What Can I Expect from a Stress Test?
A stress test is often the first step in diagnosing a heart condition. Cardiologist Michael Rocco, MD, explains the standard stress EKG and several other variations that your doctor may order.
If your doctor orders a stress test, there’s no need to be concerned, even if you’ve suffered a prior heart attack. This simple, straightforward test is a safe way to evaluate the blood supply to your heart and how well your heart pumps.
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There are several variations of a stress test that may be ordered for different reasons. The most common reason is to look for the presence and extent of coronary artery disease (CAD) in someone who is experiencing symptoms.
“In general, the test allows us to differentiate between healthy heart muscle and muscle that has been damaged by heart attack and whether the blood supply to areas of muscle is compromised,” says Michael Rocco, MD, Medical Director of Cardiac Rehabilitation and Stress Testing.
The basic, no-frills stress test is known as a stress EKG. The patient is wired with a standard 12-lead EKG, then walks on a treadmill. As the speed and incline of the treadmill are gradually increased, their heart’s response is monitored.
“There are characteristic changes to an EKG that indicate blood flow problems and rhythm abnormalities,” says Dr. Rocco. “We also look at blood pressure response and symptoms.”
The test — which can also be done with a stationary bicycle — is commonly done to look for the presence of CAD. It can also be used on high-risk patients prior to starting an exercise or cardiac rehabilitation program, and after the program has been completed to assess progress.
Sometimes, the heart is imaged before and after a stress test. The addition of imaging helps diagnose CAD in situations where an EKG alone is less likely to be accurate; for example, in patients who take digoxin, and in women.
In this test, echocardiography is used to image the heart before and after the patient walks on a treadmill.
“This enables us to see the motion of the heart. If we spot an area of the heart muscle that looks normal at rest but does not contract normally after exercise, this indicates there is a problem with blood flow to that area,” says Dr. Rocco.
Instead of echocardiography, a stress imaging test can be done using a nuclear tracer injected intravenously. The tracer, which is not iodine-based and will not cause an allergic reaction, is taken up by the heart and reveals the pattern of blood flow to the muscle.
“An abnormality that appears after the heart is stressed by exercise suggests that the flow of blood to that area is compromised. An abnormality present both before and after exercise generally indicates scar tissue or prior heart attack,” he says.
In order for a stress test to be useful, the patient must be able to achieve a high heart rate (85 percent of predicted maximum). In someone who is very elderly or has a medical condition that prevents this extent of exercise, medications can be given intravenously to achieve the desired result.
One of these is adenosine, a medication that increases coronary blood flow. “It doesn’t really mimic exercise, but it does tell us how well blood perfuses the heart muscle during the stimulation,” says Dr. Rocco.
Alternatively, dobutamine can be given. This drug mimics exercise somewhat by increasing heart rate, blood pressure and the force of contractility. When the heart is imaged with echocardiography, the cardiologist looks for abnormalities in wall motion or EKG that indicate the presence of CAD.
This is a special type of stress test ordered to evaluate heart failure or a potential heart transplant recipient, or to determine whether shortness of breath is caused by heart or lung disease.
It is performed on a treadmill or cycle with EKG, but a breathing apparatus is used to measure oxygen use and carbon dioxide production.
Cardiologists combine the information provided by a stress test with a patient’s medical history and symptoms to make decisions about the need for further testing or management.
“Not every abnormal stress test requires additional testing. Some patients simply need to modify their risk factors,” says Dr. Rocco. “However, if the abnormality occurs at a low level of exercise, affects a large segment of heart muscle, or the pattern suggests multivessel disease, we will often proceed with cardiac catheterization.”
This article originally appeared in Cleveland Clinic Heart Advisor.