UNSTABLE ANGINA

• Acute coronary artery syndromes comprise myocardial infarction and unstable angina, and are currently distinguished by history, ECG and presence or absence of cardiac biomarkers of myocardial injury. The history is important and severe disease can be present even without elevation of cardiac biomarkers of myocardial injury

Unstable angina is:

• onset of frequent attacks of angina for the first time, or
• sudden worsening of previously stable angina without change in medical treatment, or
• recurrent angina at rest

Symptoms and signs

• Central chest pain/tightness or discomfort (pain can also occur in arms, shoulders, throat, jaw, teeth, back or upper abdomen)
• Breathlessness

Investigations

• ECG on admission, during further episodes of chest pain, and 24 hr after admission
• ST segment depression occurring only during pain suggests myocardial ischaemia (consider acute posterior infarction if seen in leads V1–3 only and slow to resolve; check V4R and V7–9)
• ST segment elevation occurring only during pain suggests coronary artery spasm (Prinzmetal angina) or acute infarction
• ST segment elevation that does not resolve rapidly after giving GTN suggests acute infarction – see Acute myocardial infarction
• subsequent occurrence of deep symmetrical T-wave inversion without Q waves suggests ischaemia or NSTEMI
• Locally available cardiac biomarkers
• FBC, INR, APTT U&E
• Random cholesterol
• Random glucose and HbA_1c

Cardiac biomarkers

• Raised markers signify myocardial infarction, not unstable angina
• A raised troponin I concentration can suggest myocardial necrosis but can also occur in a number of other conditions:
• auto-immune disease
• congestive cardiac failure
• critical illness
• dilated cardiomyopathy
• extreme physical effort
• hypertension
• hypothyroidism
• multiple injury
• myocarditis
• pericarditis
• pneumonia
• pulmonary embolism
• renal failure
• sepsis/septic shock
• subarachnoid haemorrhage
• tachyarrythmias
• vasculitis

Notes on clinical interpretation of troponin I results

• Two serial results <40 ng/L indicate a low risk of myocardial necrosis
• A rise or fall in troponin I of 20% reflects a potentially significant change. The greater the magnitude of change between 2 results, the greater the likelihood of acute myocardial infarction (AMI)
• Troponin I is a marker of myocardial necrosis and not a specific marker of AMI. Always interpret results in conjunction with clinical history and ECG findings
• A stable elevation in troponin I indicates chronic structural heart disease. All troponin I results ≥40 ng/L are important and predict an adverse outcome; it is therefore important to determine the cause
• Troponin is a tool to assist in diagnosis. Other findings and clinical judgement must be used when determining the cause of acute chest pain

Differential diagnosis

Chest pain with possible ECG changes

• Pulmonary embolism
• Aortic valve disease
• Hypertrophic cardiomyopathy

Chest pain where ECG changes unlikely

• Biliary colic
• Peptic ulcer
• Oesophageal pain
• Musculoskeletal pain
• Mitral valve prolapse

• Aspirin 300 mg oral (chew and swallow)
• Glyceryl trinitrate spray to relieve symptoms: 400 microgram/metered dose spray 1–2 doses under tongue then close mouth
• Bisoprolol 2.5 mg oral daily (or diltiazem 60 mg oral 8-hrly if beta-blocker contraindicated)
• Prescribe fondaparinux 2.5 mg once daily by SC injection
• Risk of bleeding is increased in patients with low body weight (<50 kg), physiological frailty, severe liver or renal failure (eGFR <20 mL/min), thrombocytopenia or defective platelet function and following surgery, trauma or haemorrhagic stroke
• seek advice from appropriate team (e.g. cardiology, renal, liver or haematology)
• If troponin I raised and myocardial necrosis suspected, start clopidogrel (300 mg loading dose followed by 75 mg daily) whilst awaiting cardiology opinion – see Management of NSTEMI in Acute myocardial infarction

Referral to cardiology

• Admit all patients with unstable angina with dynamic ECG changes (ST or T wave inversion) under the care of the duty consultant cardiologist via CCU
• Consider patients with ST segment depression on ECG for urgent coronary angiography with a view to revascularisation. Contact on-call cardiology SpR/SHO
• Refer to on-call cardiology team for further management, patients who have:
• failed to respond to initial treatment
• ECG changes as above
• ongoing pain or ST segment depression/T-wave inversion
• positive cardiac biomarkers indicative of myocardial injury
• haemodynamic instability, arrhythmia
• early post-infarction unstable angina

• Aspirin 75 mg oral daily
• Continue beta-blocker (use diltiazem only if beta-blocker contraindicated)
• Atorvastatin 80 mg once daily for all acute coronary syndromes, unless history of CKD present when atorvastatin 20 mg once daily is used

If responding:

• After 48 hr, if pain controlled, substitute isosorbide mononitrate SR 60 mg each morning for GTN spray (to minimise possibility of headache)

If not responding:

• GTN infusion – see Glyceryl trinitrate
• Diamorphine 5 mg (2.5 mg in elderly or frail patients) by slow IV injection (1 mg/min)
• Metoclopramide 10 mg IV over 1–2 min (5 mg in young adults 15–19 yr <60 kg); allow ≥8 hr before repeating
• If ECG changes or markers of myocardial injury suggest acute infarction – see Acute myocardial infarction
• Consider patients who fail to settle or whose GTN infusion cannot be withdrawn for urgent coronary angiography with a view to revascularisation. Contact on-call cardiology SpR/SHO

• Hourly pulse and BP during GTN infusion until stable, then 4-hrly
• Repeat ECG after 24 hr

• Discharge patients if pain has settled, if ECG had no dynamic changes and if markers of myocardial injury did not become abnormal
• Patients should be fully mobile and be able to climb stairs (assuming no other handicap precludes this)
• Patients with ongoing chest pain or dynamic ECG changes during their admission – refer to cardiology
• Positive troponin in the context of typical chest pain and dynamic ECG changes constitutes myocardial infarction in most cases – refer to cardiology
• Reconsider diagnosis and investigate further if appropriate
• If diagnosis of cardiac chest pain speculative, order an exercise test directly under admitting consultant rather than through a cardiologist
• If no alternative diagnosis more likely than unstable angina:
• continue aspirin, and beta-blocker or diltiazem (convert to equivalent once daily dose), statin and isosorbide mononitrate SR. Ensure GTN 400 microgram spray for sublingual use has been prescribed TTO and patient has been counselled on use
• give dietary advice to all patients
• review and address risk factors (smoking, hypertension, hyperlipidaemia, diabetes, obesity)
• if patient suitable for revascularisation, refer to cardiologist for further evaluation by stress testing. If patient able to perform exercise test and has no clinical signs suggestive of aortic stenosis or hypertrophic cardiomyopathy, request exercise ECG testing at the same time as an outpatient appointment