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Diagnostic Tests in Cardiovascular Diseases

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7. Nuclear Stress Testing

What is a nuclear stress testing?

Nuclear stress testing is also known as myocardial perfusion scan, or MIBI scan. The nuclear stress test combines a nuclear scan of the heart and an electrocardiogram (EKG) with an exercise or pharmacological (medication) stress test. This allows the doctor to understand the degree and distribution of blood flow (perfusion) to the heart at rest and at stress.

What is a nuclear stress for?

The most common reason for having a nuclear stress test is to determine the presence of blockages in the coronary arteries and the extent of heart muscle involvement in the evaluation of chest pain, shortness of breath, or pre-surgical evaluation. It is often ordered when there are difficulties in using EKG alone to infer whether there is lack of blood supply to the heart. This occurs in some patients who have conditions that can cause erroneous (false positive) changes in the EKG during exercise, such as pre-menopausal females, patients on certain medication such as Digoxin, or patients who have an abnormal EKG to start with. Alternatively, the patient may have difficulties in walking such as having a stroke or arthritis; or a patient is on certain medications which make it difficult to achieve the target heart rate; then a medication, such as Persantine, can be given intravenously to create a transient mal-distribution of coronary blood supply necessary for the evaluation of the heart.

How is it performed?

Cardiolyte (Sestamibi) is the radioactive tracer that is often used which allows the visualization of the blood flow. Occasionally, Thallium is used to assess the viability (amount of living tissue) of the heart muscle. These nuclear tracers contain a small amount of radiation. The amount of radiation that you are going to be exposed is comparable to that of a chest X-ray.

Specially trained technicians will be performing the test. As discussed you may be asked to have an exercise stress nuclear test or a Persantine stress test. In either case you will have a nuclear scan at rest first and then after the exercise or pharmacologically induced stress. You will be hooked up with surface EKGs, and a blood pressure monitor. During the test you should report any symptom, such as chest pain, palpitation, or shortness of breath to the supervising doctor, nurse or technician.

During the rest scan an injection of Cardiolyte will be given. You will be asked to lie in a nuclear scanner for 20-40 minutes with you hands held behind your head to avoid the obstruction of the scanning. It is important to avoid any motion during the scanning as it may interfere with the image quality and renders interpretation difficult.

In an exercise nuclear stress test, you will be asked to walk on a treadmill where the speed and slope of the treadmill is increased at predefined intervals that is usually every three minutes. You should exercise as much as you can tolerate. When you decide you have exercise as much as you can, you should let the technicians know and they will end the test. Most patients can exercise between three to 15 minutes depending on the age and physical state. An injection of Cardiolyte, a nuclear isotope, is given just before you finish the exercise. Then, you will be asked to lie in a nuclear scanner for 20-40 minutes.

In a Persantine stress nuclear test, an intravenous line will be established and Persantine will be infused. You may feel chest pain, dizziness, palpitation, nausea or headache with this infusion but usually the sensation is transient. An injection of Cardiolyte is then given and you will be asked to lie in a nuclear scanner.

The nuclear stress test usually takes about 4 hours to complete.

How should I prepare for the test?

You should let your doctor whether you have any major lung disease such as asthma or chronic obstructive lung disease(COPD) and any medication for the lungs that you are taking. You should check with you doctor whether or not to hold some of your cardiac or hypertensive medications before the test and for how long. For the purpose of diagnosing ischemia (lack of blood supply to the heart), medications like beta-blockers ( e.g. Atenolol, Lopressor), calcium-channel blockers (e.g. Cardiazem) may need to be held 24 to 48 hours prior to the test. Bring all the medications or a list of medications with you to the test so that that the doctors will know what you are taking. If you are undergoing an exercise stress echocardiogram, you should wear light clothing with sneakers or comfortable shoes. If Persantine is going to be used then you should avoid any foods, drinks, or medicines that may contain caffeine for at least 48 hours prior to the test.

Food and drinks that may contain caffeine are:

  • All forms of coffee (including caffeinated and decaffeinated)
  • All forms of tea (including caffeinated and decaffeinated)
  • All cola drinks including but not limited to: Coke, Pepsi, Root Beer, Mountain Dew, Tab, Mellow Yellow etc.

Some medications that contain caffeine and should also be avoided:

  • Anacin, Excedrin, NoDoz, Cafegot, Fiorinal, etc.

What happens after the test?

The doctor will interpret the rest and stress information and generate a report to the referring doctor. There is no special precaution after this test. You may continue your usual activities after the test.