Frequency domain heart period and QT interval variability markers are linked to arrhythmic risk in long QT syndrome type 2

Long QT syndrome type 2 (LQT2) isan inherited disease leading to arrhythmiasandsudden deathoften in response to an abruptsympatheticstimulus. Heart period (HP) and QT interval variability analyses were carried out overasymptomatic (ASYMP, n=10, age 39.0±11.0yrs, 9 males) and symptomatic (SYMP, n=7, age 41.7±12.8yrs, 4 males) LQT2patients. Beat-to-beat series were derived from 24h Holter ECGrecordingsduring daytime and nighttime. In addition to HP and QT mean and variance,wecalculated HP power in high frequency (HF, from 0.15 to 0.5 Hz) band as a marker of vagal modulation directed to sinus node and QT power in low frequency(LF, from 0.04 to 0.15 Hz)bandas a marker ofsympathetic modulation directed to ventricles.HP and QT means exhibited significant day-night changesin both groups. ASYMP showeda shorter corrected QT anda more reactive vagalmodulationleading to significant day-night variations of respiratory sinus arrhythmia. By contrast, SYMP had no significant day-night variations of the vagalcontrol. Conversely, SYMP showed a higher sympathetic control during day compared to ASYMP,havingalarger QT variance. These findings suggest that frequency domain HP and QT variability markers can account for the different arrhythmic risk of LQT2 ASYMP and SYMP patients.