Heart Rate Variability and Circadian Rhythm in Patients with Congenital Long QT Syndrome and Syncopal Attacks

pp 203-210

Abstract

Objectives

The aim of this study was to assess the autonomic drive of the heart by measuring the spectral components (SC) of the heart rate variability (HRV) and the circadian rhythm (CR) in patients (p) with congenital long QT syndrome (LQTS) and syncopal attacks.

Methods

The study population was divided into three groups: 1) Adrenergic (A), 9 p, 3 men, mean age 27 ±15 years old (y.o.) (range 9 to 67 y.o.), with syncopal episodes during physical stress; 2) Pause dependent (R) 10 p, 6 men, mean age 30 ± 23 y.o. (range 7 to 42 y.o.), with syncopal events during sleep or at rest and 3) the control group (C) 20 healthy subjects, 9men, mean age 30 ± 25 (range 10 to 50). All p and controls underwent 3 channel, 24-hour Holter monitor-ing in drug free state. Spectral analysis was performed with the fast Fourier transform algorithm during 5 minute periods/hour. We analyzed the low frequency (LF) and high frequency (HF) SC and theLF/HF ratio. CR was assessed from the mean 5 minute periods/hour of the SC. The spectral measures were expressed as mean ± 1 SD in msec, logarithmic (ln) and normalized units (nu). Data between the groups were compared using the analysis of variance (ANOVA) and the Tukey Kramer test. Statistical significance was defined as p < 0.05. (Symbols indicate statistical significance * ~ v) 

Results

              _{HFrsec3     LFmsec'     HFbr     LFIn     HFrw LFrw LFIHF}

_{A•        591±386•  1.075±377• 6,2±0,6v 6,9±0,4• 26±772±7  2,8±1}

_{R•      1.135±4730-1.602±80007,1±0,307,3±0,5032±1266±12 2±1}

_{C       344±7060r   600±259  0•5,4±10• 6,1±0,90r31±1065±102±1}

LF and HF SC were significantly higher in group R as compared with the controls; the LF/HF ratio remained unchanged. HRV in group A showed a decrease in the HF SC with a simultaneous increase in the LF SC during the morning and afternoon hours. There was a biphasic increase in the LF/HF ratio in the morning and in the afternoon.

Conclusions

Both SC and HRV are increased in p with LQTSand syncopal attacks. In group A patients, a relative significant increase in the adrenergic tone wasobserved, in coincidence with the CR of suddendeath in the general population.