title: Left ventricular function after monophasic and biphasic waveform defibrillation: the impact of cardiopulmonary resuscitation time on contractile indices.
abstract: Previous work has suggested that low-energy biphasic waveform defibrillation (BWD) is followed by less post-resuscitation left ventricular (LV) dysfunction when compared with higher-energy monophasic waveform defibrillation (MWD). To the best of the authors' knowledge, the effect of cardiopulmonary resuscitation (CPR) duration and total ischemia time on LV function after countershock, controlling for waveform type, has not been evaluated.
  
  
  OBJECTIVE
  To determine the effect of CPR duration on LV function after MWD and BWD.
  
  
  METHODS
  VF was electrically induced in anesthetized and instrumented swine. After 5 minutes of VF, the animals were randomized to MWD (n = 22) or one of two BWDs (n = 46). If countershock terminated VF but was followed by a nonperfusing rhythm, conventional manual CPR without drug therapy was performed until restoration of spontaneous circulation (ROSC), defined as a systolic arterial pressure >60 mm Hg for 10 minutes without vasopressor support. Systolic LV pressure (LVP), LV dP/dt (first derivative of pressure measured over time), and cardiac output (CO) were measured at intervals for 60 minutes postresuscitation. CPR times (times to ROSC) and hemodynamic variables for the three groups were compared. Multivariable linear regression was performed to assess the contribution of defibrillation waveform, total joules, and CPR time on LVP, LV dP/dt, and CO at 15, 30, and 60 minutes postresuscitation.
  
  
  RESULTS
  When analyzed as groups, significant differences in median number of shocks to terminate VF, total joules, or CPR time were not observed between waveform groups. Regression analysis demonstrated that increasing CPR time was associated with a significant effect on indices of LV function at 15 and 30 minutes postresuscitation. Global LV function was not influenced by waveform type or total joules.
  
  
  CONCLUSIONS
  Adjustment for CPR time, a determinant of total myocardial ischemia time, is necessary when defibrillation waveforms are compared for their effect on postresuscitation cardiac function and short-term outcome.
authors.affiliation: Department of Emergency Medicine, Harbor-UCLA Medical Center, UCLA School of Medicine, Torrance, CA 90509, USA. jniemann@emedharbor.edu
authors.forename: James T
authors.initials: JT
authors.lastname: Niemann
authors.forename: Daniel
authors.initials: D
authors.lastname: Garner
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Lewis
mesh_terms: D000818:Animals; D016887:Cardiopulmonary Resuscitation; D004554:Electric Countershock / Q000379:methods*; D005260:Female; D006439:Hemodynamics; D016014:Linear Models; D008297:Male; D013552:Swine; D014693:Ventricular Fibrillation / Q000628:therapy*; D016277:Ventricular Function, Left / Q000502:physiology*