Management of mi
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"myocardial infarction"[MeSH Terms] AND "management"[MeSH Terms]
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"myocardial infarction"[MeSH Terms] AND "therapy"[MeSH Terms]
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Management of Myocardial Infarction (MI)
MI management is divided into STEMI (ST-elevation MI) and NSTEMI/UA (non-ST-elevation MI/unstable angina) pathways, with additional considerations for peri-infarct care and secondary prevention.
1. Initial Assessment (First 10 Minutes)
- 12-lead ECG within 10 minutes of arrival - mandatory
- Serial ECGs if initial ECG is non-diagnostic but symptoms persist (may reveal evolving STEMI)
- Continuous telemetry for arrhythmia monitoring
- Targeted clinical exam
- Supplemental O₂ only if SpO₂ < 90% (routine O₂ is no longer recommended)
- Activate acute MI protocol in ED
2. Upstream Medical Therapy (Applies to All ACS)
Start immediately while preparing for reperfusion:
Antiplatelet Agents
| Drug | Dose | Notes |
|---|---|---|
| Aspirin (ASA) | 162-325 mg (chewed/crushed) | Non-enteric coated for rapid absorption |
| Clopidogrel | 600 mg loading, then 75-150 mg/d | 600 mg LD preferred; caution in elderly |
| Prasugrel | 60 mg loading, then 10 mg/d | More potent than clopidogrel; avoid if age >75, weight <60 kg, or prior stroke/TIA |
| Ticagrelor | 180 mg loading, then 90 mg BID | Mortality benefit over clopidogrel; limit ASA to ≤100 mg |
| Cangrelor | 30 µg/kg IV bolus, then 4 µg/kg/min | IV P2Y12 inhibitor; FDA-approved for PCI only |
Anticoagulants
| Drug | Dose | Notes |
|---|---|---|
| UFH | 60 units/kg IV bolus, then 12 units/kg/h | For all PCI patients and most thrombolytic recipients |
| Enoxaparin (LMWH) | 30 mg IV bolus + 1 mg/kg SC q12h | Alternative to UFH |
| Bivalirudin | Used in PCI | Direct thrombin inhibitor |
- Washington Manual of Medical Therapeutics, Table 4-17
3. STEMI-Specific Management - Reperfusion
The primary goal is rapid reperfusion. Time = myocardium.
Primary PCI (Preferred)
- Gold standard for STEMI reperfusion
- Goal: door-to-balloon time ≤90 minutes at a PCI-capable center
- AHA/ACC guidelines mandate PCI within 90 minutes of presentation
- Preferred over thrombolytics when achievable within the time window
Thrombolysis (If PCI Not Available in Time)
- Used when PCI cannot be performed within 90-120 minutes
- Administer within 12 hours of symptom onset
- Fibrin-selective agents are preferred:
| Agent | Dose |
|---|---|
| Alteplase (rt-PA) | 15 mg IV bolus, then 0.75 mg/kg over 30 min, then 0.5 mg/kg over 60 min |
| Reteplase (r-PA) | 10 units IV bolus × 2, 30 minutes apart |
| Tenecteplase (TNK-tPA) | 0.5 mg/kg IV single bolus (30-50 mg total) |
Combine fibrinolytics with: ASA + clopidogrel + anticoagulant (UFH). GPIIb/IIIa inhibitors should NOT be combined.
Signs of successful thrombolysis:
- Relief of chest pain
-
50% reduction in ST elevations at 90 minutes
- Reperfusion arrhythmia (e.g., accelerated idioventricular rhythm)
Post-fibrinolysis: Routine coronary angiography within 24 hours reduces adverse events. All patients should get DAPT + ≥48 hours of anticoagulation.
Absolute Contraindications to Thrombolytics
- Prior intracranial hemorrhage
- 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 mmHg)
- Active bleeding or bleeding diathesis
- Acute pericarditis
Emergency CABG
Reserved for: severe left main disease, refractory ischemia with failed PCI, anatomy unsuitable for PCI, or acute mechanical complications (papillary muscle rupture, VSD, free wall rupture).
4. NSTEMI / Unstable Angina Management
- No fibrinolytic therapy (contraindicated in ST-depression pattern)
- Risk stratify using TIMI or GRACE risk scores
- Early invasive strategy (angiography within 24-48 h) for high-risk features: elevated troponins, dynamic ECG changes, recurrent symptoms, hemodynamic instability
- Conservative strategy for low-risk patients
- Same antiplatelet and anticoagulation backbone as STEMI
5. Peri-Infarct Monitoring (CCU)
- All STEMI patients should be in CCU or ICU for at least 24 hours
- Continuous telemetry for ischemia and arrhythmias
- Daily assessment: chest pain, new HF symptoms, ECG
- Examine for new murmurs (VSD, MR due to papillary muscle rupture)
- Baseline echocardiogram: to assess EF, wall motion abnormalities, valvular lesions, and LV thrombus
- Cardiac pacing: AV block in anterior MI is often unstable with wide-QRS escape rhythms and ~80% mortality - requires temporary then permanent pacing; AV block in inferior MI is usually transient
6. Post-MI Medical Therapy (Secondary Prevention)
| Drug | Duration/Target | Notes |
|---|---|---|
| Aspirin 81 mg/d | Indefinitely | |
| P2Y12 inhibitor (clopidogrel/prasugrel/ticagrelor) | Minimum 12 months | Regardless of stent type (BMS or DES) |
| Beta-blocker | Indefinitely | Start within 24 hours; mortality benefit |
| ACE inhibitor | Start within 24 hours; continue long-term | Most benefit when EF <40%, large anterior MI, or prior MI |
| ARB | Substitute for ACE-I intolerance | |
| High-intensity statin | Indefinitely | Target LDL <70 mg/dL or ≥50% reduction; add PCSK9 inhibitor or ezetimibe if needed |
| Aldosterone antagonist (spironolactone/eplerenone) | Long-term | When LVEF <40% or diabetes; caution with hyperkalemia/renal impairment |
- Washington Manual of Medical Therapeutics
7. Special Situations
Right Ventricular MI (RVMI)
- Occurs with proximal RCA occlusion causing inferior STEMI
- Classic triad: hypotension + elevated JVP + clear lung fields
- Diagnosis: ST elevation in V1 or V4R (right-sided leads)
- Treatment: IV fluids (RV is preload-dependent) - avoid nitrates and diuretics
- If hypotension persists: dobutamine ± IABP; right-sided mechanical support if pharmacology fails
- Heart block with AV dyssynchrony: sequential AV pacing provides marked benefit
Mechanical Complications
- VSD, free wall rupture, papillary muscle rupture with acute MR - surgical emergencies
- Usually occur within days of MI
Cardiogenic Shock
- IABP, vasopressors (norepinephrine), inotropes (dobutamine)
- Urgent PCI/revascularization
- Mechanical circulatory support (Impella, ECMO) in refractory cases
8. Mnemonic - Immediate STEMI Management: MONABCH
Morphine (for pain, use cautiously) | Oxygen (if SpO₂ <90%) | Nitrates | Aspirin | Beta-blocker | Clopidogrel/P2Y12 | Heparin
Sources: Washington Manual of Medical Therapeutics; Barash's Clinical Anesthesia; Morgan & Mikhail's Clinical Anesthesiology; AHA/ACC Guidelines
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