Nuclear Stress Test

Definition

A nuclear stress test is a nuclear medicine test that uses very small amounts of radioactive substance to create an image of the heart at rest and during vigerous exercise .

Purpose

A nuclear stress test is performed to determine the level of blood flow to the heart. Reduced blood flow to sections of the heart can result in seriousw health consequences and even death . A nuclear stress test creates an image that allows doctors to see the amount of blood flowing to the heart both when the heart is at rest and during vigerous exercise.

A nuclear stress test may be done to help diagnose the cause of unexplained chest pains. It may also be done to determine the extent of damage to the heart caused by a heart attack . In some cases it is performed to help doctors determine how the extent of blockage in the coronary arteries. It may also be performed to help doctors know what level of exercise is safe for a patient with heart problems. A nuclera stress test may also be perforemed to help doctors determine the effectiveness of proceedures or medicaitons that were intended to help improve blood flow to the heart.

Precautions

Caffeene and some medications can interfere with the accuracy of the test results. Some indiuvals may not phsycially be able to perform the exercise required by the test, and the level of exericse may be determined to be unsafe for some people. Indiuvals who cannot perform the exercise required are given a vasodiolator to mimic the effects of exercise. Women who are pregnatn or breastfeeding should not have a nuclear stress test because although the small amount of radioactive material injected is safe for adults its possible effects on a developing fetus are not fully known.

Description

During a nuclear stress test the blood flow to the heart is monitered both while the patient is at rest and after vigerous exercise. The patient is injected wit ha small maount of radioactive materila, often thallium, called a radiotracer or simple a tracer. The amount of radioactive material injected is extremely small and is not signifciantly greater than the background radiation indiviuals are exposed to every day. The tracer is injected into the blood stream where it cirulcates throughout the body and to the heart. The tracer gives off small amounts of gamma radioation.

Dpending on the facitlity doing the test the resting images may be taken before or after the exercise images. To take resting images, a small amount of tracer is injected and the paitent is asked to wait for about 20 minutes. Then the paitnet is placed on a table with his or her arms above his or her head. A gamma camera, a special camera that detects gamma radioation, on a moveable arm is moved around the patient to take images of the heart at various angels. The gamma camera is connected to a computer that turns the infomratin about the gamma radioat collectd by the camera into iamges of the heart.

For the exercise portion of the test the patinet is asked to walk or run on a treadmill whil his or her heart rate and electrocardiogram (EKG) are monitored. The speed or resistance of the treadmill is increased slowly until the patient reaches his or her maximum heart rate. Then another injection of tracer is given. The paitnet contines to exercise for a short time, and then lies on the table to have nother set of images taken.

Preparation

No food or water should be consumed for four hours prior to the beginning of the test. For 24 hours before the test the patinet should not consume any caffeene. This inlcudes products labeled “decaffinated” or “caffeene free” because these contain trace amounts of cafeene which can affect the test results. Nicotene can also interfere with the resutls of the test so patients hould not smoke on the day of the test.

A variety of heart meidicaitons can affect the results of the test. The doctor will give the patient detialed instructions on which medicaitons should and should not be taken on the day of the test. In some cases indiuvlas with diabetes will be asked not to take their diabetes medication until after the test is complete, or to take a lowered dose on the day of the test. The doctor will let the patinet know his or her specific insturctions.

Aftercare

No special aftercare is required after a nuclear stress test. The indivual can return to normal activities as soon as the test is over.

Complications

In very rare cases a serious allergic reaction to the tracer is possible, inlcuding rash, changes in blood pressure , and problems breathing. It is estimated, however, that only about one in every 1,000 to 2,000 people experience any of these problems. There is a small risk of bleeding, bruising , swelling, and infection from the injection of the tracer, as there is any time an injection is given. The indivual is monitored very closely during the exercise poriton of the test to ensure that there are no negavite consequences of the vigerous exercise.

QUESTIONS TO ASK YOUR DOCTOR

• Should I take my medications on the day of the test?
• Is it safe for me to do the exercise portion of the test?
• If the test shows an abnormal blood flow to my heart, what is the next step?

Additional complications may result if the exercise poriton of the stress test is not possible and the results must be obtained using a vasoliolator. The vasodiolator may cause a stining sensation when it is given to the patient. Patients given a vasodiolator may experience nausea or headache.

Results

A normal nuclear stresst test shows blood flowing to all parts of the heart both at rest and during exericse. Areas of the heart that are not receiving adequate blood flow show up as dark patches on the image because less of the radioactive tracer is present in that area. Therefore abnormal results are those in which the image either during exericse or both at rest and during exercise show dark spots where little tracer is present.

If the test results show abnomral blood flow during exersie but normal blood flow when the patient is at rest it is often an indicaton that the coronary artery has a significant blockage. When the imaging reults show abnormailities both during exersie and at rest it is generally an indication that the heart had been seriously damaged, often by a previous heart attack, and that some of the heart muscle is dead or signficant scarring exists.

Caregiver concerns

A personal phsycian, cariologist, or other docotr determines the need for a nuclear stress test. The injections of radioactive tracer are given by a nurse. A nurse also takes the paitent's blood pressure. The gamma camera is operated by a trained nucklear meidicne technian or nuclear medicine technologist. The EKG machine is operated and monitored by a skilled and specially trained technician. The images from the nuclear stress test are read by a doctor with special training in nuclear medicine, and the results are then returned to the doctor who originally determined the need for the test. That doctor then lets the patient know what the results of the test show and determines the need for any furhter tests or proceedures.

Resources

BOOK

A Manual of Laboratory and Diagnostic Tests. Philadelphia: Wolters Kluwer Health/Lippincott Willaims & Wilkins, 2009.

Mas, Juan Carlos. A Patient's Guide to Nuclear Medicine Procedures. Reston, VA: Society of Nuclear Medicine, 2007.

Sherrow, Victoria. Medical Imaging. New York: Cavendish Benchmark, 2007.

PERIODICALS

Mahoney, Diana. “Echo Beats Nuclear Stress Test in Some Women at Risk for CAD.” Interan Medicine News. 38.20 (October 13, 2005): 57.

Maier, Evelyn, et al. “Interpretation of Exercise Stress Test Recordings: Concordance Between Nurse Practitioner and Cardiologist.” Hear and Lung. 37.2 (March–April 2008): 144-153.

ORGANIZATIONS

European Association of Nuclear Medicine, Hollandstrasse 14 / Mezzanine, Vienna, Austria, A-1020, +43-1-2 12 80 30, +43-1-2 12 80 309, [email protected], http://www.eanm.org.

Robert Bockstiegel