T wave

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For the electromagnetic waves sometimes referred to as T-waves, see Terahertz radiation.
Schematic representation of normal ECG

In electrocardiography, the T wave represents the repolarization (or recovery) of the ventricles. 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 last half of the T wave is referred to as the relative refractory period (or vulnerable period). The T wave contains more information than the QT interval. The T wave can be described by its symmetry, skewness, slope of ascending and descending limbs, amplitude and subintervals like the Tpeak–Tend interval.[1]

In most leads, the T wave is positive. This is due to the repolarization of the membrane. During ventricle contraction (QRS wave), the heart depolarizes. Repolarization of the ventricle happens in the opposite direction of depolarization and is negative current. This double negative (direction and charge) is why the T wave is positive; although the cell becomes more negatively charged, the net effect is in the positive direction, and the ECG reports this as a positive spike.[2] However, a negative T wave is normal in lead aVR. Lead V1 may have a positive, negative, or biphasic (positive followed by negative, or vice versa) T wave. In addition, it is not uncommon to have an isolated negative T wave in lead III, aVL, or aVF.

Clinical significance[edit]

Frequency of inverted T-waves in precordial leads (lead V1 to V6) according to gender and age[edit]

Numbers from Lepeschkin E in [5]

Age (ethnicity) n V1 V2 V3 V4 V5 V6
Children
1 week - 1 y 210 92% 74% 27% 20% 0.5% 0%
1 y - 2 y 154 96% 85% 39% 10% 0.7% 0%
2 y - 5 y 202 98% 50% 22% 7% 1% 0%
5 y - 8 y 94 91% 25% 14% 5% 1% 1%
8 y - 16 y 90 62% 7% 2% 0% 0% 0%
Males
12 y - 13 y 209 47% 7% 0% 0% 0% 0%
13 y - 14 y 260 35% 4.6% 0.8% 0% 0% 0%
16 y - 19 y (whites) 50 32% 0% 0% 0% 0% 0%
16 y - 19 y (blacks) 310 46% 7% 2.9% 1.3% 0% 0%
20 - 30 y (whites) 285 41% 0% 0% 0% 0% 0%
20 - 30 y (blacks) 295 37% 0% 0% 0% 0% 0%
Females
12 y - 13 y 174 69% 11% 1.2% 0% 0% 0%
13 y - 14 y 154 52% 8.4% 1.4% 0% 0% 0%
16 y - 19 y (whites) 50 66% 0% 0% 0% 0% 0%
16 - 19 y (blacks) 310 73% 9% 1.3% 0.6% 0% 0%
20 - 30 y (whites) 280 55% 0% 0% 0% 0% 0%
20 - 30 y (blacks) 330 55% 2.4% 1% 0% 0% 0%

References[edit]

  1. ^ Haarmark C, Graff C, Andersen MP, et al. (2010). "Reference values of electrocardiogram repolarization variables in a healthy population". Journal of Electrocardiology 43 (1): 31–9. doi:10.1016/j.jelectrocard.2009.08.001. PMID 19740481. 
  2. ^ http://www.kumc.edu/AMA-MSS/Study/phys2.htm
  3. ^ http://www.uhmc.sunysb.edu/internalmed/nephro/webpages/Part_D.htm
  4. ^ a b Loyola University Chicago Stritch School of Medicine. > EKG Interpretive skills Retrieved on April 22, 2010
  5. ^ Antaloczy, Z (1978). Modern Electrocardiology. Amsterdam: Excerpta Medica. p. 401.