Current distribution from defibrillation electrodes in a homogeneous torso model

Abstract

In this paper a theoretical model is derived and use to estimate parameters relevant to current flow from external defibrillating electrodes in the antero-posterior position. The mean current density in the heart was found to be 3.6 milliamperes/cm 2 . per ampere current through the electrodes. The ratio of the extreme values of current densities in the heart was 4 to 1 and the percentage of total current flowing through the heart 45%. A change in chest depth from 19 to 30 cm. caused a change in average density of 10 to 20% from that found in a typical chest while a 2 inch displacement of the anterior electrode resulted in a 14% change in average density in the heart. Neglecting possible effects due to poor electrode contacts, theoretically computed temparature rises associated with single pulse defibrillation were found to be negligible. The validity of the theoretical model was, tested by comparing some of its predictions to corresponding measurements in a homogeneous electrolytic tank and in human subjects. Although the correlation was good, the data must be considered approximate in view of the model simplifications. A design criterion in the form of a “quality ratio” is discussed. This is the ratio of the minimum current in the heart to the maximum current density elsewhere in the body.