Your doctor may order a stress test to assess coronary artery disease, heart damage, and your risk of developing future heart problems. Most often, this will be in the form of an exercise stress test. But, if you are unable to engage in the physical activity an exercise stress test requires, or there are reasons why you should not be exercising (known as contraindications), your doctor may recommend that you undergo a pharmacologic stress test to evaluate your heart.
What Does a Pharmacologic Stress Test Entail?
As with an exercise stress test, you will need to provide consent to undergo a pharmacologic stress test.A medication (either adenosine or dipyridamole) is given via an IV catheter to help dilate the blood vessels in your heart. This is called the pharmacologic stress agent. As the drug flows into your IV, you'll be asked to lie down or walk very slowly on a treadmill. This is what is known as the "stress" portion of the test, which takes four to six minutes.
The drug allows more blood to flow to healthy areas of the heart; those areas that experience less blood flow may have a blockage. In order for a doctor to be able to actually identify those areas that may be blocked, though, all pharmacologic stress tests must include imaging.
In addition to the pharmacologic stress agent, you will also be given two doses of a radioactive material (isotope) through your IV catheter -- one when you're at rest, and another after the medication runs its course (which usually takes two to six minutes). Thallium and technetium are those most commonly used radioactive materials for this test. The material travels through the blood into the heart. Then, to obtain the image, a nuclear camera is used to detect the radiation from the material. The camera creates images on a computer screen that reflect the amount of radiation, and therefore the amount of blood flow to the heart muscle.
As is the case with exercise stress tests, blood pressure readings and ECGs (assessments of the electrical activity of the heart) are recorded during the test as well as in recovery. These readings are similar from test to test.
The test is stopped once the adenosine or dipyridamole finishes infusing and radioactive material is given. The medical staff may also decide to stop the test is you develop significant symptoms, heart rate or blood pressure changes, or an ECG abnormality.
Once your test is done, a doctor will review the images and discuss the results with you.
More details on the nuclear imaging portion of the test are available here.
What Symptoms Might a Pharmacologic Stress Test Cause?
It is not unusual to feel flushed, mildly short of breath, nauseous, or to have chest discomfort while the adenosine or dipyridamole is being injected through your IV. If you experience any of these, it's important to report your symptoms to the staff in the room immediately.If concerning symptoms persist after the test, your doctor can order aminophylline, a medicine that reverses the adenosine and dipyridamole. Some labs actually give patients aminophylline medicine routinely.
Before You Get a Pharmacologic Stress Test
Discuss the risks, benefits, and alternatives to the drugs used in this test with your doctor prior to proceeding. Specifically, mention if you have ever had or are currently being treated for asthma.Sources:
ACC/AHA/ASNC 2003 Guidelines for the Clinical Use of Cardiac Radionuclide Imaging