Cardiac stress testing - also called exercise testing - can be useful in identifying partial blockages in your coronary arteries.
Many times, the presence of coronary artery disease (CAD) is easily missed when a person is at rest, because at rest there may be no sign of a problem either on physical examination or on the ECG. In these cases, cardiac abnormalities may become apparent only when the heart is asked to perform at increased workloads.
The stress test is used to evaluate the heart and vascular system during exercise. It helps answer to two general questions: 1) Is CAD present that only becomes apparent when the heart is stressed by exercise? 2) If there is underlying heart disease, how severe is it likely to be?
How is a stress test performed?First, you will have leads (wires) to an ECG machine attached to your chest, and a blood pressure cuff is placed on your arm. A clothespin-like sensor may be placed on your finger to measure the amount of oxygen in your blood. After a baseline ECG is obtained, you will be asked to begin performing a low level of exercise, either by walking on a treadmill, or pedaling a stationary bicycle. The exercise is "graded" - that is, every three minutes, the level of exercise is increased. At each "stage" of exercise, your pulse, blood pressure and ECG are recorded, along with any symptoms you may be experiencing.
With a "maximal" stress test, the level of exercise is gradually increased until you cannot keep up any longer because of fatigue, or until you experience symptoms (chest pain, shortness of breath, or lightheadedness) that prevent further exercise, or until changes on your ECG indicate a cardiac problem. Maximal stress tests should be performed when the goal is to look for any evidence of CAD.
With a "submaximal" stress test, you will exercise only until a pre-determined level of exercise is attained. Submaximal tests are used in patients with known CAD, in order to measure whether a specific level of exercise can be performed safely. This type of testing is useful to the doctor in recommending exactly how much exercise a person with CAD can safely perform.
After the test, you will be monitored until any symptoms disappear, and until your pulse, blood pressure and ECG return to baseline.
What kinds of heart disease can the stress test help to evaluate?The stress test is useful chiefly in the diagnosis of CAD that is producing blockages in the coronary arteries, the arteries that supply blood to the heart muscle. If a partial blockage is present, the heart muscle supplied by that partial blockage may be getting all the blood it needs in the resting state. But if the person with this partial blockage exercises, the artery may not be able to supply all the blood the heart muscle needs to perform at the high level now needed. When a portion of the heart muscle is suddenly not receiving enough blood flow, it becomes oxygen-starved, or ischemic. Ischemic heart muscle often causes chest discomfort (a symptom called "angina") and characteristic changes on the ECG. Exercise can also cause changes in the heart rhythm, or in the blood pressure. By "stressing" the heart with exercise, the stress test can bring out abnormalities caused by partial blockages in the coronary arteries - abnormalities that are often completely unapparent at rest.
It is important to note that the stress test can only help to diagnose CAD that is producing partial blockages - so-called obstructive CAD. CAD often produces plaques in the arteries that are not actually causing obstruction, and these non-obstructive plaques can (and do) rupture, causing acute blood clot formation, which produces an acute obstruction of the artery, often leading to myocardial infarction (heart attack). So it is certainly possible to have a "normal" stress test while still having CAD.
Because exercise raises adrenaline levels, stress tests can also be useful in diagnosing certain cardiac arrhythmias that tend to occur at times when adrenaline levels are increased.
Stress tests are also useful in measuring the "functional capacity" of patients with heart disease. If a patient has CAD, for instance, the stress test can help assess the significance of partial blockages. If signs of ischemia occur at a low level of exercise, the blockages are likely to be very significant. But if ischemia does not occur, or if it occurs only at very high levels of exercise, the blockages are likely to be much less significant.
Performing periodic stress tests can also be a useful way of monitoring the progress of patients with congestive heart failure. If the peak level of attainable exercise is worsening over time, either the underlying heart disease may be worsening, or the patient's medical therapy may need to be re-adjusted.