Transfer Entropy between RR and QT Intervals in Long QT Syndrome

Healthy subjects exhibit strong information transfer from RR to QT intervals. In this study, we assess the dynamic coupling between RR and QT intervals for subjects with long QT syndrome (LQTS) - a potentially fatal genetic cardiac disease characterized by delayed myocardial repolarization. We use transfer entropy (TE) to quantify the magnitude and direction of the information exchange between the RR and QT intervals. Using 24-hour Holter ECGs, we calculate TE as a function of RR and QT histories up to 50 beats and compare the results between the healthy controls and the subjects of LQTS type 1 and 2. Asymmetry between TERR→ QT and TEQT RR was observed for the LQTS subjects. Compared to the healthy, the LQTS subjects had significantly smaller TERR→QT at RR history lengths longer than about 18 beats, while TEQT→ RR was significantly larger at all RR and QT history lengths. The average characteristic RR history length that maximized TERR→ QT was 27 beats for the healthy subjects, which was significantly longer than 21 and 22 beats for LQTl and LQT2, respectively. Aging had no significant effect on TERR→QT, but reduced TEQT→ RR for the LQTS subjects, whereas the gender and beta blocker were found to have relatively small effects on the TE. In conclusion, the dynamic coupling between RR and QT intervals is altered by LQTS.