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Computer simulation of optimum electrode configuration for the induction of noninvasive Wedensky phenomenon in man

Wedensky phenomenon (WP) is the effect of subthreshold stimulation on the subsequent suprathreshold excitation. To produce non-invasive WP optimally, sufficient myocardial current density (MCD) has to be combined with minimum MCD variance. A computer model of transthoracic currents was used to study the effects of different electrode systems on mean MCD and its variance. Three 2D horizontal thorax cross-sections were considered with high, middle, and lower sections of ventricular myocardium. Tissue characteristics were represented by conductivities within a rectangular grid of 460/spl times/700 nodes. A finite difference model of current flow investigated 30 different frontal electrodes used in 13 different positions against 5 different positions of a dorsal patch (1950 experiments with each cross-section). The current densities within the modelled myocardium of all three cross-sections were combined (79956 nodes). Independent of the position, there was a positive relationship between the area of the frontal electrode with mean MCD (3.78 to 5.39 [technical units] for linearly increasing length of the frontal electrode of simulated sizes from 15 to 120 mm) while the coefficient of variance of MCD decreases with the increasing area of the frontal electrode (0.52 to 0.36). The coefficient of variance of MCD was further improved by perforations into the largest size electrodes (lowest coefficient of variance of 0.36 and 0.33 was achieved with un-perforated and perforated electrodes, respectively 7% reduction). In conclusion, non-invasive induction of Wedensky phenomenon requires a large precordial electrode. The variance of myocardial current density is slightly reduced by using perforated electrodes.