What is the latest protocol for MI?
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I now have comprehensive information from the textbooks and the 2025 ACC/AHA guidelines. Let me compile the full answer.
Latest Protocol for Myocardial Infarction (MI) — 2025 Guidelines
The most current authoritative reference is the 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for the Management of Patients With Acute Coronary Syndromes (Rao SV et al., Circulation 2025; PMID 40014670), which supersedes the 2013 STEMI and 2014 NSTE-ACS guidelines. Note: an erratum was published (PMID 41212941).
Initial Approach — All ACS
Immediate priorities within the first minutes:
- 12-lead ECG within 10 minutes of arrival
- Cardiac biomarkers (high-sensitivity troponin) — drawn immediately and at 1–3 hours
- IV access + continuous ECG monitoring
- Oxygen only if SpO₂ < 90% (avoid routine hyperoxia)
- Aspirin 162–325 mg (chewed, immediately) — continue 81 mg/day indefinitely
- Nitroglycerin (sublingual, then IV if persistent pain) — avoid with hypotension, RV infarction, or PDE5 inhibitor use within 24–48 h
- Morphine — use cautiously; may mask ischemic symptoms and delays oral antiplatelet absorption
- β-blocker — early oral β-blocker (e.g., metoprolol) unless signs of heart failure, low output, or significant bradycardia/heart block
STEMI — ST-Elevation MI
Reperfusion Strategy (Core Principle)
"All other therapies are secondary and should not delay the timely goal of achieving coronary reperfusion." — Washington Manual of Medical Therapeutics
1. Primary PCI (preferred)
- Goal: door-to-balloon ≤ 90 minutes from first medical contact (≤120 min if transferred)
- Indication: symptom onset < 12 hours (extend to 12–24 h if ongoing symptoms)
- Superior to fibrinolysis: better TIMI 3 flow, less reinfarction, lower intracranial hemorrhage risk, improved survival
- Stent choice: drug-eluting stents preferred over bare-metal stents
2. Fibrinolysis (when PCI not available within time window)
- Use if PCI cannot be performed within 120 minutes of first medical contact
- Administer within 12 hours of symptom onset
- Preferred agents: tenecteplase (weight-based, single IV bolus), alteplase, reteplase
- Post-fibrinolysis: routine coronary angiography at 3–24 hours (pharmacoinvasive strategy); immediate rescue PCI if:
- Chest pain not relieved
- < 50% ST-segment reduction at 90 minutes
- Hemodynamic instability or recurrent arrhythmias
- After fibrinolysis: minimum 48 hours of anticoagulation + DAPT
Absolute contraindications to fibrinolysis:
- Prior intracranial hemorrhage or hemorrhagic stroke
- Ischemic stroke within 3 months
- Known intracranial AVM, aneurysm, or tumor
- Closed head injury within 3 months
- Suspected aortic dissection
- Active bleeding or bleeding diathesis
- Severe uncontrolled HTN (SBP > 180 / DBP > 110 mmHg)
3. Emergency CABG — reserved for left main disease, failed PCI, or mechanical complications (VSD, papillary muscle rupture, free wall rupture)
NSTE-ACS — NSTEMI & Unstable Angina
Risk Stratification
- Use validated tools: TIMI, GRACE, or HEART score
- High-sensitivity troponin serial measurements
- ECG for dynamic ST/T changes
Invasive vs. Conservative Strategy
- Immediate invasive (< 2 h): refractory ischemia, hemodynamic instability, sustained VT/VF, Killip class ≥ III
- Early invasive (< 24 h): GRACE score > 140, significant troponin rise, new ST depression
- Selective invasive: low-risk patients (TIMI score 0–1, normal troponins, no high-risk features) may be managed medically
Antithrombotic Therapy — Both STEMI & NSTEMI
Antiplatelet Agents
| Drug | Dose | Notes |
|---|---|---|
| Aspirin | 162–325 mg load → 81 mg/day indefinitely | Give to all ACS patients immediately |
| Ticagrelor | 180 mg load → 90 mg BID × 12 months | Preferred P2Y12 inhibitor; reversible; avoid if prior stroke/TIA |
| Prasugrel | 60 mg load → 10 mg/day × 12 months | Preferred in PCI-treated patients; contraindicated if prior stroke/TIA, age >75, weight <60 kg |
| Clopidogrel | 300–600 mg load → 75 mg/day × 12 months | Use if fibrinolysis planned (not prasugrel/ticagrelor); or if P2Y12 alternatives not tolerated |
- DAPT duration: up to 12 months for drug-eluting stents; de-escalation to clopidogrel or low-dose prasugrel (5 mg) at 3–6 months acceptable in high-bleeding-risk patients
- CYP2C19 inhibitors (omeprazole, esomeprazole, fluconazole) reduce clopidogrel efficacy — avoid coadministration
Anticoagulation
| Drug | Setting |
|---|---|
| UFH (unfractionated heparin) | PCI or fibrinolysis |
| Bivalirudin | PCI (especially high bleeding risk) |
| Enoxaparin (LMWH) | Fibrinolysis + medical management; validated for rescue PCI |
| Fondaparinux | Medical management of NSTEMI (caution: not alone for PCI — risk of catheter thrombosis) |
Medical Adjunct Therapies
| Drug | Indication | Notes |
|---|---|---|
| β-blockers (metoprolol, carvedilol) | All MI patients without contraindications | Reduce arrhythmias, reinfarction, mortality |
| ACE inhibitors / ARBs | EF < 40%, HTN, DM, anterior MI | Start within 24 h, continue long-term |
| High-intensity statin (atorvastatin 40–80 mg, rosuvastatin 20–40 mg) | All ACS patients | Start immediately, continue indefinitely |
| Aldosterone antagonists (eplerenone, spironolactone) | EF < 40% + HF or DM | Avoid if Cr > 2.5 (M) / > 2.0 (F) or K⁺ > 5.0 |
| Nitroglycerin IV | Ongoing ischemia, HTN, pulmonary edema | Avoid in RV infarction, hypotension |
| Calcium-channel blockers (diltiazem, verapamil) | When β-blocker contraindicated | Only if EF preserved; diltiazem preferred for NSTEMI |
Post-MI Monitoring & CCU Care
- CCU monitoring for ≥ 24 hours post-STEMI
- Echo within 24 hours to assess EF and mechanical complications
- Watch for: re-infarction, arrhythmias, HF, pericarditis, thrombus, mechanical complications (VSD, papillary muscle rupture, free wall rupture — peak 3–5 days)
- Cardiogenic shock: early revascularization + vasopressors (norepinephrine preferred); consider IABP or MCS device
Secondary Prevention at Discharge
- Aspirin 81 mg + P2Y12 inhibitor for 12 months
- High-intensity statin (indefinitely)
- ACE inhibitor / ARB (especially if EF < 40%)
- β-blocker (at least 1 year, longer if reduced EF)
- Cardiac rehabilitation referral
- Smoking cessation, BP and glucose control
- Reassess DAPT duration at 3–6 months based on bleeding vs. ischemic risk balance
Sources:
- 2025 ACC/AHA/ACEP/NAEMSP/SCAI Guideline for ACS, Circulation 2025 — PMID 40014670
- Washington Manual of Medical Therapeutics (Reperfusion strategies, DAPT protocols)
- Goldman-Cecil Medicine, International Edition (Antiplatelet agents, P2Y12 inhibitors)
- Harrison's Principles of Internal Medicine, 22nd Ed. (2025, McGraw Hill)
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