Repolarization variability independent of heart rate during sympathetic activation elicited by head-up tilt
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The fraction of repolarization variability independent of RR interval variability is of clinical interest. It has been linked to direct autonomic nervous system (ANS) regulation of the ventricles in healthy subjects and seems to reflect the instability of the ventricular repolarization process in heart disease. In this study, we sought to identify repolarization measures that best reflect the sympathetic influences on the ventricles independent of the RR interval. ECG was recorded in 46 young subjects during supine and then following 45 degrees head-up tilt. RR intervals and five repolarization features (QTend, QTpeak, RTend, RTpeak, and TpTe) were extracted from the ECG recordings. Repolarization variability was separated into RR-dependent and RR-independent variability using parametric spectral analysis. Results show that LF power of TpTe is independent of RR in both supine and tilt, while the LF power of QTend and RTend independent of RR and respiration increases following tilt. We conclude that TpTe is independent of RR and is highly affected by respiration. QTend and RTend LF power might reflect the sympathetic influences on the ventricles elicited by tilt.
KeywordsRepolarization Heart rate variability QT interval Tpeak-Tend Sympathetic activation Head-up tilt Autonomic nervous system
MJ was supported by grants APVV-0235-12, VEGA 1/0117/17, and project “Biomedical Center Martin,” ITMS code: 26220220187, the project co-financed from EU sources.
Compliance with ethical standards
In compliance with Declaration of Helsinki for studies involving human subjects, all procedures were approved by Ethical Committee of the Jessenius Faculty of Medicine, Comenius University and all participants or their legal guardian (if the subject was aged below 18 years) signed written informed consent.
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