Heart Electrical Activity during Ventricular Repolarization in Rats after Acute Exhaustive Treadmill Running

The article is focused on the evaluation of the electrical activity of the heart in rats during ventricular repolarization after a single bout of forced treadmill running until exhaustion. Electrophysiological properties of the myocardium were studied by conventional ECG and body surface potential mapping. Cardiac potentials were registered in zoletil-anesthetized rats 3–5 days before (baseline) and 5, 10, 20 and 30 min after exhaustive treadmill running. Compared with baseline, an increase in the duration of the QT II , JT II and Tpeak–Tend II intervals, an earlier onset and a later completion, as well as an increase in the duration of ventricular repolarization on body surface equipotential maps (BSPMs) were revealed in rats 5 min after exhaustive exercise. Ten min following treadmill running to exhaustion, the temporal parameters of the heart electrical activity returned to pre-exercise values. Changes in the amplitude characteristics of both ECG II (ST segment depression, a decrease in the T-wave amplitude) and BSPMs (a decrease in the maximum amplitudes of positive and negative extrema during ventricular repolarization) were showed after 5–10 min and persisted up to 20–30 min after running to exhaustion. A positive correlation was found between changes in the maximum amplitude of negative extremum of BSPMs and changes in the amplitude of the T II -wave in the analyzed time periods after exhausting exercise. It is assumed that the observed changes in the electrical properties of the heart in rats during ventricular repolarization after forced treadmill running were due to ischemic myocardial damage induced by exhaustive physical exercise.