Nonlinear properties of cardiac rhythm abnormalities

Many physical processes have distributions of times between events that hav e non-normalizable, power law probability density functions (PDF's). The mo ments of such distributions are not defined. We found that the PDF's of the times between events of ventricular tachyarrhythmia (rapid heart rate) and premature ventricular contractions have a power law form indicative of a n on-normalizable distribution, and that the timing between these events cann ot be meaningfully characterized by the mean frequency of such events. The Hurst analysis showed that there were self-similar correlations in the data . These results indicate that the physical processes that disrupt the norma l rhythm of the heart produce a fractal pattern in the timing between these events. It also suggests that the mean and the variance of the frequency o f these events may not be good measures to assess the status of patients wi th these arrhythmias and determine the effectiveness of therapeutic procedu res. [S1063-651X(98)01209-3].