What is a Nuclear Stress Test?
A nuclear stress test is an imaging technique to evaluate how well blood flows into the heart muscle, both during activity and at rest. The test involves the administration of a small amount of radioactive material, such as thallium or sestamibi, into the bloodstream through a vein and capturing your heart images using a positron emission technology (PET) scanner or single photo emission computed tomography (SPECT) scanner. The test helps to show areas with poor blood flow or damage in your heart and determine if you are at risk of a heart attack or other cardiac event if you have coronary artery disease (CAD).
Coronary artery disease occurs due to the narrowing of the blood vessels that supply oxygen-rich blood to the heart. The blood vessels become narrow when fatty deposits accumulate inside the arterial wall. This process is called atherosclerosis. When the arteries become clogged, the blood flow to the heart muscle (myocardium) is hindered and a heart attack can occur.
A nuclear stress test may also be referred to as a myocardial perfusion imaging (MPI) study, nuclear cardiac imaging, cardiac SPECT study, or cardiac PET study.
Indications for Nuclear Stress Test
Your physician may recommend a nuclear stress test for the following:
- To identify if you are at high risk of heart attack
- To determine if someone has had a heart attack
- Establish the location and size of a heart attack
- To assess damage to the heart muscle following a heart attack
- To assess the extent of coronary stenosis (a narrowing of arteries that supply blood to the heart)
- To determine if you are a candidate for revascularization (a surgery that restores blood flow)
- Monitor blood flow to the heart and help detect blockages or CAD
- Assess a patient’s condition after angioplasty or bypass surgery
- Assess how well your heart is pumping blood, which could indicate heart injury, infection, or cardiomyopathy
- Monitor the effects of medications or chemotherapy on your heart
- Determine if your heart-related symptoms such as chest pain and shortness of breath are due to CAD
Preparation for Nuclear Stress Test
Preparation for a nuclear stress test may involve the following:
- You may be advised not to eat anything or use caffeinated or nicotine products for a specified period before the test.
- Your doctor should be alerted in case you are pregnant or breastfeeding or have any conditions such as heart or lung disorders.
- Your doctor and the technologist should be aware of your medical history, any allergies, and the details of your medications and vitamin supplements.
- You may need to avoid some medicines such as beta-blockers and calcium channel blockers for at least a couple of days before the test.
- Your doctor or technologist should be informed beforehand if you are claustrophobic.
- Do not use lotions or powder on your chest region the day of your test.
- You should wear a comfortable 2-piece outfit and comfortable walking shoes.
Procedure for Nuclear Stress Test
The nuclear stress test procedure involves two sets of images by the SPECT or PET camera; one with the patient at rest and another under stress that induces the heart to work harder. There are two ways to induce stress on the heart, which include:
- Exercising on a treadmill: This is the usual way of inducing stress on the heart.
- Drug-induced stress: Generally used for patients who are unable to exercise or physically disabled. The drugs employed may include dipyridamole, adenosine, regadenoson, or dobutamine.
The basic steps involved in a nuclear stress test are as follows:
- The patient will be asked to lie down on the procedure table and the radioactive material, such as sestamibi/tetrofosmin for SPECT or ammonia/rubidium for PET scan is injected into the arm vein.
- The patient will be asked to relax on the table for 15 to 45 minutes to enable the radioactive active substance to travel through the bloodstream into the heart muscle.
- After 45 minutes, the patient is asked to place both arms overhead and remain motionless and a series of images are taken with the specially designed SPECT or PET camera while at rest.
- The leads of an electrocardiogram are then placed on the chest of the patient to monitor the rhythm of the heart.
- The patient is then exposed to a stress test either through treadmill exercise or drug induced, depending on the patient’s condition, to scan the heart while at stress in the same pattern as at rest.
- The patient’s maximum level of exercise is assessed and the second injection of radioactive tracer is administered.
- The possibility of adverse symptoms such as breathing problems, chest pain, arm pain, palpitations, headache, difficulty in walking, or any other discomfort, after the test, are discussed with the patient.
- After 45 minutes, the second set of images is taken in the same pattern and with the same instruments to scan the heart a second time.
- Finally, your doctor will compare the first and second set of pictures using a computer and interpret the images and prepare the report.
Post-Procedure Care and Recovery
Other than intravenous injections, the nuclear stress test procedure is painless. Reports of side effects or significant discomfort are rare. You may feel a slight pinprick sensation during the injection of the radiotracer into the vein. You may feel fatigued or short of breath during exercise; however, you will recover naturally after a period of resting. If you are given medication because you are unable to exercise, you may experience dizziness, nausea, anxiety, mild chest discomfort, or shortness of breath for a brief period. These symptoms usually resolve on their own after the infusion is complete. You may resume your normal activities post exam unless your physician instructs otherwise. The small amount of radioactive tracer used in the exam will lose its radioactivity over time through the natural process of radioactive decay or will pass out of your body through your urine or stool. You need to make sure to drink plenty of water following the procedure to help flush the material out of your body.
Risk and Complications
A nuclear stress test is usually safe. However, as with any medical procedure, there is a possibility of complications, which may include:
- Arrhythmias (abnormal heart rhythms)
- Chest pain
- Shortness of breath
- Low blood pressure
- Allergic reaction to the radioactive dye
- Heart attack (extremely rare)