Acute coronary syndrome

Platelet activation in acute coronary syndrome

Acute coronary syndrome (ACS) refers to a spectrum of coronary ischaemic events arising from partial or complete occlusion of an epicardial coronary artery. ACS is the most severe manifestation of coronary artery disease (CAD)¹, presenting as unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI) or ST-segment elevation myocardial infarction (STEMI)^1,2; unstable angina and NSTEMI are grouped together as non-ST-segment elevation acute coronary syndrome (NSTE-ACS). The precipitating event in ACS is usually rupture of an atherosclerotic plaque in the coronary vessel, which leads to platelet activation and formation of a thrombus that reduces or blocks blood flow to the heart. ACS is one of the most common causes of morbidity and mortality worldwide, accounting for 1.8 million deaths per year^1,3,4. NSTE-ACS in particular is a leading cause of emergency hospitalisations⁵ and is increasing in incidence relative to STEMI⁴; in 2015 NSTEMI accounted for more than half of all cases of myocardial infarction⁴.

Diagnostic challenges in acute coronary syndrome

Acute chest pain, usually described as crushing or heavy pain, is a hallmark of ACS and signals a medical emergency. Chest pain is the second most common reason for presentation to the emergency department^6,7 but most cases can be attributed to non-cardiac causes that do not require emergency treatment⁶. Given that ACS-induced chest pain is potentially fatal, accurate diagnosis and timely initiation of treatment are critical. Chest pain is not always present, however, and many patients, particularly women and those with diabetes, have vague ACS symptoms, including light-headedness, nausea, difficulty breathing or isolated jaw or left arm pain. These patients are at a high risk of underdiagnosis and suspicion of cardiac causes is warranted⁷. Careful history-taking and physical examination are essential in the evaluation of patients with symptoms suggestive of ACS⁶. Rapid rule-in rule-out algorithms have also been developed to expedite triage of patients and promptly commence treatment for those identified as having ACS or at risk of developing ACS within 30 days^1,8.

How is acute coronary syndrome diagnosed?

A resting 12-lead electrocardiogram (ECG) should be taken to assess for ACS, ideally at first medical contact or within 10 minutes of presentation to the emergency department^4,6,9 as this differentiates between NSTE-ACS and STEMI. Serial blood sampling for measurement of cardiac biomarkers is also mandatory for diagnosis and risk assessment of patients with suspected NSTE-ACS⁹. Current guidelines favour cardiac troponins as the biomarker of choice as they are more sensitive and more specific than other available biomarkers of myocardial infarction⁹.

What do current guidelines recommend for management of acute coronary syndrome?

Management of ACS consists of pharmacological treatment and, where indicated, reperfusion therapy with percutaneous coronary intervention (PCI), fibrinolysis or coronary artery bypass grafting (CABG). Antiplatelet therapy is the mainstay of pharmacological treatment for ACS; all guidelines agree that aspirin should be given as soon as possible to patients with suspected ACS, unless contraindicated^4,9–11. Dual antiplatelet therapy (DAPT), where a P2Y₁₂ inhibitor is added to aspirin treatment, is recommended for patients with a confirmed diagnosis of ACS. DAPT consists of an initial loading dose followed by a maintenance dose. The standard duration of DAPT is 12 months, although this can be shortened if the risk of bleeding outweighs ischaemic risk, or extended in the reverse scenario^12,13. In addition to antiplatelet therapy, pharmacological treatment for ACS includes glycoprotein IIb/IIIa antagonists, beta-blockers, statins, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). In the acute setting, when patients with ACS present to the emergency department, nitrates and opioids may also be administered to relieve breathlessness, anxiety and pain^4,9.