An electrocardiogram, or ECG, measures the electrical activity of the heart and is often used in the acute setting to rule out a heart attack. One of the common signs of myocardial ischemia, or lack of blood flow to the heart, is T-wave inversion on an ECG. The normal T-wave is upright on an ECG, and when this waveform inverts, it alerts medical professionals to a potential problem with the heart.
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What Is a T-Wave?
A T-wave is a component of an ECG test. It signifies the repolarization of the heart ventricles after a contraction. In the adjacent image, the T-wave is the hump on the right. Every time your heart beats, the muscle is depolarised by an electrical current that originates in the sinoatrial node of the heart. This is also known as the heart's pacemaker. As the current travels from that node in the atria, it depolarises the heart muscle along its path. Once it makes its way around the heart, the muscle will then re-polarise to attain its original state. The atrial repolarization signal is covered up by the tall QRS complex (the large spike in the image).
Why Does a T-Wave Invert?
There are a wide variety of causes for T-wave inversion. Some of these occur in perfectly normal, healthy individuals, but others signify a problem with the heart. One of the most common causes for T-wave inversion is transient ischemia, or lack of blood flow to the heart muscle. This can occur during a myocardial infarction (heart attack). Other causes include subacute pericarditis, myocarditis, myocardial contusion (bruising from blunt trauma to the chest), central nervous system disease such as a subarachnoid haemorrhage, valvular disease or drug side effects.
Why Is This Test Useful?
When someone comes to the emergency room with chest pain, he will always get an ECG to look for changes in the QRS complex as well as possible T-wave inversion. If signs of T-wave inversion are noted -- in addition to abnormalities in certain lab test results -- the protocol for a heart attack will be implemented. T-wave inversions are also helpful in noting heart disease other than an acute heart attack. They can indicate strain on the heart muscle, inflammation, valvular disease or even a brain haemorrhage. The noninvasive nature of this test makes it particularly useful in the acute setting. By simply placing a few electrodes on an individual, a wealth of data can be determined about the heart's activity.
What Should Occur if the Test Is Positive?
In the acute setting, if a patient is exhibiting chest pain, has an ECG with T-wave inversion and has lab values positive for elevated heart enzymes, he or she will be treated for a heart attack. They will receive morphine, oxygen, nitroglycerine and aspirin. They will also be monitored for signs of decompensation and possibly be taken to the heart catheterisation lab for more invasive procedures to open up blocked blood vessels to the heart. In a less acute setting -- for a patient not exhibiting other signs of a heart attack with no elevation in heart enzymes -- further testing, such as a stress test or heart echocardiogram, might be warranted to evaluate the inverted T-wave.
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