Placement of electrodes for defibrillation--a review of the evidence.

Defibrillation is the only reliable treatment for ventricular fibrillation. Its success depends on the passage of an adequate current through the chest rather than on the administration of a preset energy. The final determinant of both efficacy and cellular damage is myocardial current density. Therefore, the current should be evenly distributed with an average value that exceeds the defibrillation threshold throughout a critical mass of myocardium but does not cause further local dysfunction. The distribution of current is altered by the relative positions of the two electrodes. European guidelines for electrode (paddle) placement during defibrillation are based on empirical studies and traditional practice. However, there is increasing evidence to suggest that bi-axillary electrode placement may be superior to traditional antero-apical and antero-posterior positions.