ST-Elevation Myocardial Infarction (STEMI)

A 58 year old male with hypertension, diabetes mellitus, and smoking history presents with severe central crushing chest pain radiating to the left arm and jaw for 1 hour, associated with diaphoresis, nausea, and dyspnea. On examination, pulse is 108/min and blood pressure is 92/60 mmHg. ECG demonstrates ST-segment elevation in leads II, III, and aVF with reciprocal ST depression in leads I and aVL. High-sensitivity troponin is elevated. Diagnosis?

Diagnosis is ST-elevation myocardial infarction (STEMI).

1. Definition

STEMI is an acute myocardial infarction caused by acute coronary atherothrombosis resulting in complete or near-complete coronary artery occlusion and transmural myocardial ischemia.

2. Pathophysiology

  1. Atherosclerotic plaque rupture or erosion occurs
  2. Exposure of thrombogenic material activates platelets and coagulation cascade
  3. Acute thrombus formation leads to coronary artery occlusion
  4. Severe reduction in coronary blood flow causes transmural ischemia
  5. Prolonged ischemia results in irreversible myocardial necrosis

Mortality is primarily related to:

  1. Ventricular arrhythmias
  2. Cardiogenic shock
  3. Mechanical complications

3. Risk Factors

  1. Hypertension
  2. Diabetes mellitus
  3. Smoking
  4. Dyslipidemia
  5. Obesity
  6. Family history of premature coronary artery disease
  7. Chronic kidney disease
  8. Cocaine use

4. Clinical Features

4.1 Typical Symptoms

  1. Severe central crushing chest pain
  2. Pain radiating to left arm, neck, jaw, or back
  3. Diaphoresis
  4. Dyspnea
  5. Nausea and vomiting
  6. Palpitations

4.2 High-Risk Presentations

  1. Syncope
  2. Cardiogenic shock
  3. Ventricular arrhythmias
  4. Sudden cardiac arrest

4.3 Atypical Presentations

More common in:

  1. Elderly patients
  2. Women
  3. Diabetics

May present with:

  1. Dyspnea
  2. Fatigue
  3. Epigastric discomfort
  4. Syncope

5. ECG Findings

STEMI Criteria

New ST-segment elevation in ≥2 anatomically contiguous leads:

  1. ≥1 mm in all leads other than V2–V3
  2. In V2–V3:
    • ≥2 mm in men ≥40 years
    • ≥2.5 mm in men <40 years
    • ≥1.5 mm in women

STEMI Equivalents

Posterior MI

  1. ST depression in V1–V3
  2. Confirm with posterior leads V7–V9

Left Bundle Branch Block

  1. New or presumed new LBBB with ischemic symptoms may suggest occlusive MI
  2. LBBB alone is not independently diagnostic of STEMI

Reciprocal Changes

  1. ST depression in opposite leads increases specificity for STEMI

STEMI Localization

Anterior Wall MI

  • V1–V4
  • Usually LAD occlusion

Inferior Wall MI

  • II, III, aVF
  • Usually RCA occlusion

Lateral Wall MI

  • I, aVL, V5, V6
  • Usually LCX occlusion

6. Cardiac Biomarkers

High-Sensitivity Troponin

  1. Most sensitive and specific biomarker of myocardial injury
  2. Elevated due to myocardial necrosis
  3. Serial measurements improve diagnostic accuracy
  4. Reperfusion therapy should not be delayed while awaiting troponin results

7. Initial Evaluation

  1. ECG within 10 minutes of first medical contact
  2. Serial ECGs if initial ECG nondiagnostic
  3. Immediate assessment of hemodynamic stability
  4. Cardiac troponin measurement
  5. Continuous cardiac monitoring

8. Reperfusion Strategy

Key Principle

Fastest effective reperfusion is the most important determinant of outcome

8.1 Primary Percutaneous Coronary Intervention (PCI)

Preferred Reperfusion Strategy

  1. Preferred if performed in a timely manner
  2. Door-to-balloon time ≤90 minutes at PCI-capable center
  3. FMC-to-device time ≤120 minutes if transfer required

PCI Components

  1. Coronary angiography
  2. Balloon angioplasty
  3. Coronary stenting
  4. Intracoronary imaging in selected cases

8.2 Fibrinolytic Therapy

Indications

  1. PCI delay >120 minutes
  2. Symptom onset <12 hours
  3. No contraindications to fibrinolysis

Timing Goals

  1. Door-to-needle time ≤30 minutes
  2. Greatest benefit occurs within first 2–3 hours of symptom onset

Preferred Agent

  1. Tenecteplase

Contraindications

  1. Prior intracranial hemorrhage
  2. Active bleeding
  3. Ischemic stroke within previous 3 months
  4. Suspected aortic dissection

Pharmaco-Invasive Strategy

  1. Routine angiography/PCI within 2–24 hours after successful fibrinolysis

8.3 Rescue PCI

Indications

  1. Failed fibrinolysis
  2. Persistent chest pain
  3. Persistent ST elevation
  4. Hemodynamic instability

Timing

  1. Immediate, ideally within 2 hours

8.4 Late Presentation

Presentation >12–24 Hours

PCI indicated if:

  1. Ongoing ischemia
  2. Heart failure
  3. Cardiogenic shock
  4. Malignant arrhythmias
  5. Large myocardial territory at risk

Routine PCI of a totally occluded infarct artery in stable asymptomatic patients presenting >24 hours after STEMI is generally not recommended

Fibrinolysis is generally not recommended beyond 12 hours after symptom onset unless ongoing ischemia is present and PCI is unavailable

9. Antithrombotic Therapy

9.1 Dual Antiplatelet Therapy (DAPT)

  1. Aspirin immediately unless contraindicated
  2. P2Y12 inhibitor:
    • Ticagrelor preferred
    • Prasugrel preferred in selected PCI patients
    • Clopidogrel if contraindications exist

Important Prasugrel Contraindications / Precautions

  1. Contraindicated in prior stroke or TIA
  2. Use caution or avoid in:
    • Age ≥75 years
    • Body weight <60 kg

9.2 Anticoagulation

  1. Unfractionated heparin
  2. Enoxaparin
  3. Bivalirudin in selected PCI patients

9.3 GP IIb/IIIa Inhibitors

  1. Consider in selected patients with high thrombus burden

10. Adjunctive Medical Therapy

Oxygen

  1. Only if hypoxemia, respiratory distress, or shock

Nitroglycerin

  1. Used for ongoing ischemic chest pain
  2. Avoid in:
    • Hypotension
    • Right ventricular infarction
    • Recent phosphodiesterase-5 inhibitor use

Morphine

  1. May be used for refractory pain
  2. May delay absorption of oral P2Y12 inhibitors

Beta-Blockers

  1. Reduce myocardial oxygen demand and arrhythmia risk
  2. Avoid in:
    • Cardiogenic shock
    • Severe bradycardia
    • High-grade AV block

ACE Inhibitors / ARBs

Recommended especially in:

  1. Reduced LVEF
  2. Anterior STEMI
  3. Heart failure
  4. Diabetes mellitus

High-Intensity Statins

  1. Initiate early in all STEMI patients
  2. Examples:
    • Atorvastatin
    • Rosuvastatin

11. Cardiogenic Shock

  1. Hypotension with end-organ hypoperfusion
  2. Requires urgent revascularization regardless of timing
  3. Vasopressors, inotropes, and mechanical circulatory support may be required
  4. Culprit-vessel PCI is preferred initially
  5. Routine immediate multivessel PCI during shock is not recommended

12. Multivessel Disease

  1. Complete revascularization is generally recommended in stable STEMI patients with multivessel disease
  2. PCI may be performed during index hospitalization or as a staged procedure
  3. Culprit-only PCI preferred initially in cardiogenic shock

13. Complications

13.1 Electrical Complications

  1. Ventricular tachycardia
  2. Ventricular fibrillation
  3. AV block
  4. Bradyarrhythmias

13.2 Mechanical Complications

Papillary Muscle Rupture

  • Acute severe mitral regurgitation

Ventricular Septal Rupture

  • New harsh holosystolic murmur

Free Wall Rupture

  • Cardiac tamponade and sudden death

13.3 Other Complications

  1. Cardiogenic shock
  2. Heart failure
  3. Left ventricular aneurysm
  4. Pericarditis
  5. Left ventricular thrombus

14. Secondary Prevention

  1. Smoking cessation
  2. Cardiac rehabilitation
  3. High-intensity statin therapy
  4. Blood pressure and diabetes control
  5. Long-term antiplatelet therapy
  6. Lifestyle modification and exercise

15. Prognosis

  1. Prognosis depends largely on:
    • Time to reperfusion
    • Infarct size
    • LV function
    • Presence of shock or arrhythmias
  2. Early reperfusion significantly reduces mortality and preserves myocardium

16. Key Clinical Insight

Patient with acute crushing chest pain, diaphoresis, and ST-segment elevation in contiguous leads should be treated immediately as STEMI with rapid reperfusion therapy

17. Key Exam Points

  1. STEMI is usually caused by acute coronary thrombotic occlusion following plaque rupture
  2. ECG should be obtained within 10 minutes of first medical contact
  3. Primary PCI is the preferred reperfusion strategy
  4. Door-to-balloon time goal is ≤90 minutes
  5. FMC-to-device time goal is ≤120 minutes
  6. Troponin should not delay reperfusion therapy
  7. Inferior STEMI commonly involves the RCA
  8. Anterior STEMI usually results from LAD occlusion
  9. Ventricular fibrillation is a major cause of early death
  10. Early reperfusion is the most important determinant of myocardial salvage and survival
By Prabin Duwadee at

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