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_c=100±50 μm), diameter (d_c 20 ± 10 μm), thickness of extracellular space (t_e=1.18±0.59 μm), and junctional resistance (R_j=2±1 MΩ) are studied. Simulations demonstrate that randomizing spatial structure introduces to the field-induced potential (V_m) a randomly varying baseline, which arises due to polarization of groups of cells. This polarization appears primarily in response to randomizing t_e; R_j, l_c, and d_c have less influence. The maximum V_m increases from 3.5 mV in a periodic fiber to 20.5±4.7 mV in random fibers (1 V/cm field applied for 5 ms). Field stimulation threshold E_th decreases from 6.9 to 1.59±0.43 V/cm, which is within the range of experimental measurements. Thresholds for normal and reversed field polarities are statistically equivalent: 1.59±0.43 versus 1.44±0.41 V/cm, (p value = 0.453). Thus, V_m arising due to random structure of the myocardium may play an important role in field stimulation and defibrillation.