Acute Coronary Symptoms

Definitions and Epidemiology

Definitions

Acute coronary syndrome (ACS) is a broad term that includes the diagnoses of unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI)and ST-segment elevation myocardial infarction (STEMI).¹ UA and STEMI are sometimes referred to collectively as non-ST-segment elevation ACS (NSTE-ACS).²

In all cases of ACS, there is disruption of the blood supply to a part of the myocardium, usually due to the development of an occlusive thrombus in a coronary artery. Loss of tissue oxygenation leads to myocardial dysfunction,the consequences of which may include the development of arrhythmias andacute heart failure.

The presentation and diagnosis of ACS will be discussed in a separate section. Briefly, however, the classic symptom of ACS is chest pain, which is frequently described as retrosternal pressure or heaviness, that may radiate to the jaw,neck or arms.² Other symptoms include diaphoresis, nausea, dyspnoea,abdominal pain and syncope.²

The term ‘myocardial infarction’ applies when there is biochemical evidence of myocardial necrosis (e.g. raised cardiac enzymes) in combination with symptoms and signs consistent with myocardial ischaemia.³ STEMI is characterised by persistent ST-segment elevation on ECG.⁴ In STEMI, there is usually complete occlusion of a coronary artery,² and the infarcted zone is often transmural.¹ In contrast, the ECG in patients with NSTEMI does not show ST-segment elevation; more typically, there is ST-segment depression or T-wave inversion, which indicates that the infarct zone is limited to the subendocardium.^2,5

UA is distinguished from NSTEMI by the absence of elevated troponin levels on repeated testing,² which suggests that myocardial necrosis may not have occurred to a significant extent.

The spectrum of ACS is shown in Figure 1.

Epidemiology

The incidence and prevalence of MI are difficult to determine accurately, partly because MI can be clinically silent (i.e. the usual symptoms and signs are absent) and because the diagnosis of NSTE-ACS can be difficult to make.²

There is no centralised European database for the collation and analysis of statistics on MI.² According to the European Society of Cardiology, however, the incidence of hospitalisation for NSTE-ACS is approximately 3 per 1000 inhabitants per year; the incidence of NSTE-ACS is higher than that of STEMI.²

Among hospitalised patients, in-hospital mortality is higher for STEMI than NSTEMI (8% vs 5%, respectively), but mortality at 6 months is similar in both groups (12% vs 13%, respectively).^6,7 In-hospital mortality has fallen from approximately 25-30% in the 1960s to under 10% today,^4,7 but community studies have shown that mortality within the first hours of symptom onset has changed little in recent years.⁴ A high proportion of deaths from presumed ACS and MI occur within the first 2 hours.⁴

Figure 1. The spectrum of acute coronary syndromes (ACS).

Adapted from Bassand et al. 2007²