Aims: We aimed at detecting the ST segment variation (ischemic and non-ischemic) by analyzing the informational transfer between the coupled dynamics of QT segment time intervals and the heart rate (HR). This technique can be used in a broader context of measuring the degree of coupling between electrical properties of the ventricles and HR, which often arises in the medical practice (e.g. the QT-correction problem).
Methods: We used the transfer entropy method from information theory. This method allows for a quantitative and uni-directional measure of coupling between two temporal processes. Thus, one is able to quantify how much information is transferred from QT to HR and from HR to QT separately.
Results: We analyzed the Long-Term ST variation and MIT-BIH Normal Sinus Rhythm databases from PhysioNet. We found the asymmetry between QT-to-HR and HR-to-QT information transfers in healthy individuals and in the ST-segment change patients. Namely, the HR-to-QT transfer is larger than the opposite transfer. However, the HR-to-QT information transfer for the ST patients is larger than the corresponding transfer for the normal group. This indicates a larger degree of uncertainty in the QT dependency on HR. Additionally, as other studies suggest (Cardiac Electrophysiology Review 2002;6:282) that the QT-HR relationship exhibits inter-subject variability and intra-subject stability, we examined the variability of the information transfers within and between the subjects with ST variations. We found that only the HR-to-QT transfer agrees with the previous findings: namely, the mean intra-subject variability of the transfer is 1.7 times smaller than the inter-subject variability.
Conclusion: The degree of inter-dependency between QT and HR time series can be a marker of the ST variation pathology.