Effect of Atrial Electrical Stimulation on the Transmural Sequence of Ventricular Wall Depolarization in the Rat Heart under Zoletil-Xylasine Anesthesia.

The transmural sequence of ventricular free wall depolarization in the Wsitar rat heart was studied with an increase in the heart rate against the background of zoletil-xylazine anesthesia. An increase in the heart rate was elicited by an atrial electrical stimulation. Zoletil-xylazine anesthesia with intramuscular injection at a dose of 0.15 mg/kg of zoletil and 3 mg/kg of xylazine caused a significant negative chronotropic effect with pronounced bradycardia, characterized by a twofold decrease in heart rate vs its baseline. With a reduced sinoatrial rhythm with a frequency of 237 ± 34 bpm, the subendocardial layers depolarized first, then the intramural, and lastly the subepicardial layers of the left and right free walls of the heart ventricles. The basal areas of the free ventricular walls depolarized later than the apical areas by approximately 2–4 ms also due to activation wave propagation from the endocardium to the epicardium. With an increase in heart rate, the sequence and transmural depolarization gradient did not change. At the same time, an increase in the stimulation frequency from 300 to 500 bpm led to a decrease in the arrival time of the depolarization wave to the subendocardial, intramural, and subepicardial layers of the left and right ventricular walls. Despite a depressive effect of zoletil-xylazine anesthesia on the heart and its chronotropic function, at a high frequency of atrial electrical stimulation, the depolarization gradient from the endocardium to the epicardium and from the apex to the base of the ventricles was retained intact, there were only minor changes in the duration of the process of transmural depolarization of the ventricular walls. This indicates the resistance of ventricular activation in the heart of Wistar rats to the toxic effect of zoletil-xylazine anesthesia. [ABSTRACT FROM AUTHOR]