Circadian pattern and sex differences of QT/RR and T-peak-to-end/RR curvatures and slopes in chronic heart failure patients

Increased QT/RR and T
_pe
/RR slopes have been shown to be independent predictors of sudden cardiac death (SCD) when analyzed over a 24-hour ECG recording. The circadian influence on the QT/RR slope is well-known but it has never been tested on the T
_pe
/RR slope. This work studied the inter-individual variability of the curvature and slope of QT/RR and T
_pe
/RR, as well as their circadian pattern in women and men. Holter ECG recordings of 385 patients with chronic heart failure (CHF) from the “MUSIC” database were analyzed. ECGs were delineated using a single-lead procedure over the first principal component lead derived to emphasize the T-wave. RR, QT and T
_pe
series were obtained and for each patient, a regression equation was fitted, where λ is the QT/RR or T
_pe
/RR curvature, and Δ is the slope of the regression pattern evaluated at the medium RR value. The median (IQR) slope was Δ
_QT
= 0.194 (0.11), and Δ
_Tpe
= 0.018 (0.04). The median (IQR) curvature was γ
_QT
= 0.993 (0.17) and γ
_Tpe
= 1.000 (0.04), respectively. The circadian pattern modulated the QT/RR and T
_pe
/RR curvature and slope, with statistically significant differences between day and night for QT/RR slope. No statistically significant differences in gender were found in this study. According to the results in this work, the time of the day should be considered when using QT/RR slope for SCD risk prediction, but the T
_pe
/RR slope is less sensitive to the circadian pattern.