What are ST elevation equivalents?

ST Elevation Equivalents

ST elevation equivalents are ECG patterns that indicate acute coronary occlusion requiring emergent reperfusion therapy despite lacking classic ST elevation, including posterior MI (ST depression in V1-V3 with positive terminal T-waves confirmed by ST elevation ≥0.5 mm in V7-V9), right ventricular MI (ST elevation >0.5 mm in V3R-V4R with inferior MI), and de Winter T-waves (tall symmetric T-waves with upsloping ST depression >1 mm in precordial leads). 1

Posterior Myocardial Infarction

Posterior MI is the most clinically important ST elevation equivalent and should be managed as a STEMI. 1

• Horizontal ST-segment depression in V1-V3 with a dominant R-wave (R/S ratio >1) in V2, upright T-waves in anterior leads, and prominent broad R-wave (>30 ms) suggests posterior MI 1
• The ST depression represents reciprocal changes from posterior ST elevation, making it electrocardiographically equivalent to posterior ST elevation from a spatial vector perspective 1
• Confirmation requires ST elevation ≥0.5 mm in at least one of the posterior leads V7-V9 (V7 at posterior axillary line, V8 below scapula, V9 at paravertebral border, all in the same horizontal plane as V6) 1
• The specificity increases at a cut-point >0.1 mm ST elevation in posterior leads, and this higher threshold should be used in men <40 years old 1
• Recording posterior leads V7-V9 is strongly recommended when there is high clinical suspicion for acute circumflex occlusion, especially with initial non-diagnostic ECG or isolated ST depression in V1-V3 1

Right Ventricular Infarction

Right ventricular MI occurs with inferior wall infarction and requires specific management considerations. 1

• Recording right-sided precordial leads (V3R and V4R) during acute inferior-wall MI is recommended to identify concomitant right ventricular involvement 1
• ST elevation >0.5 mm (>1 mm in men <30 years old) in V3R or V4R provides supportive criteria for right ventricular infarction 1
• Standard V1 can be considered equivalent to V2R, and standard V2 equivalent to V1R within the right-sided electrode array 1
• ST elevation exceeding 0.1 mV in one or more right precordial leads is moderately sensitive and specific for right ventricular injury and has been associated with underlying right ventricular dysfunction and greater in-hospital complications 1

Left Bundle Branch Block (LBBB)

New or presumably new LBBB with ischemic symptoms should prompt urgent coronary angiography, but is NOT automatically a STEMI equivalent requiring immediate reperfusion. 1

Modified Sgarbossa Criteria (Most Accurate Approach)

The revised Sgarbossa criteria using proportional ST/S ratio has superior diagnostic utility compared to the original criteria. 2

• A total score ≥3 points using the following weighted criteria:

  • Concordant ST elevation ≥1 mm in leads with a positive QRS complex (5 points) 1
  • Concordant ST depression ≥1 mm in V1-V3 (3 points) 1
  • Discordant ST elevation ≥5 mm in leads with a negative QRS complex (2 points) 1

• Alternative unweighted approach (positive if ANY of the following):

  • Concordant ST elevation of 1 mm in leads with a positive QRS complex 1
  • Concordant ST depression of 1 mm in V1-V3 1
  • ST elevation at the J-point with an ST/S ratio ≤-0.25 (this replaces the ≥5 mm criterion and has 91% sensitivity and 90% specificity) 1, 2

Important Caveats About LBBB

• Only 39% of patients with new LBBB and suspected AMI actually have acute coronary syndrome, and only a minority have occluded culprit arteries 3
• The presence of concordant ST elevation (in leads with positive QRS deflections) is one of the best indicators of ongoing MI with an occluded infarct artery 1
• LBBB should NOT be considered diagnostic of acute MI in isolation 4
• A previous ECG is extremely helpful in determining whether LBBB is truly new 1

De Winter Sign

De Winter T-waves represent hyperacute proximal LAD occlusion and require immediate reperfusion. 1

• Tall, prominent, symmetrical T-waves arising from upsloping ST depression >1 mm at the J-point in precordial leads 1
• May have 0.5-1 mm ST elevation in lead aVR 1
• These represent hyperacute changes that may precede classic ST elevation 1

Ventricular Pacing

Ventricular pacing prevents interpretation of ST-segment changes and may require urgent angiography to confirm diagnosis. 1

• Reprogramming the pacemaker to allow evaluation of intrinsic rhythm may be considered in non-pacemaker-dependent patients, without delaying invasive investigation 1

Critical Pitfall: ST Elevation in aVR

ST elevation in aVR with multilead ST depression should be managed as NSTE-ACS, NOT as a STEMI equivalent. 5

• This pattern suggests severe global myocardial ischemia (often left main or proximal LAD disease) but does NOT typically represent acute coronary occlusion requiring emergent reperfusion 5
• Fibrinolytic therapy should NOT be administered to patients with ST depression associated with ST elevation in aVR 5
• Manage with urgent evaluation, serial troponins, continuous monitoring, and antiplatelet/anticoagulation therapy 5

Hyperacute T-Waves

Broad, asymmetric, peaked T-waves may be seen early in STEMI before ST elevation develops. 1

• Serial ECGs over very short intervals are useful to assess for progression to STEMI 1
• Some patients with acute coronary occlusion present very early with hyperacute T-waves preceding ST elevation 1

Clinical Algorithm for Non-Diagnostic ECGs

When clinical suspicion for acute coronary occlusion is high but the ECG lacks classic ST elevation:

1. Immediately obtain posterior leads (V7-V9) if ST depression in V1-V3 or suspected circumflex occlusion 1
2. Obtain right-sided leads (V3R-V4R) if inferior MI is present 1
3. Perform serial ECGs at short intervals to detect dynamic changes or evolution to STEMI 1
4. Consider urgent coronary angiography even without diagnostic ST elevation if suspicion of ongoing ischemia remains high 1
5. In the presence of LBBB, apply modified Sgarbossa criteria with ST/S ratio ≤-0.25 for best diagnostic accuracy 2