A simple method of enhancing tolerance and efficacy during noninvasive transcutaneous cardiac pacing

Tolerance of noninvasive transcutaneous cardiac pacing depends on minimizing the stimulation threshold, expressed as current density. Achieving a uniform current density has been the chief aim of several investigations because this reduces skeletal muscle contraction and painful skin receptor stimulation. In beagle dogs, we used two pregelled electrode models (metal-disk or carbon-fiber*) of various area (75, 31, 8 and 7* cm2) to measure experimentally the pacing threshold required to capture the heart, and to measure impedance in a static system comprising electrodes arranged opposite each other, using the same pacing parameters (20 to 60 mA and 65 ipm). The heart rate was about 65 ipm with negative polarity in the sub-apical region and with constant topographical geometry and position of the successively placed electrodes, maintaining the animal in the same position. The tolerance score and pacing threshold were lowest with three carbon fiber electrodes (surface area : 21 cm2). In our dogs, gel impedance seemed to be of smaller importance than the distribution of current density which was more accurately expressed as perimeter current density.