What are some of the variations used with stress tests?
The accuracy of the stress test in diagnosing CAD is greatly increased by performing a nuclear perfusion study in conjunction with the stress test. A radioactive substance called thallium (or a similar substance called sestamibi or Cardiolite) is injected into a vein during exercise. The thallium collects in the parts of the heart that have good blood flow. Pictures of the heart are taken with a special camera that can image the radioactivity of the thallium. From these pictures, portions of the heart that are not receiving good blood flow (because of blockage in the coronary arteries) can be identified. The thallium study greatly increases the accuracy of the exercise study in diagnosing CAD. The amount of the patient receives from thallium is less than that from a chest x-ray.Echocardiograms are sometimes used in conjunction with stress tests. An echo test is made at rest, and then with exercise, looking for changes in the function of the heart muscle during exercise. Deterioration in muscle function during exercise can indicate coronary artery disease.
Sometimes patients are not able to perform exercise because of physical limitations. The drugs persantine and dobutamine can be used in these cases to simulate the effects of exercise on the heart.
What are the limitations of the stress test?
In some patients, ECG changes suggestive of ischemia can occur even in the absence of CAD. (In other words, "false positive" stress tests are not uncommon.) In other patients, no significant ECG changes are seen even in the presence of CAD. (So "false negative" stress tests can be seen.) False positive and false negative studies can significantly limit the usefulness of the stress test in many patients. By adding a nuclear perfusion study to the stress test, this limitation is minimized, and the diagnostic capacity of the stress test is greatly improved.
What are the risks of having a stress test?
The stress test has proven to be remarkably safe. It poses about the same level of risk as taking a brisk walk or walking up a hill. While it is possible that the ischemia provoked by such stress can lead to a myocardial infarction or to serious heart rhythm disturbances, in practice this event is rare. Further, when these serious events do occur during a stress test, they occur in the presence of trained medical personnel who can deal with them immediately.Sources:
Gibbons, RJ, Abrams, J, Chatterjee, K, et al. ACC/AHA 2002 guideline update for the management of patients with chronic stable angina. Available at: www.acc.org/qualityandscience/clinical/statements.htm (accessed August 24, 2006)
