What are the key differences in diagnosis and treatment between ST-elevation myocardial infarction (STEMI) and other causes of ST elevation, such as pericarditis, in adult patients with a history of cardiovascular disease or risk factors?

Distinguishing STEMI from Other Causes of ST Elevation

When ST elevation appears on ECG with chest pain, assume STEMI and activate emergency reperfusion protocols immediately unless specific features definitively indicate an alternative diagnosis—this approach prioritizes mortality reduction over diagnostic precision in the acute setting. 1

Initial Approach: Assume STEMI Until Proven Otherwise

In settings with limited expertise, any ST elevation with appropriate chest pain syndrome should be treated as coronary occlusion and referred for immediate reperfusion therapy. 1 This "treat first, differentiate later" approach reduces mortality by preventing delays in time-critical interventions. 1

Key Clinical Context to Obtain Immediately

• Pain characteristics: STEMI presents with pressure/tightness lasting >10-20 minutes, not fully responsive to nitroglycerin, radiating to neck/jaw/left arm 1
• Pericarditis pain: Sharp, pleuritic, positional, worse with lying flat, relieved by sitting forward, radiates to trapezius ridge 1
• Vital signs: Blood pressure differential >15 mmHg between arms mandates evaluation for aortic dissection 2
• Physical exam: Pericardial friction rub strongly suggests pericarditis 1

ECG Features That Distinguish Diagnoses

STEMI-Specific Findings (High Specificity)

• ST depression in reciprocal leads (OR 31 for STEMI vs pericarditis) 3
• Greater ST elevation in lead III than lead II (OR 21 for STEMI) 3
• Absence of PR depression (OR 12 for STEMI) 3
• Upward/horizontal ST convexity (the "tombstone" pattern) 3
• Abrupt ST segment take-off (RT checkmark sign) 3

Pericarditis-Specific Findings

• Diffuse, concave ST elevation across multiple leads (not confined to single coronary territory) 4
• PR segment depression in multiple leads, most commonly lead II (sensitivity 88%, specificity 78%) 5
• PR depression in BOTH precordial AND limb leads (positive predictive value 97%, negative predictive value 90% for pericarditis) 5
• Spodick's sign (downsloping TP segment): present in 29% of pericarditis but also 5% of STEMI, so not definitive 3
• Ratio of ST elevation to T wave >0.24 in lead V6 4
• Absence of reciprocal ST depression (except in aVR and V1) 3

Other Causes to Consider

• Old MI with aneurysm: Persistent ST elevation with pathologic Q waves, unchanged from prior ECGs 1
• Early repolarization: Benign pattern with notching at J-point, stable over time, asymptomatic 6
• Left bundle branch block: Wide QRS (>120ms) with discordant ST changes 7
• Left ventricular hypertrophy: Voltage criteria met with strain pattern 7
• Hyperkalemia: Tall peaked T waves, widened QRS 7

Critical Diagnostic Steps

Step 1: Compare with Prior ECGs Immediately

Unchanged ST elevation from previous tracings dramatically reduces likelihood of acute MI. 6 This single step can prevent unnecessary catheterization lab activation. 6

Step 2: Obtain Serial ECGs and Cardiac Biomarkers

• Repeat ECG every 15-30 minutes if initial diagnosis unclear 6
• Dynamic ST changes during symptoms strongly suggest ischemia (high-risk feature) 6
• Troponin elevation: Measure immediately and repeat at appropriate intervals 6
• Note: 5% of acute coronary syndromes have normal initial ECG, so serial testing is mandatory 6

Step 3: Bedside Echocardiography

• Regional wall motion abnormalities in coronary distribution = STEMI 1
• Global pericardial effusion with normal wall motion = pericarditis 4
• Exclude aortic dissection if clinical suspicion exists 1

Treatment Implications

For STEMI (Confirmed or Presumed)

Activate catheterization laboratory immediately, administer aspirin, establish IV access, and initiate reperfusion therapy without delay. 2 Primary PCI is preferred; fibrinolysis if PCI unavailable within appropriate timeframe. 1

For Pericarditis (After STEMI Excluded)

• Aspirin is first-line therapy (Class I recommendation) 1
• Colchicine or acetaminophen if aspirin ineffective 1
• NSAIDs and glucocorticoids are potentially harmful and should be avoided (Class III: Harm) 1
• Anticoagulation should be discontinued if pericardial effusion ≥1 cm to prevent hemorrhagic conversion 1

Common Pitfalls to Avoid

• Do not delay reperfusion therapy while attempting to differentiate STEMI from pericarditis in ambiguous cases—mortality from missed STEMI exceeds morbidity from unnecessary catheterization 1
• Do not rely on single normal troponin to exclude ACS; serial measurements required 6
• Do not confuse benign early repolarization with STEMI—inappropriate thrombolysis carries unnecessary hazards 6
• Do not miss posterior MI—obtain posterior leads (V7-V9) if inferior ST changes present, as 4% of acute MIs show isolated posterior elevation 6
• Do not use NSAIDs for post-STEMI pericarditis—they impair myocardial healing and increase mortality risk 1

When Diagnosis Remains Uncertain

If clinical features and ECG findings are equivocal after initial evaluation, proceed with coronary angiography rather than observation. 1 The risk of catheterization in a patient without STEMI is substantially lower than the mortality risk of delayed treatment in actual STEMI. 1 Normal coronary arteries on angiography definitively exclude STEMI and allow confident diagnosis of alternative causes. 4