Current Density Distribution by Ring and Diagonally Arranged Half-Ring Electrodes in Bipolar and Overlapping Biphasic Impulse Stimulation

Abstract

We have studied the acute and long-term efficacy of overlapping biphasic impulse (OLBI) stimulation for atrial pacing with VDD pacemakers and demonstrated the feasibility of DDD pacing in OLBI with diagonally arranged half-ring (Half-Ring) electrodes. We made two three-dimensional computational analysis models to verify our clinical studies. Model I was composed of a heart, a pacemaker, and a human body. Model II was a cube with dimensions of 20 by 20 by 20 mm quarried from Model I for the detailed study of current density distributions. Laplace's equation was solved using the finite element method and the current density J was calculated. For Model I, the distal and proximal voltages were -10 V, 0 V in bipolar and -5 V, +5 V in OLBI, using Ring electrodes. In Model II, the actual measurements of electrode impedances obtained from the clinical study (1,180 Ω for Ring and 630 Ω for Half-Ring) were added to the analysis conditions. Model I showed that OLBI produced more concentrated current density distributions than those by bipolar. According to Model II, at the atrial myocardium position current density produced by Half-Ring was larger than that by Ring electrodes, 70 μA/mm(2) versus 30 μA/mm(2) in OLBI configuration. It also indicated that even if electrode impedances were equal between Half-Ring and Ring electrodes, the maximum current density produced by Half-Ring would be greater than that by Ring electrodes. It was considered that OLBI configuration with Half-Ring electrodes provides more effective current density distributions.