T wave abnormalities have been categorized as primary or secondary.
Primary T wave changes result from non-uniform changes in the shape and/or duration of the action potential that alter the voltage gradients created during repolarization and may,or may not, alter the sequence of repolarization.
Secondary T wave changes occur as the result of changes in the sequence of repolarization but without a change in the shape or duration of the individual action potentials. Such secondary changes in the sequence of repolarization typically occur as the necessary result of changes in the sequence of depolarization.