Transthoracic Atrial Defibrillation Energy Thresholds are Correlated to Uniformity of Current Density Distributions

Previous studies have shown that successful defibrillation depends on the uniformity of current density in the heart and the percentage of total current reaching the heart. This study uses an anatomically-realistic finite element computer model of the human torso for external atrial defibrillation to (1) examine the defibrillation energy thresholds and current density distributions for common clinical paddle placements and (2) investigate the effects of electrode shifts on these defibrillation parameters. The model predicts atrial defibrillation threshold (AD FT) energy by requiring a voltage gradient of 5 V/cm over at least 95% of atrial myocardium. This study finds that variation in electrode placement by only a few centimeters increases ADFTs by up to 46% with a corresponding change of 38% between the average current density in the left and right atria and 34% between the heterogeneity indices of atrial current density distributions. Additionally, the heterogeneity index, or degree of uniformity, is linearly correlated to the ADFT (R²=0.9). We suggest that uniformity of current density distribution, in addition to minimum current density, may be an important parameter to use for predicting successful defibrillation when testing new electrode placements