In a female patient with ST‑segment elevation in leads II, III, V5 and V6 and persistent back pain in the T12–L3 region, what is the most appropriate acute management and differential diagnosis?

ST-Elevation Myocardial Infarction with Extensive Lateral Extension and Concerning Back Pain

This patient requires immediate activation of the cardiac catheterization laboratory for primary PCI while simultaneously ruling out aortic dissection given the atypical back pain distribution extending to T12-L3, which is a life-threatening differential that would contraindicate standard STEMI management.

Critical Differential Diagnosis

Primary Concern: Extensive STEMI with Lateral Extension

• ST elevation in leads II, III (inferior), V5, and V6 (lateral) indicates a large territory myocardial infarction involving both inferior and lateral walls 1, 2
• This ECG pattern suggests either a dominant right coronary artery (RCA) occlusion extending to lateral branches (mega-artery) or a proximal left circumflex (LCx) occlusion 2
• ST elevation in V5-V6 with inferior STEMI is associated with larger infarct size, impaired myocardial reperfusion (myocardial blush grade 0-1), and worse outcomes 2
• The presence of ST elevation in both inferior and lateral leads indicates a perfusion territory score ≥0.7 (mega-artery occlusion) 2

Life-Threatening Alternative: Aortic Dissection

• The T12-L3 back pain is highly atypical for uncomplicated STEMI and raises concern for aortic dissection, which can cause coronary ostial involvement mimicking STEMI 1
• Aortic dissection is an absolute contraindication to thrombolytic therapy and anticoagulation 3
• Two-dimensional echocardiography should be performed emergently (if available without delaying catheterization) to evaluate for aortic dissection, pericardial effusion, or regional wall motion abnormalities 1

Immediate Management Algorithm

Step 1: Simultaneous Assessment (Do Not Delay Reperfusion)

• Obtain bilateral arm blood pressures immediately - difference >20 mmHg suggests dissection 1
• Assess for pulse deficits in all extremities 1
• Perform focused physical examination for aortic regurgitation murmur, neurological deficits 1
• If bedside echocardiography available within 5 minutes, perform to assess ascending aorta and regional wall motion 1

Step 2: Reperfusion Decision Based on Dissection Risk

If LOW suspicion for dissection (equal pulses, no blood pressure differential):

• Activate catheterization laboratory immediately with goal door-to-balloon time <90 minutes 4, 5
• Proceed with standard STEMI protocol below 1

If HIGH suspicion for dissection (pulse deficits, blood pressure differential >20 mmHg):

• HOLD all anticoagulation and antiplatelet therapy 3
• Obtain emergent CT angiography of chest/abdomen/pelvis (if catheterization lab not immediately available) 1
• If dissection confirmed, emergent cardiac surgery consultation 1
• If dissection ruled out, proceed immediately to catheterization laboratory 1

Step 3: Standard STEMI Medical Therapy (If Dissection Ruled Out)

Antiplatelet Therapy:

• Aspirin 150-325 mg chewed immediately (non-enteric formulation) 4, 5
• Ticagrelor 180 mg loading dose (preferred) OR prasugrel 60 mg if no contraindications 4

Anticoagulation:

• Unfractionated heparin bolus 60-70 units/kg (maximum 5,000 units) followed by infusion 12-15 units/kg/hour, targeting aPTT 50-70 seconds 4

Symptom Management:

• Morphine 4-8 mg IV with additional 2 mg doses every 5 minutes until pain relieved 1, 4
• Avoid nitroglycerin until right ventricular infarction excluded 4
• Oxygen 2-4 L/min by nasal cannula if oxygen saturation <90% 1

Beta-Blocker:

• Metoprolol 25-50 mg orally targeting heart rate 50-60 bpm, unless contraindicated by hypotension, bradycardia, or heart failure 4

Step 4: Assess for Right Ventricular Involvement

• Obtain right-sided ECG leads (V3R, V4R) immediately - ST elevation >0.5 mm indicates RV infarction occurring in up to 50% of inferior STEMIs 1, 4, 5
• If RV infarction present: avoid nitrates, diuretics, morphine, and ACE inhibitors 4
• Treat hypotension with aggressive IV fluid resuscitation (500-1000 mL bolus) as first-line 4

Step 5: Determine Culprit Artery Based on ECG Pattern

• If ST elevation in lead III > V6: Suggests RCA occlusion (96% probability), likely proximal given lateral extension 2
• If ST elevation in lead III ≤ V6: Suggests proximal LCx occlusion (96% probability, 74% proximal) 2
• Record posterior leads V7-V9 if available to assess for additional posterior involvement 1, 6, 5

Critical Pitfalls to Avoid

• Never delay reperfusion for cardiac biomarker results - treatment decisions are based on ECG and clinical presentation 1, 5
• Do not administer fibrinolytic therapy if aortic dissection cannot be excluded - this is absolutely contraindicated and potentially fatal 3
• Avoid nitrates, diuretics, and morphine if RV infarction suspected - these can cause catastrophic hypotension 4
• Do not assume back pain is musculoskeletal - the T12-L3 distribution is atypical for STEMI and warrants investigation for dissection extending to abdominal aorta 1
• ST elevation in V5-V6 with inferior STEMI indicates high-risk anatomy - these patients have larger infarcts, impaired reperfusion, and require aggressive management 2

Post-Catheterization Management

• Continue dual antiplatelet therapy (aspirin + P2Y12 inhibitor) for minimum 12 months 4
• Initiate ACE inhibitor within 24 hours (unless RV infarction with hypotension) 4
• Echocardiography within 24-48 hours to assess left ventricular function, wall motion abnormalities, and screen for complications including left ventricular thrombus 4
• If back pain persists post-revascularization, obtain CT angiography to definitively exclude aortic pathology 1