title: Post-shock myocardial stunning: a prospective randomised double-blind comparison of monophasic and biphasic waveforms.
abstract: BACKGROUND
  Compared with monophasic defibrillation, biphasic defibrillation is associated with less myocardial stunning and earlier activation of sodium channels. We therefore hypothesised that earlier sodium channel activation would result in earlier restoration of the first sinus beat following elective DC cardioversion.
  
  
  METHODS
  Adults undergoing elective DC cardioversion were randomised to receive either monophasic or biphasic escalating transthoracic shocks. The ECG was recorded electronically during defibrillation and the time from delivery of the shock to restoration of the first sinus beat, measured from the beginning of the 'P' wave, was calculated.
  
  
  RESULTS
  Seventy four patients were studied. Data were unavailable from 18 patients. There was no demographic difference between groups. Median time to the first sinus beat following monophasic defibrillation (n=25) was 3.66 s (95% CI 2.55-4.61 s) and following biphasic defibrillation (n=33) was 2.21s (95% CI 1.76-2.56 s; P<or=0.0001). Linear regression confirmed that the waveform was an independent predictor of time to restoration of sinus rhythm; P<0.0001. The final defibrillation energy level used to achieve cardioversion was not an independent predictor of time to restoration of sinus rhythm; P=0.49.
  
  
  CONCLUSIONS
  Biphasic defibrillation for elective DC cardioversion achieved more rapid restoration of the first sinus beat compared with a monophasic waveform. Waveform, but not energy level that achieved defibrillation, was an independent predictor of time to restoration of the first sinus beat. The mechanism for this may be related to the earlier reactivation of sodium channels associated with the biphasic waveform.
authors.affiliation: Shackleton Department of Anaesthetics, Southampton University Hospital NHS Trust, Tremona Road, Southampton SO16 6YD, UK. charlesdeakin@doctors.org.uk
authors.forename: Charles D
authors.initials: CD
authors.lastname: Deakin
authors.forename: Jonathan J S
authors.initials: JJ
authors.lastname: Ambler
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000503:physiopathology / Q000628:therapy*; D047548:Defibrillators; D004311:Double-Blind Method; D004554:Electric Countershock / Q000379:methods*; D004562:Electrocardiography; D006801:Humans; D008875:Middle Aged; D017682:Myocardial Stunning / Q000503:physiopathology*; D011446:Prospective Studies; D013997:Time Factors