Doctors use electrocardiograms (ECGs) to measure the electrical nerve waves produced by the heart. Changes in the T wave, which represents the relaxation of the ventricles, can indicate potential heart problems or general health issues. Flattened or inverted T waves can indicate poor blood flow to the heart, while abnormally high T waves can be the first sign of a heart attack. The QT interval and ST segment can also reveal abnormalities in heart function.
When the heart muscle alternately contracts and relaxes to pump blood, the electrical nerve waves that produce those contractions ripple throughout the body. This produces a characteristic pattern that can be measured by an electrocardiogram (ECG) when recorded from leads placed on the trunk or extremities. The T wave represents the electrical wave that accompanies the relaxation of the ventricles, the two large pumping chambers at the bottom of the heart.
Doctors can look for changes in the T wave, which is the most volatile of the various waves measured by an ECG, to identify potential heart problems or a patient’s general health. Abnormalities in the T wave may simply reflect a patient’s advanced age, but many other conditions produce T wave disorders. Damage in the area of the heart valves, reduced blood flow to the heart, and heart attacks can cause fluctuations in the T wave.
Inflammation in or around the heart, such as in myocarditis or pericarditis, can also contribute to T-wave distortions. Doctors also notice T-wave changes following chest bruising with bruising or bleeding around the heart . Finally, some central nervous system problems, particularly bleeding into the lining membranes of the brain, cause a longer interval between QRS waves and T waves, called the long QT interval.
When doctors see flattened or inverted T waves, they may suspect poor blood flow to the heart. This can also occur when the left ventricle has increased in size due to prolonged hypertension or atherosclerosis. Digoxin, a common heart drug, can also produce this effect. Abnormally high T waves can be the first sign of a myocardial infarction or heart attack.
The QT interval exemplifies the time for both electrical waves to cause the heart to contract and release. On average, the QT interval lasts 0.2 to 0.4 seconds. A prolonged QT interval can reveal some abnormally fast heart rhythms, called tachyarrhythmias, which can lead to sudden death, while a short QT interval can indicate high blood calcium levels. The ST segment, which is the distance on the ECG from the S wave following the QRS wave to the peak of the T wave, indicates the time interval between the maximum contraction of the ventricles and the onset of their relaxation. In cases of poor ventricular blood flow, ST segments can become elevated or depressed.
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