Oftentimes when a patient complains of intermittent chest pain, or shortness of breath with exertion, we might suspect blockage in the Coronary Arteries (see Diagram: The Heart – Anatomy). So we order an EKG, which commonly winds up normal at rest, when the chest pain is gone. However, if the symptoms sound convincing, and the person has risk factors, we can’t rely on the EKG (see Diagnosing Coronary Artery Disease). So we order a Stress Test to see if abnormalities arise during exertion. There are a few ways to do this.
1. The standard stress test is the “Exercise Treadmill Test” (“ETT”) — a regular EKG while walking on a treadmill that inclines steeper & steeper. If the EKG now becomes abnormal, we’re on our way to diagnosis.
2. But if there are non-specific abnormalities on our initial EKG (when the patient is resting peacefully on a table), the ETT result will be uninterpretable. So the patient must exercise during either of the following:
- Echocardiogram (but specifically a “Stress Echo”): to see if any part of the cardiac muscle (called the “heart wall”) fails to contract enough, indicating a blockage in circulation of blood to it (“wall motion abnormality”); OR
- Perfusion Scan: inject a radioactive tracer which shows up by a Nuclear Medicine scan, & see if a blockage prevents it from circulating into a part of the heart muscle during exercise.
If the Echo or Perfusion Scan is abnormal during rest, it just indicates a scar, permanent damage from an old Heart Attack. But if it’s normal at rest, and abnormal with exercise, that’s Ischemia — insufficient oxygen delivery due to a blockage in coronary arteries, that shows itself under stress (exertion), which may eventually get worse to cause a future Heart Attack (with permanent damage).
Some ERs do Echo’s or Perfusion Scans without stress in patients who have ongoing chest pain but normal EKGs and normal Cardiac Enzymes. A negative test during ongoing pain is very reassuring that symptoms are not due to ischemia (i.e. not active coronary artery disease). A positive test during chest pain may mean either active ischemia, or old Heart Attack as described above.
3. If the person can’t exercise (bad knee, too frail, etc.), we do a “Pharmacologic Stress Test.” Inject a drug to rev up the heart (dobutamine, dipyridamole, adenosine, etc.), & then do an Echo or a Perfusion Scan to see what’s happening in the coronary arteries. Some resting EKGs, like those with “Left Bundle Branch Block,” require perfusion scans for optimal interpretation.
Like the regular resting EKG, all stress tests carry a certain chance of being false-positive or false-negative. The problem is greater in women than men.
While we’re in the process of ordering stress tests, we give our best medical treatment for coronary artery disease, just in case. This includes a daily aspirin, high-dose “statin” (to lower cholesterol, even if cholesterol is normal, since the statin protects the heart), and maybe a “beta-blocker” medication to protect the heart.