Effect of Diurnal Rhythm on RR Interval Correlations of Long QT Syndrome Patients

We studied the effect of diurnal rhythm in RR interval (RRI) correlations of long QT syndrome (LQTS) patients. We focused on discrimination of healthy controls and LQTS subjects based on the variation of the HRV between the day and the night. We used 24-hour Holter recordings from Telemetric and Holter ECG Warehouse with 149 healthy controls and 88 genetically confirmed LQTS patients (LQT1 = 70, LQT2 = 18, LQTS without beta blocker (BB) medication = 54, LQTS with BB medication = 29). The data was split into daytime (hours 15–19) and night-time (00–04). We assessed the RRI correlations with detrended fluctuation analysis (DFA) and its dynamical extension (DDFA) by considering time- and scale-dependent scaling exponents α(t, s). We observed reduced diurnal variability in the RRI correlations of LQTS patients, resulting in greater divergence from healthy controls during the day for all subsets. The effect was increased in the BB-treated subgroup (ROC-AUC 0.88, p = 3.7 × 10–5), but the results persisted in the absence of BBs (ROC-AUC 0.83, p = 3.6 × 10–7) with statistical significance (p > 0.05). The overall reduction in both the RRI correlations and their diurnal variability could potentially be exploited in QT-free risk assessment of LQTS.