Fig. 3

Abnormal ECG recorded during induction of hypothermia in rats anesthetized with sodium pentobarbital. Rectal temperature of rats injected with sodium pentobarbital (50 mg/kg, i.p.) decreased chronologically in each experiment (n = 6) (a). Heart rate decreased constantly until body temperature dropped to 25 °C. When body temperature dropped below 22.5 °C, heart rate rapidly decreased (b). Abnormal ECGs were not recorded when rectal temperature was above 25 °C (c). In contrast, when rectal temperature dropped to about 22.5 °C, complete atrioventricular block and ventricular fibrillation were observed in three and one of the six rats, respectively (d). P wave and QRS complex are indicated by arrowheads and arrows, respectively