Myocardial Perfusion Heart Scan

Myocardial Perfusion Heart Scan

Synonym/acronym: Sestamibi scan, stress thallium, thallium scan.

Common use

To assess cardiac blood flow to evaluate for and assist in diagnosing coronary artery disease and myocardial infarction.

Area of application

Heart, chest/thorax.

Contrast

IV or oral radionuclide.

Description

Cardiac scanning is a nuclear medicine study that reveals clinical information about coronary blood flow, ventricular size, and cardiac function. Thallium-201 chloride rest or stress studies are used to evaluate myocardial blood flow to assist in diagnosing or determining the risk for ischemic cardiac disease, coronary artery disease (CAD), and myocardial infarction (MI). This procedure is an alternative to angiography or cardiac catheterization in cases in which these procedures may pose a risk to the patient. Thallium-201 is a potassium analogue and is taken up by myocardial cells proportional to blood flow to the cell and cell viability. During stress studies, the radionuclide is injected at peak exercise, after which the patient continues to exercise for several minutes. During exercise, areas of heart muscle supplied by normal arteries increase their blood supply, as well as the supply of thallium-201 delivery to the heart muscle, to a greater extent than regions of the heart muscle supplied by stenosed coronary arteries. This discrepancy in blood flow becomes apparent and quantifiable in subsequent imaging. Comparison of early stress images with images taken after 3 to 4 hr redistribution (delayed images) enables differentiation between normally perfused, healthy myocardium (which is normal at rest but ischemic on stress) and infarcted myocardium.

Technetium-99m agents such as sestamibi (2-methoxyisobutylisonitrile) are delivered similarly to thallium-201 during myocardial perfusion imaging, but they are extracted to a lesser degree on the first pass through the heart and are taken up by the mitochondria. Over a short period, the radionuclide concentrates in the heart to the same degree as thallium-201. The advantage to technetium-99m agents is that immediate imaging is unnecessary because the radionuclide remains fixed to the heart muscle for several hours. The examination requires two separate injections, one for the rest portion and one for the stress portion of the procedure. These injections can take place on the same day or preferably over a 2-day period. Examination quality is improved if the patient is given a light, fatty meal after the radionuclide is injected to facilitate hepatobiliary clearance of the radioactivity.

If stress testing cannot be performed by exercising, dipyridamole (Persantine) or adenosine, a vasodilator, can be administered orally or IV. A coronary vasodilator is administered before the thallium-201 or other radionuclide, and the scanning procedure is then performed. Vasodilators increase blood flow in normal coronary arteries twofold to threefold without exercise, and they reveal perfusion defects when blood flow is compromised by vessel pathology. Vasodilator-mediated myocardial perfusion scanning is reserved for patients who are unable to participate in treadmill, bicycle, or handgrip exercises for stress testing because of lung disease, neurological disorders (e.g., multiple sclerosis, spinal cord injury), morbid obesity, and orthopedic disorders (e.g., arthritis, limb amputation).

Single-photon emission computed tomography can be used to visualize the heart from multiple angles and planes, enabling areas of MI to be viewed with greater accuracy and resolution. This technique removes overlying structures that may confuse interpretation of the results.

This procedure is contraindicated for

  • high alert Patients who have taken sildenafil (Viagra) within the previous 48 hr, because this test may require the use of nitrates (nitroglycerin) that can precipitate life-threatening low blood pressure.
  • high alert Patients who are pregnant or suspected of being pregnant, unless the potential benefits of a procedure using radiation far outweigh the risk of radiation exposure to the fetus and mother.
  • high alert Patients with bleeding disorders.
  • high alert Patients with left ventricular hypertrophy, right and left bundle branch block, and hypokalemia, and patients receiving cardiotonic therapy.
  • high alert Patients with anginal pain at rest or patients with severe atherosclerotic coronary vessels in whom dipyridamole testing cannot be performed.
  • high alert Patients with asthma, because chemical stress with vasodilators can cause bronchospasms.

Indications

  • Aid in the diagnosis of CAD or risk for CAD
  • Determine rest defects and reperfusion with delayed imaging in unstable angina
  • Evaluate the extent of CAD and determine cardiac function
  • Assess the function of collateral coronary arteries
  • Evaluate bypass graft patency and general cardiac status after surgery
  • Evaluate the site of an old MI to determine obstruction to cardiac muscle perfusion
  • Evaluate the effectiveness of medication regimen and balloon angioplasty procedure on narrow coronary arteries

Potential diagnosis

Normal findings

  • Normal wall motion, coronary blood flow, tissue perfusion, and ventricular size and function

Abnormal findings related to

  • Abnormal stress and resting images, indicating previous MI
  • Abnormal stress images with normal resting images, indicating transient ischemia
  • Cardiac hypertrophy, indicated by increased radionuclide uptake in the myocardium
  • Enlarged left ventricle
  • Heart chamber disorder
  • Ventricular septal defects

Critical findings

    N/A

Interfering factors

  • Factors that may impair clear imaging

    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • Medications such as digitalis and quinidine, which can alter cardiac contractility, and nitrates, which can affect cardiac performance.
    • Single-vessel disease, which can produce false-negative thallium-201 scanning results.
    • Conditions such as chest wall or cardiac trauma, angina that is difficult to control, significant cardiac arrhythmias, and recent cardioversion procedure.
    • Suboptimal cardiac stress or patient exhaustion preventing maximum heart rate testing.
    • Excessive eating or exercising between initial and redistribution imaging 4 hr later, which produces false-positive results.
    • Improper adjustment of the radiological equipment to accommodate obese or thin patients, which can cause overexposure or underexposure and a poor-quality study.
    • Patients who are very obese or who may exceed the weight limit for the equipment.
    • Incorrect positioning of the patient, which may produce poor visualization of the area to be examined.
    • Metallic objects (e.g., jewelry, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.
  • Other considerations

    • Failure to follow dietary restrictions before the procedure may cause the procedure to be canceled or repeated.
    • Improper injection of the radionuclide that allows the tracer to seep deep into the muscle tissue produces erroneous hot spots.
    • Inaccurate timing for imaging after radionuclide injection can affect the results.
    • Consultation with a health-care provider (HCP) should occur before the procedure for radiation safety concerns regarding younger patients or patients who are lactating. Pediatric & Geriatric Imaging Children and geriatric patients are at risk for receiving a higher radiation dose than necessary if settings are not adjusted for their small size. Pediatric Imaging Information on the Image Gently Campaign can be found at the Alliance for Radiation Safety in Pediatric Imaging (www.pedrad.org/associations/5364/ig/).
    • Risks associated with radiation overexposure can result from frequent x-ray or radionuclide procedures. Personnel working in the examination area should wear badges to reveal their level of exposure to radiation.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in assessing blood flow to the heart.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, sedatives, or radionuclides.
  • Obtain a history of the patient’s cardiovascular system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Review the procedure with the patient. Address concerns about pain and explain that some pain may be experienced during the test, or there may be moments of discomfort. Inform the patient that the procedure is performed in a special department, usually in a radiology or vascular suite, by an HCP specializing in this procedure, with support staff, and takes approximately 30 to 60 min.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Explain that an IV line may be inserted to allow infusion of IV fluids such as normal saline, anesthetics, sedatives, radionuclides, medications used in the procedure, or emergency medications.
  • Instruct the patient to wear walking shoes (if treadmill exercise testing is to be performed), and emphasize the importance of reporting fatigue, pain, or shortness of breath.
  • Instruct the patient to remove dentures, jewelry, and other metallic objects from the area to be examined prior to the procedure.
  • Instruct the patient to fast for 4 hr, refrain from smoking for 4 to 6 hr, and withhold medications for 24 hr before the test. Instruct the patient to avoid taking anticoagulant medication or to reduce dosage as ordered prior to the procedure. Protocols may vary among facilities.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.
  • This procedure may be terminated if chest pain, severe cardiac arrhythmias, or signs of a cerebrovascular accident occur.

Intratest

  • Potential complications:
  • Although it is rare, there is the possibility of allergic reaction to the radionuclide. Have emergency equipment and medications readily available. If the patient has a history of allergic reactions to any substance or drug, administer ordered prophylactic steroids or antihistamines before the procedure.

  • Establishing an IV site and injecting radionuclides is an invasive procedure. Complications are rare but do include bleeding from the puncture site related to a bleeding disorder, or the effects of natural products and medications known to act as blood thinners; hematoma related to blood leakage into the tissue following needle insertion; infection that might occur if bacteria from the skin surface is introduced at the puncture site; or nerve injury that might occur if the needle strikes a nerve.

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Ensure that the patient has complied with dietary, tobacco, and medication restrictions and other pretesting preparations for 4 to 6 hr prior to the procedure.
  • Ensure that the patient has removed external metallic objects from the area to be examined prior to the procedure.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Have emergency equipment readily available.
  • Administer ordered prophylactic steroids or antihistamines before the procedure if the patient has a history of allergic reactions to any substance or drug. Use nonionic contrast medium for the procedure.
  • Instruct the patient to void prior to the procedure and change into the gown, robe, and foot coverings provided.
  • Record baseline vital signs and assess neurological status. Protocols may vary among facilities.
  • Establish an IV fluid line for the injection of saline, anesthetics, sedatives, radionuclides, or emergency medications.
  • Instruct the patient to cooperate fully and to follow directions.
  • Place electrocardiographic (ECG) electrodes on the patient for cardiac monitoring. Establish baseline rhythm; determine if the patient has ventricular arrhythmias. Monitor the patient’s blood pressure throughout the procedure by using an automated blood pressure machine.
  • Assist the patient onto the treadmill or bicycle ergometer and ask the patient to exercise to a calculated 80% to 85% of the maximum heart rate, as determined by the protocol selected.
  • Wear gloves during the radionuclide injection and while handling the patient’s urine.
  • Thallium-201 is injected 60 to 90 sec before exercise is terminated, and imaging is done immediately in the supine position and repeated in 4 hr.
  • Patients who cannot exercise are given dipyridamole 4 min before thallium-201 is injected.
  • Inform the patient that movement during the resting procedure affects the results and makes interpretation difficult.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, or bronchospasm).
  • Remove the needle or catheter and apply a pressure dressing over the puncture site.
  • Observe/assess the needle/catheter insertion site for bleeding, inflammation, or hematoma formation.
  • The results are recorded on film or in a computerized system for recall and postprocedure interpretation by the appropriate HCP.

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume normal diet and activity, as directed by the HCP.
  • Unless contraindicated, advise patient to drink increased amounts of fluids for 24 to 48 hr to eliminate the radionuclide from the body. Inform the patient that radionuclide is eliminated from the body within 6 to 24 hr.
  • No other radionuclide tests should be scheduled for 24 to 48 hr after this procedure.
  • Evaluate the patient’s vital signs. Monitor vital signs and neurological status every 15 min for 1 hr, then every 2 hr for 4 hr, and then as ordered by HCP. Take temperature every 4 hr for 24 hr. Monitor intake and output at least every 8 hr. Compare with baseline values. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
  • Observe for delayed allergic reactions, such as rash, urticaria, tachycardia, hyperpnea, hypertension, palpitations, nausea, or vomiting.
  • Instruct the patient to immediately report symptoms such as fast heart rate, difficulty breathing, skin rash, itching, chest pain, persistent right shoulder pain, or abdominal pain. Immediately report symptoms to the appropriate HCP.
  • Instruct the patient in the care and assessment of the injection site.
  • If the patient must return for additional imaging, advise the patient to rest in the interim and restrict diet to liquids before redistribution studies.
  • If a woman who is breastfeeding must have a nuclear scan, she should not breastfeed the infant until the radionuclide has been eliminated. This could take as long as 3 days. She should be instructed to express the milk and discard it during the 3-day period to prevent cessation of milk production.
  • Instruct the patient to flush the toilet immediately after each voiding following the procedure and to meticulously wash hands with soap and water after each voiding for 24 hr after the procedure.
  • Instruct all caregivers to wear gloves when discarding urine for 24 hr after the procedure. Wash gloved hands with soap and water before removing gloves. Then wash hands after the gloves are removed.
  • Nutritional Considerations: Abnormal findings may be associated with cardiovascular disease. Nutritional therapy is recommended for the patient identified to be at risk for developing CAD or for individuals who have specific risk factors and/or existing medical conditions (e.g., elevated LDL cholesterol levels, other lipid disorders, insulin-dependent diabetes, insulin resistance, or metabolic syndrome). Other changeable risk factors warranting patient education include strategies to encourage patients, especially those who are overweight and with high blood pressure, to safely decrease sodium intake, achieve a normal weight, ensure regular participation in moderate aerobic physical activity three to four times per week, eliminate tobacco use, and adhere to a heart-healthy diet. If triglycerides also are elevated, the patient should be advised to eliminate or reduce alcohol. The 2013 Guideline on Lifestyle Management to Reduce Cardiovascular Risk published by the American College of Cardiology (ACC) and the American Heart Association (AHA) in conjunction with the National Heart, Lung, and Blood Institute (NHLBI) recommends a “Mediterranean”-style diet rather than a low-fat diet. The new guideline emphasizes inclusion of vegetables, whole grains, fruits, low-fat dairy, nuts, legumes, and nontropical vegetable oils (e.g., olive, canola, peanut, sunflower, flaxseed) along with fish and lean poultry. A similar dietary pattern known as the Dietary Approaches to Stop Hypertension (DASH) diet makes additional recommendations for the reduction of dietary sodium. Both dietary styles emphasize a reduction in consumption of red meats, which are high in saturated fats and cholesterol, and other foods containing sugar, saturated fats, trans fats, and sodium.
  • Social and Cultural Considerations: Numerous studies point to the prevalence of excess body weight in American children and adolescents. Experts estimate that obesity is present in 25% of the population ages 6 to 11 yr. The medical, social, and emotional consequences of excess body weight are significant. Special attention should be given to instructing the child and caregiver regarding health risks and weight-control education.
  • Recognize anxiety related to test results, and be supportive of fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services. Provide contact information, if desired, for the American Heart Association (www.americanheart.org) or the NHLBI (www.nhlbi.nih.gov).
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include antiarrhythmic drugs, apolipoprotein A and B, AST, atrial natriuretic peptide, BNP, calcium, cholesterol (total, HDL, LDL), CT cardiac scoring, CRP, CK and isoenzymes, echocardiography, echocardiography transesophageal, ECG, exercise stress test, glucose, glycated hemoglobin, Holter monitor, homocysteine, ketones, LDH and isos, lipoprotein electrophoresis, magnesium, MRI chest, MI infarct scan, myoglobin, PET heart, potassium, triglycerides, and troponin.
  • Refer to the Cardiovascular System table at the end of the book for related tests by body system.
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