CHAPTER 36: DEFINITIONS OF ACUTE CORONARY SYNDROMES

INTRODUCTION: EPIDEMIOLOGY AND PUBLIC HEALTH IMPACT

Coronary artery disease (CAD) accounts for 30% of all global deaths, representing the single most common cause of adult mortality and equivalent to the combined number of deaths caused by nutritional deficiencies, infectious diseases, and maternal/perinatal complications.^1,2 Recent growth in the global burden of cardiovascular disease (CVD) is primary attributable to the rising incidence across low- and middle-income countries.³ Among European member states of the World Health Organization (WHO), for example, CVD death rates for men and women were highest in the Russian Federation and Uzbekistan, respectively, whereas risk was lowest in France and Israel.⁴ Conversely, in the United States, over 15 million Americans, or 6.2% of the adult population, have coronary heart disease (CHD), with a myocardial infarction (MI) occurring once every 43 seconds.⁵ Health care resource utilization as a result of CHD is significant, as over 1.1 million hospital discharges in 2010 listed MI or unstable angina (UA) as a primary or secondary diagnosis.⁵ Health care expenditures are also substantial; costs for MI and CHD were approximately $11 billion and $10 billion, respectively, in 2011.⁶ These diagnoses constitute two of the most expensive discharge diagnoses and are expected to increase by 100% by 2030.

Despite these sobering statistics, important strides in the diagnosis, prevention, and management of CHD have occurred over the past 50 years. In the United States, for example, several population-based studies have shown a reduction in both the incidence and case fatality rate associated with MI.^7,8 These favorable trends have been attributed to greater utilization of evidence-based therapies and improvements in control and burden of risk factors.⁹ Concordant changes in the epidemiology of acute coronary syndromes (ACS) have occurred over the past 10 years as a result of changing demographics and updated definitions of MI. In this chapter, we focus primarily on the definition and diagnostic criteria for ACS.

ACUTE CORONARY SYNDROMES

The term ACS is a unifying construct representing a pathophysiologic and clinical spectrum culminating in acute myocardial ischemia. This is usually, but not always, caused by atherosclerotic plaque rupture, fissuring, erosion, or a combination with superimposed intracoronary thrombosis and is associated with an increased risk of myonecrosis and cardiac death.¹⁰ ACS encompasses UA and ST-segment elevation MI (STEMI) or acute non–ST-segment elevation MI (NSTEMI). Distinguishing these presentations is predicated on the presence or absence of myocyte necrosis coupled with the electrocardiographic tracing at the time of symptoms. ACS without myocardial necrosis is defined as UA, whereas myocardial necrosis is a necessary, but not sufficient, component of either STEMI or NSTEMI, respectively. Recognizing a patient with ACS is important because the diagnosis triggers both triage and management. Those deemed to have an ACS in the emergency department should be triaged immediately to an area with continuous electrocardiographic monitoring and defibrillation capability. Patients with suspected ACS should be managed ...