In this issue of the Journal, Uen and colleagues’ article entitled ‘‘Early Morning Surge and Dipping Status of Blood Pressure: Are These of Predictive Value for Silent Myocardial Ischemia?’’ revisits the entity of circadian rhythms and coronary ischemia. In their study, the group evaluated 76 patients of 344 who demonstrated ST depression on 24-hour monitoring for ST-segment characteristics and blood pressure (BP). They determined that the degree of overnight BP dipping and concomitant early morning BP surge did not correlate with the presence of ST-segment depression indicative of myocardial ischemia. Notable within the data presented, but not specifically addressed by the authors in the discussion section, is the fact that in all of the time frames measured with the ambulatory BP monitoring system, the patients who did not demonstrate ST depression during the course of the day had statistically significantly lower mean systolic BP. Therefore, the most important fact to arise from these authors’ work is that overall BP control is more predictive of silent ischemia than either overnight BP dipping or early morning surges. The presence of a morning peak for acute myocardial infarction (MI) has been noted for decades but was disregarded from the earliest papers as being a reporting bias from patients sleeping through their symptoms. The Multicenter Investigation of Limitation of Infarct Size (MILIS) study demonstrated an increase in cardiac events during the hours of 6 am to 12 noon, utilizing time to peak creatinine kinase–MB fraction to determine the time of onset for the MI. A second study, the Intravenous Streptokinase in Acute Myocardial Infarction (ISAM) trial corroborated these results in more than 1700 patients, demonstrating a 4-fold greater likelihood of events between 8 am and 9 am compared with overnight hours. Similar patterns have emerged in patients presenting with sudden cardiac death (SCD) in several studies. There are several physiologic events demonstrating circadian rhythms that could account for the morning peak in acute ischemic cardiac events. There is an increase in sympathetic activity that accompanies and readies the body for awakening in the morning. Coincident with this is a rise in BP, pulse pressure, and heart rate, which may increase the hemodynamic stresses across the coronary arteries, most notably at the shoulder regions of the vulnerable plaques. Additionally, higher sympathetic tone may promote increased vascular tone and coronary vasoconstriction, while increasing metabolic demands on the myocardium. Furthermore, there is an early morning increase in platelet aggregability and a reduction in the fibrinolytic From the Cardiology Division, Department of Internal Medicine, University of Rochester Medical Center, Rochester, NY 14642 Address for correspondence: John D. Bisognano, MD, PhD, Cardiology Division, Department of Internal Medicine, University of Rochester, 601 Elmwood Avenue, Box 679-7, Rochester, NY 14642-8679 E-mail: john_bisognano@urmc.rochester.edu Manuscript received May 18, 2009; accepted May 22, 2009
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Apr 26, 2019
Dr Vinod Kumar 
