T wave

The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the absolute refractory period.

The T wave can be described by its symmetry, skewness, slope of ascending and descending limbs, amplitude and subintervals like the Tpeak–Tend interval.

Nerves that innervate skeletal muscle have an extremely short refractory period after being subjected to an action potential (of the order of 1 ms).

This prevents the heart from undergoing sustained contractions because it forces the refractory period and cardiac action potential firing to be of the same length of time.

First, sodium ions flow into the cell to depolarize it and cause skeletal muscle contraction.

This causes the repolarization to occur more slowly, making the refractory period as long as the action potential, preventing sustained contractions.

An absent or strangely shaped T wave may signify disruption in repolarization or another segment of the heartbeat.

ST segment depression in eight or more leads, associated with ST segment elevation in aVR and V1 are associated with left main coronary artery disease or three-vessel disease (blockage of all three major branches of coronary arteries).

[5] Wellens' syndrome is caused by the injury or blockage of the left anterior descending artery, therefore resulting in symmetrical T wave inversions from V2 to V4 with depth more than 5 mm in 75% of the cases.

T wave inversion less than 5 mm may still represents myocardial ischaemia, but is less severe than Wellens' syndrome.

Characteristic ECG changes would be large QRS complex associated with giant T wave inversion[4] in lateral leads I, aVL, V5, and V6, together with ST segment depression in left ventricular thickening.

[4] Both right and left bundle branch blocks are associated with similar ST and T wave changes as in hypertrophic cardiomyopathy, but are opposite to the direction of the QRS complex.

[5] In pulmonary embolism, T wave can be symmetrically inverted at V2 to V4 leads but sinus tachycardia is usually the more common finding.

[5] Inversion of T waves in most of the ECG leads except aVR indicates many causes most commonly myocardial ischaemia and intracranial haemorrhage.

Additionally, patients exhibiting the early stages of STEMI may display these broad and disproportional waves.

Since these T wave abnormalities may arise from different events, i.e. hypothermia and severe brain damage, they have been deemed as nonspecific, making them much more difficult to interpret.