Acute coronary syndrome (ACS) is an umbrella term for a group of clinical conditions that cause reduced blood flow to the myocardial tissue, resulting in ischaemia. These patients present with a similar clinical picture, with the main symptom being chest pain or discomfort. 

The predominant underlying pathology of ACS is coronary artery disease due to atherosclerosis. Atherosclerosis results from the build up of cholesterol-containing deposits (atheroma/plaque) in the blood vessels that supply the heart (coronary arteries) causing a narrowing and hardening of these vessels and a reduction in blood flow. This can result in chest pain and breathlessness. Atherosclerotic plaques can then erode or erupt, causing bleeding, vasoconstriction and thrombosis formation and occlusion of the vessel.

• Acute sustained chest pain

• Acute ST-segment elevation or new left bundle branch block (LBBB) present on 12-lead ECG

This presentation indicates ongoing myocardial damage likely from an acute, complete block of a coronary artery. Urgent reperfusion is required to prevent further myocardial damage by either primary percutaneous coronary intervention (PCI) or fibrinolytic therapy.

• Acute sustained chest pain

• ECG may be normal, show ST-segment depression or non-specific abnormalities

• Raised cardiac enzymes such as troponin indicate cardiac damage has occurred

This presentation indicates there has likely been a partial or intermittent occlusion causing myocardial damage.

Angina refers to chest pain that is provoked by exertion that improves when the exertion stops. It becomes defined as unstable angina if these episodes occur:

• with increasing frequency over a few days, with less provocation.

• occur unpredictably without provocation.

• with prolonged and unprovoked chest pain, without definite ECG changes and cardiac markers indicating myocardial infarction. i.e. troponin may be normal.

The management of NSTEMI and unstable Angina is similar. Unlike STEMI, there is no evidence that these patients would benefit from early reperfusion with primary PCI or fibrinolysis. Instead this group of patients should be assessed, based on risk of future events, as to whether they may benefit from PCI, coronary artery bypass surgery or medical treatment.