Abstract 21357: Qt Intervals During Nighttime Sleep and Circadian Autonomic Activities in Healthy and Long Qt Syndrome (lqts) Infants

Abstract

Background: Few data were available about the QT intervals during nighttime/daytime sleep and daytime activity, and circadian autonomic nerve activities in healthy and LQTS infants. Methods: Holter ECGs were recorded in infants with 12 LQTS infants (2 KCNQ1 , 5 KCNH2 , and 5 not mutation-identified; 12±7 weeks after birth; M/F=6/6) before treatment. Ten age-matched healthy infants (M/F=4/6) were evaluated at the same period (12±3 weeks) and at 40±6 weeks. Three consecutive QT/RR intervals were measured at maximum (max), minimum, and mean heart rates (HRs) at nighttime/daytime and daytime activity and QT intervals were corrected by Bazett’s formula. The power spectral density was computed hourly as low-frequency (LF) and high-frequency (HF) components and was log-transformed. Ln(HF) and the ratio of Ln(LF)/Ln(HF) were used as surrogate markers of para-sympathetic activity and sympathovagal balance, respectively. Results: LQTS infants showed a significantly longer QTc value (490±19 ms) at max HR at nighttime sleep than that (478±20 ms, P =0.008) at max HR in daytime sleep; On the other hand, healthy infants showed no difference in the QTc values between nighttime and daytime sleep in both early and late infantile periods (439 vs 435 in early and 433 vs 423 ms in late infantile periods, respectively). LQTS infants showed a significantly decreased (or premature) parasympathetic than controls during early infancy during nighttime (Figure). In healthy controls, nighttime parasympathetic activity significantly increased at late infancy. QTc values during nighttime sleep was inversely associated with parasympathetic activity ( P =0.002) and positively associated with sympathovagal imbalance ( P <0.001). Conclusions: In early infantile periods, parasympathetic activity was not fully functioned, especially in LQTS infants. A long QTc values associated with impaired autonomic activity during nighttime sleep is one of risk factors of lethal arrhythmia in LQTS infants.