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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 T_{peak}–T_{end} 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.
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% 
