Unstable angina

Overview

Unstable angina (UA) is one of three ACS presentations. The key distinguishing feature from NSTEMI is a negative troponin - both are managed identically acutely until the result returns.

Pathophysiology

•Plaque rupture → platelet aggregation → partial (non-occlusive) thrombus → ischaemia without myocyte necrosis → troponin negative
ACS spectrum
FeatureUANSTEMISTEMI
ThrombusPartial occlusionPartial occlusionComplete occlusion
TroponinNegativePositivePositive
ECGST depression / T inversion / normalST depression / T inversion / normalST elevation
Myocyte necrosisNoYesYes

Presentation

•Rest pain - central, heavy/tight, >20 minutes; or crescendo pattern breaking previous stable angina
•Radiation to jaw, left arm, or back
•Diaphoresis, dyspnoea, nausea, palpitations
•Atypical presentations (women, diabetics, elderly) - epigastric pain, fatigue, syncope, exertional dyspnoea
⚠️
A normal ECG does NOT exclude UA. GTN response does NOT confirm angina - oesophageal spasm also responds to nitrates.

Investigations

🥇 First-line

•12-lead ECG - ST depression, T-wave inversion, or normal
•High-sensitivity troponin (0h/1h or 0h/3h protocol) - negative in UA by definition; rules in NSTEMI if positive
•FBC, U&Es, lipids, glucose, CXR - baseline and risk factor assessment

🏆 Gold standard

•Coronary angiography - defines anatomy, guides revascularisation; timing guided by GRACE score

Differential Diagnosis

•NSTEMI - clinically identical; differentiated by positive high-sensitivity troponin
•STEMI - ST elevation on ECG; requires immediate reperfusion
•Aortic dissection - tearing pain to back, asymmetric BP, widened mediastinum; CT angiography
•PE - pleuritic pain, dyspnoea, tachycardia; CTPA or V/Q scan
•Oesophageal spasm - may mimic angina and respond to GTN; normal ECG and troponin

Management

Immediate
  1. 1Admit to hospital - medical emergency
  2. 212-lead ECG and IV access
  3. 3Continuous cardiac monitoring
  4. 4Aspirin 300 mg loading dose (oral)
  5. 5Ticagrelor 180 mg loading dose (preferred) OR clopidogrel 300 mg
  6. 6Fondaparinux 2.5 mg SC (anticoagulation) - unless high bleeding risk
  7. 7GTN sublingual/IV for symptom relief
  8. 8Morphine IV for refractory pain (use cautiously - may delay antiplatelet absorption)
Early
  1. 1Beta-blocker (e.g. bisoprolol) - rate/BP control if no contraindication
  2. 2Atorvastatin 80 mg
  3. 3GRACE score to risk stratify and guide timing of angiography
High risk (GRACE >140 or refractory symptoms)
Coronary angiography within 24 hours
Intermediate risk (GRACE 109-140)
Coronary angiography within 72 hours
Low risk (GRACE <109)
Non-invasive testing or elective angiography

Follow-up

•Cardiology outpatient review typically within 6-8 weeks post-procedure
•DVLA: no driving for 1 week after successful PCI (Group 1); 4 weeks if medically managed without revascularisation
🎯
UA and NSTEMI are clinically indistinguishable at presentation - you cannot separate them before the troponin result. Manage both identically until the result is known.

Complications

•Progression to NSTEMI/STEMI - thrombus propagates to complete occlusion
•Ventricular fibrillation and sudden cardiac death
•Acute heart failure / cardiogenic shock

Secondary Prevention

•DAPT: aspirin + ticagrelor (or clopidogrel) for 12 months, then lifelong aspirin alone
•Atorvastatin 80 mg indefinitely - target LDL-C <1.4 mmol/L or >50% reduction
•ACE inhibitor (or ARB if intolerant) - especially if reduced EF, diabetes, hypertension, or CKD
•Beta-blocker long term, especially if LV dysfunction
•Smoking cessation, BP target <130/80 mmHg, HbA1c optimisation, cardiac rehabilitation