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Heart Disease in Women
|What Is A Nuclear Heart Scan?
A nuclear heart scan is a type of heart disease test. It is also known as nuclear stress testing and radionuclide myocardial perfusion imaging. It is performed to assess the condition and health of the heart. During the test, a doctor will inject a radioactive material or dye called a tracer through the vein into the bloodstream. The tracer travels along the veins towards the heart and special cameras outside the body can trace its journey. Two sets of images will be taken. First, the patient will undergo an exercise stress test or chemical stress test so that their blood flow can be monitored while ‘stressed’. The second set of images will be taken several hours or a few days later when the patient is at rest. The two sets of images will be compared for signs of any blockages and areas of damaged heart muscle.
Why Is It Performed?
Nuclear imaging provides more information than stress exercise tests (sometimes called treadmill tests) or stress echocardiograms alone can provide. The test has 4 main purposes:
To monitor blood flow to the heart. If part of the heart muscle is not receiving enough blood flow it may be a symptom of coronary heart disease. Coronary heart disease (CHD) is the number one killer for both men and women in America (see heart disease statistics). It is caused by the buildup of fatty deposits in the arteries and can lead to angina attacks and severe chest pain (noted particularly after exercise). When a scan is carried out for this purpose it is called myocardial perfusion imaging/scanning.
The test may also be carried out to check for signs of damaged heart muscle. This may be the result of previous heart attacks (including silent heart attacks), infections, medications or injury. When the test is carried out for this reason it is called myocardial viability testing.
Certain imaging techniques such as a MUGA scan (see below) check for ventricular function (also called ejection fraction). This is to assess how well the heart pumps blood out to the body. Although not standard, it is sometimes used for the diagnosis of heart failure. It allows the cardiologist to check for signs of heart enlargement, one of the symptoms of heart failure. A test carried out for this purpose is called ventricular function scanning.
It may also be used to monitor the success of treatments in patients already diagnosed and taking medications for heart disease, such as CHD and arrhythmia. It will help the doctor determine how well the treatment is doing in relieving symptoms. It may also be used to determine treatment for newly diagnosed patients by determining how much exercise (stress) their heart can actually handle.
Types of Nuclear Scans
There are two main types of nuclear heart scans: Cardiac Single Photon Emission Computed Tomography (SPECT) and Cardiac Positron Emission Tomography (PET). The PET scan is a newer test and has not yet been rolled out as widely as the SPECT. Both tests can be used for the same diagnostic purposes and studies show no clear advantages in using one or the other in all circumstances. However, a PET scan may provide clearer internal images of a woman with thick layers of breast or abdominal tissue. It may also be recommended where a SPECT could not produce good enough images. A cardiologist who specializes in nuclear imaging will select the best test for the individual patient.
How Do I Prepare For The Test?
Bring comfortable clothes and shoes with you if you are scheduled for the exercise stress test.
You may be asked not to eat, drink or smoke for several hours before the test.
You can take any medications as normal, unless told to otherwise by your doctor.
If you have diabetes or lung disease you will be given special instructions by your doctor.
After the test most people return to normal activities. The test results can take anywhere between 1 and 3 days. They may be sent to the patient's personal physician or the cardiologist may discuss the results directly with them.
What Happens During The Test?
Most tests are carried out in a hospital by either a cardiologist or radiologist. Either the doctor or a specially trained technician will insert an intravenous (IV) line into a vein in the arm. It is through this line that the radioactive tracers called radionuclides will be injected into the bloodstream. The most commonly used radionuclides are called technetium (Tc) which include rubidium, thallium and nitrogen. These radionuclides attach to other molecules creating long names such as 99m-Tc-tetrofosmin (brand name Myoview) and 99m-Tc-sestamibi (MIBI, brand name Cardiolite). If thallium is used, the test may be referred to as a Thallium Stress Test. At the same time electrocardiogram (ECG) patches will be attached to various parts of the body to monitor the heart rate during the test. The overall procedure, from start to finish can take anywhere between 2 and 5 hours. There are several stages to the procedure as follows:
Stage 1: The Stress Test
The idea of the nuclear test will be to monitor blood flow at rest and while stressed. To ‘stress’ the heart, a stress test will need to be carried out. Which stress test is used will be determined by the patients overall health. An exercise test is more common - but if the person is physically unable or too elderly for this, a chemical stress test will be used instead. During the exercise test, the patient will walk on a treadmill or pedal a stationary bike. They will be asked to continue walking or pedaling until they feel too tired to continue or chest or leg pain begins. Expect to exercise until you are breathing fast and start to sweat. You should report any symptoms such as dizziness, jaw, chest, leg or arm pain. Patients who are unable for this test will be injected with a chemical which will force their heart to artificially beat faster, mimicking the effects of exercise. Immediately after both tests, the patient will be injected with the nuclear tracer.
Stage 2: Injection of Tracer
Once the patient has reached their maximum exercise level or they have been injected with a chemical to stress the heart, the radioactive tracer is injected through the IV line. 30 minutes to an hour later they will be moved to a scanner machine which detects the flow of the tracer through the veins.
Stage 3: The Nuclear Scan
The patient is asked to lie on a padded table and remain very still. A large scanner which contains a gamma camera will be moved over the body and will take internal pictures of the heart and veins. You will need to keep your arms above your head at all times. Two sets of images will be taken - immediately after the exercise/chemical stress test and several hours later or a day or two later when the body is at rest. More radioactive tracers will need to be injected through the IV line when the person is at rest. When doctors survey the images, any areas of inadequate blood flow will show up as light spots because the radioactive material has not reached it. The scan does not hurt but some people may find it difficult to remain in one position for the 20-30 minutes required. Also others may find the room chilly because air-conditioning is required to keep the machines functioning properly.
Know Your Risk: Risk Factors For Heart Disease.
What Can The Results Show?
Normal Blood Flow: While resting and exercising
If blood flow (also called perfusion) looks normal while the patient was stressed and at rest, it is unlikely that they have CHD. They may not require any further testing but may be given information on CHD prevention.
Normal Blood Flow: While resting but not while exercising
This means that the heart is not receiving enough blood during strenuous activities. This may be an indication of CHD and blocked arteries.
Low Blood Flow: While resting and exercising
This means the heart is not receiving enough blood flow at all times and immediate treatment is usually necessary. Depending on the extent of the damage (how many light spots appeared on the scan images), treatment can range from coronary angioplasty and stent placement to coronary artery bypass. An exploratory heart catheterization may first be required. To read more about therapies, see CHD treatment.
Fixed and Reversible Defects
On the report perfusion (blood flow) is described as 'normal' or having a 'defect'. The defect can be described as fixed or reversible. The amount of tissue damaged, where blood flow is low, may also be graded as small, moderate or large in size. A fixed defect refers to an area of the heart that does not get enough blood at rest or under stress. It is called 'fixed' because the defect remains fixed on both scans, whether exercise has taken place or not. Very often a fixed defect is scar tissue and the artery supplying the area has been completely blocked off as a result of a previous heart attack. A 'reversible' defect refers to an area of the heart that still has good blood flow at rest. The distinction between fixed and reversible is important. Generally there is no point in opening the heart to operate on a fixed defect because even if the artery is opened up, the muscle tissue it would supply is dead. It is scar tissue. A reversible defect however means that the heart muscle is still salvageable and the procedure may prevent a future heart attack or relieve symptoms of angina.
On occasion however a cardiologist may discover that an area he had diagnosed as 'fixed' (or dead) may in fact not be scar tissue. If he suspects this to be the case he will order a viability study. This is carried out the same way as the original nuclear heart scan but images are taken at a later point in time. If the radiotracers are taken up late it suggests that the area of heart in question may still actually be viable or alive. In such instances an angioplasty or heart bypass surgery may be beneficial.
Are There Any Risks?
The radiotracers do expose the body to very small doses of radiation, although the radiation does disperse after 24 hours. Although it is important to pay attention to how much radiation you receive over a lifetime, the dosage associated with this test is considered safe.
Patients who do have CHD may experience chest pain during the exercise/chemical stress test. Medications can be given to help relieve those symptoms. Read about chest pain in women.
Some people are allergic to the radioactive dyes, but this is a rare complication.
Women who are pregnant or breastfeeding may be advised to postpone the test. See our related article: Heart Disease in Pregnancy
If a chemical stress test is used patients may feel the effects of a fast heart rate or flushing.
When It May Not Work
Patients with severely diseased arteries can occasionally have a 'normal' test result, despite the extent of disease. This can happen because the arteries are so blocked; there is little response difference between exercise and at rest. So when the radiotracers are injected there is little difference in blood flow movement in either situation. This is usually the only occasion when a stress test can come back negative, even though there is severe CHD.
How Much Does It Cost?
The average price of a nuclear stress test ranges from $900 to $1200. Do check with your health insurance before agreeing to the test because many will not cover it. They may only agree to cover the costs of an exercise stress test which is a more standard health screening tool. Out of pocket expenses may be an additional $150.
What Is a MUGA Scan?
MUGA - or Multiunit Gated Blood Pool Scan is another type of nuclear scan which assesses how blood pools in the heart during exercise or at rest. Some patients may only have a resting scan MUGA, some may have an exercise scan MUGA, others may have both. The procedure is carried out in much the same way as a regular nuclear scan, except that the radioactive material injected is first mixed with a sample of the patients blood before re injecting back in. The test is normally carried out to test how well the heart pumps blood and whether or not it has to compensate for any blocked arteries.
Other Heart Disease Tests
Calcium Score Test