Chronobiology in cardiology.

In these years, circadian periodicity in the onset of myocardial ischemia, myocardial infarction, sudden cardiac death and ischemic stroke has been confirmed by several investigators. There has also been reported that there exists a significant circadian rhythm in ventricular arrhythmias in patients with myocardial infarction. These recent advances in chronocardiology depend on a development of a high quality built-in A/D converter in ambulatory ECG monitoring system and a remarkably developed sophisticated software. One of the most current topics in recent years is heart rate (HR) variability. As an index of HR variability, RR50 is frequently estimated by the cosine fitting technique. Next, we analyzed the so-called Lorenz plot for another index of HR variability, that is preceding R-R intervals and coupling intervals were plotted sequentially every 3 hours on the abscissa and ordinate, respectively. Finally, we investigated HR variability by power spectral analysis of R-R intervals both by the maximum entropy method and the fast Fourier transform. Mainly, in this paper, we introduced current topics in HR variability, but recent advances in ambulatory blood pressure (BP) monitoring system are also strikingly remarkable. Our newly developed monitoring system of physical activity donated quite a few informations evaluating episodic changes of HR and BP. This device was also useful for finding out the difference between the individual life styles, such as the eveningness versus morningness. In conclusion, these very recent advances in ambulatory monitoring system should be really available for the clinical practice from this time onward.