T wave
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 hyperpolarizes to a point at which contraction is no longer possible. Through the action of the Na+/K+ pump, the heart muscle is repolarized to a state receptive to further conduction. This is why the T wave is positive; although the cell remains in a negatively charged state, the net effect is in the positive direction, and the ECG reports this as a positive spike. 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]
- T-wave inversion (negative T waves) can be a sign of coronary ischemia, Wellens' syndrome, left ventricular hypertrophy, or CNS disorder.
- A periodic beat-to-beat variation in the amplitude or shape of the T wave may be termed T wave alternans.
- Tall and narrow ("peaked" or "tented") symmetrical T waves may indicate hyperkalemia.[2]
- Flat T waves (less than 1 mV in the limb leads and less than 2 mV in the precordial leads)[3] may indicate coronary ischemia or hypokalemia[3]
- The earliest electrocardiographic finding of ST-elevation MI (STEMI) acute myocardial infarction is sometimes the hyperacute T wave, which can be distinguished from hyperkalemia by the broad base and slight asymmetry. This may also be seen in Prinzmetal angina.
- When a bundle branch block is present, the T wave should be deflected opposite the terminal deflection of the QRS complex. This is known as appropriate T wave discordance.
Frequency of inverted T-waves in precordial leads (lead V1 to V6) according to gender and age [edit]
Numbers from Lepeschkin E in [4]
| 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]
- ^ 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. PMID 19740481.
- ^ http://www.uhmc.sunysb.edu/internalmed/nephro/webpages/Part_D.htm
- ^ a b Loyola University Chicago Stritch School of Medicine. > EKG Interpretive skills Retrieved on April 22, 2010
- ^ Antaloczy, Z (1978). Modern Electrocardiology. Amsterdam: Excerpta Medica. p. 401.
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