Circadian Variation of the Myocardial Ischemic Threshold in Patients with Ischemic Heart Disease

Circadian rhythms and cardiovascular health

The functional organization of the cardiovascular system shows clear circadian rhythmicity. These and other circadian rhythms at all levels of organization are orchestrated by a central biological clock, the suprachiasmatic nuclei of the hypothalamus. Preservation of the normal circadian time structure from the level of the cardiomyocyte to the organ system appears to be essential for cardiovascular health and cardiovascular disease prevention. Myocardial ischemia, acute myocardial infarct, and sudden cardiac death are much greater in incidence than expected in the morning. Moreover, supraventricular and ventricular cardiac arrhythmias of various types show specific day-night patterns, with atrial arrhythmias--premature beats, tachycardias, atrial fibrillation, and flutter - generally being of higher frequency during the day than night--and ventricular fibrillation and ventricular premature beats more common, respectively, in the morning and during the daytime activity than sleep span. Furthermore, different circadian patterns of blood pressure are found in arterial hypertension, in relation to different cardiovascular morbidity and mortality risk. Such temporal patterns result from circadian periodicity in pathophysiological mechanisms that give rise to predictable-in-time differences in susceptibility-resistance to cyclic environmental stressors that trigger these clinical events. Circadian rhythms also may affect the pharmacokinetics and pharmacodynamics of cardiovascular and other medications. Knowledge of 24-h patterns in the risk of cardiac arrhythmias and cardiovascular disease morbidity and mortality plus circadian rhythm-dependencies of underlying pathophysiologic mechanisms suggests the requirement for preventive and therapeutic interventions is not the same throughout the day and night, and should be tailored accordingly to improve outcomes.

An interactive model of pain and myocardial ischemia

The biopsychosocial model has been used to describe the intertwined factors that may act as mechanisms in cardiovascular disease, as well as those found in pain conditions. This model may also prove useful in understanding a diagnosis that overlaps these two areas, angina. This article reviews the literature related to biological, psychological, and social mechanisms of painful ischemic episodes and discusses the interactions of those variables. We propose an integrated model that incorporates the biopsychosocial mechanisms that may be responsible for the variability in pain reporting with ischemic episodes. We show how sex differences manifested in various biopsychosocial factors may interact to influence the presence of painful versus silent myocardial ischemia. We present a plan for future research to elucidate this interaction.