Abnormal Fractal Correlation of Heart Rate in Children with Neurocardiogenic Syncope

PURPOSE: The purposes of this study were to determine short- and long-term fractal correlation behavior of heart rates during daily activity in patients with neurocardiogenic syncope. METHODS: Twenty five patients with histories of neurocardiogenic syncope episodes were included. Their analogue 24h ambulatory Holter electrocardiograms were analyzed. The tape was digitized and the digitized electrocardiograms were partioned into sections of one hour. Then their RR intervals were measured and 20,000 points of RRI were used. To quantify the fractal correlation behavior, we employed the detrended fluctuation analysis, and short-term(n16, alpha2) fractal scaling exponents were calculated. RESULTS: When compared to control, 24-hour average values of alpha1 and all alpha1 values at quarters of each day were significantly higher in patients with syncope. On the contrary, their 24-hour average value of alpha2 and all alpha2 values at quarters of each day were lower in patients with syncope. However, statistical significances were found in 24-hour average value of alpha2 and in alpha2 value at MN-6AM. CONCLUSION: In the syncope patients with neurocardiogenic syncope, short-term fractal scaling exponents of RR interval was significantly high throughout the day. Therefore, their RR intervals were smoother in the short term scale and had a tendency to continue in the same direction of increase or decrease, which may contribute to persistent decrease in heart rate during a syncopal attack.

QT and RR interval variability and spectral characteristics in response to physiologic autonomic stimulation

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 low- and high- frequency 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 pi radian(-0.9 seconds) and -0.2+/-0.3 pi radian(-0.4 seconds) in the low- and high-frequency range, respectively. CONCLUSION: During resting state, when compared to RR interval, QT interval oscillates in significantly lower amplitude in both low- and high- frequency ranges. However, the oscillations precede those of the RR interval 0.9 seconds and 0.4 seconds, respectively.