There are four types of Nuclear Stress Tests:
1. Exercise Cardiolite Stress Test
2. Adenosine Cardiolite Stress Test
3. Dobutamine Cardiolite Stress Test
4. Lexiscan Cardiolite Stress Test
What is Cardiolite?
Cardiolite is a nuclear radioactive isotope termed Technetium Tc99m Sestamibi. Cardiolite is injected through an IV and it travels in the bloodstream and through the coronary arteries until it is picked up by the heart muscle cells. The areas of the heart that have an adequate blood supply pick up the tracer right away and more completely. Areas that do not have adequate blood supply pick up the tracer very slowly or not at all.
Cardiolite gives off a small amount of radiation that is detected with a nuclear scanning camera. A computer processes the information and produces the images of the radioactivity distributed in the heart.
If an area receives less blood than the rest of the heart (because of a blocked or narrowed artery), it will pick up a lower level of radioactivity and will show up as a lighter area, called a “defect.”
Cardiolite is injected while you are at rest and while your heart is under stress. Rest and stress images are taken to allow doctors to compare how much blood flows through the heart muscle during stress and at rest.
The amount of radiation you will be exposed to is comparable to that from an X-ray or CAT (CT) scan. The half-life of Cardiolite is 6.02 hours. This means that half of the dose you are given will decay in 6.02 hours.
Generally, Cardiolite is cleared from your body in 24 hours by natural processes. You won’t feel any different after you are injected with Cardiolite. Most patients experience no side effects. Occasionally patients have a metallic taste in their mouth.
What is a Cardiolite Stress Test and what does it show?
A Cardiolite Stress Test is a diagnostic nuclear imaging study that uses a radioactive tracer, called Cardiolite, to produce images of the heart muscle. When combined with stress either through exercise or use of a pharmacological agent, the Cardiolite scan helps determine if the heart muscle is getting the blood supply it needs.
As Coronary Artery Disease (CAD) progresses, the heart muscle may not receive enough blood when under stress (for example, when exercising). This often results in chest pain called Angina Pectoris. On the other hand, there may be no outward physical signs of the disease. If CAD is limiting blood flow to part of your heart, the Stress Test with Cardiolite may be useful in detecting the presence and significance of CAD.
A Cardiolite Stress Test consists of two parts, rest and stress:
Cardiolite will be administered by injection through your IV while you are at rest, and a special camera will take pictures of your heart.
Cardiolite will be administered to you one other time by an IV injection during the stress portion of the test, and additional pictures will be taken of your heart.
This allows the doctor to compare the amount of blood flowing through the heart muscle during stress and at rest.
How do I prepare for the test?
Do not eat or drink for 4 hours prior to the test–this includes caffeine! The pictures of your heart are clearer when the stomach is not full. If you are diabetic or need to eat/drink with your medication, get special instructions from your doctor.
Avoid any strenuous physical activity on the day of the test because you will need to exert yourself maximally if you are doing an exercise test.
Bring busy material. You will have periods of waiting throughout the test so bring a book, newspaper, knitting, etc. to keep you busy.
No smoking 4 hours prior to the test. Smoking may interfere with the test results.
Wear a comfortable two-piece outfit and comfortable shoes. A hospital gown may be provided and men may be asked to take off their shirt. Slacks or shorts are preferred if you are exercising. You should wear comfortable footwear appropriate for brisk exercise if you are doing an exercise test.
Do not wear oils or lotions before your test. Small sticky patches (electrodes) will need to stick to your chest.
Do not take the following heart medications on the day of your test unless your physician tells you otherwise or if the medication is needed to treat chest discomfort:
Isosorbide Dinitrate (for example: Isordil, Sorbitrate)
Isosorbide Mononitrate (for example: Ismo)
Nitroglycerin (for example: Deponit, Nitrostat)
Your physician may also ask you to stop taking other heart medications on the day of your test. If you have any questions about your medications, ask your physician.
NOTE: Do not discontinue any medication without first talking with your physician
What happens during the test?
When you enter the Stress Testing room, the Cardiology Tech/Nurse will have you sign a consent form and he/she will make sure you understand the test. An IV will be started in a vein in your arm. The Nuclear Medicine Tech will put your first injection of Cardiolite through the IV. You will wait in the waiting room for at least 15 minutes to let the Cardiolite circulate to your heart.
Once your waiting period is over, the Nuclear Medicine Tech will put you under the camera for about 15 minutes. You will lay on your back on a table with your hand behind your head. It is important for you to remain very still while the images are being taken. The camera will move about you but never come in contact with you during the scan.
Following the completion of the scan, you will be escorted to a Stress Testing room.
Exercise Cardiolite Stress Test
The patient is brought to the exercise laboratory where the heart rate and blood pressure are recorded at rest. Sticky electrodes are attached to the chest and then connected to the EKG portion of the Stress test machine with lead wires. A 12-lead EKG is recorded on paper. Each lead of the EKG represents a different portion of the heart, with adjacent leads representing a single wall.
The treadmill is then started at a relatively slow “warm-up” speed. The treadmill speed and its slope or inclination are increased every three minutes according to a preprogrammed protocol (Bruce is the commonest protocol in the USA, but several other protocols are perfectly acceptable). The protocol dictates the precise speed and slope. Each three minute interval is known as a Stage (Stage 1, Stage 2, Stage 3, etc. Thus a patient completing Stage 3 has exercised for 3 x 3 = 9 minutes). The patient’s blood pressure is usually recorded during the second minute of each Stage. However, it may be recorded more frequently if the readings are too high or too low. Cardiolite is injected when maximum effort is achieved (Target heart rate). Sometimes Cardiolite is injected sooner if indicated.
Indications would be if chest pain developed or if there was abnormal EKG tracings that indicated coronary artery disease. After Cardiolite is injected, it is very important to walk an additional minute for circulation. Treadmill will then be terminated and then a recovery period of 5 minutes will be recorded.
Adenosine Cardiolite Stress Test
For patients who are unable to exercise adequately on the treadmill, the drug Adenosine may be given to produce an effect on the heart similar to exercise. During the test, you will be lying on the stretcher. The drug Adenosine will be infused through your IV. The Adenosine dosage you will be given is based on your body weight. Adenosine is a vasodilator so you may feel warm, flushed, experience chest pressure, headache, dizziness, nausea or shortness of breath. These symptoms are perfectly normal, but make sure to let the Cardiologist know how you feel. The Adenosine is infused over 5 minutes. Then you will be given another injection of Cardiolite three minutes into infusion. There will be a recovery period of at least 2 minutes after complete infusion of Adenosine.
What is Adenosine?
Adenosine is a coronary vasodilator that is used as a diagnostic agent in nuclear Stress Testing. Adenosine works by increasing the blood vessel circumference of the coronary arteries (arteries that feed the heart) in order to increase blood flow to the heart. Adenosine causes a 20% increase in heart rate and a mild but significant decrease in systolic and diastolic blood pressure. Adenosine is metabolized in the liver. The amount of Adenosine you will be given is based on your body weight.
Side effects include: chest pain/pressure, dizziness, headache, nausea, dizziness, shortness of breath, or a warm and flushed feeling. Adenosine is contraindicated in patients who have a hypersensitivity to this drug. Adenosine can also cause bronchospasm so your doctor may order a different test for you if you have a lung condition that will be exacerbated by using Adenosine. Albuteral breathing treatment may be given prior to and after Adenosine stress test.
Dobutamine Cardiolite Stress Test
For patients who are unable to exercise adequately on the treadmill, the drug Dobutamine may be given to produce an effect on the heart similar to exercise. During the test, you will be lying on the stretcher. A line of normal saline will be connected to your IV. The drug Dobutamine will be infused through your IV. The Dobutamine dosage you will be given is based on your body weight. Dobutamine is infused slowly through your IV, and the dose is increased every 3 minute. The Dobutamine infusion is turned off after it is infused for about 12 minutes.
The Dobutamine may be turned off early if:
You exceed a “target” heart rate based on your age
The Cardiologist or Cardio Tech/Nurse detects abnormal changes on your EKG
You experience significant symptoms, such as shortness of breath, chest pain, chest tightness, dizziness, etc. that do not permit you to exercise any longer.
Your blood pressure goes up too high
The dobutamine is infused longer than the 12 minutes if your heart rate has not reached the predicted “target” heart rate. Sometimes the Cardiologist will have the Nurse give you a drug called Atropine through your IV if your heart rate has not sufficiently increased. You will be given one more injection of Cardiolite once your heart rate is at or has exceeded your “target” heart rate.
Sometimes the Cardiologist will have the Nurse give you a drug called Lopressor through your IV if your heart rate is taking a long time to decrease.
Lexiscan Cardiolite Stress Test
For patients who are unable to exercise adequately on the treadmill, the drug Lexiscan may be given to produce an effect on the heart similar to exercise. During the test, you will be lying on the stretcher. The drug Lexiscan will be infused through your IV. Lexiscan is a vasodilator so you may feel warm, flushed, experience chest pressure, headache, dizziness, nausea or shortness of breath. These symptoms are perfectly normal, but make sure to let the Cardiologist know how you feel. The Lexiscan is Injected within one minute followed by a saline flush. Another injection of Cardiolite will then be given immediately after Lexiscan followed by another saline flush. The Lexiscan stress test is completed in 4 minutes followed by a 2 minute recovery period. If symptoms have not subsided, another drug called Aminophyline may be given to reverse effects.