Myocardial Perfusion Imaging
There are two main types of nuclear tests performed in cardiology:
1. Myocardial perfusion studies- examines the blood flow to the heart muscle, and
2. Dynamic studies- measures the contractile (pumping) function of the heart muscle.
Exercise Myocardial Perfusion Imaging
- When the results of a routine treadmill study are equivocal
- When there is known coronary artery occlusive disease and it is desirable to know the extent and severity of the disease (so-called risk stratification).
- In some patients to determine the functional significance of coronary blockage observed on an angiogram
- To determine if coronary disease is the cause of, or associated with, abnormalities on the resting electrocardiogram
- To evaluate the results of coronary bypass surgery or coronary balloon angioplasty (PTCA)
Myocardial perfusion imaging is a non-invasive test and carries no risk beyond that of the treadmill testing itself. The radioactive isotope injected for the study produces less radiation than x-ray procedures such as a CAT scan or kidney study and is non-allergenic. The heart is imaged both at rest and during exercise. The exercise portion of the test is similar to that described in Treadmill Testing. The isotope tracer is injected into an arm vein one to two minutes before you quit walking. After the termination of the treadmill test the isotope will be imaged in the heart area by a large camera. This imaging will take 20 to 25 minutes during which time you will be asked to lie on a bed with your arms over your head. You are asked not to move during the imaging. When the test is performed with Sestamibi, the resting images of the heart are obtained several hours before the treadmill test. When thallium is used, the resting images are performed 3 to 3 ½ hours after the treadmill exercise test.
Do not eat or drink anything except water for three hours before the test. Please consult your doctor regarding whether you should take your medications. Please inform your doctor if there is a possibility that you are pregnant. The results of the test are not usually available immediately, and your doctor will go over the findings with you at a subsequent visit.
Pharmacological Stress Myocardial Perfusion Imaging
Myocardial perfusion imaging is indicated in some patients who are unable to perform treadmill exercise because of orthopedic or other problems. In such patients the cardiac effect of exercise stress can be simulated by the intravenous administration of a coronary vasodilator such as Dipyridamole . The imaging of the heart proceeds as described in "Exercise Myocardial Perfusion Imaging", except an intravenous injection of Dipyridamole replaces the treadmill exercise portion of the test. Since caffeine alters the efficacy of the test, it is essential that no coffee, tea or caffeine containing beverages or medications be consumed after midnight prior to the test.
Dynamic studies measure the contractile (pumping) function of the heart muscle. An early description of the test was a "left ventricular performance study" and this was abbreviated LVPS. Other Institutions call the test a MUGA scan and others refer to it as a radionuclide ventriculogram or radionuclide angiogram (RNA). All of these names describe the same test. In this test a small dose of isotope tracer is injected into the bloodstream, followed by imaging of the region of the heart to demonstrate the isotope particles within the chambers of the heart. The dose of isotope is sufficiently small such that a number of cardiac cycles must be measured to have a quantity of isotope to be recognized by the camera. A good study will give an accurate picture of the chambers of the heart and the contraction of the ventricles, especially that of the left ventricle. Accordingly, cardiac enlargement, hypertrophy (thickening), pumping function (ejection fraction, EF) and areas of previous myocardial infarction can be well identified.
The study can be performed as a resting study and also as part of a rest/exercise study to determine whether the above parameters of cardiac function are altered favorably or deteriorate during and after exercise. The usual form of exercise is semi-supine bicycle exercising since in this fashion, the upper portion of the body is stabilized and adequate images of the heart can be obtained during exercise. The test is non-invasive and carries no risk to the patient whatsoever, other than the risk of exercise as described in the treadmill testing section above. The results of this test will not be available immediately and will be discussed with you at a subsequent office visit by your physician. Do not eat or drink anything except water for three hours prior to taking the test other than your prescribed medications.