title: Reduction of atrial defibrillation threshold with an interatrial septal electrode.
abstract: BACKGROUND
  The standard lead configuration for internal atrial defibrillation consists of a shock between electrodes in the right atrial appendage (RAA) and coronary sinus (CS). We tested the hypothesis that the atrial defibrillation threshold (ADFT) of this RAA-->CS configuration would be lowered with use of an additional electrode at the atrial septum (SP).
  
  
  RESULTS
  Sustained atrial fibrillation was induced in 8 closed-chest sheep with burst pacing and continuous pericardial infusion of acetyl-ss-methylcholine. Defibrillation electrodes were situated in the RAA, CS, pulmonary artery (PA), low right atrium (LRA), and across the SP. ADFTs of RAA-->CS and 4 other lead configurations were determined in random order by use of a multiple-reversal protocol. Biphasic waveforms of 3/1-ms duration were used for all single and sequential shocks. The ADFT delivered energies for the single-shock configurations were 1.27+/-0.67 J for RAA-->CS and 0. 86+/-0.59 J for RAA+CS-->SP; the ADFTs for the sequential-shock configurations were 0.39+/-0.18 J for RAA-->SP/CS-->SP, 1.16+/-0.72 J for CS-->SP/RAA-->SP, and 0.68+/-0.46 J for RAA-->CS/LRA-->PA. Except for CS-->SP/RAA-->SP versus RAA-->CS and RAA-->CS/LRA-->PA versus RAA+CS-->SP, the ADFT delivered energies of all of the configurations were significantly different from each other (P:<0. 05).
  
  
  CONCLUSIONS
  The ADFT of the standard RAA-->CS configuration is markedly reduced with an additional electrode at the atrial SP.
authors.affiliation: Division of Cardiovascular Diseases, Department of Medicine, University of Alabama at Birmingham, USA.
authors.forename: X
authors.initials: X
authors.lastname: Zheng
authors.forename: M E
authors.initials: ME
authors.lastname: Benser
authors.forename: G P
authors.initials: GP
authors.lastname: Walcott
authors.forename: S D
authors.initials: SD
authors.lastname: Girouard
authors.forename: D L
authors.initials: DL
authors.lastname: Rollins
authors.forename: W M
authors.initials: WM
authors.lastname: Smith
authors.forename: R E
authors.initials: RE
authors.lastname: Ideker
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000601:surgery / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D004554:Electric Countershock / Q000295:instrumentation* / Q000379:methods; D004562:Electrocardiography; D004567:Electrodes, Implanted; D022062:Electrophysiologic Techniques, Cardiac; D004735:Energy Transfer; D006321:Heart / Q000187:drug effects / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D006346:Heart Septum / Q000502:physiology / Q000601:surgery; D016210:Methacholine Chloride / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D015203:Reproducibility of Results; D012684:Sensory Thresholds; D012756:Sheep; D012815:Signal Processing, Computer-Assisted
chemical_list: D018721:Muscarinic Agonists; D016210:Methacholine Chloride