Quick answer: every patient with suspected acute coronary syndrome (ACS) needs a 12-lead ECG within 10 minutes and aspirin 300 mg. ST elevation means immediate reperfusion: primary PCI if the patient presents within 12 hours of symptom onset and PCI can be delivered within 120 minutes, otherwise fibrinolysis. If there is no ST elevation, high-sensitivity troponin is measured at presentation and repeated at 1, 2 or 3 hours depending on the local pathway. Confirmed NSTEMI is treated with fondaparinux and risk-scored with GRACE; a predicted 6-month mortality above 3% means angiography within 72 hours.
Chest pain is one of the most common ED presentations and ACS questions appear in every MRCEM sitting. Most test the timings, the troponin logic and who goes to the cath lab. This guide covers the essentials. In practice, always follow your local chest pain pathway.
The three diagnoses
- STEMI: ischaemic symptoms with persistent ST elevation or new left bundle branch block. The diagnosis is made on the ECG. Do not wait for troponin.
- NSTEMI: ischaemic symptoms with a rise or fall in troponin, at least one value above the 99th centile, and no persistent ST elevation.
- Unstable angina: ischaemic symptoms at rest or on minimal exertion with no troponin rise.
The first 10 minutes
- 12-lead ECG within 10 minutes of arrival, repeated if pain continues or changes.
- Aspirin 300 mg as soon as possible, unless there is a true allergy.
- Pain relief with GTN and, if needed, intravenous opioid.
- Oxygen only if saturations are below 94%, aiming for 94 to 98% (88 to 92% in patients at risk of hypercapnia).
- Think about the other killers: aortic dissection, pulmonary embolism, tension pneumothorax and oesophageal rupture.
STEMI on the ECG
ST elevation in two contiguous leads:
- 1 mm or more in the limb leads and most chest leads.
- In V2 to V3: 2 mm or more in men aged 40 and over, 2.5 mm or more in men under 40, and 1.5 mm or more in women.
A posterior MI shows ST depression in V1 to V3 with tall R waves. Record posterior leads V7 to V9, where 0.5 mm of ST elevation is significant.
STEMI reperfusion
| Situation | Management |
|---|---|
| Presents within 12 hours and primary PCI available within 120 minutes | Primary PCI |
| Presents within 12 hours and PCI not available within 120 minutes | Fibrinolysis with an antithrombin, then ECG at 60 to 90 minutes |
| Residual ST elevation after fibrinolysis | Immediate angiography with rescue PCI |
| Presents after 12 hours with ongoing ischaemia or cardiogenic shock | Angiography with PCI if indicated |
NICE recommends prasugrel with aspirin for patients having primary PCI. Ticagrelor or clopidogrel are alternatives, for example in patients already taking an oral anticoagulant.
High-sensitivity troponin pathways
High-sensitivity assays can measure troponin in most healthy people, which allows early rule-out. The principles are the same whichever assay your hospital uses:
- Single-sample rule-out: a very low troponin at presentation, at or near the limit of detection, rules out MI if pain began more than 3 hours earlier and the ECG is normal.
- Serial sampling: otherwise repeat at 1, 2 or 3 hours. A low value with no significant change rules out MI.
- Rule-in: a high value at presentation or a significant rise on the repeat sample.
- Observe zone: patients in between need a further sample and a senior decision.
For the ESC 0/1-hour pathway with high-sensitivity troponin T:
| Category | Troponin T |
|---|---|
| Rule out | Below 5 ng/L at 0 hours (pain over 3 hours), or below 12 ng/L with a change under 3 ng/L at 1 hour |
| Rule in | 52 ng/L or above at 0 hours, or a change of 5 ng/L or more at 1 hour |
| Observe | Everything else |
Cut-offs are assay-specific. Learn the principle, not just one set of numbers.
A raised troponin is not always an MI. Other causes include pulmonary embolism, myocarditis, sepsis, tachyarrhythmia, heart failure, chronic kidney disease and aortic dissection.
The HEART score
The HEART score is widely used in emergency departments to risk-stratify undifferentiated chest pain. It predicts major adverse cardiac events (MACE) at 6 weeks and helps identify patients who are safe for early discharge. It applies only once STEMI has been excluded on the ECG.
| Component | 0 points | 1 point | 2 points |
|---|---|---|---|
| History | Slightly suspicious | Moderately suspicious | Highly suspicious |
| ECG | Normal | Non-specific repolarisation changes, LBBB or LVH | Significant ST deviation |
| Age | Under 45 | 45 to 64 | 65 or over |
| Risk factors | None | 1 or 2 | 3 or more, or known atherosclerotic disease |
| Troponin | Normal | 1 to 3 times the upper limit | More than 3 times the upper limit |
Risk factors are hypertension, hypercholesterolaemia, diabetes, obesity (BMI over 30), smoking (current or stopped within 3 months) and a family history of premature coronary disease.
| Total score | Risk | 6-week MACE | Usual action |
|---|---|---|---|
| 0 to 3 | Low | About 1 to 2% | Consider early discharge with follow-up |
| 4 to 6 | Moderate | About 12 to 17% | Admit for observation and further testing |
| 7 to 10 | High | About 50 to 65% | Early invasive strategy |
HEART versus GRACE: the two scores answer different questions. HEART is applied at the front door to patients with possible ACS, to decide who can go home. GRACE is applied after NSTEMI or unstable angina is diagnosed, to predict 6-month mortality and decide the timing of angiography. NICE recommends GRACE for confirmed NSTEMI and unstable angina and does not specify HEART, although many UK departments build HEART into their chest pain pathways. The HEART Pathway combines a score of 0 to 3 with negative serial troponins.
NSTEMI and unstable angina
- Aspirin 300 mg, then continued long term.
- Fondaparinux, unless the patient has a high bleeding risk or is going for immediate angiography.
- Do not give a second antiplatelet until the diagnosis is confirmed.
- Calculate the GRACE score to predict 6-month mortality.
- Immediate angiography if clinically unstable: ongoing pain, haemodynamic instability, dynamic ECG changes or arrhythmia.
- Angiography within 72 hours if predicted 6-month mortality is above 3%.
- Conservative management may be considered at 3% or below, with ischaemia testing before discharge.
Common exam traps
- Waiting for troponin in STEMI: the ECG makes the diagnosis and reperfusion should not be delayed.
- Routine oxygen: only give it if the patient is hypoxic.
- One normal troponin soon after onset: it cannot rule out MI if pain started less than 3 hours ago.
- Missing a posterior MI: ST depression in V1 to V3 needs posterior leads.
- Assuming every troponin rise is ACS: look for a rise or fall and a clinical picture that fits.
- Forgetting dissection: check for tearing pain, pulse deficit or a wide mediastinum before anticoagulating.
Summary
- ECG within 10 minutes and aspirin 300 mg for all suspected ACS.
- STEMI: primary PCI if within 12 hours of onset and deliverable within 120 minutes; otherwise fibrinolysis.
- High-sensitivity troponin at 0 hours with a repeat at 1 to 3 hours; a very low single value rules out only if pain began over 3 hours ago.
- NSTEMI: fondaparinux and a GRACE score. Above 3% means angiography within 72 hours.
- Unstable patients go for immediate angiography.
Frequently asked questions
When is primary PCI indicated in STEMI?
When the patient presents within 12 hours of symptom onset and PCI can be delivered within 120 minutes of the time fibrinolysis could have been given.
Can a single troponin rule out MI?
Yes, if a high-sensitivity result is at or near the limit of detection, the ECG is normal and pain began more than 3 hours before the sample.
What GRACE score triggers early angiography in NSTEMI?
A predicted 6-month mortality above 3% means angiography within 72 hours of first admission.
Should all patients with chest pain receive oxygen?
No. Give oxygen only if saturations are below 94%.
What is the difference between the HEART and GRACE scores?
HEART risk-stratifies undifferentiated chest pain in the ED and identifies low-risk patients (0 to 3) for early discharge. GRACE predicts 6-month mortality in confirmed NSTEMI or unstable angina and guides the timing of angiography.
Next steps
Test yourself with our 20 free MRCEM SBA sample questions. For more, explore our Cardiology resources and the Cardiology course, or see the full question bank and mock tests in our membership plans.
Clinical content checked against NICE guideline NG185 (acute coronary syndromes) on 5 October 2026. This article is for exam preparation. In clinical practice, always follow your local chest pain pathway.