Acute coronary syndrome
Acute coronary syndrome (ACS) encompasses ischaemic cardiac chest pain of recent origin. It includes the following:
¬∑ Unstable angina describes clinical states between stable angina and acute myocardial infarction. Unstable angina is considered to be present in patients with ischaemic chest pain and symptoms suggestive of ACS without elevation of markers of cardiac damage. It includes angina at rest lasting more than 20 minutes, crescendo angina and angina occurring more than 24 hours after an acute myocardial infarction.
¬∑ Non-ST elevation myocardial infarction (previously known as non-Q wave MI) differs primarily in that the myocardial ischaemia is severe enough to cause myocardial damage sufficient to produce a detectable rise in markers of cardiac damage (troponins and creatine kinase).
¬∑ An acute, evolving or recent myocardial infarction is defined as a rise and fall of biochemical markers of myocardial damage (e.g. troponin or CK-MB) with at least one of the following:
- Ischaemic symptoms.
- Development of pathologic Q waves on the ECG.
- ECG changes indicative of ischaemia (ST segment elevation or depression).
- Following coronary artery intervention (e.g. angioplasty).
As with stable angina, the underlying pathological lesion is the atheromatous plaque. In ACS there is fissuring of an atheromatous plaque, which initiates thrombosis with a subsequent risk of total occlusion of the vessel. Eccentric plaques with a lipidrich morphology are at greatest risk of fissuring. Over the course of minutes, hours or days the plaque may fissure, thrombose over and reseal several times, causing recurrent episodes of pain at rest or markedly reduced exercise tolerance. Depending on the severity and duration of occlusion, the vessel affected and the presence of any collateral blood supply, this process may result in unstable angina, NSTEMI or myocardial infarction with ST elevation.
Patients present with severe ischaemic chest pain, which is identical to that of angina pectoris (central crushing chest pain, radiating to jaw and left arm) but occurs at rest or is provoked more easily, persists for longer and often fails to respond to medical treatment. Patients require emergency assessment and investigation to allow rapid thrombolytic therapy for those with an acute myocardial infarction with ST elevation. It is essential to identify risk factors for and previous history of ischaemic heart disease.
The initial emergency investigation is a 12-lead ECG. If there is ST segment elevation or new left bundle branch block, the diagnosis is acute myocardial infarction (STEMI,). If there is no ST segment elevation, the patient may have unstable angina or NSTEMI (see below).