Etiology of Bifid T Wave in Electrocardiogram of Rats

Abstract

Using male Wistar rats, the bipolar limb lead electrocardiogram (ECG), the vectorcardiogram (VCG), the unipolar chest lead ECG and the unipolar lead electrogram (EG) from the cardiac ventricular surface were recorded before and after the procedure of a hypothermic (30°C-25°C) condition and/or the administration of isoproterenol (1.5 or 3.0μg/kg, i. v.). The hypothermia caused a sudden prolongation of QT interval with an increased heart rate which was followed by the bifid change of T wave in the record of limb lead ECG, but the vectorcardiographical changes of T loops occurred only in the frontal and horizontal planes, with no marked change in the figures of QRS loops. Bifid T waves were constantly observed either in the precordial lead ECG or the cardiac surface lead EG when the lead positions were on the sternal line or near the cardiac septal area. By the hypothermic or the isoproterenol treatment, bifid T waves could be recorded from much wider area. These results suggested that the bifidity of the T wave recorded in the limb lead ECG is due to locally limited electrical events which can be magnified or exaggerated by hypothermia or sympathetic tension.