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 microm), diameter (d(c) = 20 +/- 10 microm), thickness of extracellular space (t(e) = 1.18 +/- 0.59 microm), and junctional resistance (R(j) = 2 +/- 1 M(omega)) 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.
Krassowska
Wanda
W
Department of Biomedical Engineering, Box 90281, Duke University, Durham, NC 27708-0281, USA. wanda.krassowska@duke.edu
D003198:Computer Simulation; D004553:Electric Conductivity; D004554:Electric Countershock / Q000379:methods; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D006321:Heart / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology*; D008954:Models, Biological; D008955:Models, Cardiovascular; D015233:Models, Statistical; D009200:Myocardial Contraction / Q000502:physiology; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000528:radiation effects*; D009210:Myofibrils / Q000502:physiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity