Acute Coronary Syndrome (Heart Attack): STEMI, NSTEMI and Unstable Angina

Acute coronary syndrome (ACS) is the umbrella term for conditions caused by a sudden reduction in blood flow to the heart muscle, usually due to rupture of an atherosclerotic plaque and clot formation in a coronary artery. It includes the condition commonly called a "heart attack". Rapid recognition saves heart muscle and lives.

Types of ACS

• ST-elevation myocardial infarction (STEMI) — complete blockage of a coronary artery; ST elevation on the ECG and raised troponin.
• Non-ST-elevation myocardial infarction (NSTEMI) — raised troponin without ST elevation; the ECG may show ST depression, T-wave inversion or be normal.
• Unstable angina — ischaemic chest pain at rest or worsening angina, without a rise in troponin.

Risk factors

• Smoking.
• Diabetes.
• Hypertension.
• High cholesterol.
• Obesity and physical inactivity.
• Family history of premature heart disease.
• Male sex and older age.
• Chronic kidney disease.

Clinical features

Typical pain is central, heavy, crushing or tight, lasting more than 15–20 minutes, often radiating to the left arm, jaw or neck, with sweating, nausea and breathlessness. Elderly patients, women and people with diabetes may present atypically — with breathlessness, fatigue, epigastric discomfort or even no pain ("silent" infarction).

Investigations

• 12-lead ECG within 10 minutes of arrival, repeated if pain continues.
• STEMI on ECG: new ST elevation in two or more anatomically contiguous leads, or certain STEMI-equivalent patterns. The leads involved suggest the territory, for example inferior (II, III, aVF) or anterior (V1–V4).
• High-sensitivity cardiac troponin, measured on arrival and repeated according to the local protocol.
• Other blood tests: full blood count, kidney function, electrolytes, glucose and lipids.
• Chest X-ray.
• Echocardiography to assess heart function.

Immediate management

Treatment must follow current local protocols and cardiology advice. Key principles:

• ABCDE assessment, continuous monitoring and IV access.
• Oxygen only if saturation is low (below about 94%).
• Analgesia, and nitrates for ongoing ischaemic pain if blood pressure allows.
• Aspirin loading dose, plus a second antiplatelet agent as per protocol.
• STEMI: urgent reperfusion. Primary percutaneous coronary intervention (PCI) is preferred if it can be delivered promptly (generally within 120 minutes of diagnosis); otherwise fibrinolysis, if there are no contraindications.
• NSTEMI / unstable angina: antiplatelet therapy and anticoagulation, risk stratification (for example the GRACE score), and coronary angiography with timing based on risk.

Secondary prevention

• Dual antiplatelet therapy, usually for 12 months.
• High-intensity statin.
• Beta-blocker.
• ACE inhibitor (or ARB).
• Smoking cessation.
• Cardiac rehabilitation.
• Control of blood pressure, diabetes and weight.

Complications

• Arrhythmias, including ventricular fibrillation (the main cause of early death).
• Heart failure and cardiogenic shock.
• Mechanical complications: papillary muscle rupture with mitral regurgitation, ventricular septal rupture, and free wall rupture with tamponade.
• Pericarditis, including Dressler syndrome weeks later.
• Left ventricular aneurysm.
• Thromboembolism.

Exam pearls

• Time is muscle: always mention the ECG within 10 minutes and the reperfusion time targets.
• Inferior STEMI may involve the right ventricle. Check right-sided leads and avoid nitrates if the patient is hypotensive.
• A new pansystolic murmur after MI suggests papillary muscle rupture or a ventricular septal defect.

See also our articles Approach to Acute Chest Pain and Reading an ECG, and the cardiology part of the Medicine Companion.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. ST elevation in leads II, III and aVF indicates which territory?

   1. Lateral
   2. Inferior
   3. Septal
   4. Posterior only
   5. Anterior
   Show answer

   Answer: B. Inferior
   II, III and aVF look at the inferior wall, usually supplied by the right coronary artery.

2. Which ACS has a raised troponin but no ST elevation?

   1. Unstable angina
   2. Stable angina
   3. Prinzmetal angina only
   4. STEMI
   5. NSTEMI
   Show answer

   Answer: E. NSTEMI
   NSTEMI: myocardial necrosis (raised troponin) without ST elevation. Unstable angina has no troponin rise.

3. When is oxygen indicated in suspected ACS?

   1. Always at high flow
   2. Only if oxygen saturation is low (about below 94%)
   3. Never
   4. Only in women
   5. Only after PCI
   Show answer

   Answer: B. Only if oxygen saturation is low (about below 94%)
   Routine oxygen in normoxic patients gives no benefit; give it for hypoxaemia.

4. A patient with inferior STEMI is hypotensive with clear lungs and a raised JVP. Which drug should be avoided?

   1. Heparin
   2. Aspirin
   3. IV fluids
   4. Nitrates
   5. Analgesia
   Show answer

   Answer: D. Nitrates
   This suggests right ventricular infarction, which is preload-dependent; nitrates can cause severe hypotension.

5. Five days after MI, a patient develops a new pansystolic murmur and acute pulmonary oedema. Likely cause?

   1. Left ventricular aneurysm
   2. Pericarditis
   3. Papillary muscle rupture or ventricular septal rupture
   4. Dressler syndrome
   5. Atrial fibrillation
   Show answer

   Answer: C. Papillary muscle rupture or ventricular septal rupture
   A new pansystolic murmur after MI suggests acute mitral regurgitation (papillary muscle rupture) or a VSD — both surgical emergencies.

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Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.