ST-T Changes
Definition
ST-T abnormalities are deviations of the ST segment or T-wave morphology from normal on the surface ECG. They are classified as primary (repolarization abnormalities — caused by ischemia, electrolytes, drugs, tachycardia) or secondary (depolarization abnormalities — caused by LBBB, LVH, pre-excitation, PVCs, pacemaker). This distinction is clinically essential because primary changes imply a primary myocardial process, while secondary changes are a downstream consequence of abnormal depolarization.
Key Concepts
Measurement
- ST deviation is measured as the vertical distance from the PR-segment baseline to the J-point, taken 40 ms after the J-point (J+40).
- When the baseline is unclear or J-point is non-isoelectric (due to AP dispersion), measure at J-60 or J-80 — standard in exercise stress testing.
- Significant ST depression: >0.5 mm horizontal or downsloping below baseline.
- Significant ST elevation: >0.1 mV in limb leads or >0.2 mV in precordial leads. (sources/STT-mechanism-ACA-2026, rating: medium)
- AHA/ACCF/HRS 2009 ST elevation normal limits (J-point, 98th percentile):
- White men <40 years in V2: ~0.30 mV (up to 0.33 mV ages 24–29)
- White men ≥40 years in V2: ~0.25 mV; White women in V2: ~0.15 mV
- Black men ≥40 years in V2: ~0.20 mV; Black women: ~0.15 mV
- Normal J-point elevation in V1–V2 characteristically shows steeply downsloping ST segment; ischemia shows more horizontal ST — morphology is as important as amplitude (sources/ecg-sttu-aha-2009, rating: high)
- AHA/ACCF/HRS 2009 thresholds for abnormal J-point elevation:
- V2–V3: ≥0.20 mV (men ≥40); ≥0.25 mV (men <40); ≥0.15 mV (women)
- All other leads: ≥0.1 mV (men and women) (sources/ecg-sttu-aha-2009, rating: high)
- AHA/ACCF/HRS 2009 threshold for abnormal J-point depression: ≥0.05 mV in V2–V3; ≥0.1 mV in all other leads (sources/ecg-sttu-aha-2009, rating: high)
Primary ST-T Changes — Myocardial Ischemia
- Hypoxia → ↓ ATP → ↓ Na⁺/K⁺ ATPase + ATP-sensitive K⁺ channel opening → ↑ extracellular K⁺ → partial depolarization (resting membrane potential less negative than −90 mV).
- Partial depolarization shortens APD → ischemic myocardium repolarizes earlier than normal → reversal of the normal epicardium-to-endocardium repolarization direction.
- Subendocardial ischemia (NSTE-ACS): Partial coronary occlusion; during TP/PQ segment, ischemic subendocardium (higher resting voltage) drives current toward overlying normal myocardium → TP/PQ baseline is elevated; ST segment, which remains at its true normal position during phase II of AP, appears depressed relative to the elevated baseline. T-wave becomes inverted (arrow-shaped tip) due to reversal of repolarization direction.
- Transmural ischemia (STE-ACS): Total coronary occlusion; during TP/PQ segment, current flows away from ischemic zone toward surrounding normal myocardium → TP/PQ baseline is depressed; ST segment appears elevated relative to the depressed baseline.
- Key ECG rule: In ischemia-related ST-T changes, the preceding QRS complex has normal morphology — this is the critical distinguisher from secondary ST-T changes. (sources/STT-mechanism-ACA-2026)
- de Winter pattern (exception): Total proximal LAD occlusion may present with upsloping ST depression + prominent T waves rather than classic ST elevation. (sources/STT-mechanism-ACA-2026)
ECG Recording Prerequisites for Accurate ST Assessment
- Mason-Likar torso lead placement (used in exercise ECG and ambulatory monitoring) is NOT interchangeable with the standard 12-lead ECG for ST assessment — distorts augmented limb leads and precordial leads; can produce false-positive and false-negative ischemia criteria; tracings must be labeled as such (sources/ecg-technology-aha-2007, rating: high)
- Cabrera lead display (aVL→I→−aVR→II→aVF→III) is the AHA-recommended alternative display for frontal plane leads; improves visual identification of contiguous infarction territories and spatial vector analysis (sources/ecg-technology-aha-2007, rating: high)
Coronary Artery Localization from ST-Segment Patterns (AHA 2009)
ST-segment spatial vector analysis correlates with occluded artery and occlusion site. The affected anatomic region is identified by which leads show STE; reciprocal STD confirms the vector direction. (sources/ecg-ischemia-aha-2009, rating: very high)
Anterior wall — LAD occlusion:
- Proximal LAD (above 1st septal and 1st diagonal): STE in V1–V4, I, aVL, often aVR; reciprocal STD in II, III, aVF, often V5; more STE in aVL than aVR; more STD in III than II
- Mid-LAD (between 1st septal and 1st diagonal): V1 not elevated (basal septum spared); STE in aVL, STD in III
- Distal LAD (below both branches): no STE in V1/aVR/aVL; STE in II/III/aVF may occur; STE more prominent in V3–V6, less in V2
Inferior wall — RCA vs LCx:
- RCA occlusion: greater STE in III vs II; often STD in I and aVL; right ventricular involvement when proximal (STE in V3R/V4R and often V1)
- LCx occlusion: greater STE in II vs III; isoelectric or elevated in I/aVL; no V1 STE
- Posterior (lateral) ischemia: STD in V1–V3; reciprocal of STE that would be seen in posterior/V7–V9 leads
Left main / multivessel disease: STD >0.1 mV in ≥8 leads + STE in aVR and/or V1 at rest → 75% predictive accuracy for 3-vessel or left main stenosis; automated algorithms should suggest this pattern. (sources/ecg-ischemia-aha-2009, rating: very high)
Right ventricular infarction (proximal RCA): V3R/V4R STE ≥0.05 mV (men <30 years: ≥0.1 mV); RV STE is transient — V3R/V4R must be recorded immediately after symptom onset; recommended in all patients with inferior wall ischemia. (sources/ecg-ischemia-aha-2009, rating: very high)
Wellens Syndrome — Postischemic Proximal LAD T-Wave Pattern
- Pattern: Deeply inverted T waves (>0.5 mV) in V2–V3–V4 (occasionally V5) + significant QT prolongation, occurring in a pain-free state after chest pain, without STE or new Q waves
- Indicates severe proximal LAD stenosis with collateral circulation; identical pattern also occurs after intracranial hemorrhage ("CVA pattern")
- If unrecognized, high proportion proceed to anterior STEMI from proximal LAD occlusion
- Stress testing is contraindicated — may precipitate complete occlusion
- AHA 2009 recommendation: interpret as consistent with severe proximal LAD stenosis or recent intracranial hemorrhage (sources/ecg-ischemia-aha-2009, rating: very high)
- See concepts/Wellens-Syndrome for full detail
Primary ST-T Changes — Electrolyte Disturbances
Hypokalemia
- Inhibits Na⁺/K⁺ ATPase → hyperpolarization (resting potential more negative); unlike ischemia, no partial depolarization.
- Inhibits IKr (delayed rectifier) → reduced repolarization reserve → prolonged APD.
- ECG: ST depression, T-wave inversion or flattening, prolonged QT interval, prominent U waves.
- Mechanism of arrhythmia risk: wide transmural APD gradient → EAD-triggered tachyarrhythmias; treatment by IV KCl infusion. (sources/STT-mechanism-ACA-2026)
Hyperkalemia
- ↑ Extracellular K⁺ → partial depolarization → shortened APD → exaggerated phase 2–3 slope → fast repolarization.
- Mild hyperkalemia ECG: Tall, peaked ("tented") T waves + shortened QT interval.
- Severe hyperkalemia ECG: Na⁺ channel inactivation → slowed phase 0 → widened QRS + prolonged PR + flattened/absent P waves + sine-wave pattern + conduction block + ST depression (may mimic MI).
- Represents impending cardiac arrest; emergency management: NaHCO₃, IV calcium (membrane stabilisation), K⁺ binding resins, dialysis. (sources/STT-mechanism-ACA-2026)
Primary ST-T Changes — Tachycardia and Sympathetic Activation
- ST depression and T-wave inversion can result from subendocardial ischemia secondary to demand-supply mismatch: increased myocardial O₂ demand + reduced diastolic filling time + reduced coronary perfusion time.
- Resolves on rate/rhythm control — clinical differentiator from coronary artery disease. (sources/STT-mechanism-ACA-2026)
Secondary ST-T Changes
Common mechanism across all secondary causes: abnormal (slow, cell-to-cell) endocardium-to-epicardium depolarization → subendocardium repolarizes before subepicardium → reversed repolarization → discordant ST-T changes relative to QRS complex.
| Condition | Key ECG Feature | ST-T Change |
|---|---|---|
| LBBB | QRS >120 ms; broad S in V1-2; notched R in V5-6 | T-wave inversion discordant to QRS |
| LVH | Increased QRS voltage; R-wave peak time >50 ms (V5-6); SV1+RV5 >35 mm | ST depression + T inversion ("secondary ST-T abnormality" — term "strain" is discouraged per AHA 2009) in I, aVL, V5-6 |
| Pre-excitation (WPW) | Short PR (<120 ms); delta wave; prolonged QRS | ST depression + T inversion in leads with positive delta wave |
| PVCs | Widened QRS; absent P wave | Discordant ST-T; T opposite to QRS direction |
| RV Pacing | Pacing spike; QRS >120 ms; retrograde or absent P | Discordant ST-T (normal finding in paced rhythm) |
| Hyperkalemia (severe) | Sine-wave pattern; absent P waves | ST depression (may mimic MI) |
(sources/STT-mechanism-ACA-2026)
LBBB Mechanism
LV depolarized by RV-to-LV cell-to-cell spread (bypassing Purkinje) → slower spread → subendocardial myocytes repolarize before subepicardial → repolarization direction reversed → discordant T-wave. (sources/STT-mechanism-ACA-2026)
Sgarbossa Criteria — Ischemia Detection in LBBB
LBBB secondary ST-T changes mask ischemic changes; only concordant or excessively discordant ST shifts indicate superimposed ischemia:
| Criterion | Finding | Performance |
|---|---|---|
| 1 | Concordant STE ≥1 mm in leads with positive QRS | High specificity, low sensitivity |
| 2 | Concordant STD ≥1 mm in V1–V3 (leads with dominant S) | High specificity, low sensitivity |
| 3 (original) | Discordant STE ≥5 mm in leads with negative QRS | Very low specificity and sensitivity |
| 3 (modified) | Discordant STE:S ratio ≥0.25 in any lead | Improved accuracy; replaces ≥5 mm rule |
- RBBB and fascicular blocks do NOT require Sgarbossa criteria — standard STE thresholds apply
- LBBB + concordant ST changes = higher 30-day mortality than LBBB + enzyme rise without concordant changes
- Also applied to ventricular paced rhythms (same secondary ST-T mechanism)
- (sources/ecg-ischemia-aha-2009, rating: very high); see concepts/Sgarbossa-Criteria for full detail
LVH Mechanism
Reversal of the normal endocardial/epicardial APD gradient (APD75 reversal); interstitial fibrosis disrupts conduction → repolarization heterogeneity → T-wave inversion. Mechanism not fully established. (sources/STT-mechanism-ACA-2026)
AHA 2009 terminology: The term "strain" is discouraged; "secondary ST-T abnormality" is the preferred descriptor. "Systolic overload" and "diastolic overload" are also deprecated — both have limited accuracy and should not appear in ECG reports. ST-T abnormalities in LVH are associated with larger LV mass and higher CV risk than voltage criteria alone; they serve as major supporting evidence for the LVH diagnosis. (sources/ecg-chambers-aha-2009, rating: high); see concepts/ECG-Ventricular-Hypertrophy
OMI ECG Patterns Beyond STEMI Criteria
Standard STEMI ECG criteria (≥1–2.5 mm STE at J-point in ≥2 contiguous leads) have only 43% sensitivity for acute coronary occlusion by meta-analysis and miss 38% of total LAD occlusions (TIMI-0 flow) on all serial ECGs. The following OMI ECG findings, when identified by expert or AI interpretation, achieve 100% sensitivity for LAD OMI where STEMI criteria fail: (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
| OMI ECG Finding | Prevalence in Subtle LAD OMI |
|---|---|
| Subtle STE (<1 mm, not meeting criteria) | 85% |
| Hyperacute T-waves (incl. de Winter pattern) | 85% |
| Pathologic Q-waves (associated with subtle STE) | 70% |
| Reciprocal STD and/or T-wave inversion | 50% |
| Terminal QRS distortion | 20% |
| Inferior STE + aVL STD/T-wave inversion | 20% |
- Hyperacute T-waves are not defined by amplitude alone: the T/R amplitude ratio is the key discriminator from benign early repolarization; excessive symmetry and increased T-wave "bulk" are additional features. See concepts/Hyperacute-T-waves.
- Terminal QRS distortion: absence of both J-wave and S-wave in a lead where an S-wave would be expected, preceding any subtle STE.
- de Winter pattern: upsloping STD in V1–V6 with peaked T-waves ± STE in aVR; signifies proximal LAD occlusion; subset of the hyperacute T-wave category.
- Modified Sgarbossa criteria (concordant STE ≥1 mm, concordant STD ≥1 mm in V1–V3, discordant STE:S ratio ≥0.25): apply when LBBB or ventricular paced rhythm are present.
- Critically, serial ECGs do not reliably evolve from subtle patterns to STEMI criteria in total LAD occlusion: in 16/16 patients with serial ECGs, hyperacute T-waves never progressed to diagnostic STE. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
- For the full OMI/NOMI framework see concepts/OMI-NOMI-Paradigm.
Q-Wave Formation and Regression in Myocardial Infarction
- Pathological Q waves (ESC/ACCF/AHA/WHF criteria: ≥0.02 s in V2–V3; ≥0.03 s and ≥0.1 mV in I, aVL, V4–V6, II, III, aVF) develop within hours of STEMI onset and represent transmural myocardial loss large enough to generate depolarization vectors directed away from the recording electrode.
- Presence of Q waves is determined primarily by infarct size (endocardial extent), not transmurality: in reperfused STEMI patients, 23% have non-diagnostic ECGs at 1 week despite confirmed LGE-CMR infarction; 44% are non-diagnostic by 5 years due to infarct shrinkage post-PCI. (sources/qwave-mri-jacc-imaging-2012, rating: high)
- A relative infarct size ≥6.2% of LV mass at 1 year is the optimal threshold for Q-wave presence (sensitivity 89%, specificity 74%); anterior MIs are reliably detected, while nonanterior (inferior/lateral) MIs are frequently electrically silent. (sources/qwave-mri-jacc-imaging-2012, rating: high)
- Q-wave regression represents pseudo-normalization: LGE-CMR confirms persistent irreversible scar even when Q waves have disappeared. Electrically silent MIs carry equivalent prognosis to overt Q-wave MIs. (sources/qwave-mri-jacc-imaging-2012, rating: high)
- See concepts/Q-Wave-Remodeling for the full framework on post-infarct ECG limitations.
T-Wave Normal Values and Quantitative Descriptors (AHA/ACCF/HRS 2009)
- Normal T-wave polarity in adults ≥20 years: inverted in aVR; upright or inverted in aVL, III, V1; upright in I, II, V3–V6
- Normal T-wave amplitude in V2: up to 1.0–1.4 mV in men (up to 1.6 mV in men 18–29); 0.7–1.0 mV in women
- T-wave in V5–V6 slightly negative (<0.1 mV) in only 2% of White men/women ≥60 — lateral T-wave negativity is clinically important
- Quantitative T-wave classification (leads I, II, aVL, V2–V6):
- Inverted: −0.1 to −0.5 mV
- Deep negative: −0.5 to −1.0 mV
- Giant negative: < −1.0 mV
- Low: <10% of R-wave amplitude in same lead
- Flat: between +0.1 and −0.1 mV in leads I, II, aVL (R wave >0.3 mV), V4–V6
- Giant T-wave inversion (< −1.0 mV) is generally limited to three entities: hypertrophic cardiomyopathy, NSTEMI, and neurological events (especially intracranial hemorrhage)
- Minor T-wave abnormalities: classify as "slight" or "indeterminate"; list most common causes; always compare with prior ECGs (sources/ecg-sttu-aha-2009, rating: high)
U Wave (AHA/ACCF/HRS 2009)
- Mechanoelectric phenomenon: low-amplitude, low-frequency deflection following the T wave; most evident in V2–V3
- Normal amplitude: ~0.33 mV or ~11% of T-wave amplitude in V2–V3
- Heart-rate dependent: rarely present at HR >95 bpm; present in 90% of cases at HR <65 bpm
- Apparent increased U-wave amplitude with hypokalemia is more likely T-U fusion than true U-wave increase; T-U fusion also occurs with sympathetic activation and prolonged QT (LQTS)
- Inverted U wave in V2–V5 is abnormal: associated with acute ischemia (transient) and hypertension
- Abnormal U waves are subtle and frequently overlooked; ECG report should include U wave statements when: U wave is inverted; U wave is merged with T; U wave amplitude exceeds T-wave amplitude (sources/ecg-sttu-aha-2009, rating: high)
Contradictions / Open Questions
- LVH strain pattern vs. ischemia overlap: The strain pattern (ST depression + T inversion in lateral leads) in LVH is mechanistically secondary, but clinically it can coexist with or mask underlying subendocardial ischemia in hypertensive or HCM patients — no validated ECG criteria reliably differentiate the two. (sources/STT-mechanism-ACA-2026)
- Sgarbossa original vs. modified discordant criterion: The original criterion 3 (discordant STE ≥5 mm) was shown in HERO-2 analysis to have very low specificity and sensitivity; it is superseded by the modified criterion (STE:S ratio ≥0.25), yet the AHA 2009 document retains the 5 mm threshold. The modified criterion is not yet formally guideline-endorsed. (sources/ecg-ischemia-aha-2009, rating: very high); (sources/STT-mechanism-ACA-2026)
- Injury current theory completeness: The injury current / diastolic current model of ST changes (TP/PQ baseline shift) is the dominant teaching model, but its quantitative accuracy in human ischemia has been questioned; alternative models exist. (sources/STT-mechanism-ACA-2026)
- STEMI criteria inadequacy for occlusion MI: Standard STEMI STE criteria have only 43% sensitivity for acute coronary occlusion by meta-analysis and miss 38% of total LAD TIMI-0 occlusions on all serial ECGs. Serial ECGs do not reliably evolve to STEMI criteria in subtle OMI. Expert interpretation and AI (PMCardio Queen of Hearts) both achieved 100% sensitivity on the first ECG for all LAD TIMI-0 cases, highlighting that STEMI criteria alone are insufficient gatekeepers for reperfusion. See concepts/OMI-NOMI-Paradigm. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
- Hyperacute T-wave definition: No validated quantitative threshold exists for hyperacute T-waves — the most prevalent OMI ECG finding in subtle cases (85%). The T/R ratio approach has empirical support but no guideline-endorsed cutoff. (sources/failure-stemi-criteria-lad-omi-ehjacc-2025, rating: high)
Connections
- Related to concepts/Cardiac-Action-Potential
- Related to concepts/Cardiac-Repolarization
- Related to concepts/Torsades-de-Pointes
- Related to entities/Atrial-Fibrillation
- Related to entities/HCM
- Related to entities/Long-QT-Syndrome
- Related to concepts/OMI-NOMI-Paradigm — OMI ECG findings beyond STEMI criteria; paradigm shift
- Related to concepts/Hyperacute-T-waves — most common OMI ECG finding in subtle cases
- Related to entities/Acute-Coronary-Syndrome — clinical context for ischemia-related ST-T changes
- Related to sources/STT-mechanism-ACA-2026
- Related to concepts/Q-Wave-Remodeling
- Related to sources/qwave-mri-jacc-imaging-2012
- Related to sources/failure-stemi-criteria-lad-omi-ehjacc-2025
- Related to concepts/Wellens-Syndrome — proximal LAD T-wave warning pattern
- Related to concepts/Sgarbossa-Criteria — LBBB ischemia recognition
- Related to concepts/ECG-Ventricular-Hypertrophy — LVH secondary ST-T criteria and AHA terminology
- Related to concepts/ECG-Conduction-Disturbances — secondary ST-T in LBBB/RBBB; concordance principles; AHA 2009 LBBB criterion 7 (negative concordance = abnormal)
- Related to concepts/ECG-Lead-Standards — Mason-Likar not interchangeable for serial ST comparison; Cabrera sequence for infarction localization; right-sided leads (V3R/V4R) for RV infarction