title: Comparison of biphasic and monophasic waveforms in epicardial atrial defibrillation.
abstract: OBJECTIVE
  Because biphasic waveforms have previously been shown to be more efficient than monophasic waveforms in defibrillation of the ventricle, we compared the efficiency of the two waveforms in defibrillation of the atria.
  
  
  BACKGROUND
  The development of an implantable atrial defibrillator would offer significant advantages over current approaches to the management of atrial fibrillation. Patient tolerance of atrial shocks from such a device, however, would depend critically on the deployment of an efficient waveform.
  
  
  METHODS
  Both the monophasic and biphasic shocks were of 8-ms duration, and the biphasic was a dual-capacitor waveform with equal first- and second-phase duration and leading-edge voltage. One hundred randomized atrial shocks were evaluated in 21 patients during cardiopulmonary bypass. Atrial fibrillation was induced by the application of alternating current. Atrial shocks were delivered through customized, contoured epicardial paddles applied to the posterior left atrial wall (surface area 11 cm2) and to the anterior right atrial wall (surface area 26 cm2).
  
  
  RESULTS
  For the monophasic waveform the delivered energy (joules) associated with 50% success (E50) was 1.44 J (95% confidence interval [CI] 0 to 11.2) and with 80% (E80) success 3.9 J (95% CI 2.42 to 109.8); for the biphasic waveform 50% success was achieved with 0.37 J (95% CI 0.36 to 0.38) (p = NS) and 80% success with 0.57 J (95% CI 0.56 to 0.58) (p < 0.05).
  
  
  CONCLUSIONS
  A biphasic waveform is more efficient than a monophasic waveform in atrial defibrillation. This may have implications for the development of an implantable atrial defibrillator for paroxysmal atrial fibrillation in addition to improvement of elective transthoracic and endocardial cardioversion of chronic atrial fibrillation.
authors.affiliation: Department of Cardiology, Guy's Hospital, London, England, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Keane
authors.forename: E
authors.initials: E
authors.lastname: Boyd
authors.forename: D
authors.initials: D
authors.lastname: Anderson
authors.forename: A
authors.initials: A
authors.lastname: Robles
authors.forename: P
authors.initials: P
authors.lastname: Deverall
authors.forename: R
authors.initials: R
authors.lastname: Morris
authors.forename: G
authors.initials: G
authors.lastname: Jackson
authors.forename: E
authors.initials: E
authors.lastname: Sowton
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D016001:Confidence Intervals; D001026:Coronary Artery Bypass; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D004562:Electrocardiography / Q000706:statistics & numerical data; D005069:Evaluation Studies as Topic; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006801:Humans; D007430:Intraoperative Care / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D012306:Risk