Acute coronary syndrome (heart attack)
ECG within 10 minutes. STEMI: primary PCI if it can happen within 120 minutes, otherwise thrombolysis within 30 minutes of arrival. NSTEMI: antiplatelets, anticoagulation and risk-guided angiography.
A 46-year-old man with diabetes has had crushing central chest pain for 2 hours with sweating and vomiting. ECG: ST elevation of 3 mm in V1–V4. The nearest cath lab is 4 hours away by road. BP 128/80, pulse 96.
What do you do in the next 30 minutes?
- ECG within 10 minutesRepeat every 15–30 minutes while in pain. Defibrillator pads on.
- Aspirin 300 mg chewedUnless true allergy or suspected dissection.
- STEMI? Decide reperfusion nowPrimary PCI if it can happen within 120 minutes of diagnosis. Otherwise thrombolysis, aiming within 30 minutes of arrival.
- Second antiplatelet and anticoagulantClopidogrel or ticagrelor, plus enoxaparin or fondaparinux, per pathway.
- Pain reliefGTN if BP allows, IV morphine if needed. Oxygen only if SpO₂ below 94%.
- BloodsTroponin, CBC, creatinine, electrolytes, sugar, lipids, clotting.
- Look for complicationsLow BP, heart failure, arrhythmias, new murmur.
- Call cardiologyEarly, for every STEMI and every high-risk NSTEMI.
- ST elevation or a STEMI equivalent
- Low BP, cold and clammy
- Arrhythmia or heart block
- New loud murmur or sudden breathlessness
- Ongoing pain despite treatment
- Pain after thrombolysis
- STEMI equivalents: posterior MI, new LBBB with symptoms, de Winter, Wellens
- Right ventricular infarction
- Cardiogenic shock
- Mechanical complications: VSD, papillary muscle rupture, free wall rupture
- Aortic dissection mimicking MI
| ECG | Within 10 minutes of arrival |
| Primary PCI | If it can be done within 120 minutes of diagnosis |
| Thrombolysis | Within 30 minutes of arrival if PCI not possible in time, up to 12 hours from symptom onset. After the contraindication checklist |
| Aspirin | 300 mg chewed, then 75 mg daily |
| After thrombolysis | Repeat ECG at 60–90 minutes. Less than 50% ST resolution: rescue PCI |
Check every dose against a current drug reference and your hospital protocol.
On this page
What it is
An acute coronary syndrome (ACS) is a sudden reduction in blood flow to the heart muscle, usually from a clot on a ruptured cholesterol plaque in a coronary artery.
- ST elevation (or equivalent)
- The artery is usually completely blocked
- Needs reperfusion now
- No ST elevation
- Troponin rises
- Partial blockage
- No ST elevation
- Troponin normal
- Pain at rest or worsening pattern
Heart attacks happen at younger ages in South Asians. A 35-year-old smoker with diabetes is not "too young". Women, diabetics and the elderly often have atypical symptoms: breathlessness, tiredness, epigastric pain or no pain.
Reading the ECG for STEMI
New ST elevation at the J point in two adjacent leads:
- At least 1 mm in limb leads and chest leads other than V2–V3.
- In V2–V3: at least 2 mm in men aged 40 or over, 2.5 mm in men under 40, 1.5 mm in women.
| Leads with ST elevation | Territory | Usual artery |
|---|---|---|
| II, III, aVF | Inferior | Right coronary (sometimes circumflex) |
| V1–V4 | Anterior and septal | Left anterior descending |
| I, aVL, V5–V6 | Lateral | Circumflex or diagonal |
| ST depression V1–V3 with tall R waves | Posterior | Circumflex or right coronary. Do V7–V9 |
- Inferior STEMI: do right-sided leads (V4R). ST elevation in V4R means right ventricular infarction: avoid GTN and give fluid for low BP.
- New LBBB with ongoing ischaemic symptoms: treat as STEMI.
- De Winter pattern (upsloping ST depression with tall T waves in V1–V6) and Wellens (deep T inversion in V2–V3 after pain): high-risk LAD disease. Call cardiology.
STEMI: reperfusion
- Call the cath lab now
- Aspirin plus ticagrelor or clopidogrel
- Transfer immediately
- Thrombolysis within 30 minutes of arrival, after the checklist
- Then transfer for angiography within 2–24 hours
- Usually no thrombolysis
- PCI if ongoing pain, shock or arrhythmia
- Discuss with cardiology
Absolute: any previous brain haemorrhage; ischaemic stroke in the last 6 months; brain tumour or vascular malformation; major trauma, surgery or head injury in the last month; GI bleeding in the last month; known bleeding disorder; suspected aortic dissection; non-compressible punctures in the last 24 hours (for example lumbar puncture, liver biopsy).
Relative (senior decision): TIA in the last 6 months, oral anticoagulants, pregnancy or within a week after delivery, uncontrolled BP above 180/110, advanced liver disease, active peptic ulcer, traumatic or prolonged CPR, infective endocarditis.
- ECG at 60–90 minutesST elevation should fall by at least 50% and the pain should ease.
- Not resolvedFailed thrombolysis: rescue PCI. Call cardiology now.
- ResolvedTransfer for angiography within 2–24 hours.
- Watch for bleedingEspecially brain: new headache, confusion, weakness. Stop the infusion and CT head.
- Reperfusion arrhythmiasAccelerated idioventricular rhythm is common and usually harmless.
NSTEMI and unstable angina
- Risk assessment: your senior uses GRACE or a similar score. High risk (ongoing pain, unstable, arrhythmia, heart failure, dynamic ECG changes): angiography within 24 hours, immediately if unstable.
Pain, oxygen and other drugs
- Oxygen only if SpO₂ is below 94%.
- ACE inhibitor (for example ramipril) within 24–48 hours once BP and kidneys allow.
- Sugar: treat high sugar, avoid low sugar.
Complications
| Complication | Clues | Action |
|---|---|---|
| Cardiogenic shock | Low BP, cold, confused, little urine | Senior and cardiology now. Urgent PCI |
| Heart failure | Crackles, low SpO₂ | See Acute heart failure |
| VF or VT | Cardiac arrest or fast broad rhythm | Defibrillate. ALS |
| Heart block | Slow pulse, especially inferior MI | Atropine, pacing if unstable |
| Right ventricular infarction | Inferior MI, low BP, clear lungs, raised JVP | Fluids, avoid GTN |
| Mitral regurgitation (papillary rupture) | New murmur, sudden pulmonary oedema | Echo, cardiac surgery |
| Ventricular septal rupture | New loud murmur, shock | Echo, cardiac surgery |
| Pericarditis or Dressler's syndrome | Sharp pain days to weeks later, rub | Aspirin, senior advice |
Before discharge
- Dual antiplatelets for 12 months (aspirin plus clopidogrel or ticagrelor) unless a different plan is given. Stress: never stop them without asking the cardiologist, especially after a stent.
- Statin, beta-blocker, ACE inhibitor (and others if the heart is weak).
- Stop smoking, including huqqa and naswar. Diabetes and BP control.
- Cardiac rehabilitation and gradual return to activity.
- Sublingual GTN and what to do if pain returns.
Common mistakes
- Treating chest pain in a young man as "gas" without an ECG.
- Missing posterior MI (ST depression in V1–V3).
- Giving GTN to a right ventricular infarct with low BP.
- Thrombolysing tearing pain to the back (dissection).
- Waiting for troponin before treating a clear STEMI.
- Repeating streptokinase in a patient who had it within the last year.
Frequently asked questions
What is the door-to-needle time for thrombolysis in STEMI?
Thrombolysis should start within 30 minutes of arrival when primary PCI cannot be done within 120 minutes of diagnosis.
What is the dose of streptokinase in myocardial infarction?
1.5 million units in 100 mL of 0.9% sodium chloride IV over 30–60 minutes, after checking for contraindications.
What is the loading dose of clopidogrel?
300 mg with thrombolysis (75 mg if over 75 years), and 600 mg before primary PCI, then 75 mg daily.
How do you know thrombolysis has worked?
The pain eases and the ST elevation falls by at least 50% on an ECG at 60–90 minutes. If not, the patient needs rescue PCI.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 55-year-old has an anterior STEMI with 2 hours of pain. The nearest cath lab is 4 hours away. What is the best reperfusion strategy?
Answer: Thrombolysis, then transfer. When primary PCI can't be delivered within 120 minutes of diagnosis, give thrombolysis (no contraindications) with aspirin, clopidogrel and an anticoagulant, then transfer.
- Aspirin only and wait: Reperfusion is needed.
- Heparin infusion alone: Not reperfusion.
- Transfer for primary PCI: Delay over 120 minutes makes thrombolysis better.
- Thrombolysis only if pain exceeds 12 hours: Benefit is greatest early.
2. 90 minutes after streptokinase for STEMI, the ST elevation has fallen by only 20% and pain continues. What is the next step?
Answer: Rescue PCI. Less than 50% ST resolution at 60–90 minutes indicates failed thrombolysis: urgent transfer for rescue PCI.
- Observe for another 6 hours: Failed reperfusion needs action.
- Discharge after troponin peaks: Inappropriate.
- Repeat streptokinase: Antibodies make repeat streptokinase ineffective and risky.
- Start a GTN infusion only: Doesn't reperfuse.
3. A patient has ongoing chest pain and ST depression in V1–V3 with tall R waves. What should be done?
Answer: Record posterior leads V7–V9 to look for posterior STEMI. ST depression with tall R waves in V1–V3 may be a posterior STEMI. ST elevation in V7–V9 confirms it; treat as STEMI.
- Echo next week: Too late.
- Treat as stable angina: Ongoing pain needs urgent assessment.
- Exercise test: Contraindicated with ongoing pain.
- Give thrombolysis immediately without further ECG: Confirm posterior STEMI first.
4. A 60-year-old has chest pain at rest for 20 minutes, now resolved. ECG shows dynamic ST depression; high-sensitivity troponin is normal at 0 and 3 hours. What is the diagnosis?
Answer: Unstable angina. Acute coronary syndromes: STEMI (ST elevation/new LBBB with symptoms), NSTEMI (ischaemic symptoms with troponin rise above the 99th percentile without ST elevation), unstable angina (ischaemic symptoms at rest or crescendo, without troponin rise). NSTE-ACS management: aspirin + P2Y12 inhibitor, anticoagulation (fondaparinux/enoxaparin), nitrates, beta-blocker, statin; risk stratify (GRACE) for angiography timing.
- NSTEMI: In NSTEMI troponin would rise.
- STEMI: There is no ST elevation.
- Stable angina: Pain at rest makes it unstable, not stable.
5. Which ECG pattern favours acute pericarditis over STEMI?
Answer: Widespread saddle ST elevation + PR depression. Pericarditis ECG: diffuse concave (saddle-shaped) ST elevation across multiple territories, PR depression (PR elevation in aVR), no reciprocal ST depression (except aVR, V1), no Q waves; evolves through stages over days. STEMI: convex ST elevation in a coronary territory with reciprocal depression, Q waves later. Echo looks for effusion; troponin may rise in myopericarditis.
- Regional ST elevation with reciprocal depression: Regional ST elevation with reciprocal depression indicates STEMI.
- New left bundle branch block: New LBBB is treated as an MI equivalent.
- Q waves in the inferior leads: Inferior Q waves indicate infarction.
6. What does the left circumflex artery mainly supply?
Answer: Lateral and posterior left ventricle. The circumflex branch of the left coronary artery runs in the left atrioventricular groove and supplies the left atrium and the lateral and posterolateral left ventricle. In about 10–15% of people (left-dominant), it also gives the posterior interventricular artery.
- Right atrium and SA node: Usually supplied by the right coronary artery.
- Anterior two-thirds of the septum: Supplied by the left anterior descending artery.
- Most of the right ventricle: Supplied mainly by the right coronary artery.
- The cardiac apex alone: The apex is supplied mainly by the LAD.
7. What is the main determinant of coronary blood flow?
Answer: Local metabolites such as adenosine. The heart extracts about 70% of the oxygen in coronary blood even at rest, so more oxygen can only come from more flow. Local metabolites (adenosine, low O₂, high CO₂, H⁺, K⁺) dilate coronary arterioles when demand rises. Left ventricular flow happens mostly in diastole, so tachycardia reduces it.
- Sympathetic nerve activity: Has only a small direct effect; metabolic effects override it.
- Parasympathetic nerve activity: Minor role.
- Aortic systolic pressure alone: Perfusion depends on diastolic pressure and time.
- Blood viscosity: Minor factor normally.
References and dose sources
- ESC 2023 guidelines for acute coronary syndromes
- NICE NG185: Acute coronary syndromes
- NICE CG167: STEMI, acute management
- NICE CG95 — recent-onset chest pain
- Streptokinase dosing: Drugs.com: Streptokinase (see also our streptokinase dose page)
- Tenecteplase dosing: Drugs.com: Tenecteplase dosage (see also our tenecteplase dose page)
- Alteplase dosing: Drugs.com: Alteplase dosage (see also our alteplase dose page)
- Aspirin dosing: Drugs.com: Aspirin dosage (see also our aspirin dose page)
- Clopidogrel dosing: Drugs.com: Clopidogrel dosage (see also our clopidogrel dose page)
- Enoxaparin dosing: Drugs.com: Enoxaparin dosage (see also our enoxaparin dose page)
- Ticagrelor dosing: Drugs.com: Ticagrelor dosage (see also our ticagrelor dose page)
- Fondaparinux dosing: Drugs.com: Fondaparinux dosage (see also our fondaparinux dose page)
- Glyceryl trinitrate (GTN) dosing: Drugs.com: Nitroglycerin dosage (see also our glyceryl trinitrate (gtn) dose page)
- Morphine dosing: Drugs.com: Morphine dosage (see also our morphine dose page)
- Atorvastatin dosing: Drugs.com: Atorvastatin dosage (see also our atorvastatin dose page)
- Bisoprolol dosing: Drugs.com: Bisoprolol dosage (see also our bisoprolol dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.