Myocardial Infarction Treatment

The Core Principle

"The majority of patients who suffer an acute STEMI have thrombotic occlusion of a coronary artery. Early restoration of coronary perfusion limits infarct size, preserves LV function, and reduces mortality. All other therapies are secondary and should not delay the timely goal of achieving coronary reperfusion."

• Washington Manual of Medical Therapeutics

1. Immediate / Upstream Therapy (All MI Types)

2. STEMI Reperfusion Strategy

STEMI reperfusion and risk stratification pathway - Washington Manual of Medical Therapeutics

Primary PCI (Preferred)

• Target: Door-to-balloon time ≤90 minutes from first medical contact
• Superior to fibrinolysis for: vessel patency (TIMI 3 flow), less reinfarction, lower intracranial hemorrhage risk, improved survival
• Preferred when diagnosis is uncertain, cardiogenic shock is present, bleeding risk is high, or symptoms >2-3 hours (clot less lysable)
• PCI is preferred over fibrinolysis unless time to first coronary device delivery exceeds 120 minutes
• Complete revascularization: In STEMI patients without shock, PCI of non-culprit vessels (either at index procedure or within 45 days) reduces cardiovascular events. Exception: In cardiogenic shock, routine PCI of non-culprit arteries during initial primary PCI is contraindicated.
• P2Y12 choice for PCI: Ticagrelor, prasugrel, or clopidogrel

Fibrinolytic Therapy (when PCI not timely)

• Target: Door-to-needle time ≤30 minutes
• Agents: tPA, Tenecteplase (TNK - 0.5 mg/kg IV bolus, max 50 mg), Reteplase (rPA), Streptokinase
• TNK: slower clearance, improved fibrin specificity, equivalent mortality to tPA with less bleeding
• Always combine with ASA, clopidogrel (not prasugrel/ticagrelor - not studied with fibrinolytics), and anticoagulation (LMWH preferred over UFH when fibrinolysis used)
• Do NOT use GPIIb/IIIa inhibitors with fibrinolytics

• Prior intracranial hemorrhage / hemorrhagic stroke
• Ischemic stroke within 3 months
• Known intracranial structural lesion (AVM, aneurysm, tumor)
• Closed head injury within 3 months
• Aortic dissection
• Severe uncontrolled hypertension (SBP >180, DBP >110)
• Active bleeding or bleeding diathesis
• Acute pericarditis

Rescue PCI

• For failed fibrinolysis (persistent chest pain, <50% ST resolution at 90 min, hemodynamic instability)
• Class IIa recommendation - reduces HF and recurrent infarction even if no clear mortality benefit
• Repeat fibrinolysis is not recommended

Emergency CABG

• Reserved for: left main disease, failed PCI, coronary anatomy not amenable to PCI, mechanical complications (papillary muscle rupture, VSD, free wall rupture, ventricular aneurysm with refractory arrhythmia)

3. Anticoagulation in Detail

4. NSTEMI / UA Management

• All patients: ASA + P2Y12 inhibitor (DAPT) + anticoagulation + beta-blocker + statin
• High-risk features (elevated troponin, dynamic ST changes, refractory ischemia, hemodynamic instability, Killip class >1): Early invasive strategy - coronary angiography within 24-48 hours
• Lower-risk: Conservative (medical) strategy with stress testing for risk stratification

Recent meta-analysis (PMID: 40549394, JAMA Internal Medicine 2025) found early invasive strategy benefits older patients with ACS as well - this challenges older conservative approaches in the elderly.

5. Peri-Infarct Care (CCU)

• All STEMI patients: monitored CCU/ICU for ≥24 hours
• Continuous telemetry for ischemia and arrhythmias
• Daily ECGs, exam for new murmurs (VSD, MR) or HF signs
• Baseline echocardiogram: assess EF, wall motion, valvular lesions, ventricular thrombus
• Cardiac pacing: AV block in anterior MI is often unstable with wide QRS escape - usually requires temporary then permanent pacemaker. AV block in inferior MI tends to be transient.

6. Post-MI Long-Term / Secondary Prevention

7. Mechanical Complications (Post-MI)

2025 Guideline Update (ACC/AHA)

• Intracoronary imaging during PCI upgraded from Class IIa to Class I recommendation for complex lesions
• Ticagrelor monotherapy (after ≥1 month of DAPT post-PCI) now a recommended de-escalation strategy to reduce bleeding
• For patients needing long-term anticoagulation post-PCI: discontinue aspirin 1-4 weeks after PCI, continue P2Y12 (preferably clopidogrel) with anticoagulant
• Dissolving the artificial STEMI/NSTEMI divide in initial evaluation and medical management

PubMed Literature Review: Primary PCI vs. Fibrinolysis in STEMI

Evidence Summary

Tier 1 Evidence - Systematic Reviews & Meta-Analyses

Intracoronary Thrombolysis Adjunct to Primary PCI

• IC thrombolysis significantly reduced MACE: RR 0.65 (95% CI 0.51-0.82, p<0.0004)
• Improved LVEF: +1.87% (WMD, 95% CI 1.07-2.67, p<0.0001)
• No significant reduction in mortality alone (RR 0.91, p=0.77)
• No increase in major or minor bleeding
• Subgroup findings: benefit was significant with non-fibrin-specific (RR 0.39) and moderately fibrin-specific agents (RR 0.62), but not with highly fibrin-specific agents (RR 1.10, p=0.75)

Intracoronary Adjunctive Therapies - Network Meta-Analysis

• No IC adjunctive therapy significantly reduced all-cause mortality, non-fatal MI, or HF hospitalization vs. conventional primary PCI
• However, several strategies significantly reduced post-PCI TIMI 0-2 flow (a surrogate for microvascular obstruction):
  • Fibrinolytic + manual thrombus aspiration: OR 0.24 (0.12-0.48) - strongest effect
  • Verapamil: OR 0.22; Tirofiban: OR 0.43; Adenosine: OR 0.40; Manual aspiration alone: OR 0.61
• Safety signals: IC tirofiban increased any bleeding (IRR 1.65); IC adenosine increased peri-procedural AV blocks (OR 2.80)

Tier 3 Evidence - Randomized Controlled Trials

STREAM-2 Trial (Landmark RCT)

STREAM-1 vs. STREAM-2 Inter-Trial Comparison

• Half-dose vs. full-dose TNK: similar ST resolution ≥50% (71.2% vs. 68.7%, p=0.519) and similar ICH risk (2.1% vs. 1.5%, p=0.605) in ages 60-74
• Major non-ICH bleeding was dramatically lower in STREAM-2: 0.3% vs. 7.1% in the PI arm - attributed to refined anticoagulation protocols

Pharmaco-Invasive Strategy with Half-Dose Prourokinase vs. Primary PCI

Rescue PCI in the Pharmaco-Invasive Era (STREAM-2 Sub-Analysis)

• Rescue PCI patients had significantly worse outcomes vs. those with successful fibrinolysis + scheduled PCI: 30-day composite 16.7% vs. 6.0% (p<0.001); higher ICH risk 2.4% vs. 0.5%
• Primary PCI patients had intermediate outcomes (30-day composite 12.2%)
• Delays in deploying rescue PCI were shortened in hub-and-spoke systems, resulting in comparable outcomes regardless of initial setting (ambulance vs. community hospital)

Review-Level Evidence

Comprehensive ACS Diagnosis & Treatment Review (JAMA)

• Primary PCI within 120 min reduces STEMI mortality from 9% → 7%
• For NSTE-ACS: early invasive strategy (angiography + revascularization within 24-48h) reduces mortality from 6.5% → 4.9%
• Fibrinolytic dosing protocol: full-dose for patients <75 years; half-dose for patients ≥75 years (or full-dose streptokinase if cost is a concern)
• ACS affects >7 million people/year globally, >1 million hospitalizations/year in the US

Rural STEMI: Fibrinolysis vs. Primary PCI

Synthesis: What the Current Evidence Says