Gurjão de Godoy Carlos Marcelo, de Magalhães Galvão Kleber, de Almeida Bacarin Tatiana, Franco Gisela Rosa
Laboratório de Eletrofisiologia Cardíaca, Núcleo de Pesquisas Tecnológicas, Universidade de Mogi das Cruzes, Avenida Dr Cândido Xavier de Almeida e Souza 200, Mogi das Cruzes, SP, 08780-911, Brazil.
Physiol Meas. 2002 Nov;23(4):649-59. doi: 10.1088/0967-3334/23/4/305.
Cardiac excitability is determined by the direction of the electric field, which is defined by the positioning of electrodes. However, important morphological and physiological modifications that happen during the postnatal development of the heart may affect the cardiac threshold. In this work we have evaluated the effect of electrode positioning on the excitability threshold of isolated Wistar rat atria (left auricles) during postnatal development. This was performed by determining the parameters of strength-duration curves for stimuli (rheobase, chronaxie and normalized minimum pulse energy) of atria from rats at ages (days) 5, 15, 30, 60, 90 and 120. These parameters were determined using electric field stimulation in four different orientations (apex-base, base-apex, left-right and right-left). Atrial rheobase decreased by 1.5- to 4-fold with animal age and was altered by electric field orientation in a diversified way, whereas atrial chronaxie increased only with animal age. The minimum pulse energy decreased two- to nine-fold with ageing. This was mainly due to rheobase dependence with electric field direction. We showed that the appropriate cardiac stimulation depends on the effects of three combined factors (pulse parameters, electrode position and animal age) on the atrial tissue excitability.
心脏兴奋性由电场方向决定，而电场方向由电极位置定义。然而，心脏出生后发育过程中发生的重要形态和生理改变可能会影响心脏阈值。在这项研究中，我们评估了电极位置对出生后发育过程中分离的Wistar大鼠心房（左心耳）兴奋性阈值的影响。这是通过确定5日龄、15日龄、30日龄、60日龄、90日龄和120日龄大鼠心房刺激的强度-时间曲线参数（基强度、时值和归一化最小脉冲能量）来进行的。这些参数是在四种不同方向（心尖-心底、心底-心尖、左-右和右-左）使用电场刺激来确定的。心房基强度随动物年龄增长下降了1.5至4倍，并且因电场方向的不同而改变，而心房时值仅随动物年龄增长而增加。最小脉冲能量随年龄增长下降了2至9倍。这主要是由于基强度对电场方向的依赖性。我们表明，合适的心脏刺激取决于脉冲参数、电极位置和动物年龄这三个综合因素对心房组织兴奋性的影响。
