Definition and Overview
A nuclear stress test is a diagnostic exam used to assess a person’s risk of heart disease by checking how well blood flows into the heart, both at rest and during activity or when the person is under stress. Increased blood flow during times of stress is simulated using either actual exercise or medications that have the same effect. The test is conducted by injecting a radioactive tracer substance into a vein; as it moves through the veins, its movement is captured by a special gamma camera and is translated into a computer-generated image. Any abnormalities in the flow of blood, such as blockages and damaged heart muscles, will then be detected.
This test is usually prescribed after a regular exercise stress test fails to show accurate or adequate diagnostic results.
Who Should Undergo and Expected Results
Those who undergo a nuclear stress test are patients who:
Are suspected of having coronary artery disease
Are experiencing some symptoms, such as shortness of breath and chest pain – A nuclear stress test can help identify the underlying cause of these symptoms, such as blockages in the veins, enlargement of the heart, or compromised pumping function (also called ejection fraction).
Are diagnosed with an existing heart condition – A person who has been diagnosed with a heart problem such as arrhythmia or coronary artery disease can expect the test results to be used as the basis for treatment and as a guide as to how much stress the heart can withstand despite the existing condition.
The results of the test may be:
Normal blood flow in times of rest and stress – No further tests will be required and the patient is deemed healthy.
Normal blood flow while at rest but abnormal blood flow during stress – Some parts of the heart do not receive adequate blood flow when the heart is exerting a specific amount of effort; one possible cause is a blocked artery, which means the patient may have coronary artery disease.
Low blood flow in times of rest and stress – Some parts of the heart do not receive adequate blood flow at all times, which means the blockages in the arteries are already at a more severe stage. In such cases, the doctor may prescribe more tests, such as a coronary angiography in order to closely examine the blood vessels that supply blood flow to the heart.
Radioactive dye unable to pass through certain parts of the heart – This may indicate that the heart has some tissue damage, possibly due to a previous heart attack.
If the test results show that the patient suffers from severe blockages in his heart, medical or surgical intervention may be required. Treatment options include:
- Balloon angioplasty
- Stent placement
- Coronary artery bypass
How the Procedure Works
There are some precautions and preparations necessary before doing the exam. These include the following:
- 24 hours before the test: Avoid caffeine consumption, i.e. drinking coffee and soda, eating chocolates, and drinking decaffeinated products
- 4 hours before the test: No foods and beverages should be consumed. Only small sips of water are allowed, and only if there are medications that need to be taken.
- For asthmapatients, inhalers should be brought to the test.
- Wear loose, comfortable clothing.
- Wear walking shoes (as they may be necessary for the exercise).
The test usually takes anywhere between two and five hours. It begins with the preparation of the materials and equipment needed for the test, such as placing the electrodes on the patient’s chest, arms, and legs to connect him to an ECG machine, inserting an IV line into the patient’s arm (for the medication if the patient is unable to exercise), and setting up the blood pressure monitor.
Patients who have no problems with exercise are first asked to walk on a treadmill at an increasing speed and inclination, and this may be followed by a stationary bike exercise with increasing resistance so that the patient exerts an increasing amount of effort in pedaling. The patient will then be asked to continue exercising until a target heart rate has been met. However, if the patient experiences any symptoms such as dizziness, spikes and crashes in blood pressure level, moderate to severe chest pains, and severe shortness of breath, the test may be stopped. The patient can also request to have the test stopped at any time, in case he or she is feeling too uncomfortable. However, the patient should expect to feel fatigue, muscle cramps in the legs, or at least mild chest pain during the test; these are normal symptoms that are felt during exercising and increased activity. A mild headache and some nausea may also be felt as an effect of the dobutamine, the medication that’s used to simulate the effects of exercise on the heart.
Patients who have just undergone a nuclear stress test may resume their normal activities after the test, as long as they feel fit to do so or they do not or did not experience any severe symptoms. Doctors usually advise patients if they need to refrain from strenuous activities for a short while after the test; this will depend on the symptoms experienced during the exam.
Possible Risks and Complications
A nuclear stress test is a generally safe procedure with rare chances of complications. Possible complications may include:
- An allergic reaction to the radioactive dye substance
- Flushing sensation as blood flow increases
- Abnormal heart rhythm either caused by the exercise or the medication that increases blood flow; this usually goes away after the test or once the effects of the medication wear off.
- Moderate to severe chest pain
Myocardial infarction or a heart attack
Cramer CM, Beller GA. Noninvasive cardiac imaging. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 56.
Fihn SD, Gardin JM, Abrams J, et al. 2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines, and the American College of Physicians, American Association for Thoracic Surgery, Preventive Cardiovascular Nurses Association, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. Circulation. 2012;126:e354-471.