ST segment evaluation

ST Segment - The Baseline Shift

• Represents the interval between ventricular depolarization and repolarization; should be isoelectric.

• J-point: Junction where QRS complex ends and ST segment begins; the point of deviation measurement.

• ST Elevation (STE): Myocardial injury.

  • Causes: Acute MI, concave STE in pericarditis, Prinzmetal angina, ventricular aneurysm.
  • Threshold: >1 mm limb leads; >2 mm precordial leads.

• ST Depression (STD): Myocardial ischemia.

  • Causes: NSTEMI, angina, digoxin effect (scooped), LVH strain.

⭐ Convex (tombstone) ST elevation is highly specific for acute myocardial infarction, whereas concave elevation is more characteristic of pericarditis.

ST Elevation - The Tombstone Terror

Signifies transmural myocardial injury, demanding immediate attention. Defined as new ST elevation at the J point in ≥2 contiguous leads.

• Thresholds:
  • ≥1 mm in most leads.
  • ≥2 mm in leads V2-V3 (men >40), ≥2.5 mm (men <40), ≥1.5 mm (women).
• Morphology:
  • Convex (coved): Suggests STEMI. "Tombstone" appearance.
  • Concave: Can be STEMI, but also seen in pericarditis.

⭐ Reciprocal ST depression in leads electrically opposite to the elevated leads is highly specific for acute myocardial infarction (STEMI).

📌 Mnemonic (Causes): ELEVATION

• Electrolytes (Hyperkalemia)
• LBBB
• Early Repolarization
• Ventricular Aneurysm
• Acute MI
• Takotsubo Cardiomyopathy
• Injury (Contusion)
• Osborne Wave (Hypothermia)
• N-Vasospasm (Prinzmetal Angina)

ST Depression - The Ischemic Dip

• Represents subendocardial ischemia, an imbalance in myocardial oxygen supply and demand affecting the inner heart wall.
• Criteria: New horizontal or downsloping ST depression ≥0.5 mm in ≥2 contiguous leads.
• Morphology is Key:
  • Downsloping/Horizontal: High specificity for coronary ischemia.
  • Upsloping: Less specific; often benign but can indicate ischemia if J-point is significantly depressed.
• Associated Conditions:
  • NSTEMI / Unstable Angina
  • Positive exercise stress test
  • Digoxin toxicity (scooped, "Salvador Dalí

ST Mimics - The ECG Imposters

Key non-ischemic causes of ST segment changes:

• Pericarditis: Diffuse, concave ("saddle-back") ST elevation and specific PR depression. No reciprocal changes.
• Benign Early Repolarization (BER): Widespread concave ST elevation with J-point notching ("fish-hook"). Common in young, healthy patients.
• Left Ventricular Hypertrophy (LVH): Lateral leads (I, aVL, V5-V6) show ST depression and T-wave inversion (strain pattern).
• Left Bundle Branch Block (LBBB): "Appropriate discordance" where ST segments oppose the main QRS vector.
• Brugada Syndrome: Coved ST elevation >2 mm in V1-V2 with a negative T-wave.
• Takotsubo Cardiomyopathy: Mimics anterior MI; transient apical dysfunction without coronary stenosis.

⭐ The ST/T wave ratio in V6 < 0.25 strongly suggests pericarditis over STEMI.

High‑Yield Points - ⚡ Biggest Takeaways

• ST elevation (STE) in ≥2 contiguous leads is the hallmark of acute transmural ischemia (STEMI).
• ST depression (STD) suggests subendocardial ischemia, reciprocal changes, or posterior MI.
• Convex (tombstone) STE is more specific for infarction than concave STE.
• Diffuse, concave STE with PR depression is characteristic of acute pericarditis.
• Benign Early Repolarization (BER) presents with mild, notched, concave STE, common in young athletes.
• Digoxin effect classically causes downsloping or "scooped" ST depression.