QUANTIFYING ELECTROCARDIOGRAM RT-RR VARIABILITY INTERACTIONS

A dynamic linear parametric model is designed to quantify the dependen ce of ventricular repolarisation duration variability on heart period changes and other immeasurable factors. The model analyses the beat-to -beat series of the RR duration and of the interval between R-and T-wa ve apexes (RT period). Directly from these two signals, a parametric i dentification procedure and spectral decomposition techniques allow RT variability to be divided into RR-related and RR-unrelated parts and allow the RT-RR transfer function to be calculated. RT variability is driven by RR changes at low frequency (LF, around 0.1 Hz) and high fre quency (HF, at the respiratory rate), whereas, at very low frequencies , the RR-unrelated contribution to the fetal RT variability is remarka ble. During tilt at LF the RR-related RT percentage power increases (p < 0.02), the RR-unrelated RT percentage power remains unchanged, the gain of the RT-RR relationship largely increases (p<0.001), and the ph ase is not significantly modified. Both the RR-related and the RR-unre lated RT percentage powers at LF are not affected by controlled respir ation, and an increase in the RT-RR gain at HF is observed (p<0.02). T he proposed analysis may help to describe the regulation of the ventri cular repolarisation process and to extract indexes quantifying the co upling between heart period and ventricular repolarisation interval ch anges.