What is ischemia? What are its type? And how ECG is affected by them?
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myocardial ischemia AND electrocardiography
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ECG features myocardial ischemia subendocardial subepicardial ST T wave authoritative
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diagram showing ECG changes myocardial ischemia ST depression T wave inversion ST elevation infarction
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Ischemia means inadequate blood flow to a tissue, causing insufficient oxygen and nutrient delivery for its metabolic needs. In the heart, myocardial ischemia usually results from reduced coronary blood flow, most commonly due to coronary artery narrowing or an acute clot.
It is initially reversible. If severe ischemia lasts long enough, myocardial cells die, which is myocardial infarction (MI).
Main types of myocardial ischemia and ECG changes
| Type | Typical mechanism | ECG effect |
|---|---|---|
| Subendocardial ischemia | Reduced flow to the inner myocardial layer. Often due to partial coronary obstruction or increased oxygen demand, such as tachycardia, exercise, anemia, hypertension, or hypotension | ST-segment depression, usually horizontal or downsloping. May also show T-wave inversion |
| Transmural ischemia | Ischemia extends through the full thickness of the ventricular wall, often from acute complete coronary occlusion or coronary vasospasm | ST-segment elevation in leads facing the affected area, often with early tall "hyperacute" T waves. There may be reciprocal ST depression in opposite leads |
The ST segment is the ECG component most sensitive to acute myocardial ischemia. Transmural ischemia generally shifts the ST segment upward, whereas subendocardial ischemia shifts it downward. Miller's Anesthesia, 10e, p. 4731.
Other practical clinical forms
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Stable angina
- Predictable chest discomfort with exertion or stress.
- Usually reflects fixed coronary narrowing and a supply-demand mismatch.
- Resting ECG may be normal.
- During pain or an exercise test: ST depression may occur.
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Unstable angina / NSTEMI spectrum
- New, worsening, prolonged, or rest angina, usually due to plaque disruption and partial coronary obstruction.
- ECG may show ST depression, T-wave inversion, or sometimes no diagnostic change.
- In NSTEMI, troponin is elevated. In unstable angina, it is not.
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ST-elevation MI (STEMI)
- Usually acute, persistent complete coronary occlusion causing transmural injury and later necrosis.
- ECG: regional ST elevation in contiguous leads, often with reciprocal ST depression.
- Later: T-wave inversion and possibly pathological Q waves.
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Vasospastic (Prinzmetal) angina
- Transient coronary vasospasm, often at rest.
- ECG during the spasm: transient ST elevation.
- The ECG may normalize after the spasm resolves.
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Silent ischemia
- Ischemia without typical chest pain, more common in diabetes and older adults.
- Detected by ambulatory monitoring or stress testing, often as ST depression.
Simple ECG sequence in acute coronary occlusion
- Very early: tall, broad, "hyperacute" T waves
- Acute transmural ischemia/injury: ST elevation
- Evolution: T-wave inversion
- Established infarction in some patients: pathological Q waves
Important distinction
- T-wave inversion can suggest ischemia but is not specific. It may occur with ventricular hypertrophy, bundle branch block, pulmonary embolism, CNS events, and other conditions.
- ST depression also has non-ischemic causes, including digoxin effect, tachycardia, hypokalemia, or baseline ECG abnormalities.
- A normal ECG does not exclude ischemia or acute coronary syndrome. ECG findings must be interpreted with symptoms, serial ECGs, and troponin testing.
Memory aid:
- Inner layer ischemia = ST depression
- Full-thickness ischemia = ST elevation
Acute chest pressure, breathlessness, sweating, syncope, or pain radiating to the arm, jaw, back, or epigastrium requires urgent emergency evaluation.
What is wellness syndrome?
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Wellens syndrome
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Wellens syndrome ECG biphasic deeply inverted T waves proximal LAD authoritative
You likely mean Wellens syndrome, not “wellness syndrome.”
Wellens syndrome is a high-risk ECG pattern that indicates critical narrowing of the proximal left anterior descending (LAD) coronary artery. It is a warning sign of a potentially large anterior-wall myocardial infarction.
Typical clinical setting
- Recent episodes of chest pain
- Patient is often pain-free when the ECG is recorded
- Cardiac troponin may be normal or only mildly elevated
- Little or no ST elevation
ECG features
Usually seen in the anterior chest leads, especially V2-V3, sometimes extending from V1 to V6:
| Pattern | ECG appearance |
|---|---|
| Type A | Biphasic T waves, typically initially positive then negative, in V2-V3 |
| Type B | Deep, symmetrical T-wave inversions in V2-V3, sometimes V2-V4 or more widely |
Additional usual findings:
- Isoelectric ST segment or only minimal ST elevation, less than 1 mm
- No pathological Q waves
- Preserved R-wave progression
- Often prolonged QT interval
About 75% of patients have deep symmetrical T-wave inversion, while about 25% have biphasic T waves. Tintinalli's Emergency Medicine, section “Serum Markers of Myocardial Injury.” The pattern in a pain-free patient after recent chest pain should raise concern for a critical LAD lesion. The Washington Manual of Medical Therapeutics, section “Electrocardiography.”
Why it matters
This is a pre-infarction pattern, not a reassuring ECG. Without prompt assessment and coronary reperfusion when indicated, the patient can develop a large anterior STEMI.
What to do
Wellens syndrome needs urgent cardiology assessment and coronary angiography. A routine exercise stress test should generally be avoided because it can provoke severe ischemia or infarction in someone with critical LAD obstruction.
The NIH clinical review describes the characteristic deeply inverted or biphasic T waves in V2-V3. If this ECG pattern is present with chest pain or recent chest pain, seek emergency care immediately.
Localisation of ischemic area.
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ECG localization myocardial ischemia infarction leads anterior inferior lateral posterior right ventricular guideline
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12 lead ECG myocardial infarction localization territories anterior inferior lateral posterior leads diagram
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ECG localization of the ischemic or infarcted myocardial area
Localization is based on ST-T changes in contiguous ECG leads. It is most accurate for regional ST elevation due to acute coronary occlusion. In subendocardial ischemia, ST depression may be widespread and is less precise for locating one single area.
| Area involved | ECG leads showing ischemic changes | Usual coronary artery |
|---|---|---|
| Septal | V1-V2 | Septal branches of LAD |
| Anterior | V3-V4 | LAD |
| Anteroseptal | V1-V4 | LAD, usually proximal |
| Extensive anterior | V1-V6, I, aVL | Proximal LAD or left main coronary artery |
| Lateral | I, aVL, V5-V6 | Left circumflex or diagonal branch of LAD |
| Anterolateral | V3-V6, I, aVL | LAD plus diagonal branch, sometimes left circumflex |
| Inferior | II, III, aVF | Usually right coronary artery; sometimes left circumflex |
| Posterior | Reciprocal ST depression in V1-V3, often with tall R waves and upright T waves. Confirm with ST elevation in V7-V9. | Usually left circumflex, sometimes RCA |
| Right ventricle | ST elevation in right-sided leads, especially V4R | Proximal RCA, usually with inferior MI |
Important reciprocal changes
Reciprocal change means ST depression in leads facing the opposite side of the heart.
| Primary ischemic area | ST elevation | Reciprocal ST depression commonly seen in |
|---|---|---|
| Inferior | II, III, aVF | I, aVL, sometimes V1-V3 |
| Anterior | V1-V4 | II, III, aVF may show reciprocal depression |
| Lateral | I, aVL, V5-V6 | III, aVF |
| Posterior | V7-V9 | V1-V3 show reciprocal ST depression |
Easy lead map
- V1-V2 = septal
- V3-V4 = anterior
- V5-V6, I, aVL = lateral
- II, III, aVF = inferior
- V7-V9 = posterior
- V3R-V4R = right ventricle
Clinical clues to the culprit artery
- Inferior MI with ST elevation III > II suggests an RCA occlusion.
- Inferior MI plus ST elevation in V4R suggests right ventricular infarction from proximal RCA occlusion.
- Inferior MI plus ST depression in V1-V3 raises suspicion of associated posterior involvement.
- Widespread ST depression with ST elevation in aVR, especially if prominent, can indicate severe global subendocardial ischemia, including possible left-main or proximal multivessel coronary disease. It is not a simple territorial STEMI pattern.
Rosen’s table summarizes the core localizations: anterior STEMI in V1-V4, lateral STEMI in I/aVL/V5-V6, inferior STEMI in II/III/aVF, posterior MI with ST elevation in V8-V9 and reciprocal depression in V1-V3. ROSEN's Emergency Medicine, “Anatomic Location of Acute Myocardial Infarction.”
Key caution: ST depression and T-wave inversion alone can be caused by ischemia but may be nonspecific. Interpret them with symptoms, serial ECGs, troponin, and comparison with prior ECGs.
Godtus, S.T. elevation and reciprocal leads and changes mean in ECG.
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