrically induced VF, each pig received transthoracic shocks, using either a truncated exponential triphasic waveform (5 ms positive pulse duration, 5 ms negative pulse duration and 5 ms positive pulse duration, total waveform duration 15 ms) or a quadriphasic waveform (5/5/5/5 ms, total waveform duration 20 ms). Each pig received transthoracic triphasic and quadriphasic shocks at three selected energy levels (50, 100 and 150 J) in random sequence. Four shocks were delivered at each energy level to construct an energy versus % success curve. Success was defined as VF termination at 5 s after shock. The total shocks were divided into three groups based on the delivered energy actually delivered to the animal: <40, 40-65 and >65 J. Delivered energy = (animal impedance/total impedance) times selected energy of the shock.
  
  
  RESULTS
  For high-impedance animals (86-102 ohms), quadriphasic waveform shocks achieved significantly higher percent shock success than triphasic shocks for the termination of VF at the energy levels of >65 J actually delivered (quadriphasic 72.7+/-12.2%, triphasic 38.9+/-7.7%, p<0.02). No differences in the shock success between quadriphasic and triphasic waveforms were found for other two energy levels. There were no differences in ventricular tachycardia or asystole after shocks between quadriphasic and triphasic waveforms.
  
  
  CONCLUSIONS
  In this porcine model, 20 ms (5/5/5/5) quadriphasic shocks were superior to 15 ms (5/5/5) triphasic shocks for transthoracic defibrillation in animals with impedances that simulated high impedance in humans.
authors.affiliation: The Cardiovascular Center, College of Medicine, University of Iowa Hospital, Department of Internal Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Benjamin
authors.initials: B
authors.lastname: Rhee
authors.forename: Loyd R
authors.initials: LR
authors.lastname: Davies
authors.forename: M Bridget
authors.initials: MB
authors.lastname: Zimmerman
authors.forename: David
authors.initials: D
authors.lastname: Snyder
authors.forename: Janice L
authors.initials: JL
authors.lastname: Jones
authors.forename: Richard E
authors.initials: RE
authors.lastname: Kerber
mesh_terms: D000818:Animals; D002307:Cardiography, Impedance; D004195:Disease Models, Animal; D004554:Electric Countershock / Q000379:methods*; D017097:Electric Impedance; D006323:Heart Arrest / Q000628:therapy*; D013552:Swine; D016896:Treatment Outcome