Blood pressure, heart rate, and double product (2017)

Despite the advances in therapies for cardiovascular disease over the decades, risk factor control [including blood pressure (BP) control] remains suboptimal. High BP is considered the leading single risk factor for global burden of disease [1]. In fact, uncontrolled hypertension has been linked to increased long-term all-cause mortality [2]. It has been estimated that in 2015, almost 874 million adults worldwide had SBP at least 140 mmHg [3]. In contrast, excessively lowering the DBP in those with controlled SBP has been linked to increased adverse events, particularly in those with coronary artery disease [4–6]. Furthermore, an elevated resting heart rate (HR) has been demonstrated to be an independent risk factor for cardiovascular disease in healthy men and women [7]. In countries with a relatively long life expectancy, like Japan, one would anticipate that these risk factors would be better controlled compared with other countries. In this issue of the Journal, Asayama et al.[8] provide data regarding automated BP, HR, and double product measurements from a geographically pooled Japanese cohort of over 100 000 participants in an ambulatory setting. Even in the country with the longest life expectancy on the planet, average SBP rises with increasing age among untreated individuals (i.e., those not on antihypertensive treatment). In addition, average SBP for treated participants was suboptimal (∼140 mmHg), and only 25% of the treated participants aged less than 65 years had an SBP less than 130 mmHg. Suboptimal SBP control remains a global concern. For example, an analysis of the NCDR PINNACLE registry (an outpatient registry for cardiovascular patients in the United States) found that only approximately two-thirds of the patients achieved an SBP less than 140 mmHg [9]. The SPRINT trial found that a lower SBP goal (i.e. <120 mmHg) as opposed to less than 140 mmHg that was associated with a lower risk of cardiovascular events as well as all-cause mortality [10]. Interestingly, the Japanese population, with the longest life expectancy, has SBP control that is far from optimal. These data indicate that other risk factors, in addition to SBP control, could be implicated in the higher burden of cardiovascular events in the Western countries as opposed to Japan, such as the difference in dietary habits (i.e. fish and lean meat in Japan compared with red meats in the Western countries), activity status, and smoking. A lower DBP is considered an index of increased arterial stiffness; thus, it would be expected that DBP would decrease as the population ages. Moreover, the combination of a lower DBP and higher SBP has been linked to increased cardiovascular mortality [11]. In the current study, the authors found that DBP plateaued around age 60 years in individuals not receiving antihypertensive treatment. High-income Asian Pacific countries (such as Japan) are considered to have among the lowest global rates for ischemic heart disease-related mortality [12]. Perhaps, the lower prevalence of atherosclerosis could explain why DBP levels reached their zenith in those aged 60 years. Another interesting finding was the increase in the double product (i.e. product of SBP and HR) with aging, even though HR did not differ across age groups. This increase in double product reflects a disproportionate increase in the SBP compared with HR, which accordingly would increase myocardial oxygen demand. Epidemiological data show that risk of diastolic heart failure rises with age [13]. Whether the increase in the double product and vulnerability to ischemia is an underlying pathophysiological mechanism for diastolic heart failure deserves further study. How to reconcile the findings of this study? Although this report included a large number of individuals from 34 prospective cohorts, these data were collected from 1999 to 2005 (i.e. >10 years ago), thus might not be a true representation for the current Japanese population. Moreover, given the cross-sectional study design, no causal inferences could be made. In addition, as the participants were enrolled from ambulatory settings, the participants in this study, especially the elderly patients, are likely to be the healthier rather than the sicker patients. Despite these limitations, this study provides important insights about BP, HR, and double product in Japan and suggests that further effort should be devoted to better SBP control. This remains a worldwide problem that deserves close attention. Even in patients who survived a myocardial infarction, a multicenter European registry suggested that the majority of patients had elevated BP (i.e., >140/90 mmHg) [14]. Counseling of these patients and highlighting the magnitude of this disease remains an important key. The variation in the pattern of DBP in this study compared with other parts of the world also deserves a closer look. Clearly, novel approaches are needed. For example, with the emerging field of intestinal microbiota and roles of gut dysbiosis and increased permeability in cardiovascular disease and hypertension [15], it is important to better understand if important differences exist in gut microbiota among Japanese compared with others. In summary, although the mortality of cardiovascular disease and hypertension has been decreasing over the past few decades, optimal BP control remains an important factor that deserves better control as well as new approaches, not only in Japan, but also globally. ACKNOWLEDGEMENTS C.J.P. receives support from the Gatorade Trust through funds distributed by the Department of Medicine, University of Florida; NIH NCATS – University of Florida Clinical and Translational Science UL1TR001427; and PCORnet-OneFlorida Clinical Research Consortium CDRN-1501-26692. Conflicts of interest There are no conflicts of interest.