[Effect of the heart electric stimulation on repolarization of fish and amphibian ventricular myocardium].

By the method of synchronous multielectrode cartography (24-unipolar leads), distribution of durations and time of end of repolarization were studied on ventricular epicardium of pikes (Esox lucius) and frogs (Rana esculenta) and in ventricular intramural layers of toads (Bufo bufo) at the ectopic heart excitation. The time of arrival of the excitation wave and of the end of repolarization in each lead was determined from the minimum of time derivative of potential at the period of the QRS complex and by minimum of the T wave, respectively. It has been established that at the ventricle electrostimulation, alongside with deceleration and a change of sequence of the myocardium activation, there occurs redistribution of local repolarization durations: in areas of late activation the repolarization being longer than in zones of early activation (p < 0.

[Repolarization pattern of the ventricular myocardium in pikes].

The study aimed at investigation into the repolarization pattern in the myocardium of fish. Activation times, activation-recovery intervals and repolarization times were determined in the intramural layers of the heart ventricle in eight pikes with multiple plunge electrodes. In the heart ventricle of the pike, the earliest end of repolarization was found in the subendocardium of the base and the subepicardium of the apex, the areas corresponding to the earliest and latest depolarization, respectively.

[Cardiac electric field at the period of depolarization and repolarization of the frog heart ventricle].

Multichannel mapping of electrical field on heart ventricle epicardium and the body surface in frogs Rana esculenta and Rana temporaria was performed at periods of the ventricular myocardium depolarization and repolarization. The zone of the epicardium early depolarization is located on epicardium of the ventricle base posterior wall, while the late depolarization zone--on its apex and on the base anterior wall. The total vector of sequence of the ventricle epicardium depolarization is directed from the base to the apex.

[Structure of the cardiac systole in mammals and birds].

The comparative analysis of the contractile function of the heart left ventricle in four species of homoeothermic tetrapods (chicken, quail, rat, sheep) who differ in their spatio-temporal pattern of ventricular excitation, heart rate, and heart weight was performed. The analysis of cardiac cycle structure was performed on the basis of synchronous recording of ECG, phonocardiogram, and apex cardiogram. Indices of myocardial contractility of the left ventricle calculated on the basis of the analysis of the cardiac dynamics indicate disadvantageous contractile function of the left ventricle in rodents and non-flying birds in comparison with sheep.

[Sequence of ventricular repolarization under body cooling in the frog].

Lowering the temperature is known to prolong the repolarization of cardiomyocytes. However, whether the prolongation of action potentials is uniform throughout the myocardium, and whether this prolongation is obvious in ECG, remains unclear. Ventricular repolarization sequences and body surface potential distributions were studied in 20 frogs Rana temporaria using epicardial and body surface potential mapping.