Electric field stimulation of cardiac myocytes during postnatal development

Studies on cardiac cell response to electric field stimulation are important for understanding basic phenomena underlying cardiac defibrillation. In this work, the authors used a model of a prolate spheroidal cell in a uniform external field (Klee and Plonsey, 1976) to predict the threshold electric field (ET) for stimulation of isolated ventricular myocytes of rats at different ages. The model assumes that ET is primarily determined by cell shape and dimensions, which markedly change during postnatal development. Neonatal cells showed very high ET, which progressively decreased with maturation (experimental mean values were 29, 21, 13, and 5.9 and 6.3 V/cm for 3-6, 13-16, 20-21, 28-35, and 120-180 day-old rats, respectively, P<0.001; theoretical values were 24, 18, 11, 9, and 6 V/cm, respectively). Estimated maximum membrane depolarization at threshold (/spl Delta/V/sub T//spl ap/35 mV, under the authors' experimental conditions) was reasonably constant during development, except for cells from 1-mo-old animals, in which /spl Delta/VT was lower than at other ages. It is concluded that the model reasonably correlates ET with cell geometry and size in most cases. The authors' results might be relevant for the development of efficient procedures for defibrillation of pediatric patients.