Multiscale complexity analysis of short QT interval variability series stratifies the arrhythmic risk of long QT syndrome type 1 patients

A linear model-based multiscale complexity (MSC) approach was here applied to short heart period (HP) and QT interval variability series derived from 24 hours Holter ECG recordings in a group of long QT syndrome type 1 (LQT1) patients. The MSC approach allows to assess complexity in the typical frequency bands of HP and QT variability, i.e. low frequency (LF, from 0.04 to 0.15 Hz) and high frequency (HF, from 0.15 to 0.5 Hz). MSC was computed along with a single scale complexity over 7 LQT1 asymptomatic mutation carriers (AMC), 22 symptomatic mutation carriers (SMC) and 13 healthy non-mutation carriers (NMC) belonging to the same family line during daytime and nighttime. Time domain markers and HP variability complexity analyses were unable to separate groups. While single scale QT variability complexity analysis could distinguish NMC from mutation carriers, solely MSC of QT variability distinguished AMCs from SMCs, showing that AMCs have a reduced complexity in LF band during daytime. We conclude that a reduced complexity of the sympathetic drive directed to the ventricles might be protective against life threatening arrhythmias especially during day being the most risky period for LQT1 patients. MSC of QT variability could be fruitfully exploited to improve risk stratification in LQT1 population.