Acute coronary syndrome (ACS) refers to a spectrum of acute myocardial ischaemia and/or infarction. Classically ACS has been divided into three clinical categories according to the presence or absence of ST-segment elevation on the initial ECG, together with measurement of myocardial biomarkers, such as troponin or creatine kinase. In ST-elevation myocardial infarction (STEMI) the ECG shows persistent ST-segment elevation in two or more anatomically contiguous leads. Unstable angina and non-ST-elevation myocardial infarction (NSTEMI) represent a continuum of pathology, differing mainly by the presence of markers of myocardial damage in NSTEMI. Therefore some guidelines have grouped unstable angina and NSTEMI as 'non-ST-elevation acute coronary syndromes'.
Unstable angina (UA) is an acute coronary syndrome that is defined by the absence of biochemical evidence of myocardial damage. The clinical features include prolonged (>20 minutes) angina at rest; new onset of severe angina; angina that is increasing in frequency, longer in duration, or lower in threshold; or angina that occurs after a recent episode of myocardial infarction. The ECG typically shows ST-segment depression and T-wave inversion, but may be normal. The early management of patients with suspected UA is focused on initial interventions and triage according to the presumptive diagnosis. When the cardiac biomarkers are available, a diagnosis of UA is established if there is no elevation in creatine kinase-MB or troponin. However, with the availability of increasingly sensitive markers, a diagnosis of UA has become less common.
Non-ST-elevation myocardial infarction (NSTEMI) is an acute ischaemic event causing myocyte necrosis. The ECG may show ST-segment depression, transient ST-segment elevation, or T-wave inversion; however, it may also be normal or show non-specific changes. The distinction from unstable angina (UA) is based on cardiac biomarkers; these are elevated at presentation or after several hours in NSTEMI, but are normal on serial measurement in UA. Treatment is directed towards relief of ischaemia, prevention of further thrombosis or embolism, and stabilisation of haemodynamic status, followed by early risk stratification for further treatment.
ST-elevation myocardial infarction (STEMI) is suspected when a patient presents with a consistent clinical history and the ECG shows persistent (>20 minutes) ST-segment elevation in two or more anatomically contiguous leads, or new left bundle branch block. Cardiac biomarkers are elevated. Immediate and prompt revascularisation with percutaneous coronary intervention within 90 minutes of first presentation, or thrombolysis within 12 hours of symptom onset, can prevent or decrease myocardial damage and decrease morbidity and mortality by preventing acute complications. [ ]
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