The T-wave: physiology, variants and ECG features

The normal T-wave

Assessment of the T-wave represents a difficult but fundamental part of ECG interpretation. The normal T-wave in adults is positive in most precordial and limb leads. The T-wave amplitude is highest in V2–V3. The amplitude diminishes with increasing age. As noted above, the transition from the ST segment to the T-wave should be smooth. The T-wave is normally slightly asymmetric since its downslope (second half) is steeper than its upslope (first half). Women have a more symmetrical T-wave, a more distinct transition from ST segment to T-wave and lower T-wave amplitude. The T-wave should be concordant with the QRS complex, meaning that a net positive QRS complex should be followed by a positive T-wave, and vice versa (Figure 17). Otherwise there is discordance (opposite directions of QRS and T) which might be due to pathology. A negative T-wave is also called an inverted T-wave.

Figure 17. Discordance and concordance between QRS and ST-T.
Figure 17. Discordance and concordance between QRS and ST-T.

T-wave changes are notoriously misinterpreted, particularly inverted T-waves. Below follows a discussion which aims to clarify some of the common misunderstandings. All T-waves are illustrated in Figure 18.

Figure 18. Normal and pathological T-waves.
Figure 18. Normal and pathological T-waves.

Positive T-waves

Positive T-waves are rarely higher than 6 mm in the limb leads (typically highest in lead II). In the chest leads the amplitude is highest in V2–V3, where it may occasionally reach 10 mm in men and 8 mm in women. Usually, though, the amplitude in V2–V3 is around 6 mm and 3 mm in men and women, respectively. T-waves that are higher than 10 mm and 8 mm, in men and women, respectively, should be considered abnormal. A common cause of abnormally large T-waves is hyperkalemia, which results in high, pointed and asymmetric T-waves. These must be differentiated from hyperacute T-waves seen in the very early phase of myocardial ischemia. Hyperacute T-waves are broad based, high and symmetric. Their duration is short; they typically disappear within minutes after a total occlusion in a coronary artery occurs (then of course, the ST segment will be elevated).

T-wave inversion (inverted / negative T-waves)

T-wave inversion means that the T-wave is negative. The T-wave is negative if its terminal portion is below the baseline, regardless of whether its other parts are above the baseline. T-wave inversions are frequently misunderstood, particularly in the setting of ischemia.

Normal T-wave inversion

An isolated (single) T-wave inversion in lead V1 is common and normal. It is generally concordant with the QRS complex (which is negative in lead V1). Isolated T-wave inversions also occur in leads V2, III or aVL. In any instance, one must verify whether the inversion is isolated, because if there is T-wave inversion in two anatomically contiguous leads, then it is pathological.

T-wave inversion in myocardial ischemia

Ischemia never causes isolated T-wave inversions. It is a general misunderstanding that T-wave inversions, without simultaneous ST-segment deviation, indicate acute (ongoing) myocardial ischemia. T-wave inversions without simultaneous ST-segment deviation are not ischemic! However, T-wave inversions that are accompanied by ST-segment deviation (either depression or elevation) is representative of ischemia (but in that scenario, it is actually the ST-segment deviation that signals that the ischemia is ongoing). Then one might wonder why T-wave inversions are included as criteria for myocardial infarction. This is explained by the fact that T-wave inversions do occur after an ischemic episode, and these T-wave inversions are referred to as post-ischemic T-waves. Such T-waves are seen after periods of ischemia, after infarction and after successful reperfusion (PCI).

Post-ischemic T-wave inversion is caused by abnormal repolarization. These T-wave inversions are symmetric with varying depth. They may be gigantic (10 mm or more) or less than 1 mm. Negative U-waves my occur when post-ischemic T-wave inversions are present. T-wave inversions may actually become chronic after myocardial infarction. Normalization of T-wave inversion after myocardial infarction is a good prognostic indicator. Please refer to Figure 37.

Secondary T-wave inversion

Secondary T-wave inversions – similar to secondary ST-segment depressions – are caused by bundle branch block, pre-excitation, hypertrophy and ventricular pacemaker stimulation. T-wave inversions that are secondary to these conditions are typically symmetric and there is simultaneous ST-segment depression. Note that the T-wave inversion may actually persist for a period after normalization of the depolarization (if it occurs). This is referred to as T-wave memory or cardiac memory. Secondary T-wave inversions are illustrated in Figure 19 (as well as Figure 18 D).

Figure 19. Secondary T-wave inversions.
Figure 19. Secondary T-wave inversions.

Flat T-waves

T-waves with very low amplitude are common in the post-ischemic period. They are commonly seen in leads V1–V3 if the stenosis/occlusion is located in the left anterior descending artery. If the stenosis/occlusion is located in the left circumflex artery or right coronary artery, the flat T-waves are seen in leads II, aVF and III.

Biphasic (diphasic) T-waves

A biphasic T-wave have a positive and a negative deflection (Figure 37, panel C). It should be noted that the term “biphasic” is unfortunate because (1) biphasic T-waves carry no particular significant and (2) a T-wave is classified as positive or inverted based on its terminal portion; if the terminal portion is positive then the T-wave is positive and vice versa. Thus, a biphasic T-wave should be classified accordingly.

The T-waves in children and adolescents

The T-wave vector is directed to the left, downwards and to the back in children and adolescents. This explains why these individuals display T-wave inversions in the chest leads. T-wave inversions may be present in all chest leads. However, these inversions are normalized gradually during puberty. Some individuals may display persisting T-wave inversion in V1–V4, which is called persisting juvenile T-wave pattern. If all T-waves persist inverted into adulthood, the condition is referred to as idiopathic global T-wave inversion.

T-wave progression

T-wave progression follows the same rules as R-wave progression (see earlier discussion).

T-wave checklist

  • I, II, -aVR, V5 and V6: should display positive T-waves in adults. aVR displays a negative T-wave.
  • III and aVL: These leads occasionally display an isolated (single) T-wave inversion.
  • aVF: positive T-wave, but occasionally flat.
  • V1: Inverted or flat T-wave is rather common, particularly in women. The inversion is concordant with the QRS complex.
  • V7–V9: should display a positive T-wave.

This article is part of the comprehensive chapter: How to read and interpret the normal ECG

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