What ECG patterns are considered STEMI equivalents and how should they be managed acutely?

STEMI Equivalents: ECG Patterns and Acute Management

Patients with acute coronary occlusion may present without classic ST-elevation, and these "STEMI equivalents" mandate the same urgent reperfusion strategy as traditional STEMI—immediate coronary angiography with primary PCI or fibrinolysis within guideline-recommended time windows. 1

Core STEMI Equivalent Patterns Requiring Immediate Reperfusion

Posterior Myocardial Infarction

• Isolated ST-depression ≥0.5 mm in leads V1-V3 with upright terminal T-waves represents posterior wall STEMI and should be managed identically to anterior STEMI. 1, 2
• Confirm the diagnosis by recording posterior leads V7-V9, where ST-elevation ≥0.5 mm establishes transmural posterior infarction. 1, 3, 2
• This pattern reflects acute circumflex artery occlusion and is frequently missed if providers rely solely on standard 12-lead criteria. 1

New or Presumed New Left Bundle Branch Block (LBBB)

• New LBBB in the setting of ischemic symptoms is a STEMI equivalent requiring immediate reperfusion therapy. 1, 3
• The challenge: most LBBB cases at presentation are "not known to be old" because prior ECGs are unavailable. 1
• Concordant ST-elevation (elevation in leads with positive QRS deflections) is the most reliable marker of acute coronary occlusion in LBBB. 2
• Do not delay emergency angiography in patients with LBBB and ongoing ischemic symptoms, even without meeting specific ECG criteria. 1, 2

Left Main or Proximal LAD Occlusion Pattern

• Diffuse ST-depression in ≥8 leads with concomitant ST-elevation in aVR and/or V1 indicates left main or severe multivessel disease requiring immediate catheterization. 1, 3, 4
• This pattern carries extremely high mortality and often presents with hemodynamic instability. 2
• Treat as a STEMI equivalent with urgent angiography, not as NSTEMI with delayed invasive strategy. 5

Hyperacute T-Waves

• Tall, peaked, symmetric T-waves (hyperacute T-waves) may precede ST-elevation in the earliest phase of coronary occlusion. 1, 3, 4
• Perform serial ECGs at 5-10 minute intervals to capture evolution to frank ST-elevation. 3
• If clinical suspicion is high and hyperacute T-waves are present, activate the catheterization laboratory without waiting for ST-elevation to develop. 1, 3

De Winter T-Wave Pattern

• Upsloping ST-depression at the J-point in precordial leads with tall, symmetric T-waves in V2-V6, often with ST-elevation in aVR, represents acute proximal LAD occlusion. 3, 6
• This pattern occurs in 2-3% of anterior STEMIs and requires immediate reperfusion despite absence of ST-elevation. 6, 7

Right Ventricular Infarction

• In inferior STEMI (ST-elevation in II, III, aVF), obtain right-sided leads V3R-V4R; ST-elevation ≥1.0 mm in these leads indicates RV involvement. 1, 3, 2
• RV infarction alters hemodynamic management: avoid nitrates and diuretics, maintain preload with IV fluids. 1

Diagnostic Approach Algorithm

Step 1: Rapid ECG Acquisition and Interpretation

• Obtain and interpret 12-lead ECG within 10 minutes of first medical contact. 3, 2
• Initiate continuous ECG monitoring immediately to detect arrhythmias. 3, 2

Step 2: Identify STEMI Equivalents

• If standard STEMI criteria are absent but any of the following are present with ischemic symptoms, activate reperfusion protocol:
  • ST-depression V1-V3 with positive T-waves (posterior MI) 1, 2
  • New/presumed new LBBB 1
  • ST-depression ≥8 leads + ST-elevation aVR/V1 (left main pattern) 1, 4
  • Hyperacute T-waves 3, 4
  • De Winter pattern 3, 6

Step 3: Obtain Additional Leads When Indicated

• Record V7-V9 for suspected posterior MI. 1, 3, 2
• Record V3R-V4R for all inferior STEMIs. 1, 3, 2

Step 4: Do Not Wait for Biomarkers

• Initiate reperfusion therapy immediately based on ECG findings; do not delay for troponin results. 3, 2
• Cardiac biomarkers confirm diagnosis retrospectively but should never postpone treatment. 3

Step 5: Activate Reperfusion Strategy

• Primary PCI is preferred if door-to-balloon time ≤90 minutes. 1, 3
• Fibrinolysis if door-to-needle time ≤30 minutes and anticipated PCI delay >120 minutes from STEMI diagnosis. 1, 3

Critical Pitfalls and How to Avoid Them

Pitfall 1: Dismissing ST-Depression as "Non-Specific"

• ST-depression in V1-V3 with positive T-waves is NOT non-specific—it represents posterior STEMI. 1, 2, 5
• Always obtain posterior leads V7-V9 to confirm. 1, 3

Pitfall 2: Assuming LBBB Precludes STEMI Diagnosis

• Do not withhold reperfusion therapy in patients with LBBB and ischemic symptoms. 1, 2
• Look for concordant ST-elevation as the strongest indicator of acute occlusion. 2
• When in doubt, proceed directly to emergency angiography. 1

Pitfall 3: Treating Diffuse ST-Depression as NSTEMI

• Diffuse ST-depression with ST-elevation in aVR indicates left main occlusion, not NSTEMI. 1, 4
• These patients require immediate catheterization, not delayed invasive strategy. 5

Pitfall 4: Waiting for Serial Troponins

• Never delay reperfusion to await biomarker results in patients meeting ECG criteria for STEMI or STEMI equivalents. 3, 2
• Treatment decisions are driven by ECG findings and clinical presentation. 3

Pitfall 5: Missing Circumflex Occlusions

• Up to 30% of acute coronary occlusions do not meet traditional STEMI criteria, particularly circumflex territory infarctions. 1, 6, 7
• Maintain high suspicion for ongoing ischemia even with non-diagnostic ECG; proceed to urgent angiography. 1

Special Circumstances Requiring Urgent Angiography

Ventricular Pacing

• Pacemaker rhythm obscures ST-segment interpretation; consider reprogramming if patient is not pacemaker-dependent. 1, 3
• If reprogramming would delay care, proceed directly to emergency angiography based on clinical suspicion. 1

Left Ventricular Hypertrophy

• LVH produces baseline ST-elevation in precordial leads, complicating STEMI diagnosis. 3
• Compare to prior ECGs when available; use portable echocardiography to assess wall motion abnormalities. 3

Suspected Aortic Dissection

• Screen for pulse deficits, blood pressure differentials, and mediastinal widening before administering reperfusion therapy. 3
• Aortic dissection is an absolute contraindication to fibrinolysis and may mimic STEMI. 3
• Use CT angiography or transesophageal echocardiography to exclude dissection when clinical suspicion exists, but do not delay PCI if dissection is unlikely. 3

Ancillary Testing (When Diagnosis Remains Uncertain)

• Portable echocardiography identifies regional wall motion abnormalities when ECG is confounded by LBBB, pacing, or LVH. 1, 3
• Imaging must not delay reperfusion unless aortic dissection is strongly suspected. 3
• Point-of-care troponin may aid in ambiguous scenarios but should not postpone definitive management. 3

Management After STEMI Equivalent Identification

Immediate Pharmacotherapy (Pre-Catheterization)

• Aspirin 162-325 mg loading dose. 5
• P2Y12 inhibitor: prasugrel or ticagrelor preferred over clopidogrel. 1
• Anticoagulation: unfractionated heparin, enoxaparin, or bivalirudin. 1
• Avoid routine morphine due to delayed antiplatelet absorption. 1

Reperfusion Strategy Selection

• Primary PCI is the preferred reperfusion strategy for all STEMI equivalents. 1, 3
• Radial access and drug-eluting stents are standard of care. 1
• Routine thrombus aspiration is contraindicated. 1

Post-Reperfusion Care

• Continue dual antiplatelet therapy for 12 months. 1
• Initiate high-intensity statin, ACE inhibitor/ARB, and beta-blocker. 5
• Assess for non-infarct-related artery lesions before discharge; treat severe stenoses either during index procedure or staged. 1