In electrocardiography, T wave represents repolarization, or recovery, of the ventricle. The interval from the beginning of the QRS complex to the peak of the T wave is referred to as absolute refractory period . The last half of the T wave is called the relative refractory period or the vulnerable period. T wave contains more information than QT interval. T waves can be described with symmetry, slope, slope of the legs, amplitude and substraint rising and falling as the interval T top -T end .
In most prospects, T waves are positive. This is caused by membrane repolarization. During ventricular contraction (QRS complex), the heart is depolarized. Ventricular repolarization occurs in the opposite direction of depolarization and negative current, indicating relaxation of the ventricular heart muscle. This is a double negative of the direction and charge of why the T wave is positive; although the cell becomes more negatively charged, the net effect is a positive direction, and the ECG reports this as a positive spike. However, the negative T wave is normal in leading aVR. Lead V1 may have a positive, negative, or biphasic T wave in which a positive is followed by a negative, or vice versa. In addition, it is not uncommon to have an isolated negative T wave in lead III, aVL, or aVF. The periodic beat-to-beat variation in amplitude or T-waveform can be referred to as T wave alternation.
Video T wave
Heart physiology
The heart muscle refractory period is different from skeletal muscle. The nerves that conserve skeletal muscle have very short refractory periods after having an action potential (1 ms). This can cause continuous or tetanic contractions. In the heart, contractions must be spaced to maintain rhythm. Unlike in muscles, repolarization occurs at a slow rate (100 ms). This prevents the heart from undergoing sustained contractions because it forces the refractory period and the potential for heart action for the same time period.
Repolarization depends on the ion charge and its flow across the membrane. In skeletal muscle cells, repolarization is simple. Sodium ions flow into the previous cell to depolarize and cause skeletal muscle contraction. Once the action potential ends, the potassium ions flow out of the cell as the permeability of the cell membrane increases to the ions. This high permeability contributes to the rapid repolarization of the membrane potential. This repolarization happens fast enough so that other action potentials can cause depolarization, even before the last potential action is lost. Cardiac muscle is different because there are more channels of calcium against the potassium canal. While potassium rapidly flows out of the cell, calcium slowly flows into the cell. This causes repolarization to occur more slowly, creating a refractory period during action potential, preventing continuous contraction.
The T wave is representative of membrane repolarization. In the ECG reading, the T wave is important because it must exist before the next depolarisation. The absent or odd-shaped T waves may signal a disturbance in repolarization or other segments of the heartbeat.
Maps T wave
Normal T wave
Typically, T waves are upright in all leads, except aVR, aVL, III and V1 leads. The highest T wave amplitude is found on V2 and V3 leads. T waveforms are usually asymmetrical with rounded tops. The inversion wave from V1 to lead V4 is often found and normal in children. In normal adults, T wave inversions are rarer, but can be normal from V1 to V3. Bedusesm T wave depth also becomes increasingly shallow from one to the next lead. The height of the T wave may not exceed 5 mm in the extremity and more than 10 mm in the precordial lead.
Abnormality
Both ST segment abnormalities and T waves indicate abnormal or ventricular repolarization abnormalities due to abnormalities in ventricular depolarization.
Inverted T wave
The inverted T wave is considered abnormal if the inversion is deeper than 1.0 mm. The inverted T wave found in the instructions other than V1 to lead V4 is associated with an increase in cardiac death. The inverted T-wave associated with cardiac signs and symptoms (chest pain and cardiac murmur) is highly suggestive of myocardial ischemia. Other ECG changes associated with myocardial ischaemia are: ST segment depression with an upright T wave; ST segment depression with biphasic T wave or inverted T wave with negative QRS complex; The T wave is symmetrically inverted with a pointy peak, while the ST segment is bent upward or horizontally depressed, or does not deviate; and ST segment depression develops into abnormal abnormal T abnormalities during the ischemic free interval. However, ST segment depression does not indicate the ischemic location of the heart. ST segment depression at eight or more leads, related to ST segment elevation in aVR and V1 associated with left coronary artery disease or triple-vessel disease (blockage of the three major branches of the coronary artery). ST segment of the most prominent depression from V1 to V3 is suggestive of posterior infarction. Furthermore, high or wide QRS complexes with upright T waves are further suggestive of posterior infarction.
Wellens' syndrome is caused by injury or blockage in the left anterior descending artery, resulting in a symmetrical T wave inversion from V2 to V4 with a depth of more than 5 mm in 75% of cases. In the meantime, the remaining 25% of the cases show the morphology of the B waves of bhifasik. The ST segment remains neutral in this syndrome. Those treated without angiography will have myocardial infarction on the anterior wall within an average of 9 days. Episodes of chest pain in Wellens syndrome are associated with ST eleveation or depression and subsequently develop into T-wave abnormalities after chest pain subsides. The inverse T wave less than 5 mm may still be myocardial ischemia, but less severe than the Wellens syndrome.
Hypertrophic cardiomyopathy is the thickening of the left ventricle, sometimes the right ventricle. This may be associated with left ventricular outflow obstruction or may not be associated with it in 75% of cases. The ECG will be abnormal in 75 to 95% of patients. The characteristic ECG changes will be large QRS complexes associated with a giant T-wave inversion in lateral leads I, aVL, V5, and V6, forwards with depressive ST segments in left ventricular thickening. For right ventricular thickening, the T wave is reversed from lead V1 to V3. Changes in ST and T waves may not be apparent in hypertrophic cardiomyopathy, but if any changes in ST and T waves indicate severe hypertrophy or ventricular systolic dysfunction. According to the Sokolow-Lyon criterion, the height of the R wave at V5 or V6 S wave heights at V1 over 35 mm will imply left ventricular hypertrophy.
Both the right and left bundle blocks are associated with changes in ST and T waves similar to hypertrophic cardiomyopathy, but in contrast to the QRS complex direction.
In pulmonary embolism, the T wave can be symmetrically inverted in leads V1 to V4 but the tachycardia sinus is usually a more general finding. T wave inversion exists only in 19% mild pulmonary embolism, but T inversion can be found in 85% of cases in severe pulmonary embolism. In addition, T inversion can also exist in lead III and aVF.
T-wave reversal in most ECG leads except aVR indicates many of the most common causes of myocardial ischemia and intracranial haemorrhage. Others include: hypertrophic cardiomyopathy, Takotsubo cardiomyopathy (stress induced cardiomyopathy), cocaine abuse, pericarditis, pulmonary embolism, and advanced or complete atrioventricular block.
The figures from Lepeschkin E at
Biphasic Wave T
As the name suggests, Biphasic T waves move in the opposite direction. The two main causes of this wave are myocardial ischaemia and hypokalemia.
- The ischemic T wave is increased and then falls below the resting heart membrane potential
- Hypocalemic T waves fall and then rise above the resting heart membrane potential
Wellens' syndrome is a Biphasic B wave pattern in V2-3. Usually occurs in patients with ischemic chest pain.
- Type 1: T-wave is symmetrical and highly reversed
- Type 2: Biphasic-t wave with negative terminal deflection and positive initial deflection
Flat T wave
T waves are considered flat when waves vary from -1.0 mm to 1.0 mm. Hypokalemia or digitalis therapy can cause flat T waves with prominent U waves. As hypokalemia worsens, T waves become more flat while U waves become more prominent, with depressive ST segments deepening. For digitalis toxicity, there will be sagging QT intervals, flat T waves, and prominent U waves with shortened QT intervals.
Hyperacute T Wave
This T wave can be seen in patients presenting Prinzmetal angina. In addition, patients who demonstrate the early stages of STEMI may display this broad and disproportionate wave.
' Camel hump 'T wave
This T wave name shows the shape on display (double top). Because these T wave abnormalities may arise from various events, namely hypothermia and severe brain damage, they are considered to be nonspecific, making it much more difficult to interpret.
See also
- EKG (Electrocardiography)
- Potential Heart Action
- QRS complex
- P wave
- Pacemaker Heart
References
Source of the article : Wikipedia
0 Comments