Global Evolving Epidemiology, Natural History, and Treatment Trends of Myocardial Infarction

Introduction

Cardiovascular disease (CVD) was the single most important cause of death worldwide in 2013, when it was responsible for 17 million deaths and the loss of 329 million disability-adjusted life-years (DALYs). Of all causes of CVD, ischemic heart disease (IHD) remains the major contributor, accounting for half of all CVD-associated morbidity and mortality. IHD as measured by the Global Burden of Disease project is driven predominantly by acute myocardial infarction (MI) and, to a lesser extent, angina. Over the past two decades, while age-standardized IHD mortality in most world regions has decreased, the global burden of IHD has increased by 29 million DALYs (representing a 29% increase), owing in large part to overall population growth and to the aging of the population.

This chapter presents a review of the global burden of IHD, with an emphasis on low- and middle-income countries (LMICs). Also considered are the trends in management of acute MI. Concluding the chapter is a discussion of challenges that IHD poses to the global community and solutions that may help to reduce IHD morbidity and mortality.

Mortality and Morbidity Due to Myocardial Infarction

Age-adjusted IHD death rates in HICs are declining; however, the current high burden of IHD is primarily the consequence of deaths among 85% of the world’s population living in LMICs ( Figure 2-1 ). Globally, between 1990 and 2010, the age-adjusted death rate decreased by 21% from 131/100,000 to 106/100,000, but the number of IHD-associated deaths is increasing. In this same period, the number of deaths increased by 35%. Approximately a third of the increase in DALYs attributable to IHD is due to aging of the world population, and another 22% is due to population growth. Globally, the incidence of acute MI declined over the period 1990 to 2010, dropping from 222.7/100,000 to 195.3/100,000 for males and from 136.3/100,000 to 115.0/100,000 for females ( Figure 2-2 ). The greatest declines occurred in HICs, with only modest declines in LMICs, whereas increases in acute MI incidence were observed in Eastern Europe ( Figure 2-3 ). Despite a meaningful decline in age-adjusted IHD deaths, the DALYs lost due to IHDs have decreased only marginally, by 0.6%, from 1895/100,000 to 1884/100,000.

The reduction in MI mortality appears to be a result of a reduction in both the age-adjusted MI incidence and the case-fatality rate. In a study of the four communities in the Atherosclerosis Risk in Communities (ARIC) Study in the United States, rates in both in-hospital and out-of-hospital mortality declined. Over the period 1987 to 2008, the age-adjusted MI incidence decreased in black and white men and in women, but at different rates. Adjusted for biomarkers, the rates of decline were 4.3%, 3.8%, 2.9%, and 1.5% among white men, white women, black women, and black men, respectively. Age-adjusted in-hospital deaths declined annually by an average of 7.2% for men and 6.9% for women, with most of the reductions coming in the later years (1997 to 2008) compared with the earlier time period (1987 to 1996). Out-of-hospital mortality also declined by 4.9% and 3.7% per year for men and women, respectively. The Kaiser Permanente Northern California health care system reported a 24% decline in MI incidence from 1999 to 2008. This reduction was almost entirely driven by reductions in ST-elevation MIs (STEMIs) from 133 per 100,000 person-years in 1999 to 50 per 100,000 person-years in 2008 ( Figure 2-4 ). Thirty-day mortality also declined, with an odds ratio of 0.76 on comparing 2008 rates to 1999 rates. Over a similar time period in the Worcestor, Massachusetts area, STEMI incidence declined by nearly 50%, with no significant change in that of non ST-elevation MI (NSTEMI). In England, the reduction in MI mortality appears to be split between reductions in MI incidence and in case-fatality rate. From 2000 to 2010, MI case-fatality rates dropped by approximately 3.6% and 4.2% annually, respectively, for men and women, and MI incidence declined by 4.8% and 4.5%, respectively, for men and women. Similarly, over a 25-year period (1984 to 2008) in a large Danish study of more than 234,000 patients with first-time MI, MI incidence declined by 48% and 37% for men and women, respectively, and 30-day mortality declined by greater than 50% in both men and women in the same time period ( Figure 2-5 ).

In addition to the decline in incidence and case-fatality rates over recent decades, the morbidity associated with MI also has changed. For example, patients with MI in Olmsted County, Minnesota, presented with lower severity of heart failure despite more comorbid conditions. Furthermore, the incidence of heart failure (HF) developing both early (within 7 days of MI) and late (8 days up to 5 years later) declined dramatically by 5.7% and 5.8%, respectively, in absolute terms over the time frame 1990 to 1996, compared with 2004 to 2010 (see Chapter 25 ). The entire decline was accounted for by a decreased frequency of HF associated with reduced ejection fraction, because no decline was observed in the risk of HF with preserved ejection fraction after MI. An analogous decline in HF during the index admission for MI also was seen in Worcester, Massachusetts, after 1991.

Variation in the Global Burden of Ischemic Heart Disease

Although global trends show a larger IHD burden in LMICs in comparison with HICs, significant variation in IHD burden is evident across the six LMIC regions, and among countries within a given region or World Bank income category. Described next are those regional variations in acute MI incidence and burden.

High-Income Countries

For the GBD 2010 Study, HICs were divided into five regions: Asia Pacific, High Income; Europe, Western; Australasia; North America, High Income; and Latin America, Southern. Among males in 2010, the regions from highest to lowest in terms of MI incidence per 100,000 were Latin America, Southern (194.47), North America (191.28), Western Europe (191.04), Australasia (185.21), and Asia Pacific, High Income (106.84). Among females the MI incidence rates were lower with the rate per 100,000 females in each region: Latin America, Southern (95.15), North America (98.91), Western Europe (88.24), Australasia (93.61), and Asia Pacific, High Income (50.77). In all regions the male-to-female ratio was approximately 2:1 ( Figure 2-6 ). All of these regions had declines of approximately 22% (Asia Pacific) to 40% (Europe, Western) from 1990 rates. The age-standardized loss in DALYs attributed to IHD decreased, with Japan, South Korea, and France reporting the lowest DALYs lost among high-income countries.