What is a T wave abnormality on an electrocardiogram (ECG)?

T Wave Abnormalities on ECG

T wave abnormalities are deviations from normal T wave morphology on an electrocardiogram that reflect alterations in ventricular repolarization, which may be primary (due to intrinsic myocardial changes) or secondary (resulting from altered ventricular depolarization patterns). 1

Types of T Wave Abnormalities

Normal T Wave Characteristics

• In adults 20 years and older, normal T waves are:
  • Inverted in aVR
  • Upright or inverted in leads aVL, III, and V1
  • Upright in leads I, II, and chest leads V3-V6 1
• Normal T wave amplitude is highest in lead V2 or V3
• Normal upper limits for T wave amplitude in V2:
  • Men: 1.0-1.4 mV (up to 1.6 mV in 18-29 year age group)
  • Women: 0.7-1.0 mV 1

Abnormal T Wave Patterns

T wave abnormalities can be quantitatively described as:

1. Inverted T waves: T wave amplitude from -0.1 to -0.5 mV
2. Deep negative T waves: T wave amplitude from -0.5 to -1.0 mV
3. Giant negative T waves: T wave amplitude more negative than -1.0 mV
4. Low T waves: Amplitude less than 10% of the R wave amplitude in the same lead
5. Flat T waves: Peak amplitude between -0.1 and 0.1 mV in leads I, II, aVL, and V4-V6 1

Other qualitative descriptors include:

• Peaked T waves
• Symmetrical T waves
• Biphasic T waves 1

Primary vs. Secondary T Wave Abnormalities

Primary T Wave Abnormalities

• Result from changes in the shape and/or duration of ventricular action potential repolarization phases
• Occur without changes in depolarization
• Caused by:
  • Myocardial ischemia
  • Myocarditis
  • Drugs
  • Toxins
  • Electrolyte abnormalities (particularly calcium and potassium)
  • Abrupt heart rate changes
  • Hyperventilation
  • Body position changes
  • Catecholamines
  • Sympathetic stimulation
  • Temperature changes 1

Secondary T Wave Abnormalities

• Result directly from changes in sequence/duration of ventricular depolarization
• Manifest as changes in QRS shape/duration
• Do not require changes in action potential phases of individual cells
• Examples include T wave changes associated with:
  • Bundle branch blocks
  • Ventricular preexcitation
  • Ectopic ventricular complexes
  • Paced ventricular complexes 1

Clinical Significance

T wave abnormalities in lateral chest leads (V5-V6) are particularly important clinically:

• T wave negativity in these leads is rare in normal individuals
• Only 2% of white men and women ≥60 years and black men and women ≥40 years have slightly negative T waves (<0.1 mV)
• Only 5% of black men and women ≥60 years have negative T waves ≥0.1 mV 1

Prognostic Implications

• T wave abnormalities in non-ST-segment elevation acute coronary syndromes are associated with adverse outcomes when they are the sole manifestation of ischemia 2
• Isolated T wave abnormalities are strongly associated with myocardial edema in non-ST-segment elevation acute coronary syndromes (highly specific at 93%) 3
• T wave alternans (alternating T wave amplitude every second beat) indicates latent instability of repolarization and predicts risk of malignant arrhythmias 1, 4

Common Pitfalls in Interpretation

1. Misdiagnosis of ischemia: Isolated T wave abnormalities are often misinterpreted as indicating myocardial ischemia or infarction when they may have other causes 1

2. Overlooking right ventricular contribution: T waves represent repolarization from both ventricles, and abnormal T waves may originate from right ventricular pathology rather than left ventricular ischemia 5

3. Failure to distinguish primary from secondary changes: Secondary T wave changes due to conduction abnormalities should be labeled as such to avoid misdiagnosis 1

4. Ignoring normal variants: Normal T wave patterns vary by age, gender, and race, and these variations must be considered when interpreting ECGs 1

5. Overlooking the prominent T wave: Prominent T waves may represent hyperacute T waves of early ST-elevation MI, but can also be seen in hyperkalemia, early repolarization, and left ventricular hypertrophy 6

T wave abnormalities should be carefully evaluated in clinical context, as they can provide important diagnostic and prognostic information when properly interpreted.