Norm of Heart Scan
Technetium-99m Stannous Pyrophosphate (Radiolabeled PYP).
No evidence of myocardial ischemia.
No evidence of myocardial ischemia or infarction.
Multigated Blood Pool Study (MUGA).
Normal (55%–65%) ejection fraction, symmetric contraction of the left ventricle.
Normal (55%–65%) ejection fraction, symmetric contraction of the left ventricle.
Sestamibi or Sestamibi-Dipyridamole Exercise Testing and Scan.
No evidence of diminished perfusion, ischemia, or infarction.
Usage of Heart Scan
Aneurysm, angina, cardiomegaly, coronary artery disease, myocardial infarction, and presurgical evaluation.
Replaces the treadmill portion of the test for clients with chronic lung disease, peripheral vascular disease, impaired mobility, medication therapy that prevents demonstration of maximal exercise effort (calcium-channel blockers, beta-adrenergic blockers), or post–myocardial infarction risk stratification.
Description of Heart Scan
Heart scan encompasses any of several noninvasive scans that involve radiopharmaceutical injection.
The PYP scan is used to determine the occurrence, extent, and prognosis of myocardial infarction. Technetium-99m stannous pyrophosphate is believed to combine with the calcium in damaged myocardial cells, forming a spot on the scan. Such spots appear within 12 hours of infarction, are most prominent 48–72 hours after an infarction, and disappear within 1 week. A spot that does not disappear indicates continued myocardial damage.
The thallium-201 scan is used to show myocardial perfusion, location, and extent of acute or chronic myocardial infarction or coronary artery disease; also shows effectiveness of angioplasty, angina therapy, or grafted coronary arteries. An analog of potassium, this radionuclide is absorbed into healthy tissue while avoiding damaged tissue, forming spots on the scan. Ischemic areas (which eventually absorb isotope) can be differentiated from infracted areas (which never absorb isotope) by repeating the scan within 5 minutes. May be performed under stress. Thallium scans are often combined with dipyridamole administration (described below) because this causes greater thallium uptake and improved quality of images and accuracy of diagnoses. The combination is used for clients who are unable to perform exercise treadmill or bicycle testing in conjunction with their scan.
The MUGA scan is used to assess the function of the left ventricle and show myocardial wall abnormalities. Once the isotope is injected, the heart appears as a map with all four chambers, and the great vessels are visualized simultaneously. A series of images are taken during systole (low isotope in left ventricle) and diastole (high isotope in left ventricle). These can be shown like a movie or superimposed to show the left ventricular function, and the ejection fraction can be calculated. May be performed under stress.
The nitroglycerin scan is an additional feature of the MUGA scan. Another series of images is taken to evaluate the effectiveness of sublingual nitroglycerin administration. May be performed under stress.
The sestamibi exercise testing and scan is used to evaluate cardiac perfusion before and after a treadmill exercise test. The injected radiopharmaceutical 99mTc-pertechnetate (sestamibi) is taken up by ischemic or infarcted cardiac cells that did not improve in perfusion with exercise and is seen as a “hot spot” in nuclear imaging.
The sestamibi-dipyridamole stress test and scan is used in clients who cannot walk on a treadmill or pedal a bicycle because of physical mobility limitations. Dipyridamole is an antiplatelet drug used in nuclear medicine for its coronary artery vasodilatory action. It causes increased endogenous adenosine levels, which causes an effect on the perfusion of the heart muscle similar to that of an exercise test. For this test, the cardiac perfusion is compared in scans taken before and after the tracer and dipyridamole injections. Because the areas that vasodilate can draw blood flow from less perfused areas, the test can cause ischemia and infarction. Thus this test carries specific risks related to the radiopharmaceutical administered and requires a cardiologist to be present in many institutions.
The single-photon emission computed tomography (SPECT) scan is a newer nuclear medicine procedure in which the radiopharmaceutical technetium-99m hexamethyl propylene amine oxime is injected intravenously. This substance decomposes and remains for several hours in the heart and other tissues, where it can be detected with the SPECT camera. The camera sends images to a computer that can reproduce visual images, or “slices,” of the heart along several planes. An advantage of SPECT imaging over older nuclear medicine scans is that it can produce clear, more accurate images.
Professional Considerations of Heart Scan
Consent form IS required.
Persantine (dipyridamole): chest pain (angina), ECG changes, and ischemia, including infarction, bronchospasm, nausea, vomiting, hypotension, headache, dyspnea, facial flushing.
Radiopharmaceutical or radiolabeled albumin: allergic reaction (itching, hives, rash, tight feeling in the throat, shortness of breath, bronchospasm, anaphylaxis, death).
Treadmill testing: cardiac ischemia, including myocardial infarction, dysrhythmias, hypotension, hypertension, dizziness.
Clients who are unable to lie motionless for the scan; women who are breast-feeding; previous allergic reaction to radiopharmaceutical or radiolabeled albumin if use is planned.
Previous allergy to dipyridamole; unstable cardiac status; allergy to aminophylline (which is used as an antidote to adverse effects of dipyridamole); aminophylline or pentoxifylline taken within the last 48 hours; severe asthma or bronchospasm.
Relative Contraindications, Dipyridamole.
Congestive heart failure, status post heart transplantation, bilateral carotid artery disease, days 1–3 after acute myocardial infarction.
Active unstable angina, recent significant changes in ECG, alcohol intoxication, uncontrolled dysrhythmias, chest pain, acute infection, cardiac inflammation (myocarditis, pericarditis), acute congestive heart failure, coronary insufficiency syndrome, digitalis toxicity, heart blocks (2°, 3°), thrombophlebitis, recent pulmonary embolism, inability to walk on a treadmill or pedal a bicycle.
During pregnancy, risks of cumulative radiation exposure to the fetus from imaging studies must be weighed against the benefits of the procedure. Although formal limits for client exposure are relative to this risk:benefit comparison, the United States Nuclear Regulatory Commission requires that the cumulative dose equivalent to an embryo/fetus from occupational exposure not exceed 0.5 rem (5 mSv). Radiation dosage to the fetus is proportional to the distance of the anatomy studied from the abdomen and decreases as pregnancy progresses. For pregnant clients, consult the radiologist/radiology department to obtain estimated fetal radiation exposure from any of these procedures.
- Assess for history of hypersensitivity to radioactive dyes.
- Have emergency equipment readily available. This includes aminophylline to counteract the side effects of dipyridamole if the dipyridamole test is to be performed.
- For scans conducted with stress testing, obtain a baseline 12-lead ECG.
- See Client and Family Teaching.
- Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.
- PYP: Technetium-99m stannous pyrophosphate (20 mCi) is injected 2–3 hours before the test. Images are taken from different angles, with a total of 30–60 minutes being used for imaging.
- Thallium-201: Resting imaging takes place within the first few hours of cardiac symptoms. The radionuclide is injected, and scanning begins within 5 minutes. For stress scanning, an intravenous line is started, and a blood pressure cuff and ECG leads are attached. After 15 minutes on a treadmill or bicycle, the client is injected with radioactive thallium; 15 minutes later, imaging occurs for 1 hour, with a repeat scan performed within the next 24 hours. The thallium-201 dose is 1.5–3 mCi.
- Thallium-dipyridamole: ECG and blood pressure are monitored continuously throughout this scan. After the resting image is taken and the radionuclide is injected, dipyridamole is injected intravenously over 4 minutes. Some clients may be asked to perform mild exercise, which improves blood flow through the coronary arteries, increases uptake of the thallium, and reduces the side effects of the dipyridamole. Thallium is then injected about 4 minutes later, when peak coronary blood flow is expected, and the final scan is taken. Aminophylline may be infused prophylactically or in response to adverse side effects of the dipyridamole. The client may then return for redistribution imaging in about 4 hours.
- MUGA: 15–20 mCi of 99mTc-pertechnetate is tagged to serum albumin or red blood cells; 1 minute after injection, imaging begins. The client should be in a supine position though the client may be asked to exercise. The procedure takes 1 hour.
- Nitroglycerin: A cardiologist assesses a baseline MUGA scan, injects nitroglycerin, takes another scan, and repeats this procedure until blood pressure reaches desired level.
- Sestamibi exercise testing and scan: After a 12-lead ECG machine is attached to chest electrodes, the nuclear medicine technician injects the tracer and completes a resting scan, which lasts approximately 30 minutes. The ECG and blood pressure are then measured continuously as the client completes the exercise portion of the test on a treadmill. Heart rate, blood pressure, and ECG are recorded every 1–2 minutes during each 3-minute stage. If vital signs and ECG have remained stable, the nuclear medicine technician then injects additional tracer 1 minute before the client comes off the treadmill. The final scan of another 30 minutes is then completed.
- Sestamibi-dipyridamole stress test and scan: After a 12-lead ECG machine is attached to chest electrodes, the nuclear medicine technician injects the tracer and completes a resting scan, which lasts approximately 30 minutes. The client is instructed to perform isometric hand grips until dipyridamole injection to help prevent the drug's side effects. The ECG and blood pressure are then monitored continuously as a dose of dipyridamole is injected over 4 minutes. 2–7 minutes later, the nuclear medicine technician injects the sestamibi tracer. The side effects of Persantine may include chest pain, dysrhythmias, nausea, vomiting, bronchospasm, headache, flushing, or dizziness and hypotension. The side effects may be treated with intravenous aminophylline, which acts as an adenosine receptor agonist. 30 minutes after the tracer injection, the final scan is completed.
- Single-photon emission computed tomography (SPECT) scan: The client is transported to the nuclear medicine department, positioned supine on the scanning table, and left to rest quietly for approximately 10 minutes. A radiopharmaceutical is injected intravenously and allowed to circulate. The SPECT scan is then taken while the client lies motionless.
- Monitor the pulse, blood pressure, and respirations every 15 minutes × 2.
- For scans that involved stress testing or administration of dipyridamole, the client is monitored until vital signs or ECG patterns, or both, return to baseline values.
Client and Family Teaching
- Do not take drugs or drink caffeine-containing beverages for 6 hours before testing (24 hours for the SPECT scan).
- Some tests take several hours. Bring reading material or other diversional activity.
- PYP, thallium-201, dipyridamole: Fast for 4 hours before the test.
- Dipyridamole: Do not take drugs containing aminophylline for 48 hours before the test.
- Thallium-201, MUGA, nitroglycerin: Report fatigue, pain, or shortness of breath immediately, particularly if stress (exercise) is used.
- You may be asked to move into different positions during the scan.
- Drink plenty of fluids for 24 hours after the procedure.
Factors That Affect Results
- Digitalis and quinidine alter contractility. Notation should be made on the chart.
- Bundle branch block, left ventricular hypertrophy, or hypokalemia.
- Thallium-201 scans may produce false-negative results in clients with single-vessel disease.
- MUGA does not give positive results for 24 hours after myocardial infarction (MI), and so it cannot be used to diagnose acute MI.
- Radionuclides or radioactive tracers with long half-lives from recent scans will interfere with the quality of the images.
- The larger the perfusion defect, the poorer the prognosis.
- Abnormalities of the heart scan may indicate the need for further studies or cardiac catheterization.
- Health care professionals working in a nuclear medicine area should wear a film badge at waist level (the level closest to the client).
- Technetium half-life is 6 hours. Thallium half-life is 73 hours.
- Health care professionals working in a nuclear medicine area must follow federal standards set by the Nuclear Regulatory Commission. These standards include precautions for handling the radioactive material and monitoring of potential radiation exposure.
- The MUGA scan is used to monitor cardiac function in clients receiving cardiotoxic antineoplastic chemotherapy.
- See also Stress/exercise test; Stress test, Pharmacologic.