Gomes Paulo Alberto Paes, de Galvão Kleber Magalhães, Mateus Evandro Fallaci
Laboratório de Electrofisiologia Cardíaca/Núcleo de Pesquisas Technológicas, Universidade de Mogi das Cruzes, SP, Brazil.
J Cardiovasc Electrophysiol. 2002 Apr;13(4):355-60. doi: 10.1046/j.1540-8167.2002.00355.x.
After birth, cardiac myocytes undergo substantial growth and differentiation that affect their stimulation threshold. Cells from younger animals have a higher stimulation threshold than cells from adults. The aim of this work was to compare the excitability of isolated hearts of rats during postnatal development by measuring the stimulation threshold at several pulse durations.
Stimulation threshold of isolated hearts were measured at eight different pulse durations between 0.1 to 20 msec. For each heart, a strength-duration curve was constructed and data were fitted using both Weiss-Lapicque and Blair models. Analysis of variance showed significant age-dependent differences in both rheobase field (E(reob)) and chronaxie (c). E(reob) decreased while c increased during development (E(reob) was 0.21, 0.16, 0.13, 0.10, and 0.09 V/cm and c was 2.0, 2.2, 2.3, 2.7, and 3.2 msec for rats aged 1, 2, 4, 8, and 20 weeks, respectively). There was a decrease in the threshold field with heart weight between 0.1 and 0.7 g, whereas the threshold was almost constant in the range from 0.7 to 2.0 g. Estimation of the energy density needed to defibrillate the heart was performed and appeared to be higher for younger than for adult animals.
Hearts from younger animals have higher stimulation threshold than those from adults. This probably is due to changes in the cellular threshold as a result of maturation. The smaller excitability of younger hearts can have consequences with regard to the energy levels required for younger patients.
出生后，心肌细胞会经历显著的生长和分化，这会影响它们的刺激阈值。幼龄动物的细胞比成年动物的细胞具有更高的刺激阈值。本研究的目的是通过测量不同脉宽下的刺激阈值，比较出生后发育阶段大鼠离体心脏的兴奋性。
在0.1至20毫秒的八个不同脉宽下测量离体心脏的刺激阈值。对于每颗心脏，构建强度-时间曲线，并使用魏斯-拉皮克模型和布莱尔模型对数据进行拟合。方差分析显示，基强度场（E(reob)）和时值（c）均存在显著的年龄依赖性差异。在发育过程中，E(reob)降低而c增加（1周、2周、4周、8周和20周龄大鼠的E(reob)分别为0.21、0.16、0.13、0.10和0.09 V/cm，c分别为2.0、2.2、2.3、2.7和3.2毫秒）。心脏重量在0.1至0.7克之间时，阈值场随心脏重量降低，而在0.7至2.0克范围内阈值几乎恒定。对心脏除颤所需的能量密度进行了估算，结果显示幼龄动物比成年动物所需的能量密度更高。
幼龄动物的心脏比成年动物的心脏具有更高的刺激阈值。这可能是由于成熟导致细胞阈值发生变化。幼龄心脏较小的兴奋性可能会对幼龄患者所需的能量水平产生影响。
