What is the management of St Elevation Myocardial Infarction (STEMI)?

ST-Elevation Myocardial Infarction (STEMI)

Etiology

STEMI results from acute thrombotic occlusion of a coronary artery, typically following rupture or erosion of an atherosclerotic plaque. 1

• The underlying pathophysiology involves atherosclerotic plaque destabilization, leading to platelet aggregation, thrombus formation, and complete vessel occlusion 1
• Less common causes include coronary vasospasm, coronary dissection, or embolic phenomena 1

Epidemiology and Risk Factors

STEMI remains a major cause of cardiovascular morbidity and mortality worldwide, though incidence has declined with improved prevention strategies. 2

Traditional Risk Factors:

• Hypertension - major modifiable risk factor 1
• Diabetes mellitus - significantly increases risk 1
• Dyslipidemia - elevated LDL cholesterol 3
• Tobacco smoking - most important modifiable risk factor 1
• Age and sex - risk increases with age, males at higher baseline risk 1
• Family history of premature coronary disease 1

Pathophysiology

Complete thrombotic occlusion of a coronary artery leads to transmural myocardial necrosis if reperfusion is not achieved within 12 hours. 1

• Plaque rupture exposes thrombogenic material, triggering platelet adhesion and activation 1
• Thrombus propagation causes complete vessel occlusion with cessation of distal blood flow 1
• Myocardial cell death begins within 20-40 minutes of complete occlusion 4
• Infarct size correlates directly with duration of ischemia - time is myocardium 4, 5
• Transmural necrosis produces characteristic ST-segment elevation on ECG 3

Clinical Manifestations

Typical presentation includes severe, crushing chest discomfort lasting >20 minutes, often radiating to the left arm, neck, or jaw, accompanied by diaphoresis, nausea, and dyspnea. 1, 3

Typical Symptoms:

• Chest pain/pressure - substernal, severe, prolonged (>20 minutes) 1, 3
• Radiation to left arm, neck, jaw, or epigastrium 1
• Associated symptoms: diaphoresis, nausea, vomiting, dyspnea 1, 3

Atypical Presentations (especially in elderly, diabetics, women):

• Isolated dyspnea without chest pain 3
• Epigastric pain mimicking gastrointestinal pathology 3
• Syncope as presenting symptom 3

Physical Examination Findings:

• Tachycardia and hypotension suggest extensive infarction 3
• Pulmonary rales indicate left ventricular failure 3
• Signs of cardiogenic shock: cool extremities, altered mental status, oliguria 1, 3
• Jugular venous distension with inferior STEMI suggests right ventricular involvement 1

Diagnostics

A 12-lead ECG must be obtained and interpreted within 10 minutes of first medical contact in all patients with suspected STEMI. 1

ECG Criteria for STEMI:

• ST-segment elevation ≥0.1 mV (1 mm) in at least two contiguous precordial or adjacent limb leads 1, 3
• New or presumed new left bundle branch block 3
• Right-sided ECG leads (V3R, V4R) should be obtained in inferior STEMI to detect right ventricular infarction 1

Serial ECG Monitoring:

• If initial ECG is non-diagnostic but clinical suspicion remains high, repeat ECGs at 5-10 minute intervals or use continuous 12-lead ST-segment monitoring 1

Cardiac Biomarkers:

• Troponin elevation confirms myocardial necrosis but should never delay reperfusion therapy 1
• Biomarkers are useful for diagnosis in unclear cases and for risk stratification 1

Echocardiography:

• Routine echocardiography during hospitalization to assess LV/RV function, detect mechanical complications, and exclude LV thrombus 1, 3

Management

Immediate Pre-Hospital Management

Patients with suspected STEMI should immediately call 9-1-1 for EMS transport rather than self-transport, and should chew 162-325 mg non-enteric-coated aspirin while awaiting EMS arrival. 1, 3

• EMS personnel must perform 12-lead ECG at the site of first medical contact 1
• Pre-hospital ECG transmission to receiving hospital reduces door-to-balloon time and improves outcomes 1
• EMS should be equipped for early defibrillation and staffed with ACLS-trained personnel 1

Reperfusion Strategy Selection

Primary PCI is the preferred reperfusion method when it can be performed by an experienced team within 90 minutes (if presenting to PCI-capable hospital) or 120 minutes (if requiring transfer) from first medical contact. 1

Primary PCI Strategy:

• Direct EMS transport to PCI-capable hospital with goal first medical contact-to-device time ≤90 minutes 1
• Patients at non-PCI-capable hospitals should be immediately transferred with goal first medical contact-to-device time ≤120 minutes 1
• Patients transferred for primary PCI should bypass the emergency department and go directly to catheterization laboratory 1

Fibrinolytic Therapy Strategy:

• Fibrinolytic therapy should be administered within 30 minutes of hospital arrival when anticipated first medical contact-to-device time exceeds 120 minutes 1
• Pre-hospital fibrinolysis is preferred over in-hospital administration when this capability exists 1, 6
• Fibrin-specific agents are recommended: tenecteplase, alteplase, or reteplase 1, 6

Time Windows for Reperfusion

Reperfusion therapy should be administered to all eligible patients with symptom onset within 12 hours. 1

• Class I indication: symptoms <12 hours with persistent ST-elevation 1
• Class IIa indication: symptoms 12-24 hours with ongoing ischemia 1
• Routine PCI of occluded infarct artery >48 hours after symptom onset in asymptomatic patients is NOT indicated (Class III) 1

Antiplatelet Therapy

Aspirin 150-325 mg oral (chewable) or IV 250-500 mg should be administered immediately upon first medical contact, followed by maintenance dose of 75-100 mg daily indefinitely. 1, 3

P2Y12 Inhibitor Selection:

• A potent P2Y12 inhibitor (ticagrelor or prasugrel) should be administered before or at the time of PCI 1, 3
• Ticagrelor 180 mg loading dose, then 90 mg twice daily for 12 months 1, 3
• Prasugrel 60 mg loading dose, then 10 mg daily for 12 months (avoid if prior stroke/TIA, age ≥75 years, or weight <60 kg) 7
• Clopidogrel 300-600 mg loading dose only if ticagrelor or prasugrel unavailable or contraindicated 1
• Dual antiplatelet therapy (DAPT) should be continued for 12 months unless excessive bleeding risk develops 1, 3

Anticoagulation Therapy

For Primary PCI:

• Unfractionated heparin as weight-adjusted IV bolus with activated clotting time monitoring 1
• Bivalirudin has emerged as preferred agent with improved outcomes over UFH plus GP IIb/IIIa inhibitors 8
• Fondaparinux is NOT recommended for primary PCI 1

For Fibrinolytic Therapy:

• Enoxaparin IV followed by subcutaneous (preferred over UFH) 1, 6
• UFH as weight-adjusted IV bolus followed by infusion 1, 6
• Continue anticoagulation until revascularization or for duration of hospital stay up to 8 days 1, 6

Stent Selection in Primary PCI

Placement of either bare-metal stent or drug-eluting stent is recommended in primary PCI for STEMI. 1

• Bare-metal stents should be used in patients with high bleeding risk, inability to comply with 12 months of DAPT, or anticipated invasive/surgical procedures within the next year 1
• Drug-eluting stents should NOT be used in patients unable to tolerate or comply with prolonged DAPT due to increased stent thrombosis risk 1

Post-Fibrinolytic Management (Pharmacoinvasive Strategy)

All patients receiving fibrinolytic therapy should be transferred immediately to a PCI-capable center for angiography. 1, 6

Rescue PCI:

• Rescue PCI is indicated immediately when fibrinolysis has failed (<50% ST-segment resolution at 60-90 minutes) or with hemodynamic/electrical instability 1, 6

Routine Early PCI:

• Angiography and PCI of infarct-related artery should be performed 2-24 hours after successful fibrinolysis 1, 6
• Angiography should NOT be performed within first 2-3 hours after fibrinolytic administration 1

Emergency Angiography:

• Emergency angiography and PCI indicated for cardiogenic shock or acute severe heart failure 1
• Emergency PCI indicated for recurrent ischemia or evidence of reocclusion 1

Special Populations

Cardiogenic Shock:

• Patients with cardiogenic shock should be transferred for cardiac catheterization and revascularization as soon as possible, irrespective of time delay from MI onset 1
• Primary PCI is strongly preferred over fibrinolytic therapy 6

Cardiac Arrest:

• Immediate angiography and PCI should be performed in resuscitated out-of-hospital cardiac arrest patients whose post-resuscitation ECG shows STEMI 1, 3
• Therapeutic hypothermia should be started as soon as possible in comatose patients with STEMI and out-of-hospital cardiac arrest from VF/pulseless VT 1

Secondary Prevention and Long-Term Management

High-intensity statin therapy should be initiated immediately with target LDL-C <70 mg/dL or ≥50% reduction from baseline. 3

Lifestyle Modifications:

• Smoking cessation with repeated counseling, nicotine replacement, varenicline, or bupropion 1
• Cardiac rehabilitation program participation is strongly recommended 1

Medication Regimen:

• Low-dose aspirin 75-100 mg daily indefinitely 1, 3
• DAPT for 12 months (aspirin plus ticagrelor or prasugrel) 1, 3
• High-intensity statin continued long-term 3
• Beta-blockers, ACE inhibitors/ARBs as indicated for LV dysfunction 1

Medication to AVOID:

• NSAIDs (except aspirin) should be discontinued due to increased risks of mortality, reinfarction, hypertension, heart failure, and myocardial rupture 1

Critical Pitfalls to Avoid

• Never delay reperfusion therapy to wait for cardiac biomarkers - ECG diagnosis is sufficient 1
• Never perform PCI of non-infarct artery at time of primary PCI in hemodynamically stable patients (Class III: Harm) 1
• Never perform delayed PCI of totally occluded infarct artery >24 hours after STEMI in asymptomatic stable patients (Class III: No Benefit) 1
• Never use drug-eluting stents in patients unable to comply with 12 months DAPT 1
• Never delay primary PCI to obtain additional imaging or consultations in stable patients 1