Symbolic Analysis of Heart Period and QT Interval Variabilities in LQT1 Patients

Heart period and QT interval variabilities carry important information about the state of the autonomic nervous system. Autonomic function is impaired in the long QT syndrome type 1 (LQT1) and this impairment plays a central role in triggering fatal arrhythmias. Twenty-four hour Holter recordings from 26 mutation carrier (MC) subjects and 11 non mutation carrier (NMC) coming from the same family with founder effects were analyzed. After the extraction of heart period, approximated as the time distance between two consecutive R peak on the ECG (RR), and QT interval, approximated as the temporal distance between R apex and the apex or the end of T wave (RTa and RTe respectively), we performed symbolic analysis over the obtained RR, RTa and RTe beat-to-beat series. Results showed that, while the two groups could not be discriminated by symbolic analysis of RR series, the same analysis carried out on RTa and RTe series evidenced significant differences reflecting the impairment of the autonomic control directed to ventricles and remarking the different information achieved from RR and QT variabilities.