Right atrial septal electrode for reducing the atrial defibrillation threshold

Background-The atrial defibrillation threshold (ADFT) energy of the standar d lead configuration, right atrial appendage (RAA) to coronary sinus (CS), was reduced by >50% with the addition of a third electrode traversing the a trial septum in a previous study. This study determined whether the ADFT wo uld be lowered by a more clinically practical third electrode placed in the right atrium along the atrial septum (RSP). Methods and Results-Sustained atrial fibrillation was induced in 8 closed-c hest sheep with burst pacing and maintained with pericardial infusion of ac etyl-beta -methylcholine chloride. A custom-made, dual-defibrillation cathe ter was placed with electrodes in the lateral R-A, CS, and RSP. A separate defibrillation catheter was also placed in the RAA. ADFT characteristics of RAA --> CS and 6 other single- or sequential-shock configurations were det ermined in random order by using biphasic, truncated-exponential waveforms in a multiple-reversal protocol. The delivered-energy, peak-voltage, and pe ak-current ADFTs for the sequential-shock configuration CS --> RSP/RA --> R SP (0.53 +/- 0.31 J, 86 +/- 22 V, and 1.6 +/- 0.6 A, respectively) were sig nificantly lower than those of RAA --> CS (1.14 +/- 0.64 J, 157 +/- 34 V, a nd 2.5 +/- 1.1 A, respectively). The ADFT characteristics of RAA --> CS and RA --> CS were not significantly different, nor were those of CS --> RSP/R A --> RSP and CS --> RSP/RAA --> RSP. Conclusions-The ADFT of the standard RAA --> CS configuration may be marked ly reduced with an additional electrode situated at the RSP.