Yi-Fang Guo's research while affiliated with Henan Provincial People’s Hospital and other places

We reviewed recent progress in the study of the chronobiological aspects of the cardiovascular system. Medline was used as the main search tool, and the full texts of selected papers were obtained. More than 300 references were found, and 52 of them, representing the major findings in this field, were included in the reference list. Results of these studies confirm that most cardiovascular physiological parameters (such as heart rate, blood pressure, electrocardiogram indices) and pathophysiological events (myocardial ischemia/infarction, sudden cardiac death) show circadian rhythms. Results also suggest that consideration of these rhythms is important for the diagnosis and treatment of cardiovascular disorders and that restoration of normal circadian rhythms may be associated with clinical improvement. The study of circadian rhythms in the cardiovascular system is emerging as an important area of investigation because of its potential implications for patient management.

A class of newly developed and marketed medications, angiotensin II receptor blockers, has demonstrated efficacy equivalent to that of other leading classes of anti-hypertensives, with superior tolerability profiles [1]. One of them, irbesartan, belongs to a new class of imidazole derivatives, characterized by high selectivity for the AT1 receptor subtype, large-to-fair oral bioavailability, and lack of agonistic activity [2, 3]. Irbesartan displays its full effect without biotransformation [2]. It has been established that irbesartan is a potent angiotensin II receptor antagonist with a rapid onset of action and a long-lasting inhibitory effect on hypertension [1–3].

Most cardiovascular activities show a circadian rhythm, as do electrophysiological phenomenon. Under the influence of both external stimuli and endogenous homoeostatic mechanisms, cardiac electrophysiological properties change diurnally and enable the cardiovascular system adapt to rest-exercise cycles. According to recent reports, almost all non-invasive electrophysiological phenomena, such as electrocardiographic indices, cardiac refractoriness and conduction, pacing and defibrillation threshold, heart rate variability indices, and even Q-T dispersion and T-wave alternans, show diurnal variability. Furthermore, many of these changes are clinically significant and may affect results of some diagnostic studies. These characteristics of the cardiovascular system require us keep in mind the "time" factor any time we analyze electrophysiological results and make clinical decisions.