Reduction of atrial defibrillation threshold with an interatrial septal electrode

Background-The standard lead configuration for internal atrial defibrillati on consists of a shock between electrodes in the right atrial appendage (RA A) and coronary sinus (CS). We tested the hypothesis that the atrial defibr illation threshold (ADFT) of this RAA-->CS configuration would be lowered w ith use of an additional electrode at the atrial septum (SP). Methods and Results-Sustained atrial fibrillation was induced in 8 closed-c hest sheep with burst pacing and continuous pericardial infusion of acetyl- beta -methylcholine. Defibrillation electrodes were situated in the RAA, CS , pulmonary artery (PA), low right atrium (LRA), and across the SP. ADFTs o f 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 durati on were used for all single and sequential shocks. The ADFT delivered energ ies 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 configur ations were 0.39+/-0.18 J for RAA-->SP/CS-->SP, 1.16+/-0.72 J for CS-->SP/R AA-->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 deliv ered energies of all of the configurations were significantly different fro m each other (P<0.05). Conclusions-The ADFT of the standard RAA-->CS configuration is markedly red uced with an additional electrode at the atrial SP.