What does the T (tachycardia) wave on an electrocardiogram (ECG) show in a patient with suspected cardiac disease?

What the T Wave Shows on an Electrocardiogram

The T wave represents ventricular repolarization—specifically, the phase of rapid repolarization (phase 3) when ventricular myocardial cells return from their plateau voltage to their resting membrane potential. 1

Physiological Basis

The T wave is generated by voltage gradients created as ventricular cells undergo rapid sequential repolarization from approximately +10 mV back to -85 mV. 1 This repolarization generally proceeds from epicardium to endocardium—opposite to the direction of depolarization—because epicardial cells have shorter action potential durations than endocardial and midmyocardial cells. 1

The T wave configuration reflects the spatial-temporal characteristics of ventricular repolarization, particularly the asynchrony of phase 3 action potentials across different regions of the ventricles. 1 Both the left and right ventricles independently generate T waves, and the clinically recorded T wave is the summation of these two separate repolarizations, making it inherently biventricular. 2

Normal T Wave Characteristics

• Polarity: T waves are normally upright in leads I, II, and V3-V6, and may be inverted or upright in leads aVL, III, and V1. 3
• Amplitude: Peak amplitude is typically highest in lead V2 or V3, with upper normal limits of 1.0-1.4 mV in men and 0.7-1.0 mV in women. 3
• Concordance: Under normal conditions, T waves are concordant with the QRS complex due to the inverse relationship between activation time and action potential duration. 1

Clinical Significance of T Wave Abnormalities

Abnormalities in the T wave reflect disturbances in ventricular repolarization caused by abnormal voltage gradients during the rapid repolarization phase or changes in the sequence of repolarization. 1 These abnormalities are associated with anatomic, pathological, physiological, and pharmacological conditions. 1

Primary vs. Secondary Repolarization Abnormalities

• Primary abnormalities: Result from changes in the shape or duration of the repolarization phases of the transmembrane action potential itself. 1
• Secondary abnormalities: Occur due to abnormal ventricular conduction (such as bundle branch blocks) and should be labeled as such to avoid misdiagnosis. 1, 4

Specific T Wave Patterns and Their Implications

Flat T waves (amplitude between -0.1 and +0.1 mV in leads I, II, aVL, and V4-V6) may represent the initial phenotypic expression of underlying cardiomyopathy, even before structural changes appear on imaging. 3 They can also indicate electrolyte abnormalities (particularly hypokalemia), early ischemic changes, medication effects, or systemic hypertension. 3

Inverted T waves (amplitude from -0.1 to -0.5 mV) are rarely benign in adults and warrant systematic evaluation to exclude cardiomyopathy, ischemic heart disease, and structural abnormalities. 1, 4 T-wave inversion ≥2 mm in two or more adjacent leads is particularly concerning and common in patients with cardiomyopathy. 5

Deep negative T waves (amplitude from -0.5 to -1.0 mV) and giant negative T waves (amplitude less than -1.0 mV) require urgent comprehensive cardiac evaluation. 1

Prominent or hyperacute T waves are associated with the earliest phase of ST-segment elevation acute myocardial infarction, but can also occur with hyperkalemia, early repolarization, and left ventricular hypertrophy. 6

Common Diagnostic Pitfalls

• Inappropriate diagnoses of myocardial ischemia and infarction are common errors when interpreting isolated T-wave abnormalities. 1, 3
• A single normal echocardiogram does not exclude the possibility of developing cardiomyopathy in the future, as T-wave abnormalities may precede structural heart disease by months or years. 3, 5
• T-wave abnormalities secondary to ventricular conduction abnormalities must be distinguished from primary repolarization disorders to avoid misdiagnosis. 1, 4
• The right ventricular component of the T wave is often overlooked; many ECGs interpreted as showing left ventricular ischemia may actually reflect abnormal right ventricular repolarization. 2

Risk Stratification Value

T-wave abnormalities provide independent predictive value for cardiovascular risk in asymptomatic populations. 1 In postmenopausal women, adding resting ECG findings (including T-wave abnormalities) to the Framingham Risk Score increased the C-statistic from 0.69 to 0.74 for predicting coronary heart disease events. 1

T-wave alternans (beat-to-beat amplitude variations) indicates latent repolarization instability predictive of malignant arrhythmias, though it typically requires stress testing to provoke and holds substantial potential for identifying high-risk patients. 1