After injection of a small amount of radioactive material into the bloodstream, a special camera records the movement and uptake of the radiotracer within the heart. The resulting images provide information about the coronary arteries and heart function. There are three common types of nuclear heart scans: the myocardial infarction scan, myocardial perfusion scan, and multigated-acquisition (MUGA) scan (also termed cardiac blood pool imaging). Each of these procedures uses a different radiotracer. The latter two scans are often done while you exercise; this is known as stress testing.
Purpose of the Cardiac Nuclear Scan
Myocardial infarction scan:
- To identify a recent heart attack, define its size and location, and determine the patient’s prognosis
Myocardial perfusion scan:
- To assess the amount of blood reaching the heart muscle and detect areas with a decreased blood supply
- To pinpoint the location and extent of a past or recent heart attack
- To identify blocked coronary arteries and assess the effectiveness of coronary bypass grafts or angioplasty
- To evaluate patients who have angina (chest pain due to inadequate delivery of oxygen to the heart muscle) and inconclusive findings on an electrocardiogram, or ECG
- To evaluate the pumping function of the heart’s left ventricle by measuring the flow of blood into the left ventricle and how much blood the heart pumps with each beat (ejection fraction)
- To assess the ability of the heart’s right ventricle to pump blood into the lungs
- To detect any abnormalities of heart wall motion
Who Performs Cardiac Nuclear Scan
Special Concerns about Cardiac Nuclear Scan
- This test should not be performed in pregnant women because of possible risks to the fetus.
- Other recent nuclear imaging tests, such as a thyroid or bone scan, may interfere with the results.
- A myocardial perfusion scan may yield false-positive results in females and in people with a heart condition called hypertrophic cardiomyopathy.
- Movement during the test, abnormalities on the ECG, or an irregular heartbeat can affect the results of a MUGA scan.
- People who cannot exercise adequately because of orthopedic, arthritic, or lung disorders may instead be given dobutamine, a drug that mimics the effects of exercise by increasing the heart rate, or may be given adenosine or Persantine, which causes a relative decrease in blood flow to areas of the heart supplied by a blocked artery.
- Because this test places significant stress on the heart, it may not be appropriate for people with unstable angina, uncontrolled hypertension, severe aortic valvular heart disease, congestive heart failure, or uncontrolled heart rhythm disorders (arrhythmias).
Before the Cardiac Nuclear Scan
- If stress testing is not being performed, no special preparation is necessary.
- Antianginal drugs (such as nitroglycerin, beta-blockers, and calcium channel blockers) can affect test results by increasing your exercise tolerance. Your doctor may ask you to discontinue these medications for 1 or 2 days before the test.
- Tell the doctor who is performing your exam if you are taking any medications, including vitamins and herbal supplements, and if you have any known allergies. Also inform your doctor about recent illnesses and other medical conditions.
- Do not eat or smoke for 4 hours before the test. Avoid caffeine and alcohol for 6 hours before the test.
- Tell your doctor if you are pregnant or breastfeeding or may be pregnant.
- Jewelry and other metallic accessories may interfere with the procedure and should be removed prior to the exam.
- Wear comfortable shoes and loose, lightweight clothing.
- You will be asked to disrobe above the waist. (Women may wear a loose-fitting hospital gown that opens in the front.)
What You Experience during Cardiac Nuclear Scan
- You will lie on your back on an examination table.
- The radiotracer is injected into a vein in your arm. In some cases, an intravenous (IV) line is inserted into a vein in your arm and the radiotracer is infused through it. (Other than this injection, the procedure causes no discomfort.)
- Depending on what specific radiotracer is being used, the scanning procedure is performed from 15 minutes to 4 hours after the injection.
- A special camera is placed over the front of your chest, and you may be asked to assume various positions as the camera moves back and forth, recording multiple images of your heart. While you are being scanned, you must remain still.
- The procedure generally takes from 1 to 4 hours (sometimes there is a break of several hours between scans). Some patients may have to return 24 hours later for an additional scan.
- Your blood pressure is measured, and ECG leads are attached to your chest, arm, and leg to monitor your heart activity.
- For an exercise stress test, you will begin by walking on a treadmill or pedaling a stationary bicycle.
- The pedaling tension on the cycle or the speed and grade of the incline on the treadmill are gradually increased until you reach a target heart rate (or until you are too tired to continue or have chest pain).
- For a dobutamine stress test, the doctor infuses the drug through an IV line and gradually increases the dose to mimic the effects of intensifying exercise.
- Once you achieve your target heart rate, the radiotracer is injected. You will then lie down on the examination table, and the scanning is performed.
Risks and Complications of Cardiac Nuclear Scan
- The trace amount of radioactive material used in this test is not associated with significant risks or complications.
- In extremely rare cases, patients may be hypersensitive to the radiotracer and may experience an adverse reaction.
- Although generally safe, in rare cases stress testing may lead to complications including severe angina, heart attack, arrhythmias, a drop in blood pressure, and fainting.
- Dobutamine may cause reactions such as flushing, palpitations, headache, and nausea, but these effects usually resolve quickly once the infusion is stopped.
After the Cardiac Nuclear Scan
- Drink extra fluids to help your body eliminate the radioactive material.
- If you had stress testing, you will rest until your blood pressure, heart rate, and other vital signs return to normal.
- If you received an IV line, it is removed from your arm and pressure is applied to the infusion site for several minutes.
- If there are no complications, you are free to return to your normal activities and may resume any medications that were withheld before the test.
- Blood may collect and clot under the skin (hematoma) at the injection site; this is harmless and will resolve on its own. For a large hematoma that causes swelling and discomfort, apply ice initially; after 24 hours, use warm, moist compresses to help dissolve the clotted blood.
Cardiac Nuclear Scan Results
- The doctor analyzes the images obtained during the procedure for evidence of any cardiac abnormalities. If you underwent stress testing, your performance and symptoms during this phase of the test will also be evaluated.
- If a definitive diagnosis can be made based on the findings, your doctor will recommend that treatment be started with diet, exercise, and/or medication.
- In some cases, more invasive tests, such as cardiac catheterization, may be needed to further evaluate abnormal results.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media