Computed Tomography, Angiography


Computed Tomography, Angiography

Synonym/acronym: Computed axial tomography (CAT) angiography, CTA.

Common use

To visualize and assess the vascular structure to assist in the diagnosis of aneurysm, embolism, or stenosis.

Area of application

Vessels.

Contrast

IV iodinated contrast medium.

Description

Computed tomography angiography (CTA) is a noninvasive procedure that enhances certain anatomic views of vascular structures. It becomes invasive when contrast medium is used. This procedure complements traditional angiography and allows reconstruction of the images in different planes and removal of surrounding structures, leaving only the vessels to be studied. During the procedure, the patient lies on a motorized table. The table is moved in and out of a circular opening in a doughnut-like device called a gantry, which houses the x-ray tube and associated electronics. A beam of x-rays irradiates the patient as the table moves in and out of the scanner in a series of phases. Multiple detectors rotate around the patient to produce cross-sectional views or slices. The slices can be viewed individually or as a three-dimensional image. Multislice or multidetector CT (MDCT) scanners continuously collect images in a helical or spiral fashion instead of a series of individual images as with standard scanners. Helical CT is capable of collecting many images over a short period of time (seconds), is very sensitive in identifying small abnormalities, and produces high-quality images. Differences in tissue density are detected and recorded and are viewable as computerized digital images. These images are helpful when there are heavily calcified vessels. The axial images give the most precise information regarding the true extent of stenosis, and they can also evaluate intracerebral aneurysms. Small ulcerations and plaque irregularity are readily seen with CTA; the degree of stenosis can be estimated better with CTA because of the increased number of imaging planes. Density measurements are sent to a computer that produces a digital image of the anatomy, enabling the health-care provider (HCP) to look at slices or thin sections of certain anatomic views of the vessels. Iodinated contrast medium is given IV for vascular evaluation. Images can be recorded on photographic or x-ray film or stored in digital format as digitized computer data.

This procedure is contraindicated for

  • high alertPatients 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 alertPatients who are claustrophobic.
  • high alertPatients with conditions associated with adverse reactions to contrast medium (e.g., asthma, food allergies, or allergy to contrast medium). Although patients are still asked specifically if they have a known allergy to iodine or shellfish, it has been well established that the reaction is not to iodine, in fact an actual iodine allergy would be very problematic because iodine is required for the production of thyroid hormones. In the case of shellfish the reaction is to a muscle protein called tropomyosin; in the case of iodinated contrast medium the reaction is to the noniodinated part of the contrast molecule. Patients with a known hypersensitivity to the medium may benefit from premedication with corticosteroids and diphenhydramine; the use of nonionic contrast or an alternative noncontrast imaging study, if available, may be considered for patients who have severe asthma or who have experienced moderate to severe reactions to ionic contrast medium.
  • high alertPatients with conditions associated with preexisting renal insufficiency (e.g., renal failure, single kidney transplant, nephrectomy, diabetes, multiple myeloma, treatment with aminoglycocides and NSAIDs) because iodinated contrast is nephrotoxic.
  • high alertElderly and compromised patients who are chronically dehydrated before the test, because of their risk of contrast-induced renal failure.
  • high alertPatients with pheochromocytoma, because iodinatedcontrast may cause a hypertensive crisis.
  • high alertPatients with bleeding disorders or receiving anticoagulant therapy because the puncture site may not stop bleeding.

Indications

  • Detect aneurysms
  • Detect embolism or other occlusions
  • Detect fistula
  • Detect stenosis
  • Detect peripheral artery disease (PAD)
  • Differentiate aortic aneurysms from tumors near the aorta
  • Differentiate between vascular and nonvascular tumors
  • Evaluate atherosclerosis
  • Evaluate hemorrhage or trauma
  • Monitor and evaluate the effectiveness of medical or surgical therapies

Potential diagnosis

Normal findings

  • Normal size, position, and shape of vascular structures

Abnormal findings related to

  • Aortic aneurysm
  • Cysts or abscesses
  • Emboli
  • Hemorrhage
  • Neoplasm
  • Occlusion
  • PAD
  • Shunting
  • Stenosis

Critical findings

  • Brain or spinal cord ischemia
  • Emboli
  • Hemorrhage
  • Leaking aortic aneurysm
  • Occlusion
  • Tumor with significant mass effect

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • Factors that may impair clear imaging

    • Gas or feces in the gastrointestinal tract resulting from inadequate cleansing or failure to restrict food intake before the study.
    • Retained barium from a previous radiological procedure.
    • Metallic objects within the examination field (e.g., jewelry, body rings), which may inhibit organ visualization and cause unclear images.
    • Patients who are very obese or who may exceed the weight limit for the equipment.
    • Patients with extreme claustrophobia unless sedation is given before the study.
    • Patients who are unable to cooperate or remain still during the procedure because of age, significant pain, or mental status.

  • Other considerations

    • The procedure may be terminated if chest pain or severe cardiac arrhythmias occur.
    • Failure to follow dietary restrictions and other pretesting preparations may cause the procedure to be canceled or repeated.
    • Consultation with the 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 procedures. Personnel in the room with the patient should wear a protective lead apron, stand behind a shield, or leave the area while the examination is being done. Personnel working in the examination area should wear badges to record their level of radiation exposure.

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 the cardiovascular system.
  • Obtain a history of the patient’s complaints or clinical symptoms, including a list of known allergens, especially allergies or sensitivities to latex, anesthetics, or contrast mediums.
  • Obtain a history of patient’s cardiovascular system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Ensure results of coagulation testing are obtained and recorded prior to the procedure; BUN and creatinine results are also needed if contrast medium is to be used.
  • Note any recent procedures that can interfere with test results, including examinations using barium- or iodine-based contrast medium. Ensure that barium studies were performed more than 4 days before the CT scan.
  • 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 anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Such products should be discontinued by medical direction for the appropriate number of days prior to a surgical procedure. Note the last time and dose of medication taken.
  • Note that if iodinated contrast medium is scheduled to be used in patients receiving metformin (Glucophage) for non-insulin-dependent (type 2) diabetes, the drug should be discontinued on the day of the test and continue to be withheld for 48 hr after the test. Iodinated contrast can temporarily impair kidney function, and failure to withhold metformin may indirectly result in drug-induced lactic acidosis, a dangerous and sometimes fatal side effect of metformin related to renal impairment that does not support sufficient excretion of metformin.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be moments of discomfort and some pain experienced during the test. Inform the patient that the procedure is usually performed in a radiology 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, 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 (e.g., normal saline), anesthetics, contrast medium, or sedatives.
  • Inform the patient that a burning and flushing sensation may be felt throughout the body during injection of the contrast medium. After injection of the contrast medium, the patient may experience an urge to cough, flushing, nausea, or a salty or metallic taste.
  • Instruct the patient to remove all external metallic objects from the area to be examined.
  • Instruct the patient to fast and restrict fluids for 8 hr prior to the procedure and 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.

Intratest

  • Potential complications:

  • Injection of the contrast through IV tubing into a blood vessel is an invasive procedure. Complications are rare but do include risk for allergic reaction related to contrast reaction, cardiac arrhythmias, hematoma related to blood leakage into the tissue following insertion of the IV needle, or infection that might occur if bacteria from the skin surface is introduced at the IV needle insertion site.

  • 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, fluid, and medication restrictions for 8 hr prior to the procedure.
  • Ensure that the patient has removed all external metallic objects from the area to be examined.
  • 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.
  • 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.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still throughout the procedure because movement produces unreliable results.
  • Establish an IV fluid line for the injection of contrast, emergency drugs, and sedatives.
  • Administer an antianxiety agent, as ordered, if the patient has claustrophobia. Administer a sedative to a child or to an uncooperative adult, as ordered.
  • Place the patient in the supine position on an examination table.
  • The contrast medium is injected, and a rapid series of images is taken during and after the filling of the vessels to be examined. Delayed images may be taken to examine the vessels after a time and to monitor the venous phase of the procedure.
  • Ask the patient to inhale deeply and hold his or her breath while the x-ray images are taken, and then to exhale after the images are taken.
  • Instruct the patient to take slow, deep breaths if nausea occurs during the procedure. Monitor and administer an antiemetic agent if ordered. Ready an emesis basin for use.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis, bronchospasm).
  • Observe that the needle is removed and a pressure dressing is applied over the puncture site.
  • Observe/assess the needle 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 pretesting diet, as directed by the HCP. Assess the patient’s ability to swallow before allowing the patient to attempt liquids or solid foods. Renal function should be assessed before metformin is resumed.
  • Monitor vital signs and neurological status every 15 min for 1 hr, then every 2 hr for 4 hr, and then as ordered by the HCP. Monitor 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.
  • If contrast was used, 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.
  • Assess extremities for signs of ischemia or absence of distal pulse caused by a catheter-induced thrombus.
  • Observe/assess the needle insertion site for bleeding, inflammation, or hematoma formation.
  • Instruct the patient to apply cold compresses to the insertion site as needed, to reduce discomfort or edema.
  • Instruct the patient to increase fluid intake to help eliminate the contrast medium, if used.
  • Inform the patient that diarrhea may occur after ingestion of oral contrast medium.
  • Instruct the patient to maintain bed rest for 4 to 6 hr after the procedure.
  • 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 Approach 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).
  • Recognize anxiety related to test results. 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.
  • 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.
  • Instruct the patient in the use of any ordered medications. Explain the importance of adhering to the therapy regimen. As appropriate, instruct the patient in significant side effects and systemic reactions associated with the prescribed medication. Encourage him or her to review corresponding literature provided by a pharmacist.
  • 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 of the specific area (abdomen, adrenal, carotid, coronary, pulmonary, renal), blood pool imaging, BUN, chest x-ray, colonoscopy, CBC, CBC hematocrit, CBC hemoglobin, CT of the specific area (abdomen, biliary/liver, brain, pituitary, renal, spine, spleen, thoracic), creatinine echocardiography, echocardiography transesophageal, fluorescein angiography, fundus photography, MRA, MRI of the specific area (abdomen, brain, chest, pituitary), MRI venography, MI scan, plethysmography, PET (brain, heart), proctosigmoidoscopy, PT/INR, US carotid, and US venous Doppler extremity.
  • Refer to the Cardiovascular System table at the end of the book for related tests by body system.