Nuclear Imaging
What is a Nuclear Cardiology Stress Test?
Nuclear cardiology stress testing is performed to determine the presence and severity of coronary artery disease (CAD). This test is an effective method of viewing the circulation to the muscles of your heart under both rest and stress conditions. Motion images will also be taken to show the wall motion and efficiency of the left ventricle of your heart. If you are having a treadmill test, your physician can also obtain information regarding your blood pressure response to exercise, any EKG abnormalities, and your conditioning.
A nuclear cardiology stress test consists of 3 parts:
- A chemically induced test, regular treadmill test or a combination of the two.
- Imaging of the heart at rest
- Imaging of the heart after the stress part
The appropriate type of stress test will be decided by your physician or his / her assistant.
The reason this is referred to as a “nuclear” test is because a small amount of a radiopharmaceutical is injected into your vein to tag to the muscles of your heart to be viewed by a gamma camera. If you are having a dual isotope test, thallium-201 and 99mTc sestamibi are used. If you are having a one-day sestamibi or a two day sestamibi test, only the one isotope is used.
What Does a Nuclear Stress Treadmill Test Involve?
When you first come in, a brief medical history will be taken by a technologist or nurse. An intravenous line (IV) will be started. A radioactive dose may be injected and rest images may be done if you having a dual isotope test or a one day Sestamibi test. These images take about 15-20 minutes using a specialized gamma camera. A nurse will then put on EKG leads on your chest to monitor your heart. You will then walk on the treadmill using a standard exercise protocol. Your blood pressure, EKG rhythm and any symptoms you may have will be monitored by the nurse and a cardiologist. When you reach a certain target heart rate or when the cardiologist gives the order, the radioactive agent 99mTc Sestamibi will be injected into the intravenous line and flushed with saline. You will need to continue to walk on the treadmill for another minute to circulate the radioactive material. You will then receive some oral fluids to ensure optimal images. The stress images will be done with the gamma camera. Three EKG patches will be left on your chest and they will be wired up to acquire “gated” images to analyze the wall motion and left ventricular ejection fraction of the heart.
The stress images will be compared to rest images to look at the blood flow to the heart. If a significant blockage is present in your coronary arteries a perfusion defect will show. If there is a defect in the stress but the rest images look normal, this is called ischemia. If there are matching defects in both the stress and rest, an infarction has occurred. If there are no defects then the study is normal.
What is a “Chemical” induced Nuclear Stress Test?
When you first come in, a brief medical history will be taken by a technologist or nurse. An intravenous line (IV) will be started. A radioactive dose may be injected and rest images may be done if you having a dual isotope test or a one day Sestamibi test. These images take about 15-20 minutes using a
specialized gamma camera. A nurse will then put on EKG leads on your chest to monitor your heart.
If a patient cannot walk on treadmill very fast due to a physical reason or has certain EKG abnormalities such as a left bundle branch block, the physician may order a low level treadmill adenosine stress test or an adenosine stress test without exercising. If a patient has severe asthma or very significant lung disease, the physician may order a dobutamine stress test.
Adenosine is a pharmacological agent that will cause dilation of all the blood vessels in the body. You may experience a flushing feeling, chest pressure and/or shortness of breath, similar to exercising. This part only takes 6 minutes and any of the side effects resolve quickly after the infusion is done. It has been found that walking very slowly on a treadmill during the 6 min adenosine infusion decreases the severity of any side effects and optimizes the heart images. Your blood pressure and EKG will be monitored by a nurse and a cardiologist. The radioactive material, 99mTc Sestamibi will be injected into the IV by the Nuclear Medicine Technologist at the mid point of the adenosine infusion. After the stress test is over, you will receive a beverage and have a break before the stress images are acquired.
Dobutamine is pharmacological agent that causes the heart rate to rise and the blood pressure to increase. This test is done with the patient lying down. Your blood pressure and EKG will be monitored by a nurse and a cardiologist. The dobutamine will be slowly infused into your IV, increasing the amount every three minutes. When your heart rate has reached a certain target determined by your age, the Nuclear Medicine Technologist will inject the 99mTc Sestamibi material into the IV. The infusion will continue for another minute. This part usually takes a total of 6-12 minutes.
After the stress test is over, you will receive a beverage and have a break before the stress images are acquired. Three EKG patches will be left on your chest and they will be wired up to acquire “gated” images to analyze the wall motion and left ventricular ejection fraction of the heart.
The stress images will be compared to rest images to look at the blood flow to the heart. If a significant blockage is present in your coronary arteries a perfusion defect will show. If there is a defect in the stress but the rest images look normal, this is called ischemia. If there are matching defects in both the stress and rest, an infarction has occurred. If there are no defects then the study is normal.
Preparations for Test
- Do not have caffeine 24 hours before your test
This means NO coffee, tea, decaffeinated coffee or tea (they have traces of caffeine). NO beverages that may contain caffeine such as soda. NO chocolate. - Do not have any food or drink 4 hours before the test.
You may eat lightly 4 hours before your scheduled test time BUT it may consist only of two pieces of toast or a plain bagel with jelly and juice. Please do not use butter, milk or dairy products. - Wear comfortable clothes and sneakers.
NO sandals, slip on shoes, flip flops, high heels or open toe shoes. - Consult with your physician or medical assistant on what medications you should or should not take the morning of the test, especially if you have diabetes. You may use you nitroglycerin as needed for pain. You may also wear your nitro patch as prescribed.
- Women under the age of 55 will need to sign a waiver stating that they are not pregnant or nursing at the time of the test.
What Information Does a Nuclear Cardiology Stress Test Provide?
The treadmill part of the test will give information concerning your physical conditioning, any EKG irregularities, and blood pressure response. A pharmacological test will also show any EKG abnormalities under stress conditions.
The stress images show the perfusion of the coronary arteries to the heart muscle. If a coronary artery is significantly blocked, blood flow is reduced and the radioactive tracer will not show or be noticeably diminished in the corresponding heart muscle. Analysis of the gamma camera images can identify the location, severity and extent of the defect of reduced blood flow to the heart.
The stress images will be compared to rest images to look at the blood flow to the heart. If there is a defect in the stress but the rest images look normal, this is called ischemia. If there are matching defects in both the stress and rest, an infarction has occurred. If there are no defects then the study is normal.
How long does the test take?
A dual isotope stress or a one day Sestamibi test may take up to three to three and a half hours. A two day Sestamibi test will take about one hour and a half for the stress and about an hour for the rest part.
There may be some waiting time in between imaging so you may want to bring some reading material to pass the time. If you are diabetic you may need to bring something to eat for your blood sugar.
How Safe is a Nuclear Stress Test?
There is some risk involved in having a stress test especially if you have severe heart disease. Our staff is very experienced performing cardiac stress tests. Your vital signs will be monitored very carefully during the entire test. The test will be stopped if the physician believes that your safety may be compromised. We are prepared to handle any emergencies should they occur.
The radioactive agents are used to show the blood flow to your heart. These tracers have been used for over thirty years and are considered very safe. The amount of radioactivity that you receive is about the same amount you would normally be exposed to over a period of 1-2 years just from background radiation. The only restriction to this test would be if there is any possibility you may be pregnant, currently trying to become pregnant, or nursing.
What is the Reliability of a Nuclear Cardiology Stress Test?
If good quality images are acquired and the target heart rate is met by the treadmill test, an isotope stress test is capable of detecting significant coronary artery disease approximately 85% of the time. Nearly 10% of patients may have a “false-positive” test, i.e. when the results show a defect where none actually exists. Technical quality problems with the images may occur if a patient is extremely obese, has large breasts, has a prominent diaphragm, or has an EKG with a left bundle branch block.
