[Basic mechanisms of QRS voltage changes on ECG of healthy subjects during the exercise test]

Electrocardiography is the most commonly used technique for detection stress-induced myocardial ischemia. However, the sensitivity of ECG-criteria is not high. One of the major problem is the difficulty in differentiating ECG changes caused by various factors. The aim of this study was to evaluate the dependence of the QRS voltage changes during exercise on parameters of central hemodynamics, gender particularities and to reveal mechanisms causing these changes. To eliminate the effect of changes in cardiomyocytes transmembrane potentials under the influence of the neurotransmitters of the autonomic nervous system during stepwise increasing exercises and/or due to a lack of ATP results from inadequate myocardial blood flow only healthy subjects not older than 35 years were included in the study (7 men and 7 women) and only periods of ventricular depolarization (QRS complex on the ECG) were included in the analysis. We compared the changes of QRS waves during exercise sessions with two upper and one lower limbs in both men and women. The exercise load was twice bigger in exercise with one leg relative to exercise with two arms. Responses of heart rate and systolic arterial pressure were similar. Amplitude of S-wave in left chest leads significantly increased in both sessions without significant difference between augmentations in the sessions and in groups of men and women. Significant relationship between the S wave augmentation and the peak systolic arterial pressure were revealed. Furthermore, the QRS changes during the exercise with vertical and a horizontal torso position were compared to assess the impact of diastolic arterial pressure and displacement of the diaphragm and heart rotation due to increase of abdominal pressure during the last steps of exercise. The obtained results allow us to exclude the impact of the heart position and size changes, as well as the exercise load on S-wave changes and make a conclusion about the dependence of this parameter on the value of systolic blood pressure.