Temporal variability of the QT interval: Study in the time, frequency, and chaotic domains

There are many reports on QT dispersion (i.e., the difference of QT duration in different leads), but few on the temporal variability of this interval. We developed new algorithms for the automated measurement of RR, QT, and QaT; studied the temporal variability of QT in the time, frequency, and chaotic domains; and compared QT to RR variability. The standard deviation was higher for RR than for QT whereas the coefficients of variation were similar. The high frequency component was more pronounced and the ratio of high:low frequency power was higher for QT than for RR. Poincare plots of QT were less elongated than plots of RR, and the negative slope of log power to log frequency (fractal dimension of 1/f fluctuation) was smaller. QT(c) and QaT variability were similar to that of QT. Thus, QT variability contains different information from RR variability and shows a larger percentage of spectral power at higher frequencies.