title: Resuscitation after prolonged ventricular fibrillation with use of monophasic and biphasic waveform pulses for external defibrillation.
abstract: BACKGROUND
  Survival after prolonged ventricular fibrillation (VF) appears severely limited by 2 major factors: (1) low defibrillation success rates and (2) persistent post-countershock myocardial dysfunction. Biphasic (BP) waveforms may prove capable of favorably modifying these limitations. However, they have not been rigorously tested against monophasic (MP) waveforms in clinical models of external defibrillation, particularly where rescue from prolonged VF is the general rule.
  
  
  RESULTS
  We randomized 26 dogs to external countershocks with either MP or BP waveforms. Hemodynamics were assessed after shocks applied during sinus rhythm, after brief VF (>10 seconds), and after resuscitation from prolonged VF (>10 minutes). Short-term differences in percent change in left ventricular +dP/dt(max) (MP -16+/-28%, BP +9.1+/-24%; P=0.03) and left ventricular -dP/dt(max) (MP -37+/-26%, BP -18+/-20%; P=0.05) were present after rescue from brief VF, with BP animals exhibiting less countershock-induced dysfunction. After prolonged VF, the BP group had lower mean defibrillation thresholds (107+/-57 versus 172+/-88 J for MP, P=0.04) and significantly shorter resuscitation times (397+/-73.7 versus 488+/-74.3 seconds for MP, P=0.03).
  
  
  CONCLUSIONS
  External defibrillation is more efficacious with BP countershocks than with MP countershocks. The lower defibrillation thresholds and shorter resuscitation times associated with BP waveform defibrillation may improve survival after prolonged VF arrest.
authors.affiliation: Division of Cardiology, Department of Medicine, The Johns Hopkins Medical Institutions, Baltimore, MD, USA. cleng@mail.jhmi.edu
authors.forename: C T
authors.initials: CT
authors.lastname: Leng
authors.forename: N A
authors.initials: NA
authors.lastname: Paradis
authors.forename: H
authors.initials: H
authors.lastname: Calkins
authors.forename: R D
authors.initials: RD
authors.lastname: Berger
authors.forename: A C
authors.initials: AC
authors.lastname: Lardo
authors.forename: K C
authors.initials: KC
authors.lastname: Rent
authors.forename: H R
authors.initials: HR
authors.lastname: Halperin
mesh_terms: D000818:Animals; D001794:Blood Pressure; D009202:Cardiomyopathies / Q000209:etiology / Q000503:physiopathology; D003326:Coronary Circulation; D004285:Dogs; D004554:Electric Countershock / Q000009:adverse effects / Q000379:methods* / Q000592:standards; D006321:Heart / Q000503:physiopathology; D006323:Heart Arrest / Q000628:therapy; D012151:Resuscitation; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000628:therapy*