Cardiac scanning is a nuclear study that includes several categories of procedures depending on the radionuclide used and the suspected pathology. The various studies can reveal clinical information about wall motion (contractions), ejection fraction, coronary blood flow, ventricular size and function, valvular regurgitation, and cardiac blood shunting. Contractions are performed by wall motion of the left ventricle and the movements are graded from 31 (normal) to 0 (akinesis). Blood ejection is performed by movements of the right ventricle. The ejection fraction is calculated from the end-diastolic volume and end-systolic volume in the left ventricle and equals the percentage of the end-diastolic volume pumped per beat or contraction. Coronary blood flow is greatest during diastole because the vessels are not constricted by a contracting cardiac muscle at this time; however, the blood flow is increased with exercise.
Thallium chloride (Tl 201) rest or stress studies are performed to assist in diagnosing ischemic cardiac disease, risk for coronary artery disease (CAD), and myocardial infarct. The radiopharmaceutical is used because it is an analogue of potassium, an element that is normally taken up by heart muscle and distributed in the myocardium, depending on the blood flow in the muscle. The narrowing of the coronary vessels affects the blood flow and uptake of the radionuclide and, because the flow increases with exercise, significant narrowing can be detected during stress testing. A reduction in the uptake is an indication of pathology and appears as "cold spots" on the image. This procedure is best suited for clients who are suspected of having CAD or angina pectoris or who need physiological information about cardiac function but are not able to undergo invasive procedures such as angiography or cardiac catheterization.
If stress testing cannot be performed by exercising, dipyridamole (Persantine) can be administered orally or IV. The drug is a coronary vasodilator and is administered before thallium chloride Tl 201 and the scanning procedure. It increases the blood flow in normal coronary arteries two to three times without exercise and reveals perfusion defects when blood flow is compromised by vessel pathology. This study is reserved for clients with lung disease (chronic obstructive pulmonary disease [COPD]), neurological disorders (multiple sclerosis or spinal cord injury [SCI]), and orthopedic disorders (arthritis or amputation) who are unable to participate in treadmill, bicycle, or handgrip activities for stress testing.28 This study carries the risk of angina or coronary infarction.
Technetium Tc 99m pyrophosphate studies are performed to diagnose the presence and location of myocardial infarction. The study is usually made in combination with electrocardiography (ECG) and laboratory cardiac enzyme blood tests to provide a diagnosis. This test depends on the uptake and concentration of the radionuclide, depending on blood flow, because the material must reach the damaged tissue to be taken up. This uptake is found in abnormal areas of the myocardium, most commonly the left ventricle. The earliest uptake occurs 4 hours after coronary artery occlusion, the peak uptake in 48 hours, and a continuing diminished uptake for 5 to 7 days, depending on the size and extension of the infarct. Abnormalities are based on an increased uptake by the myocardium, and activity is graded from 4+ (activity greater than bone) to 0 (activity less than bone). A wide range of conditions causes uptake of the radionuclide, and the delay in producing a definitive myocardial infarction diagnosis limits this procedure as a useful tool. Imaging with labeled monoclonal antibodies achieves a more accurate identification and localization of an infarct site.
Gated blood pool imaging is performed to assist in diagnosing cardiac abnormalities. The radiopharmaceuticals used for this study are technetium Tc 99m pyrophosphate labeled with RBCs for multiple gated studies and technetium Tc 99m sulfur colloid for first-pass studies. Information gained from this study includes wall motion abnormalities at rest or with exercise, ejection fraction, ventricular dilation, unequal stroke volumes, and cardiac output. ECG is performed and synchronized with the imager and computer and is termed gated. Multiple gated acquisition imaging (MUGA) is the scanning of the heart in motion during the cardiac cycle to obtain multiple images of the heart in contraction and relaxation.29 The MUGA procedure is also performed after administration of nitroglycerin sublingually to determine its effect on ventricular function. These studies are less risky to the client than cardiac catheterization in obtaining information about heart function.
Nursing Alert
- Stress testing is terminated if the client develops angina, severe dyspnea, fall in blood pressure, exhaustion, or if significant ischemia or cardiac dysrhythmias are revealed by ECG.
- The use of dipyridamole in testing can precipitate myocardial infarction or angina. IV aminophylline should be on hand to reverse the effects of the drug if needed.
Nursing Care Before the Procedure
Client teaching and physical preparation are the same as for any nuclear scan study (see section under "Brain Scanning").
- Inform the client of the scanning schedule and explain that the study takes about 30 minutes.
- Advise the client that food and fluids are restricted for 2 to 4 hours, smoking for 4 to 6 hours, and medications such as theophylline for 24 hours before the study.
- Inform the client that exercising is often performed during a stress test and that medications may be administered before or during the test to evaluate heart function but that medications are not part of the routine preparation.
- If an ECG is to be performed during the test, inform the client that electrodes will be attached to the chest.
- Include cardiovascular assessment information and the client's medication regimen in the history.
Rest or Stress Cardiac Scan. For the rest study, the client is placed in an upright position for 15 minutes to reduce pulmonary flow before and during the injection of the radiopharmaceutical. The client is then placed in a supine position and requested to remain very still. Imaging by a scanner placed above the chest begins 20 minutes after the injection to allow maximum concentration because of a delay at rest that is caused by slower blood clearance. Scanning is performed to obtain anterior, left anterior-oblique, and lateral views. For the stress study, electrodes are applied to the chest, and ECG monitoring is begun; a blood pressure cuff is applied to the arm to monitor changes during the test. An IV line is initiated on the arm without the blood pressure cuff to allow access during the exercising. Exercise is carried out on a treadmill to a maximum heart rate. Alternatives to the treadmill for those unable to use it are the bicycle ergometer, isometric handgrip, or cold pressor (immersion of hand in ice water) tests. To allow distribution during stress, the radiopharmaceutical is injected into the line about 60 to 90 seconds before the exercise is to be terminated. With the client in a supine position as in the rest study, imaging takes place as soon as possible after exercising, and a computer analysis of the images is performed. Redistribution imaging can take place 4 hours after the injection to differentiate between ischemia (heart function returns to normal) and infarction (heart function remains abnormal). For clients unable to exercise, dipyridamole can be administered orally or IV 4 minutes before the injection of thallium chloride Tl 201.
Cardiac Myocardial Imaging. The client is placed on the examining table in a supine position and the radiopharmaceutical injected IV. Scanning is performed 2 to 4 hours later to obtain anterior left, left anterior-oblique, and left lateral views.
Gated Blood Pool Imaging. For MUGA studies, the client is placed at rest in a supine position and the ECG is attached for use as a reference point of electric and diastole and end systole. The reference points are to be synchronized with the data collection in frames that are recorded throughout the cardiac cycle by the computer. The client is requested to remain still during the scanning. The radiopharmaceutical is administered IV, and scanning is performed to obtain anterior, left anterior-oblique, posterior-oblique, and left lateral views. As many as 12 to 64 consecutive frames can be recorded, and the data from each beat of each cardiac cycle are added to the counts stored in the frame. Exercise imaging is also possible by taking the client through graded exercises on a bicycle in a recumbent position and imaging at each exercise level and after the exercise. For first-pass studies, scanning is performed immediately after the injection as the material passes through the right heart, to the lungs, and then to the left ventricle. Anterior or right anterior-oblique views are taken. If nitroglycerin is given after a resting multiple gated study, a scan is performed and another dose of the medication is given, with scanning to follow until the desired blood pressure level is obtained.
Heart Shunt Imaging. The client is placed on the examining table in a supine position with the head slightly elevated. The radiopharmaceutical is injected into the external jugular vein and immediate scanning is performed. This procedure is performed in conjunction with a resting multiple gated acquisition study to obtain the ejection fraction.32
PET or SPECT Imaging. This specialized three-dimensional study can be performed if the radiopharmaceutical and a positron camera are available for PET. SPECT studies can be performed to provide short axis, vertical long axis, and horizontal long axis views to obtain a more sensitive study of heart function.33
Nursing Care After the Procedure
Care and assessment after the procedure are the same as for any nuclear scan study (see section under "Brain Scanning").
- Monitor ECG and blood pressure until baselines have been achieved and maintained.
- Remove the electrodes from the sites and cleanse the areas as needed.
- Inform the client of the schedule for prescribed follow-up exercise plan.
- Phlebitis: Note and report redness or swelling at the IV site. Elevate the arm and apply warm compresses to the site.
- Exercise reactions: Note and report angina, dyspnea, nausea, headache, or exhaustion during the stress study. Also note and report a fall in blood pressure, ECG change indicating ischemia or dysrhythmias, or confusion, pallor, clammy skin, or unsteady gait. Terminate test early if symptoms appear.
- Dipyridamole administration: This medication is administered by the physician in attendance for a stress study, while aminophylline is administered IV to reverse any occurrence of ischemia, which could cause angina.
