Response to Relation Between Time of Symptom Onset of ST‐Segment Elevation Myocardial Infarction and Patient Baseline Characteristics: From the National Cardiovascular Data Registry

Abstract

We read the article by Mogabgab et al with great interest.1 The authors aimed to investigate the relationship between patient characteristics and outcomes in ST-segment elevation myocardial infarction (STEMI). This study revealed that the circadian rhythm of STEMI with a morning peak continues to exist and represents a potential target for preventative strategies. Additionally, the authors observed that some patient characteristics were consistently varied with time of symptom onset and might reflect underlying physiologic differences that alter the timing of events. The study was successfully planned and the results were presented well; thanks to the authors for their contribution. It has long been known that circadian rhythm plays a pivotal role in many biologic phenomena, including secretion of hormones and activities of the nervous system, and it has also been noted to occur in the incidences of certain cardiovascular events. Circadian variation for the onset of STEMI has been well investigated in many studies, and an early morning peak has been reported frequently. This early morning peak is often described with the changes in autonomic nervous system activity, blood fibrinolytic activity, platelet aggregability, activity of hemostasis, endothelial function, and coronary tone during the daily cycle, especially in the early morning hours.2-5 However, it is a well-known fact that different regions of the world have different circadian variations with regard to cardiovascular diseases. Studies showing the early morning peak of the onset of STEMI are very common and often come from Western populations. Furthermore, other studies that examined the circadian variation of STEMI in different population cohorts found that onset of STEMI happened between midnight and noon in British Caucasians and Indo-Asians,6 between noon and midnight in a Mediterranean Caucasian6 and Bulgarian cohort,7 between midnight and morning in a Chinese cohort,8 and with afternoon predominance in a Turkish population.9 Environmental and genetic background, customs, education, socioeconomic status, sociocultural habits, physical activity level, working hours (night people or morning people), and eating and sleeping habits might be possible underlying causes of ethnic disparities in cardiovascular risk factor profiles in different populations and should be evaluated. With respect to the effect of circadian variation in outcomes of cardiovascular disease, Khan et al10 examined the risk of cardiovascular disease outcomes among South Asian, Chinese, and white patients, and they assumed that South Asian and Chinese patients had a lower risk of death and of developing cardiovascular outcomes compared to whites. In their study, Hulten et al11 aimed to predict all-cause mortality and nonfatal myocardial infarction among Caucasian, African, and East Asian ethnicities, and found that compared to other ethnicities, East Asians had fewer events than expected. Wong et al12 showed that among the 3 ethnic groups (Malay, Chinese, and Indian), Indians had the highest risk of developing premature acute myocardial infarction. Additionally, circadian variation at the time of onset of chest pain in patients with STEMI may be different regarding infarction site in different population cohorts.13, 14 Circadian variation of STEMI might not be equally effective throughout the world. Ethnic disparities may be partly responsible for cardiovascular risk prevalence and outcomes of STEMI. Thus, instead of the term circadian rhythm, it might be more accurate to use the term population rhythm. Further large-scale clinical studies are needed to analyze the underlying pathophysiological mechanisms causing those ethnic disparities in the chronobiology of STEMI. Murat Celik, MD Baris Bugan, MD Emre Yalcinkaya, MD Uygar Cagdas Yuksel, MD Turgay Celik, MD Department of Cardiology, School of Medicine Gulhane Military Medical Academy Ankara, Turkey