Key result
Graded head-up tilt significantly increased the complexity of QT variability unrelated to heart period and respiration (r=0.199, p=0.0418), suggesting increased heterogeneity of neural inputs.
Why the study?
Fluctuations in QT interval duration are under autonomic control, but the complexity of QT variability regulation during sympathetic activation remains to be characterized.
Does graded orthostatic challenge alter the complexity of QT variability unrelated to RR variations and respiration in healthy subjects?
Observational (n=15)
No
Does graded orthostatic challenge alter the complexity of QT variability unrelated to RR variations and respiration in healthy subjects?
During sympathetic activation induced by orthostatic challenge, the complexity of QT variability unrelated to heart rate and respiration increases, suggesting heightened heterogeneity of neural inputs modulating ventricular repolarization.
The fluctuations of the duration of the electrical activity of the heart, measured as the time distance between Q-wave onset and T-wave end (QT), is under autonomic control. We studied the complexity of the QT variability regulation via the computation of sample entropy of QT variability during sympathetic activation induced by graded head-up tilt. Sample entropy was computed over the original QT series and after factorizing it into partial processes describing QT variability related to heart period, measured as the time interval between consecutive R-wave peaks (RR), linked to respiration (R) and unrelated to RR and R. We found that QT variability complexity is high and does not vary with the intensity of the stimulus. This result was the consequence of a non-significant tendency of the complexity of the QT variability related to RR to decrease and a significant raise of the complexity of the QT variability unrelated to RR and R with the magnitude of the orthostatic challenge. We suggest that the sample entropy of the QT variability unrelated to RR and R could quantify the increased heterogeneity of the neural inputs genuinely modulating QT during a sympathetic arousal.
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Porta et al. (2020) conducted an observational in Healthy (n=15). Graded head-up tilt vs. Supine position (0° tilt) was evaluated on Correlation of sample entropy (SampEn) of QTwQT dynamics (QT variability unrelated to RR and respiration) with tilt angle (r=0.199, p=4.18×10-2). Graded head-up tilt significantly increased the complexity of QT variability unrelated to heart period and respiration (r=0.199, p=0.0418), suggesting increased heterogeneity of neural inputs.
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