Field stimulation of cardiac fibers with random spatial structure

Polarization of individual cells ("sawtooth") has been proposed as a mechanism for field stimulation and defibrillation. To date, the modeling work has concentrated on the myocardium with periodic spatial structure; this paper investigates potentials arising in cardiac fibers with random spatial structure. Ten different random fibers consisting of cells with varying length (l/sub c/=100/spl plusmn/50 /spl mu/m), diameter (d/sub c/ 20 /spl plusmn/ 10 /spl mu/m), thickness of extracellular space (t/sub e/=1.18/spl plusmn/0.59 /spl mu/m), and junctional resistance (R/sub j/=2/spl plusmn/1 M/spl Omega/) are studied. Simulations demonstrate that randomizing spatial structure introduces to the field-induced potential (V/sub m/) a randomly varying baseline, which arises due to polarization of groups of cells. This polarization appears primarily in response to randomizing t/sub e/; R/sub j/, l/sub c/, and d/sub c/ have less influence. The maximum V/sub m/ increases from 3.5 mV in a periodic fiber to 20.5/spl plusmn/4.7 mV in random fibers (1 V/cm field applied for 5 ms). Field stimulation threshold E/sub th/ decreases from 6.9 to 1.59/spl plusmn/0.43 V/cm, which is within the range of experimental measurements. Thresholds for normal and reversed field polarities are statistically equivalent: 1.59/spl plusmn/0.43 versus 1.44/spl plusmn/0.41 V/cm, (p value = 0.453). Thus, V/sub m/ arising due to random structure of the myocardium may play an important role in field stimulation and defibrillation.