Unstable Angina

Myocardial ischaemia at rest or on minimal exertion without detectable troponin rise (with high sensitivity assays, true unstable angina is now uncommon).

• Mechanism: fissured or eroded coronary plaque with transient or partial thrombosis, or dynamic obstruction from spasm, causing reduced flow without necrosis.
• Risk of death or infarction without treatment is about 5 to 10% within 30 days.

• Three patterns: rest angina lasting more than 20 minutes, new onset angina limiting ordinary activity, and crescendo angina (more frequent, longer, or at lower thresholds).
• Pain is relieved slowly or incompletely by nitrates. Associated sweating, dyspnoea, nausea.
• Examination is usually normal. Look for anaemia, thyrotoxicosis, valve disease and uncontrolled hypertension as precipitants.
• Differential diagnosis: myocardial infarction, pericarditis, aortic dissection, pulmonary embolism, oesophageal spasm, aortic stenosis, hypertrophic cardiomyopathy, anaemia driven angina.
• Complications: progression to infarction, arrhythmia, heart failure, sudden death.

• Resting ECG: transient ST depression, T-wave inversion, or normal. Repeat during pain.
• Serial high sensitivity troponin at 0 and 1 to 3 hours is negative. A rise indicates myocardial infarction.
• Echocardiography, full blood count, thyroid function, glucose, lipids, renal function.
• Pain free low risk patients: exercise ECG or stress imaging after at least 12 to 24 hours without pain, or coronary CT angiography.

• Aspirin 300 mg once then 75 to 100 mg daily.
• Clopidogrel 300 to 600 mg load then 75 mg daily for intermediate and high risk patients (ticagrelor 180 mg then 90 mg twice daily if an invasive strategy is planned).
• Fondaparinux 2.5 mg SC daily (creatinine clearance greater than 20 mL/min), or enoxaparin 1 mg/kg SC 12-hourly (once daily if clearance is less than 30 mL/min).
• Glyceryl trinitrate 0.4 mg sublingual up to 3 doses, then IV 5 to 10 micrograms/min titrated to relief if pain persists. Avoid with systolic BP less than 90 mmHg, right ventricular infarction, or phosphodiesterase-5 inhibitor use within 24 to 48 hours.
• Bisoprolol 2.5 to 10 mg daily or metoprolol 25 to 50 mg 6 to 12-hourly, avoided in bradycardia, heart block, decompensated heart failure and severe asthma. If beta blockers are contraindicated, use diltiazem 60 mg three times daily (avoid with reduced ejection fraction).
• Atorvastatin 80 mg daily.
• Angiography within 24 to 72 hours for intermediate and high risk patients, immediately for refractory pain or instability. Revascularise by PCI or bypass depending on anatomy.
• Low risk patients with negative testing: discharge on aspirin, statin, beta blocker and sublingual glyceryl trinitrate with outpatient review.
• Special groups: elderly and renally impaired patients need reduced enoxaparin dosing and careful contrast use; women and diabetics need a lower threshold for investigation because presentation is often atypical.
• Red flags: pain lasting more than 20 minutes despite treatment, haemodynamic instability, ventricular arrhythmia, heart failure.
• Follow up at 1 to 2 weeks, then lipid and blood pressure control and risk factor modification (smoking cessation, glycaemic control, weight, exercise).