title: Low energy conversion of atrial fibrillation in the sheep.
abstract: OBJECTIVE
  In this study, the feasibility, efficacy and safety of low energy internal atrial cardioversion were investigated in a sheep model. The relation between the level of energy used for atrial defibrillation and the probability of successful cardioversion was examined.
  
  
  BACKGROUND
  Atrial fibrillation is a common clinical arrhythmia that frequently recurs after termination with high energy external cardioversion. In some patients with drug-refractory and poorly tolerated atrial fibrillation, an automatic implantable cardioverter may prove useful by providing rapid restoration of sinus rhythm.
  
  
  METHODS
  In 16 pentobarbital-anesthetized sheep, a right atrial spring electrode was implanted percutaneously and a left thoracic cutaneous patch electrode was placed on the thorax. Sustained atrial fibrillation was induced by rapid atrial pacing and terminated by biphasic cathodal shocks synchronized to the R wave of the surface electrocardiogram (ECG).
  
  
  RESULTS
  During 768 defibrillation attempts in 16 sheep, the percent of successful cardioversion attempts increased in a dose-response manner, reaching a plateau at the average energy level of 5 J. With greater than or equal to 1.5 and greater than or equal to 2.5 J energy levels, cardioversion was achieved, respectively, in greater than 50% and greater than 80% of attempts. Ventricular fibrillation occurred in 18 (2.4%) of 768 cardioversion attempts; in all 18 cases, the shock was poorly synchronized with the ECG R wave.
  
  
  CONCLUSIONS
  Low energy cardioversion of atrial fibrillation to sinus rhythm is feasible with use of a right atrial spring/cutaneous patch electrode configuration. The percent of successful cardioversion attempts depends on the level of energy output, and there is a risk of ventricular fibrillation if cardioversion is poorly synchronized with ventricular depolarization.
authors.affiliation: Harvard Medical School, Boston, Massachusetts.
authors.forename: A C
authors.initials: AC
authors.lastname: Powell
authors.forename: H
authors.initials: H
authors.lastname: Garan
authors.forename: B A
authors.initials: BA
authors.lastname: McGovern
authors.forename: J T
authors.initials: JT
authors.lastname: Fallon
authors.forename: S C
authors.initials: SC
authors.lastname: Krishnan
authors.forename: J N
authors.initials: JN
authors.lastname: Ruskin
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000628:therapy*; D004554:Electric Countershock / Q000009:adverse effects / Q000379:methods*; D005240:Feasibility Studies; D006325:Heart Atria / Q000473:pathology; D012756:Sheep; D014693:Ventricular Fibrillation / Q000209:etiology