In terms of the basal levels, there were no statistically significant differences among control and electromagnetic field exposure in PR interval, QRS complex interval, mean blood pressure, heart rate and pulse pressure. However, the QT interval, representing ventricular repolarization, was significantly reduced by the one day electromagnetic field exposure.
(-)-Dobutamine (beta1-adrenoceptor-selective agonist)-induced tachycardia was significantly suppressed by extremely low frequency electromagnetic field exposure in the one day exposure group. Adrenaline (nonselective beta-receptor agonist)-induced dysrhythmia was also significantly suppressed by extremely low frequency electromagnetic fields in the one day exposure group.
These data indicated that one day exposure to extremely low frequency electromagnetic fields could suppress the increase in heart rate by affecting ventricular repolarization and may have a down-regulatory effect on responses of the cardiovascular system induced by sympathetic agonists.