Key result
During the resting state, the QT interval oscillates with significantly lower amplitude in both low- and high-frequency ranges compared to the RR interval (p<0.005), but its oscillations precede those of the RR interval by 0.9 and 0.4 seconds, respectively.
Cross-Sectional (n=24)
Yes
Absolute Event Rate: 0.1% vs 4.4%
p-value: p=<0.005
In healthy adolescents, QT interval variability is significantly smaller than RR interval variability but precedes it, suggesting that ventricular repolarization changes occur prior to sinus node firing rate changes in response to physiologic autonomic stimulation.
No immediate clinical utility in adolescents; leaves open mechanistic role of QT precedence in autonomic regulation.
Purpose:The purposes of this study were to compare the magnitude and phase between the RR interval and QT interval variability in the frequency domain. Methods:Twenty four, 12-13 year old healthy males were randomly selected. At resting state and for 5 minutes, ECGs were obtained, and they were digitized to 1000Hz. After measurement of RR interval, QT interval variability was measured using template matching strategy. After normalization of the RR and QT interval time series, power spectral and cross spectral analysis were performed. From each of the time series, low(0.04-0.15 hertz) and high(0.15-0.4 hertz) frequency power were measured. From the phase spectrum, the phases and time lags between the two time series at each of the two frequency range were calculated. Results:The average of RR interval and QT interval was 616.0±71.0, 364.0±47.0 msec, respectively. Their normalized lowand highfrequency power was 4.4±7.9 NU (normalized unit), 0.1±0.1 NU (p<0.005), and 11.0±30.0 NU, 0.3±0.3 (NU, p<0.005), respectively. The phase differences and resulting time lags between the two interval were -0.5±0.4 πradian (-0.9 seconds) and -0.2 ±0.3 πradian (-0.4 seconds) in the lowand high-frequency range, respectively. Conclusion:During resting state, when compared to RR interval, QT interval oscillates in significantly lower amplitude in both lowand highfrequency ranges. However, the oscillations precede those of the RR interval 0.9 seconds and 0.4 seconds, respectively. (Korean Circulation J 2000;30(12):1507-1514)
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Shin et al. (2000) conducted a cross-sectional in Healthy (n=24). QT interval variability vs. RR interval variability was evaluated on Normalized low-frequency power (p=<0.005). During the resting state, the QT interval oscillates with significantly lower amplitude in both low- and high-frequency ranges compared to the RR interval (p<0.005), but its oscillations precede those of the RR interval by 0.9 and 0.4 seconds, respectively.
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