What are the primary differential diagnoses for a patient presenting with symptoms suggestive of ST-Elevation Myocardial Infarction (STEMI)?

Differential Diagnoses for STEMI

When a patient presents with ST-segment elevation on ECG, immediately rule out life-threatening STEMI mimics—particularly aortic dissection, acute pericarditis, and massive pulmonary embolism—before initiating reperfusion therapy, as thrombolytics can be catastrophic in these conditions. 1

Critical Life-Threatening Conditions Requiring Immediate Exclusion

Aortic Dissection

• Look for ST-depression >0.1 mV in eight or more leads combined with ST elevation in aVR and/or V1, especially with hemodynamic instability—this pattern suggests left main or proximal multivessel disease but can also indicate aortic dissection 1
• Check blood pressure in both arms; a difference >20 mmHg between limbs strongly suggests dissection 1
• Patients may present with tearing chest pain radiating to the back, which differs from the typical crushing substernal pain of MI 2
• Never administer thrombolytics or anticoagulation until dissection is excluded, as this causes catastrophic hemorrhage 1

Acute Pericarditis

• ECG shows widespread ST elevation that is concave upward (versus the convex ST elevation in STEMI) with PR segment depression in multiple leads 1
• Auscultate for pericardial friction rub, which is pathognomonic 1
• Pain is typically sharp, positional (worse when supine, better leaning forward), and pleuritic in nature 2
• Thrombolytic therapy in pericarditis can cause hemorrhagic tamponade—a fatal complication 1

Massive Pulmonary Embolism

• May present with ST elevation in leads V1-V4 or right-sided leads, mimicking anterior STEMI 1
• Look for tachycardia, hypoxemia, and signs of right heart strain on ECG (S1Q3T3 pattern, right bundle branch block) 2
• Clinical context includes recent immobilization, surgery, or known hypercoagulable state 3

Cardiac Conditions That Mimic STEMI

Type 2 Myocardial Infarction (Supply-Demand Mismatch)

• Troponin elevation occurs without acute coronary thrombosis, caused by: severe hypertension, tachyarrhythmias (atrial fibrillation with rapid ventricular response), severe anemia, hypotension/shock, respiratory failure, or coronary vasospasm 1
• Treatment focuses on correcting the precipitating condition rather than immediate catheterization 1
• These patients do not benefit from emergent reperfusion therapy 3

Coronary Vasospasm (Prinzmetal Angina)

• Transient ST elevation that resolves spontaneously or with nitrates 4
• May occur on top of atherosclerotic plaque, producing mixed-etiology ACS 4
• Typically occurs at rest, often in early morning hours 4

Takotsubo Cardiomyopathy (Stress Cardiomyopathy)

• Presents with chest pain, ST elevation, and troponin elevation mimicking STEMI 3
• Typically affects postmenopausal women following emotional or physical stress 3
• Angiography shows no obstructive coronary disease but characteristic apical ballooning on ventriculography 3

Myocarditis

• Can present with ST elevation, elevated troponins, and chest pain 3
• Often preceded by viral prodrome (fever, myalgias, upper respiratory symptoms) 3
• May have pericardial involvement with friction rub 3

Non-Cardiac Life-Threatening Conditions

Other Considerations

• Left ventricular hypertrophy can cause baseline ST elevation, particularly in precordial leads 2
• Early repolarization shows J-point elevation with characteristic notching, typically in young patients 2
• Left bundle branch block (new or presumed new) requires treatment as STEMI equivalent 2, 5

Diagnostic Approach Algorithm

Step 1: Obtain 12-Lead ECG Within 10 Minutes

• True STEMI criteria: ≥0.25 mV in men <40 years, ≥0.2 mV in men ≥40 years, or ≥0.15 mV in women in V2-V3; ≥0.1 mV in other leads at J-point in two contiguous leads 1
• Add posterior leads (V7-V9) if ST depression in V1-V3 suggests isolated posterior MI 1
• Add right-sided leads (V4R) if inferior STEMI to detect right ventricular involvement 2

Step 2: Focused Physical Examination

• Assess for blood pressure differential between arms (>20 mmHg suggests dissection) 1
• Listen for pericardial friction rub (pericarditis) or new systolic murmur (mechanical complication, endocarditis) 1
• Examine for signs of heart failure (rales, S3 gallop, jugular venous distension) 2

Step 3: Obtain High-Sensitivity Troponin

• Draw at presentation but do not delay reperfusion therapy waiting for results if ECG shows STEMI 1
• Serial troponins help distinguish Type 1 from Type 2 MI and assess infarct size 3, 5

Step 4: Risk Stratification for Immediate Catheterization

• ST elevation in aVR with diffuse ST depression (≥8 leads) indicates left main or severe multivessel disease requiring immediate angiography regardless of troponin 1
• Hemodynamic instability, cardiogenic shock, or mechanical complications mandate emergent catheterization 2

Critical Pitfalls to Avoid

• Never dismiss tachycardia as excluding MI—sympathetic activation commonly causes tachycardia in acute MI and should heighten suspicion 1
• Normal ECG does not exclude MI—the ECG is seldom completely normal even early, but repeated recordings may be necessary 1
• Do not assume young age excludes ACS—cocaine use, familial hyperlipidemia, and spontaneous coronary artery dissection occur in young patients 3
• Atypical presentations (dyspnea, fatigue, syncope without chest pain) are common in women, elderly, and diabetic patients 2, 6
• Epigastric or interscapular pain may represent inferior or posterior MI rather than gastrointestinal pathology 2