T Wave
The T wave represents ventricular repolarization — the recovery phase during which ventricular myocardial cells restore their resting membrane potential after depolarization. Because repolarization occurs in the opposite direction from depolarization (epicardium to endocardium), the T wave is normally in the same general direction (concordant) as the dominant QRS deflection in most leads.
Also known as: Ventricular Repolarization Wave, T-Wave
Measurement
| Normal Range | The T wave is normally upright in leads I, II, and V3-V6, and inverted in aVR. T waves in V1 and aVL can be upright or inverted normally. T wave amplitude is normally less than 5 mm in limb leads and less than 10 mm in precordial leads. In V1-V3 of women and children, T wave inversion is a normal finding. T waves are concordant with the QRS: upright where the QRS is predominantly positive, and inverted where the QRS is predominantly negative. |
| Measurement | Assess T wave amplitude from the isoelectric TP segment baseline to the T wave peak. Note polarity (upright, inverted, biphasic, or flat) in each lead, and compare to the QRS dominant deflection to assess concordance or discordance. For T wave inversion, note whether it is symmetric (ischemia pattern) or asymmetric (strain pattern). The end of the T wave defines the end of the QT interval. |
Clinical Significance
T wave abnormalities are among the most sensitive but least specific ECG findings. T wave inversions can reflect ischemia, ventricular hypertrophy and strain, bundle branch block, pulmonary embolism, hypertrophic cardiomyopathy, electrolyte disturbances, and normal variants. Hyperacute (tall, peaked) T waves are an early sign of myocardial infarction, often predating ST elevation. Symmetric deep T wave inversions suggest significant ischemia (including Wellens' syndrome). The overall clinical picture, particularly symptoms and cardiac biomarkers, is essential for interpreting T wave abnormalities in context.
Abnormalities
Hyperacute T Waves (Early STEMI)
Tall, broad, peaked T waves in the territory of a coronary artery that are often the earliest ECG sign of acute transmural ischemia, preceding ST elevation by minutes. They reflect the rapid accumulation of extracellular potassium in the ischemic zone, which alters repolarization. These T waves are asymmetric and have a wider base than the sharply peaked T waves of hyperkalemia. Recognizing hyperacute T waves can allow diagnosis and intervention before ST elevation develops.
Deep Symmetric T Wave Inversions (Ischemia / Wellens')
Deeply and symmetrically inverted T waves in the distribution of a coronary artery indicate significant transmural ischemia or post-ischemic reperfusion injury. The Wellens' syndrome pattern (deep symmetric T wave inversions in V2-V3, sometimes V1-V4) is the most clinically important example, indicating critical proximal LAD stenosis in a pain-free patient and requiring urgent coronary angiography.
T Wave Inversion from Ventricular Strain
Asymmetric T wave inversions with a slowly descending and rapidly ascending morphology (strain pattern) in leads overlying a hypertrophied ventricle. Right ventricular strain produces T wave inversions in the right precordial leads (V1-V3) and is seen in right ventricular hypertrophy, pulmonary hypertension, and acute pulmonary embolism. Left ventricular strain produces T wave inversions in lateral leads (I, aVL, V5-V6) in the setting of LVH.
Peaked T Waves (Hyperkalemia)
Tall, narrow, sharply peaked ('tent-shaped') T waves that are symmetric and pointed, best seen in precordial leads V3-V5. This is often the earliest ECG manifestation of hyperkalemia, appearing when serum potassium rises above 5.5–6.0 mEq/L. As hyperkalemia worsens, the PR interval prolongs, P waves flatten and disappear, QRS widens, and the rhythm deteriorates toward sine-wave pattern and ventricular fibrillation.
T Wave Inversion in Pulmonary Embolism
Anterior T wave inversions in V1-V4 (sometimes V1-V3) may accompany the S1Q3T3 pattern in large pulmonary embolism, reflecting right ventricular strain and pressure overload. These inversions can mimic anterior ischemia. Additional features such as sinus tachycardia, new right bundle branch block, and right axis deviation suggest pulmonary embolism rather than coronary disease.
Frequently Asked Questions
Why is the T wave normally concordant with the QRS complex?
Ventricular depolarization spreads from endocardium to epicardium (inward to outward), but repolarization proceeds in the opposite direction — from epicardium to endocardium. The epicardium repolarizes first because its action potentials have a shorter duration, and the endocardium repolarizes last. Because these opposing cellular events produce electrical vectors in the same net direction, the T wave ends up deflecting in the same direction as the QRS. Discordance between the QRS and T wave (T wave pointing opposite to the dominant QRS deflection) is abnormal in most leads and suggests a pathological process affecting repolarization.
How do I distinguish ischemic T wave inversions from normal variants?
Several features favor ischemic T wave inversion over normal variants. Ischemic inversions tend to be deep (greater than 2 mm), symmetric (equal limbs of the inverted T), and located in anatomically contiguous leads corresponding to a coronary territory. They may be accompanied by ST changes, prior Q waves, or dynamic changes compared to old ECGs. Normal T wave inversions in V1-V3 are common in women and children, and isolated T wave inversion in aVL is a normal variant. Lead III T wave inversion that normalizes with deep inspiration (a positional effect) is also a normal variant. Clinical context — symptoms, troponin levels, and comparison with prior ECGs — is critical.
What is T wave alternans and what does it indicate?
T wave alternans (TWA) refers to beat-to-beat alternation in the amplitude, polarity, or morphology of the T wave, creating an ABABAB pattern. Macroscopic TWA (visible to the naked eye) is a serious finding associated with extreme electrolyte abnormalities, congenital long QT syndrome, and acute ischemia, and indicates high risk of ventricular fibrillation. Microvolt T wave alternans (MTWA) is a quantified, amplified signal that is not visible on standard ECG and is used as a non-invasive risk stratification tool for sudden cardiac death, with positive MTWA indicating elevated arrhythmic risk in patients with structural heart disease.
What causes a flat or absent T wave?
Flat or very low amplitude T waves (less than 1 mm) can result from a variety of causes including hypokalemia (which often flattens T waves and produces prominent U waves), hypothyroidism (which slows metabolic processes including repolarization), pericardial effusion (which attenuates all ECG voltages due to fluid surrounding the heart), early myocarditis, and normal variants particularly in precordial leads at the transition zone. Persistent T wave flattening in the setting of chest pain suggests active ischemia until proven otherwise, even when more dramatic changes are absent.
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