Thirty-four healthy adult male guinea pigs, weighing approximately 800-1200 grams were anesthetized, and their chests opened to expose the heart. Eleven electrodes with following contact surface areas were applied: 0.1, 0.2, 0.8, 1.26, 2.01, 2.34, 3.08, 4.1, 7.91, 16.4, and 26.79 mm2.
In the first group, the relationship between electrode size and current was explored in ten guinea pigs and the current thresholds recorded when blood pressure collapse and ventricular fibrillation occured. In the second group, frequency depency (20, 40, 80, and 160 Hz) was examined on the relationship between electrode size and current in thirteen guinea pigs.
Based on the experimental data, a theoretical framework to explain the electrode size-stimulation threshold variation for both low strength alternating current stimulation and ventricular fibrillation initiation was presented.
for further information see: O. Z. Roy, G. C. Park and J. R. Scott "Intracardiac catheter fibrillation thresholds as a function of the duration of 60 Hz current and electrode area", IEEE Trans. Biomed. Eng., vol BME-24, no. 5, pp 430-435, Mays 1977
On a log-log graph (horizontal and vertical axes are logarithimic scales), electrode size had a piecewise-linear relationship with the current thresholds to induce blood pressure collapse and ventricular fibrillation. Above the liminal area, the threshold increased proportional.
The frequency had no further effect on the relationship between electrode size and current.