Nuclear cardiology studies are used to evaluate heart function, as well as the presence of coronary artery disease (CAD). Radionuclide myocardial perfusion imaging (MPI) with single photon emission computed tomography (SPECT) is one of the most commonly used noninvasive methods for assessing CAD. MPI assesses myocardial blood flow while the coronary arteries are dilated. A small amount of radioactive tracer is injected during a stress period induced by exercise or a pharmacologic agent. The myocardium extracts the tracer in proportion to blood flow. The typical radiation exposure is approximately 30% to 40% of the safe annual radiation dose.1 SPECT images visualize the coronary arteries during rest and stress periods. Myocardium areas distal to stenosed vessels will show relative hypoperfusion and appear as “cold spots” on the image. Cold spots appear blue, whereas the areas of cardiac muscle receiving blood appear yellow-orange-red.

CLINICAL USES

Prognostic information on a patient's risk of future cardiac events such as MI, unstable angina, heart failure, and even cardiac death can be ascertained by MPI images. MPI is the preferred method for evaluation of patients with and without known CAD.2 Test results can help determine whether the optimal therapy for a patient would be medical treatment or surgical intervention.

PATIENT PREPARATION

Cardiac stress testing modalities are exercise and pharmacologic agents, such as adenosine (Adenoscan), regadenoson (Lexiscan), dipyridamole, and dobutamine. Indications and contraindications are listed in the table, “Cardiac stress test modalities,” in the online version of this article.

The patient should be advised to wear comfortable clothing and shoes. Patients are usually instructed to have nothing by mouth for 4 to 6 hours before the test. Any caffeine-based medications, foods, or beverages (such as chocolate, tea, coffee, or cheese) should be avoided for 12 hours before the test, especially if adenosine, regadenoson, or dipyridamole will be used to induce stress.

Patients should bring a list of all the medications that they are taking, with dosages, to the test with them. Patients should also withhold certain medications depending on stress test modality; however, withholding medications in a patient with known CAD is at the discretion of the referring clinician.

Exercise Beta blockers, calcium channel blockers, and nitrates should be withheld for at least 48 hours prior to testing.

Adenosine (Adenoscan) Antiischemic cardiac medications (including beta blockers, nitrates, and calcium antagonists) should be withheld for 12 hours prior to testing. Oral dipyridamole (Aggrenox) should be withheld for at least 24 hours prior to testing.

Regadenoson (Lexiscan) Methylxanthines and anti-ischemic cardiac medications should be withheld for 12 hours prior to testing.

Dipyridamole Anti-ischemic cardiac medications (including beta blockers, nitrates, and calcium antagonists) should be withheld for 12 hours prior to testing.

Dobutamine Beta blockers, calcium channel blockers, and nitrates should be withheld for at least 48 hours prior to testing. This drug can be used in patients with bronchospastic airway disease. The PA or physician should discuss the patient's medication schedule with facility personnel where the test will be performed. Some patients may need to take the next dose of their medication as soon as the test is complete.

IMAGING PROTOCOL

The best images are obtained by performing the stress and rest imaging on separate days. However, both sets of images are obtained most often as a one day protocol. A lower dose of tracer is used for the rest images; a higher dose is used for the second study. For overweight patients (more than 250 lb or a body mass index higher than 30 kg/m2) or female patients who have large and/or dense breasts, a higher dose of the radiotracer is needed to obtain the rest images. In these patients, a two-day protocol is needed.3

BOTTOM LINE

Cardiac stress tests may be frightening and stressful for patients. Patient instructions should be based on the testing facility's protocols. JAAPA

Zehra Ahmed is assistant professor, Department of Physician Assistant Studies, New York Institute of Technology, Old Westbury, New York. She has indicated no relationships to disclose relating to the content of this article.

REFERENCES

1. Di Carli MF, Dorbala S. Cardiology patient page. Exercise testing and nuclear scanning. Circulation. 2003;107(16):e100-e102.

2. Clark AN, Beller GA. The present role of nuclear cardiology in clinical practice. Q J Nucl Med Mol Imaging. 2005;49(1):43-58.

3. Henzlova MJ, Cerqueira MD, Taillefer R, et al. ASNC Imaging Guidelines for Nuclear Cardiology Procedures. Updated October 27, 2008. J Nucl Cardiol. In press. http://www.asnc. org/imageuploads/Stress%20Protocols%20-%20FINAL% 202008-10-272.pdf. Accessed December 9, 2008.

WHY DO I NEED THIS TEST?

The most common reason is to find out why you feel chest pain. You may have trouble catching your breath or have other problems that are being caused by your heart.

WHAT KIND OF TEST IS IT?

A nuclear cardiac stress test is used to check heart function. A radioactive liquid is used to watch the blood flow in the arteries of your heart. The radioactive material is injected into your vein. The radioactive material makes the arteries in the heart easy to see. A special camera is used to take pictures of your heart.

IS THIS HARMFUL?

You will be exposed to an amount of radiation equal to several chest x-rays. This is a safe amount. Most of the radioactive material will wash out of your body in 1 to 3 days. You will be told not to get too close to children younger than 14 years and pregnant women during this time. You will be told to drink a lot of fluids to help your body wash out the material.

HOW DO I PREPARE FOR THE TEST?

You should not eat or drink anything for 4 to 6 hours before the test. You should avoid any foods or drinks with caffeine (such as coffee, tea, chocolate, or soda) for at least 12 hours before the test. If you take medications, you may be told not to take them before the test. You will be told to bring your medications or a list of what you take and how much with you. You should wear comfortable clothing and shoes for the test.

HOW IS THE TEST DONE?

A small plastic tube will be placed in a vein in your arm or hand. This is how the radioactive material will be put in your body. Small pads on wires will be placed on your chest to watch your heart rate. The radioactive material will be injected through the tube in your vein. You will lie down on a table with your arms raised above your head. A camera will be lowered over your chest area and will move around slowly. The camera will be taking pictures of your heart. You must lie still while the camera is taking pictures. This part will take about 20 to 25 minutes.

Next, you will exercise to increase your heart rate. At least two people will be with you at all times. If you feel any discomfort during the test, you must tell them. They will decide if you should continue the test. When this part of the test is complete, you will be asked to eat and drink. If you are taking any medication, you may be told to take the next dose. A second set of pictures of your heart will be taken after a short rest.

Sometimes the test is done in 2 days. If the test is done in 1 day, you will be taken to the stress part of the test after the first set pictures are taken.

WHAT DO YOU MEAN BY STRESS?

Stress is when your heart beats faster from exercise. The exercise for this test is to walk on a treadmill. The treadmill starts slowly. The treadmill will go a littler faster and the front of the treadmill will lift up a little bit every 3 minutes. You will feel like you are walking up a hill. Your heart rate and blood pressure will be watched during the test. You may feel shortness of breath or feel pain in your chest or arm. You may feel tired. You may have difficulty walking.

A second radioactive material will be injected into the tube in your arm when your heart rate is 85% of your maximum heart rate. You will continue to walk for another minute. Then the treadmill will be stopped. Your heart rate and blood pressure will be watched until both return to normal.

WHAT IF I CANNOT EXERCISE?

If you cannot exercise, you will be given a medication that makes your heart rate increase as if you were exercising. This type of stress test is done with you lying down on a stretcher.

WHAT MEDICATIONS ARE USED?

The medications used are adenosine, regadenoson, dipyridamole, or dobutamine. You may also be given other medications.

Adenosine, regadenoson, or dipyridamole If you are given one of these medications for the test, you may have a side effect. You may feel some chest discomfort or shortness of breath. You may have a burning feeling in your throat or abdomen. You may feel dizzy. Your face may feel flushed or warm. These feelings go away when the medication is stopped. You may be given aminophylline or a nebulizer to help you breathe.

Dobutamine If this medication is used, you may need a second medication for the test to work. If you do, you will be given atropine. Dobutamine may make you feel palpitations or chest pain. You may have shortness of breath. You may feel nauseous or vomit. You may feel weak.

BOTTOM LINE

The leading cause of death in the United States is heart disease. A nuclear cardiac stress test will help your PA or doctor predict if you may develop a problem with your heart. A doctor will review the results of the test. This person will talk to your PA or doctor about the test results. These results will help your PA or doctor decide if you need treatment. JAAPA