Overview

This lecture covers the recognition and importance of subtle STEMI (ST-elevation myocardial infarction) or occlusion MI (OMI) patterns on EKG/ECG, emphasizing why prompt identification and urgent intervention rival that of classic STEMIs.

Subtle STEMI and Occlusion MI

• 20–30% of non-STEMI cases are due to acute coronary occlusion, often involving the left circumflex or RCA.
• Subtle ST elevation and other specific EKG changes may indicate STEMI even when traditional cut points are not met.
• Immediate cath lab activation is needed for subtle STEMI, similar to classic STEMI management.

Morphological Criteria for STEMI

• Five key ST elevation morphologies suggest STEMI: straight/convex elevation, wide/inverted T-waves, Q waves, ST elevation/QRS ratio, and reciprocal depression.
• ST elevation approximating half the QRS height, or a T-wave equal to the QRS, is concerning.
• Terminal QRS distortion (S-wave above baseline) is a strong STEMI indicator.

Subtle STEMI Patterns and Clinical Examples

• Subtle ST elevation may appear in one or two leads, not always contiguous or >1mm.
• Features: shrinking QRS, wide/tall T-waves, evolving Q waves, reciprocal ST depression.
• Serial EKGs (every 5–15 minutes) help observe progression for evolving MI features.

Key STEMI EKG Patterns

• Hyperacute T-waves: wide/tall, sometimes "de Winter" pattern (upsloping depression, upright T).
• Posterior OMI: maximal ST depression V1–V4, upright T, prominent R in V1/V2.
• Left bundle branch block (LBBB): Concordant ST changes or discordant ST elevation >25% QRS or T >50% QRS height suggest STEMI.

STEMI Mimics and Differential Diagnosis

• Pericarditis: Concave ST elevation, PR depression, ST never >5mm, T-wave does not approach QRS height, lacks reciprocal depression (except in aVR/V1).
• Early repolarization: Seen in young males, S-wave below baseline with J-wave, not related to MI.

Special Morphological Patterns

• Terminal QRS distortion: S-wave pulled above the baseline with sharp J point, not seen in early repolarization.
• South African flag sign: ST elevation in aVL and V2, with inferior depression, suggests diagonal branch occlusion.
• Aslanger pattern: Diffuse ST depression with ST elevation in III (sometimes V1/AVR), often indicates subendocardial ischemia, not always acute occlusion.

Causes of Mild ST Elevation in OMI

• Partial occlusion, collateral flow, or subacute occlusion can result in subtle EKG changes.
• Posterior/lateral MI may be missed on standard 12-lead EKG.
• Late STEMI presentation or small infarct territory can lead to mild ST changes.

Diffuse ST Depression with ST Elevation in aVR/V1

• Indicates high-risk non-STEMI, not a STEMI equivalent.
• Often due to left main or three-vessel ischemia, severe supply-demand mismatch, or non-cardiac causes (e.g., anemia, hypoxia).

Key Terms & Definitions

• STEMI — ST-elevation myocardial infarction, acute heart attack with visible EKG changes.
• OMI — Occlusion myocardial infarction; acute MI due to complete coronary blockage.
• QRS Shrinkage — Decrease in QRS size; T-wave approaches or exceeds QRS height.
• Terminal QRS distortion — S-wave rises above baseline; loss of normal J-wave.
• Hyperacute T-wave — Early, broad, tall T-wave in acute MI.
• de Winter pattern — Upsloping ST depression & tall T-waves; anterior MI variant.
• Aslanger pattern — Diffuse ST depression with ST elevation in lead III.
• Left bundle branch block (LBBB) — Abnormal heart conduction, complicates MI diagnosis; specific ST criteria needed.

Action Items / Next Steps

• Review EKG examples with subtle STEMI features.
• Practice identifying key OMI patterns and mimics.
• Read up on Smith and Aslanger criteria for STEMI in special EKG situations.
• Repeat EKGs serially in chest pain patients for evolving changes.

Certainly! Here is a comprehensive, in-depth summary and review of the lecture on subtle STEMI (ST-elevation myocardial infarction) or occlusion MI (OMI), focusing on the recognition, interpretation, and clinical implications of subtle and atypical EKG patterns that indicate acute coronary occlusion.

In-Depth Summary and Review: Subtle STEMI and Occlusion MI (OMI)

1. Introduction and Clinical Importance

• Subtle STEMI or Occlusion MI (OMI) refers to acute coronary occlusions that do not meet classic STEMI criteria on EKG but still represent myocardial infarction requiring urgent intervention.
• Approximately 20–30% of non-STEMI cases are actually due to acute coronary occlusion, often involving the left circumflex artery (LCx) or right coronary artery (RCA).
• These cases are frequently STEMI equivalents or “subtle STEMIs” and should be managed emergently like classic STEMIs, including urgent cardiac catheterization and reperfusion.
• Traditional STEMI criteria based on fixed ST elevation cut points (e.g., >1 mm in contiguous leads) are flawed and insensitive for detecting many occlusive MIs.
• The morphology and context of ST elevation and other EKG changes are more important than absolute ST elevation magnitude.

2. Morphological Criteria for STEMI on EKG

Five key morphological features strongly suggest STEMI:

1. ST Elevation Morphology:

   • ST segment that is straight or convex upward, blending smoothly into the T-wave to form a dome-like shape.
   • This contrasts with concave or “scooped” ST elevation seen in benign conditions.

2. T-wave Abnormalities:

   • Wide, tall, or inverted T-waves accompanying subtle ST elevation.
   • The T-wave may be disproportionately large relative to the QRS complex.

3. Q Waves:

   • Presence of pathologic Q waves or evolving Q waves.
   • Q waves that approximate or exceed half the height of the QRS complex are concerning.

4. ST Elevation to QRS Ratio:

   • ST elevation that approximates half or more of the QRS height.
   • A T-wave height that approaches or exceeds the QRS height is also highly suggestive.

5. Reciprocal ST Depression:

   • ST depression in leads opposite the site of injury supports STEMI diagnosis.
   • Important to distinguish reciprocal changes from secondary repolarization abnormalities (e.g., LVH or LBBB).

Terminal QRS Distortion:

• A very specific sign where the S-wave is pulled above the baseline, losing its normal negative deflection.
• This distortion is not seen in early repolarization and strongly indicates STEMI.

3. Subtle STEMI Patterns and Clinical Examples

• Subtle STEMI may present with ST elevation <1 mm, sometimes in only one or two leads, which may not be contiguous.
• Key accompanying features include:
  • Shrinking QRS complexes (QRS amplitude decreases over time).
  • Wide or tall T-waves that approximate the QRS size.
  • Evolving Q waves.
  • Reciprocal ST depression or T-wave inversion.
• Serial EKGs every 5–15 minutes are critical to detect progression (e.g., further QRS shrinkage, more pronounced ST elevation, evolving Q waves).

Clinical Cases:

• Examples include patients with subtle anterior ST elevation, reciprocal inferior depression, and terminal QRS distortion, who were found to have 100% occlusion of the LAD or other arteries.
• Some patients have collateral circulation or partial occlusion, explaining subtle EKG changes despite significant infarction.

4. Key STEMI EKG Patterns Beyond Classic ST Elevation

a. Hyperacute T-waves

• Early sign of STEMI characterized by large, wide, and often fused T-waves with the ST segment.
• The de Winter pattern is a variant with upsloping ST depression in V1–V6 followed by tall upright T-waves, often indicating proximal LAD occlusion.
• These T-waves may not progress to classic ST elevation but still represent acute MI.

b. Posterior OMI

• Characterized by maximal ST depression in leads V1–V4, upright T-waves, and often a prominent R-wave in V1 or V2.
• This pattern reflects a posterior infarction, which is not well visualized on standard 12-lead EKG.
• Recording posterior leads (V7–V9) can reveal ST elevation.

c. Left Bundle Branch Block (LBBB) and LVH

• LBBB causes discordant ST changes: ST elevation when QRS is negative, and ST depression when QRS is positive.
• Diagnosing STEMI in LBBB requires identifying concordant ST changes (ST elevation or depression in leads where QRS is concordant).
• The ST elevation to QRS ratio >25% and T-wave discordance >50% are important criteria for STEMI in LBBB.
• Old criteria (e.g., Sgarbossa) using absolute ST elevation cutoffs are less sensitive and specific.

5. STEMI Mimics and Differential Diagnosis

a. Acute Pericarditis

• Diffuse concave ST elevation with PR depression.
• ST elevation rarely exceeds 5 mm.
• No reciprocal ST depression except in aVR and V1.
• T-waves do not approach QRS height.
• No terminal QRS distortion.

b. Early Repolarization

• Common in young, healthy males.
• ST elevation with S-wave below baseline and J-wave present.
• ST elevation usually <3 mm.
• Stable over time and no troponin elevation.

c. Aslanger Pattern

• Diffuse ST depression with ST elevation in lead III (sometimes V1 and aVR).
• Suggests subendocardial ischemia with critical non-culprit disease.
• Not always acute occlusion; may represent severe multivessel disease or chronic total occlusion (CTO).
• Requires urgent cath but not always immediate intervention.

6. Causes of Mild or Subtle ST Elevation in OMI

• Partial occlusion or subtotal occlusion with some residual flow.
• Collateral circulation providing some perfusion to infarcted territory.
• Subacute occlusion or ischemic preconditioning.
• Small infarct territory or infarct in areas poorly visualized by standard EKG (posterior, lateral).
• Late STEMI presentation with deep Q waves and minimal residual ST elevation.
• Concurrent ischemia in other territories attenuating ST elevation (e.g., Aslanger pattern).

7. Diffuse ST Depression with ST Elevation in aVR and V1

• This pattern is not a STEMI equivalent.
• Indicates high-risk non-STEMI with extensive subendocardial ischemia, often due to left main or three-vessel disease.
• Can also be caused by severe supply-demand mismatch (e.g., anemia, hypoxia, shock) without CAD.
• Urgent cath indicated only if ST changes are deep, persistent, and not explained by non-cardiac causes.
• ST elevation in aVR > V1 or >1.5 mm suggests left main disease.

8. Clinical Implications and Management

• Recognition of subtle STEMI and OMI patterns is critical to avoid missed diagnosis and delayed reperfusion.
• Patients with subtle STEMI should be treated urgently like classic STEMI, with immediate cath lab activation.
• Serial EKGs and clinical correlation (symptoms, troponin) are essential.
• Differentiation from mimics (pericarditis, early repolarization) prevents unnecessary interventions.
• In complex cases (e.g., Aslanger pattern, LBBB), careful analysis and consultation are needed.
• Late PCI may still benefit patients with subtle STEMI due to partial occlusion or collateral flow.

9. Summary of Key Teaching Points

Final Thoughts

This lecture emphasizes the critical need to move beyond rigid STEMI criteria and to recognize subtle, atypical EKG patterns that indicate acute coronary occlusion. Understanding the morphology, context, and evolution of EKG changes allows clinicians to identify patients who require urgent reperfusion despite not meeting classic STEMI thresholds. This nuanced approach improves patient outcomes by preventing missed or delayed diagnosis of occlusive MI.

If you want, I can help you create a detailed study guide or highlight specific EKG examples from the lecture for practice. Just let me know!