What Are the ECG Signs of Ischemia? Complete 2026 Doctor’s Guide

By Dr. Sagar Rajkuwar, ENT Specialist, Nashik, Maharashtra, India
🌐 www.entspecialistinnashik.com

Short answer: The core ECG signs of ischemia are ST-segment depression ≥0.5 mm (subendocardial ischaemia), T-wave inversion, ST-segment elevation ≥1 mm (transmural injury, STEMI), hyperacute “tented” T-waves, Wellens’ syndrome (biphasic/deep T-wave inversions in V2–V3), De Winter T-waves, new left bundle branch block with Sgarbossa criteria, and pathological Q-waves (completed infarct). These findings may appear in specific lead groups mapping to coronary territories. If you are asking what are the ECG signs of ischemia, this 2026 ENT-authored guide, aligned with WHO, CDC, NHS, Universal Definition of MI 2018, AHA/ACC 2023, and ESC 2024 ACS, walks you through every pattern.

Table of Contents

1. Introduction
2. Why the ECG Matters in Ischaemia
3. Normal ECG Review
4. Subendocardial vs Transmural Ischaemia
5. ST-Segment Depression
6. ST-Segment Elevation
7. T-Wave Changes
8. Hyperacute T-Waves
9. Wellens’ Syndrome
10. De Winter T-Waves
11. Pathological Q-Waves
12. LBBB & Sgarbossa Criteria
13. STEMI by Coronary Territory
14. Reciprocal Changes
15. Posterior MI
16. Right Ventricular MI
17. ECG Mimics of Ischaemia
18. Stress-Test ECG Changes
19. Serial ECG Importance
20. External Video Resource
21. FAQs
22. Conclusion
23. References

1. Introduction

The 12-lead electrocardiogram (ECG) remains the single most important bedside test for diagnosing myocardial ischaemia and acute coronary syndrome. It is cheap, non-invasive, available in 10 minutes, and when interpreted correctly can save a life. Learning what are the ECG signs of ischemia is therefore essential for every clinician, nurse, paramedic and informed patient.

2. Why the ECG Matters in Ischaemia

• Guides immediate reperfusion decisions in STEMI
• Risk-stratifies NSTEMI and unstable angina
• Localises the culprit coronary artery
• Identifies complications (arrhythmias, blocks)
• Documents stress-test ischaemia
• Monitors response to reperfusion

3. Normal ECG Review

• P wave: atrial depolarisation
• PR interval: 120–200 ms
• QRS complex: ventricular depolarisation, 80–120 ms
• ST segment: should be isoelectric at the J-point
• T wave: ventricular repolarisation
• QT interval: corrected (QTc) <440 ms in men, <460 ms in women

Deviations from this baseline reveal what are the ECG signs of ischemia in a particular patient.

4. Subendocardial vs Transmural Ischaemia

• Subendocardial ischaemia → ST-depression, T-wave inversion (incomplete-thickness injury, often NSTEMI)
• Transmural (full-thickness) ischaemia → ST-elevation, hyperacute T-waves, eventual Q-waves (STEMI)

5. ST-Segment Depression

5.1 Definition

ST segment ≥0.5 mm below the isoelectric baseline, 60–80 ms after the J-point, in two contiguous leads.

5.2 Types

• Horizontal — most specific for ischaemia
• Downsloping — also specific
• Upsloping — least specific, often non-ischaemic

5.3 Causes

• Subendocardial ischaemia, NSTEMI, unstable angina
• Stress-test positive response
• Reciprocal changes in STEMI
• Digoxin (“reverse-tick”), LVH strain, hypokalaemia

6. ST-Segment Elevation

6.1 STEMI definition (Fourth Universal Definition of MI 2018)

• New ST-elevation at the J-point in 2 contiguous leads
• ≥1 mm in all leads except V2–V3
• In V2–V3: ≥2 mm in men ≥40, ≥2.5 mm in men <40, ≥1.5 mm in women

6.2 Morphology clues

• Convex-upward (tombstone) → highly suggestive of STEMI
• Concave-upward with notching → pericarditis or early repolarisation

7. T-Wave Changes

7.1 Flattening

Early non-specific sign of ischaemia.

7.2 T-wave inversion

• Symmetrical inversion ≥1 mm in 2 contiguous leads
• Deep T-wave inversions >5 mm in V2–V3 → Wellens’ pattern

7.3 Dynamic changes

Changes that evolve on serial ECGs are more specific than fixed changes.

8. Hyperacute T-Waves

• Tall, broad-based, symmetric T waves — the earliest sign of transmural ischaemia
• Appear within minutes of coronary occlusion
• Often precede ST-elevation
• Must be distinguished from hyperkalaemic T-waves (narrow, peaked)

9. Wellens’ Syndrome

• Type A: biphasic T-waves in V2–V3
• Type B: deeply inverted symmetric T-waves in V2–V3
• Pain-free at presentation; critical proximal LAD stenosis
• High risk of imminent anterior STEMI if untreated
• Needs urgent coronary angiography — not stress testing

10. De Winter T-Waves

• Upsloping ST-depression at J-point in V1–V6
• Tall, symmetric, prominent T-waves
• STEMI equivalent — proximal LAD occlusion
• Needs immediate PCI

11. Pathological Q-Waves

• Width ≥40 ms or depth ≥25% of R-wave amplitude in 2 contiguous leads
• Represent completed transmural infarction (necrosis)
• Usually appear 6–12 hours after onset; may persist lifelong
• Lead distribution helps identify the infarct territory

12. LBBB & Sgarbossa Criteria

Baseline LBBB masks STEMI. Use Sgarbossa criteria (Smith modified 2015):

• Concordant ST-elevation ≥1 mm in any lead (5 points)
• Concordant ST-depression ≥1 mm in V1–V3 (3 points)
• Excessively discordant ST-elevation (ST/S ratio ≤-0.25 modified) — Smith-modified criterion

Score ≥3 is highly specific for STEMI.

13. STEMI by Coronary Territory

• Anterior (LAD): V1–V4
• Antero-septal: V1–V2
• Anterolateral: V3–V6, I, aVL
• Lateral: I, aVL, V5, V6
• Inferior (RCA / LCx): II, III, aVF
• Posterior: ST-depression & tall R in V1–V3; confirm with posterior leads V7–V9
• Right ventricular: ST-elevation in V4R (right-sided leads)

Localising the culprit vessel is a key clinical application of what are the ECG signs of ischemia.

14. Reciprocal Changes

• Inferior STEMI (II, III, aVF) → reciprocal ST-depression in I & aVL
• Anterior STEMI → reciprocal ST-depression in II, III, aVF
• Lateral STEMI (I, aVL) → reciprocal ST-depression in III

Reciprocal changes greatly increase diagnostic certainty.

15. Posterior MI

• ST-depression ≥1 mm in V1–V3
• Tall R waves (R > S) in V1
• Confirm with posterior leads V7–V9 showing ST-elevation ≥0.5 mm
• Usually due to LCx or RCA occlusion

16. Right Ventricular MI

• Occurs in 30–50% of inferior STEMIs
• ST-elevation ≥1 mm in V4R (right-sided lead)
• Clinically: hypotension, raised JVP, clear lungs (“Beck’s triad”)
• Avoid nitrates/morphine, give fluids

17. ECG Mimics of Ischaemia

• Pericarditis — diffuse concave ST-elevation, PR depression
• Early repolarisation — notched J-point, athletic young men
• Left ventricular hypertrophy with strain
• Bundle branch blocks
• Hyperkalaemia, hypothermia
• Pulmonary embolism (S1Q3T3, right-heart strain)
• Takotsubo cardiomyopathy
• Benign early repolarisation (BER)
• Brugada pattern

18. Stress-Test ECG Changes

• ≥1 mm horizontal or downsloping ST-depression 60–80 ms after J-point in 2 contiguous leads
• Occurs during or within 3 minutes of recovery
• Combined with symptoms, hypotension, failure to reach target HR, arrhythmia — more specific

19. Serial ECG Importance

• Dynamic changes are more specific than static
• Repeat ECG every 15–30 minutes if ongoing chest pain
• Compare with previous ECG wherever available
• Continuous ST-segment monitoring in high-risk patients

20. External Video Resource

Watch a trusted explainer on what are the ECG signs of ischemia:

YouTube: ECG Signs of Ischemia – Life in the Fast Lane / Osmosis

21. FAQs

Q1. Can an ECG be normal in ischaemia?

Yes. Up to 50% of patients with chest pain have a normal initial ECG — repeat serially and check troponin.

Q2. What is the earliest ECG change in a heart attack?

Hyperacute T-waves, often within minutes of coronary occlusion.

Q3. Does T-wave inversion always mean ischaemia?

No — can be seen in LVH, strain, pulmonary embolism, apical hypertrophic cardiomyopathy, juvenile T-wave pattern.

Q4. What is Wellens’ syndrome?

Deep or biphasic T-wave inversions in V2–V3 after resolution of chest pain — indicates critical proximal LAD stenosis.

Q5. What are De Winter T-waves?

Upsloping ST-depression with tall symmetric T-waves — a STEMI equivalent requiring urgent PCI.

Q6. Can smartwatches detect ischaemia?

No — they can only detect atrial fibrillation; a 12-lead ECG is required for ischaemia.

Q7. How quickly do Q-waves appear?

Typically 6–12 hours after a transmural infarct; may persist lifelong.

Q8. What ECG lead groups should I memorise?

Inferior (II, III, aVF), anterior (V1–V4), lateral (I, aVL, V5, V6), septal (V1–V2), posterior (V7–V9), right ventricular (V4R).

22. Conclusion

So, what are the ECG signs of ischemia? ST-depression, ST-elevation, T-wave inversion, hyperacute T-waves, Wellens’ and De Winter patterns, pathological Q-waves, and new LBBB with positive Sgarbossa criteria. Localising lead groups identifies the culprit coronary artery. Combined with symptoms and troponin, the ECG remains the single most important bedside tool to diagnose, risk-stratify and guide reperfusion in acute coronary syndromes.

23. References

1. Thygesen K, et al. Fourth Universal Definition of Myocardial Infarction. Circulation 2018; updated 2023.
2. Byrne RA, et al. 2023 ESC Guidelines on Acute Coronary Syndromes.
3. Lawton JS, et al. 2021 ACC/AHA/SCAI Guideline for Coronary Artery Revascularisation.
4. Smith SW, et al. Modified Sgarbossa Criteria. Ann Emerg Med 2012; updated 2015.
5. de Winter RJ, et al. A new ECG sign of proximal LAD occlusion. NEJM 2008.
6. Life in the Fast Lane ECG Library, 2024 edition.
7. NHS UK ECG Interpretation 2024.

📞 ENT Consultation & Surgery

Dr. Sagar Rajkuwar (MS-ENT)
Prabha ENT Clinic, Ambad, Nashik
📱 7387590194 | 9892596635
🌐 www.entspecialistinnashik.com

Medical Disclaimer

Medical Disclaimer: This article is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment. Audiogram results should be interpreted by a qualified audiologist or ENT specialist. If you have sudden hearing loss, severe dizziness, ear discharge, or other concerning symptoms, seek medical evaluation promptly. ECGs must always be interpreted by a qualified physician in the clinical context.