title: Biphasic shocks compared with monophasic damped sine wave shocks for direct ventricular defibrillation during open heart surgery.
abstract: BACKGROUND
  Biphasic waveform shocks are more effective than monophasic shocks for transchest ventricular defibrillation, atrial cardioversion, and defibrillation with implantable defibrillators but have not been studied for open chest, intraoperative defibrillation. This prospective, blinded, randomized clinical study compares biphasic and monophasic shock effectiveness and establishes intraoperative energy dose-response curves.
  
  
  METHODS
  Patients undergoing cardiothoracic surgery with bypass cardioplegia were randomly assigned to the monophasic or biphasic shock group. Ventricular fibrillation occurring after aortic clamp removal was treated with escalating energies of 2, 5, 7, 10, and 20 J until defibrillation occurred. If ventricular fibrillation persisted, a 20-J crossover shock of the other waveform was used.
  
  
  RESULTS
  Cumulative defibrillation success at 5 J, the primary end point of the study, was higher in the biphasic group than in the monophasic group (25 of 50 vs. 9 of 41 defibrillated; P = 0.011). In addition, the biphasic group required lower threshold energy (6.8 vs. 11.0 J; P = 0.003), less cumulative energy (12.6 vs. 23.4 J; P = 0.002), and fewer shocks (2.5 vs. 3.5; P = 0.002). Crossover-shock effectiveness did not differ between groups. Dose-response curves show biphasic shocks to have higher cumulative success rates at all energies tested.
  
  
  CONCLUSIONS
  Biphasic shocks are substantially more effective than monophasic shocks for direct defibrillation. The dose-response curve guides selection of first-shock energy for traditional step-up protocols. Starting at 5 J optimizes for lowest threshold and cumulative energy, whereas 10 or 20 J optimizes for more rapid defibrillation and fewer shocks.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, University of Innsbruck, Austria. birgit.schwarz@uibk.ac.uk
authors.forename: Birgit
authors.initials: B
authors.lastname: Schwarz
authors.forename: T Andrew
authors.initials: TA
authors.lastname: Bowdle
authors.forename: G Kimble
authors.initials: GK
authors.lastname: Jett
authors.forename: Peter
authors.initials: P
authors.lastname: Mair
authors.forename: Karl H
authors.initials: KH
authors.lastname: Lindner
authors.forename: Gabriel S
authors.initials: GS
authors.lastname: Aldea
authors.forename: Robert G
authors.initials: RG
authors.lastname: Lazzara
authors.forename: Sharon G
authors.initials: SG
authors.lastname: O'Grady
authors.forename: Paul W
authors.initials: PW
authors.lastname: Schmitt
authors.forename: Robert G
authors.initials: RG
authors.lastname: Walker
authors.forename: Fred W
authors.initials: FW
authors.lastname: Chapman
authors.forename: Willis A
authors.initials: WA
authors.lastname: Tacker
mesh_terms: D000328:Adult; D000368:Aged; D006348:Cardiac Surgical Procedures; D001026:Coronary Artery Bypass / Q000379:methods*; D017548:Echocardiography, Transesophageal; D004554:Electric Countershock / Q000379:methods; D004573:Electrolytes / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011446:Prospective Studies; D014693:Ventricular Fibrillation / Q000601:surgery*
chemical_list: D004573:Electrolytes; D010100:Oxygen