Myocardial Infarct Scan

Myocardial Infarct Scan

Synonym/acronym: PYP cardiac scan, infarct scan, pyrophosphate cardiac scan, acute myocardial infarction scan.

Common use

To differentiate between new and old myocardial infarcts and evaluate myocardial perfusion.

Area of application

Heart, chest/thorax.

Contrast

IV radioactive material, usually technetium-99m stannous pyrophosphate (PYP).

Description

Technetium-99m stannous pyrophosphate (PYP) scanning, also known as myocardial infarct imaging, reveals the presence of myocardial perfusion and the extent of myocardial infarction (MI). This procedure can distinguish new from old infarcts when a patient has had abnormal electrocardiograms (ECGs) and cardiac enzymes have returned to normal. PYP uptake by acutely infarcted tissue may be related to the influx of calcium through damaged cell membranes, which accompanies myocardial necrosis; that is, the radionuclide may be binding to calcium phosphates or to hydroxyapatite. The PYP in these damaged cells can be viewed as spots of increased radionuclide uptake that appear in 12 hr at the earliest.

PYP uptake usually takes place 24 to 72 hr after MI, and the radionuclide remains detectable for approximately 10 to 14 days after the MI. PYP uptake is proportional to the blood flow to the affected area; with large areas of necrosis, PYP uptake may be maximal around the periphery of a necrotic area, with little uptake being detectable in the poorly perfused center. Most of the PYP is concentrated in regions that have 20% to 40% of the normal blood flow.

Single-photon emission computed tomography (SPECT) 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. With the availability of newer biomarkers such as troponin, myocardial infarct imaging has become less important in the diagnosis of acute MI.

This procedure is contraindicated for

  • 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.

Indications

  • Aid in the diagnosis of (or confirm and locate) acute MI when ECG and enzyme testing do not provide a diagnosis
  • Aid in the diagnosis of perioperative MI
  • Differentiate between a new and old infarction
  • Evaluate possible reinfarction or extension of the infarct
  • Obtain baseline information about infarction before cardiac surgery

Potential diagnosis

Normal findings

  • Normal coronary blood flow and tissue perfusion, with no PYP localization in the myocardium
  • No uptake above background activity in the myocardium (Note: when PYP uptake is present, it is graded in relation to adjacent rib activity)

Abnormal findings related to

  • MI, indicated by increased PYP uptake in the myocardium

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.
    • Metallic objects (e.g., jewelry, body rings) within the examination field, which may inhibit organ visualization and cause unclear images.
    • Other nuclear scans done within the previous 24 to 48 hr.
    • Conditions such as chest wall trauma, cardiac trauma, or recent cardioversion procedure.
    • Other conditions that may interfere include:
      • Aneurysms
      • Cardiac neoplasms
      • Left ventricular aneurysm
      • Metastasis
      • Myocarditis
      • Pericarditis
      • Valvular and coronary artery calcifications

  • Other considerations

    • Improper injection of the radionuclide may allow the tracer to seep deep into the muscle tissue, producing erroneous hot spots.
    • 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 record their level of 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 assess 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.
  • Note any recent procedures that can interfere with test results, including examinations using iodine-based contrast medium.
  • 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 related to the procedure and explain that some pain may be experienced during the test, and there may be moments of discomfort. Reassure the patient that the radionuclide poses no radioactive hazard and rarely produces side effects. Inform the patient that the procedure is performed in a nuclear medicine department by an HCP specializing in this procedure, with support staff, and will take approximately 30 to 60 min. Inform the patient that the technologist will administer an IV injection of the radionuclide and that he or she will need to return 2 to 3 hr later for the scan.
  • 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 fast, restrict fluids, and refrain from smoking for 4 hr prior to the procedure. Instruct the patient to withhold medications for 24 hr before 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.
  • Instruct the patient to remove jewelry and other metallic objects from the area to be examined.

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 and medication restrictions and other pretesting preparations.
  • Ensure that the patient has removed all external metallic objects 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.
  • Instruct the patient to void prior to the procedure and to 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. Instruct the patient to lie very still during the procedure because movement will produce unclear images.
  • Place the patient in a supine position on a flat table with foam wedges to help maintain position and immobilization.
  • IV radionuclide is administered. The heart is scanned 2 to 4 hr after injection in various positions. In most circumstances, however, SPECT is done so that the heart can be viewed from multiple angles and planes.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, 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.

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 activity and diet as directed by the HCP.
  • Unless contraindicated, advise the 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 coronary artery disease (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 angiography abdominal, AST, BNP, blood pool imaging, chest x-ray, CT abdominal, CT thoracic, CK and isoenzymes, culture viral, echocardiography, echocardiography transesophageal, ECG, MRA, MRI chest, myocardial perfusion scan, pericardial fluid analysis, and PET heart.
  • Refer to the Cardiovascular System table at the end of the book for related tests by body system.