So, your doctor wants you to get a stress test?
In order to perform this important task, your heart muscle needs a specific and continuous amount of blood delivered to it. The amount of blood it requires to perform its basic function depends on many factors, most of which are determined by the amount of work the heart is doing, at a particular time. When the amount of blood delivered to the heart is reduced, the pump fails to function properly, leading to a number of different cardiac conditions and symptoms.
Stress testing is performed to determine whether or not you have evidence of abnormal blood flow to your heart under conditions of physical stress. When blood flow to the heart muscle is abnormal (reduced), this often is evidence that a blockage exists in one or more of the coronary arteries, the blood vessels which are responsible for transporting blood to the heart muscle. These blockages, when they exist, often place a patient at a high risk for having a heart attack. The stress tests helps determine the level of such risk.
A stress test measures the effect physical activity has on the heart. There are several different stress tests, but in simple terms, we can divide stress testing into two basic types: exercise stress testing and pharmacologic stress testing, which uses a medication to mimic the biologic effects of exercise. Pharmacologic stress tests are usually reserved for those patients who cannot adequately perform an exercise protocol, generally because their abilities to exercise are limited by a variety of medical conditions.
Prior to beginning a stress test, the patient is hooked up to an EKG device and heart rate and blood pressure monitors, are then recorded while the patient is resting. Exercise is then begun by walking on a treadmill. The doctor performing the stress test will follow a very specific exercise protocol, to ensure that the results obtained during the stress test are gradually increased by elevating the speed and slope of the machine. The primary indication of abnormal blood flow during the stress test is determined by measuring the changes that occur in the patient’s EKG during exercise. When a patient’s EKG findings are abnormal, then the results may indicate that a blockage exists.
The most basic form of stress testing uses only the findings from the EKG. No medical test is perfectly accurate, and this principle certainly applies to the stress test.
Two types of imaging modes are performed during a stress test: ultrasound imaging, also known as a stress test echo and nuclear imaging, often using the nuclear medicine Cardiolyte. The stress echo uses ultrasound to image the moving walls of the heart muscle during rest and following peak exercise.
The manner in which the muscle walls move during each of these conditions determines whether the test is normal or abnormal. The advantage of the stress echo is that it yields a high level of accuracy without the use of medical radiation.
Nuclear imaging during stress testing requires the injection of a nuclear medicine at rest and at peak exercise. Nuclear pictures are then taken, which measure the amount of blood flow to the heart muscle walls during each of these conditions. Comparing images under resting and stress conditions allows us to determine if flow is normal or abnormal. Pharmacologic stress tests are usually performed using nuclear imaging. The advantage of nuclear stress testing is high accuracy, especially in patients who have less than optimal echo images. A concern with nuclear stress testing is that it involves a small amount of medical radiation when performed.
Once a stress test is performed, a full report of your results will be provided, including the imaging studies when they are performed. Your doctor will use these results to determine your risk of having coronary disease or blockage in your coronary arteries. Further treatment and testing, including coronary angiography, may be indicated for patients whose results show an elevated risk of having coronary disease. There are many life-saving treatments for heart disease and patients with this condition can have long, productive lives. The road to proper treatment begins with the information this test provides.
Guest editorial submitted by Bertrand Chaffee Hospital Cardiologist Thomas Smith.