Acute Myocardial Infarction - Treatment

Classification for Management Purposes

Immediate / General Measures ("MONA" + more)

1. Oxygen

• Supplemental O2 only if SpO2 <94% - routine O2 in normoxic patients is NOT recommended (may increase infarct size).

2. Analgesia

• Morphine IV (2-4 mg, titrated) for unrelieved chest pain - but use with caution; associated with delayed P2Y12 absorption and worse outcomes in some studies.
• IV nitrates for pain relief if no hypotension (SBP >90 mmHg), no RV infarct, no PDE5 inhibitor use.

3. Antiplatelets (Dual Antiplatelet Therapy - DAPT)

• Aspirin 300 mg loading dose (crushed/chewed), then 75 mg daily indefinitely.
• P2Y12 inhibitor (choose one):
  • Ticagrelor 180 mg load, then 90 mg BD (preferred - PLATO trial; irreversible, faster onset)
  • Prasugrel 60 mg load, then 10 mg OD (preferred in STEMI if no prior stroke/TIA, age <75, weight >60 kg)
  • Clopidogrel 600 mg load, then 75 mg OD (less potent; used if others contraindicated or thrombolysis given)

4. Anticoagulation

• Unfractionated heparin (UFH): IV bolus 60 units/kg (max 4000 units), infusion 12 units/kg/hr - used with PCI or thrombolysis.
• LMWH (Enoxaparin): 1 mg/kg SC BD (preferred over UFH in NSTEMI if no renal failure).
• Fondaparinux: 2.5 mg SC OD - preferred in NSTEMI managed conservatively (OASIS-5 trial).
• Bivalirudin: Direct thrombin inhibitor; preferred option for primary PCI (lower bleeding risk).

5. Beta-blockers

• Oral beta-blocker (e.g., metoprolol 25-50 mg BD) within 24 hours if no contraindications.
• Contraindications: cardiogenic shock, acute decompensated HF, PR >0.24s, 2nd/3rd degree AV block, bronchospasm.
• IV beta-blockers only for ongoing ischaemia/tachyarrhythmia without contraindications.

6. ACE Inhibitors / ARBs

• Start within 24 hours in STEMI with:
  • Anterior MI
  • LV dysfunction (EF <40%)
  • Heart failure
  • Hypertension or diabetes
• Ramipril, Lisinopril, Captopril - start low, titrate.
• ARB (e.g., valsartan) if ACE inhibitor intolerant.

7. Statins

• High-intensity statin (Atorvastatin 80 mg or Rosuvastatin 40 mg) - started immediately, continued indefinitely.
• Target LDL <1.4 mmol/L (55 mg/dL) per ESC 2023 guidelines.

8. Nitrates

• GTN sublingual or IV for ongoing pain (avoid in RV infarct, hypotension, PDE5 inhibitor use in last 24-48h).
• No mortality benefit; not routinely continued long term.

STEMI-Specific: Reperfusion Strategy

Primary PCI (Preferred)

• Indication: STEMI within 12 hours of symptom onset (or ongoing ischaemia up to 24h).
• Target: Door-to-balloon time <90 minutes (if presenting to PCI centre) or <120 minutes from first medical contact.
• Drug-eluting stent preferred over bare metal stent.
• Culprit-only PCI preferred in cardiogenic shock (CULPRIT-SHOCK trial) - staged revascularisation of non-culprit vessels.
• Radial access preferred (lower bleeding).

Fibrinolysis (Thrombolysis)

• Used when primary PCI not available within 120 minutes of first medical contact.
• Agents:

  Agent	Dose	Type
  Alteplase (tPA)	15 mg IV bolus, then 0.75 mg/kg (max 50mg) over 30min, then 0.5 mg/kg (max 35mg) over 60min	Fibrin-specific
  Tenecteplase (TNK-tPA)	Single IV bolus weight-based (30-50 mg)	Fibrin-specific, easiest
  Reteplase	10 units IV x2 (30 min apart)	Fibrin-specific
  Streptokinase	1.5 million units IV over 60 min	Non-fibrin-specific (rarely used)

• Fibrin-specific agents (alteplase, tenecteplase) are superior to streptokinase (GUSTO trial).
• Contraindications to thrombolysis:
  • Absolute: Prior intracranial haemorrhage, stroke within 6 months, active bleeding, aortic dissection, CNS tumour/AVM.
  • Relative: SBP >180 mmHg, INR >2, major surgery <3 weeks, pregnancy, active peptic ulcer.

Pharmacoinvasive Strategy

• If thrombolysis given, PCI should be performed 2-24 hours later (coronary angiography routinely).
• Immediate rescue PCI if thrombolysis fails (ST elevation not resolving >50% at 60-90 min).

NSTEMI / Unstable Angina Treatment

Risk Stratification

• GRACE score (most validated) or TIMI score guides timing of angiography.
• High risk features: Dynamic ECG changes, troponin rise, haemodynamic instability, refractory angina, GRACE >140.

Invasive vs. Conservative Strategy

Additional Pharmacotherapy

Aldosterone Antagonists

• Eplerenone (preferred post-MI) or Spironolactone - for patients with EF <40% and HF or diabetes.
• Start after ACE inhibitor/ARB; avoid if K+ >5 mmol/L or severe renal impairment.
• Reduces mortality (EPHESUS trial - eplerenone post-MI).

Ivabradine

• Add if HR >70 bpm at rest on maximum tolerated beta-blocker with reduced EF.

Glucose Control

• Target glucose ≤10 mmol/L (180 mg/dL); avoid hypoglycaemia.
• SGLT2 inhibitors (empagliflozin, dapagliflozin) if EF <40% reduces CV death/HF hospitalisation (post-MI).

Colchicine

• Low-dose colchicine (0.5 mg OD) shown to reduce recurrent CV events post-MI (COLCOT trial, LoDoCo2 trial).

Complications and Specific Management

Secondary Prevention (Post-MI)