A nuclear stress test uses a small amount of radioactive substance to determine the health of the heart and blood flow to the heart.
The test aims to find out whether any areas of the heart muscle are not receiving enough blood flow during exercise. It is similar to the exercise stress test or pharmacological, or chemical, stress test.
It is also known at the thallium stress test, a myocardial perfusion scan, or a radionuclide test.
The test can be done while the patient is resting or doing exercise. The radioactive substance that is injected into the patient is called a radionuclide.
The test takes about 3 to 4 hours.
Although the patient is exposed to a small amount of radiation, the test is considered safe.
The nuclear stress test can help to diagnose a heart condition by giving vital information.
This data includes:
- the size of the heart chambers
- how well the heart is pumping blood
- whether there is any damage to the heart
- if there is any blockage or narrowing of the coronary arteries that provide blood to the heart
- the effectiveness of any current treatment.
The test can also help determine whether the patient is suitable for a cardiac rehabilitation program, and if so, how hard they should exercise.
Nuclear stress test with exercise
In the nuclear stress test with exercise, a radionuclide, such as thallium or technetium, is injected into a vein in the hand or arm.
When the radionuclide has circulated through the blood stream, a gamma camera takes pictures of the heart while the patient is lying down. This is known as the "rest scan" of the heart.
The patient then moves onto a treadmill. The treadmill starts slowly and gradually picks up speed and incline, to simulate walking or running uphill.
At peak exercise, more radionuclide is injected into the patient. When the radionuclide has passed through the blood stream, the gamma camera takes more pictures of the heart. This is known as the "stress scan" of the heart.
The radionuclide helps to identify blocked or partially blocked arteries on the scans, because blocked arteries do not absorb the radionuclide into the heart. They are known as "cold spots."
Patients with severe arthritis may be unable to do the physical activity required in a test with exercise. These patients may do the chemical nuclear stress test
In a chemical stress test, the patient receives medications that either speed up the heart rate or dilate the arteries. The body responds in a similar way it would to exercise.
A radionuclide is injected into the patient's arm or hand while resting. When it has circulated through the bloodstream, a gamma camera takes pictures of the heart, while the patient is lying down motionless. As in the test with exercise, this is also known as the "rest scan" of the heart.
The doctor then administers a medication to either speed up the heart rate or dilate the arteries. When the peak heart rate is reached, the patient is injected again with a radionuclide.
When it has circulated throughout the bloodstream, the gamma camera takes more pictures. This phase of the procedure is called the "stress scan" of the heart.
As in the stress test with exercise, blocked or partly blocked arteries will show up as "cold spots."
The results may be superimposed with those of CT or MRI scans, to give a more complete picture.
Possible complications and side effects include:
- allergic reaction to the dye
- abnormal heart rhythms, or arrhythmias
- fall in blood pressure during or after exercise, possibly leading to dizziness or faintness
- chest pain
- shortness of breath
In 2013, the Food and Drug Administration (FDA) warned that two drugs used in these tests, Lexiscan and Adenoscan, could increase the risk of heart problems during the test.
The drugs could cause blood to flow more effectively to unobstructed areas, leaving problem areas without blood. In rare cases, this could lead to a heart attack.
Anyone who has unstable angina or other cardiac instability may not be a suitable candidate to receive these drugs.
Both the numbers of tests and cancer rates have risen in recent years, but it remains unclear whether they are linked.
The risk will depend on the age and sex of the patient, their existing health condition, the dose used, and precautions taken. Doctors are urged to used nuclear tests only if necessary.
On the day of the test, it is important to wear comfortable clothing suitable for physical activity, including shoes for running or jogging, with non-skid soles.
The patient will need to fast, meaning they consume no food or drink for since midnight before the test. They should not take any drinks containing caffeine, including tea, coffee, and sodas, in the 24 hours before the test. Some painkillers and chocolate also contain caffeine.
It is vital for patients to tell their physician exactly what medications they are taking, and only to stop them if the physician says so.
Patients must also tell the doctor if they have a pacemaker or defibrillator.
Patients who have taken medications for erectile dysfunction within 24 hours of the test should tell their doctor. These include Viagra, vardenafil, with the trade name Levitra, and Cialis, known as tadalafil.
A person with diabetes cannot fast for too long, and they will probably be advised to have a light meal four hours before the test. Patients with diabetes must follow their doctor's instructions before and after the test.
Women should inform the doctor if she is, or could be, pregnant, or if she is breastfeeding.
The patient will have to sign a consent form, giving the medical team permission to carry out the procedure. It is important to read it carefully and ask any questions that raise doubts or concern.
The doctor will discuss the results with the patient.
If there is normal blood flow during both rest and exercise, this suggests that the heart function is normal. The patient probably does not have coronary artery disease. In most cases, no further tests are required.
If there is normal blood flow during rest but abnormal blood flow during exercise, this indicates that a part of the patient's heart muscle is not getting enough blood during physical or strenuous activity. The patient probably has coronary artery disease, or blocked arteries.
Poor blood flow during exercise and at rest means that the heart is not getting enough blood. The patient might have had a previous heart attack, or they may have severe coronary artery disease.
If the radionuclide does not show up in some areas of the heart, there may be scar tissue, or damaged tissue, from a heart attack.
Patients whose hearts have inadequate blood flow may need to undergo coronary angiography, a test that uses dye and special X-rays to show the insides of the coronary arteries.
Patients with severe blockages in their arteries may need balloon angioplasty and stent placement, or a coronary artery bypass.