What to Expect from a Nuclear Stress Test

If you’re experiencing chest pain or shortness of breath, it could be a sign that your heart isn’t getting enough blood to function properly. To find out, your doctor might order a nuclear stress test, which measures your heart at rest and during exercise to provide important information about your coronary arteries, the blood vessels servicing your heart.

“The heart pumps blood to the body, but its muscular walls get their own blood supply from the coronary arteries. Blockages in the coronaries can result in chest pain and even heart attacks. A stress test is designed to see if blood flow through the coronary arteries is normal,” says UNC Health cardiologist Christopher Kelly, MD.

We talked to Dr. Kelly about what to expect from a nuclear stress test.

What happens during a nuclear stress test?

Before a nuclear stress test, your doctor will give you instructions on how to prepare for the exam. This may include stopping certain medications that affect the heart rate, such as beta blockers, and avoiding caffeine. The test can be conducted in a doctor’s office or a hospital and takes about three to four hours.

To begin, you will have an IV placed. A radioactive material, known as a radiotracer, is injected into your blood. The radiotracer flows through your coronary arteries into your heart muscle, leaving a detectable signal that can be mapped with a scanner. Because the three coronary arteries supply different parts of the heart muscle, decreased radiotracer signal arising from one part of the heart muscle indicates problems in the artery that supplies it with blood.

A nuclear stress test involves two scans: one taken of the heart at rest and one taken after exercise.

For the exercise portion of the test, usually you walk on a treadmill while a medical professional monitors you. Every few minutes, the professional will increase the speed and incline of the treadmill so that your heart has to work harder. While this is happening, the blood flow through the coronary arteries should greatly increase, since the heart needs more oxygen-rich blood. You exercise for as long as possible, and just before you finish, you receive another injection of the radiotracer. The signal generated by this injection illustrates the coronary blood flow when the heart is working hard. You are scanned after getting off the treadmill.

Not everyone can exercise on a treadmill; in these cases, doctors can offer an alternative.

“If a person is unable to exercise on a treadmill for some reason, such as joint issues or frailty, we can do a modification of the test,” Dr. Kelly says.

To simulate exercise, you will be given medicine to relax your coronary arteries and increase blood flow.

What does a nuclear stress test show?

The two scans taken during the nuclear stress test can show your doctor whether you have significant coronary artery disease and if your heart has already been damaged by a previous heart attack.

“The radioactive substance produces a signal, and the strength of that signal is proportionate to the blood flow that part of the heart is receiving. When the heart is at rest, it’s easy for the arteries to deliver a normal amount of blood to the entire heart, so the signal should appear uniform,” Dr. Kelly says.

When your heart is working harder, it needs more blood. If one of the coronary arteries is full of plaque, it may not be able to deliver adequate blood flow to part of the heart muscle, so the signal becomes relatively weaker there.

“If there is poor blood flow to part of the heart both at rest and exercise,” he says, “it may be that there has already been damage to that part of the heart, and it has been replaced with scar tissue that doesn’t get much blood flow.”

What are the next steps after a nuclear stress test?

If your nuclear stress test is abnormal, which suggests a significant blockage in your coronary arteries, you will need further testing.

“The next step is to visualize the coronary artery directly, either with a CT scan or a cardiac catheterization,” Dr. Kelly says.

A catheterization is invasive, passing a small, flexible tube into the heart via an artery in the wrist or groin.

“But in the same procedure, your doctor may insert stents [small mesh tubes] into a blocked artery to reopen it,” he says. “A coronary CT scan is less invasive but only provides imaging.”

The CT scan or catheterization will reveal the extent of coronary artery disease, and you can discuss with your doctor how to address it. You might need stents or bypass surgery, though medication and lifestyle changes are adequate in many cases. For example, your doctor will work with you to lower your cholesterol and control your blood pressure to reduce your risk of a heart attack.

If your nuclear stress test is normal, meaning there aren’t significant differences in the scans of your heart at rest and during exercise, you might need more tests depending on your symptoms.

“A stress test doesn’t detect all blockages,” Dr. Kelly says. “Your arteries could still have mild or moderate plaque buildups that aren’t affecting blood flow but still increase the risk of heart attack.”

Is a nuclear stress test safe?

Nuclear stress tests are relatively safe. The radiation you receive from the tracer is about three to four times what you normally get from the environment in a year, and it’s similar to other medical procedures.

“It’s usually about the same amount of radiation as a CT scan,” Dr. Kelly says. “If the test is going to offer valuable information, the safety concerns are minimal. Also, the tracer is out of your system in 12 to 24 hours.”

Though the test can be an important tool in diagnosing heart disease, you and your doctor should consider it carefully. Radiation exposure can increase the risk of cancer and should always be avoided unless the test is truly necessary.

Nuclear stress tests should almost never be done on people who don’t have symptoms, Dr. Kelly says.

“The radiation involved is small, but it’s not zero, and if the test is done repeatedly, the risk of developing a cancer will add up,” he says.

If you change doctors, be sure to tell the new one if you’ve already received a nuclear stress test.

Concerned about your heart health? Talk to your doctor. If you need a doctor, find one near you.