Do stress tests really add any information?
Dr. Davis
Posted: 3/26/2009 8:48:14 PM
Stress tests are a standard test for assessing the heart. But, if you know that you have some amount of coronary plaque, does a stress test really add any useful information?
I believe they do--provided the information is viewed in the proper light. Let me explain.
First, let's assume that you have no symptoms suggestive of heart disease and that your heart scan score causes no symptoms like chest pain or breathlessness. (If symptoms are present, then there's no question that a stress test can be useful to connect plaque with the symptom, or to determine whether symptoms are due to some other cause, e.g., gallbladder disease, esophagitis, etc.).
During a standard stress test, some form of exercise is undertaken, usually a walk on a treadmill with treadmill speed and grade increased in stages. Alternatives include a stationary bike or medications that mimic the effects of exercise in people who are unable to walk (bad hip, knee surgery, polio, etc.; this is commonly achieved with drugs like dobutamine, adenosine, or persantine). Heart rate is monitored by EKG, blood pressure taken every several minutes.
The effects on the heart are then assessed with EKG, echocardiography, or nuclear imaging. All are meant to assess coronary flow. If coronary artery flow is reduced, then the EKG shows specific abnormalities, the echo shows an area of reduced contraction of the heart muscle, the nuclear imaging shows an area of reduced radioactivity due to a reduction in flow to an area of the heart.
So what kind of information comes from this exercise? Observations that can be made include:
1) Blood pressure response to exercise--VERY important. Excessively high blood pressure responses (e.g., 170/80 or greater at an exercise level of 10 METS) is a provocateur of coronary plaque growth and has been associated with increased risk for cardiovascular events. This alone can be a reason for an increasing heart scan score when everything else is at desirable levels. Rarely, drops in blood pressure during exercise can be a sign for near-term danger ahead.
2) Provocability of abnormal heart rhythms--This is not an uncommon phenomenon.
3) Assessment of safety of exercise--Beyond abnormal heart rhythms, areas of poor coronary blood flow ("ischemia") can occasionally generate dangerous effects. This may factor into your overall management or generation of an "exercise prescription."
4) A tool for future comparison--Not all stress tests yield black or white results. Sometimes a result will need to be compared over time to gauge improvement or deterioration.
Stress tests, sadly, are prone to misuse and misinterpretation. The most common misuse is to subject a person without symptoms to a stress test, they "pass," and that person is advised that their heart is normal. This is not necessarily so, as many people in the TYP program with coronary plaque detected by heart scan can attest.
So stress tests can be a reasonable and often helpful tool that yields information complementary to that of your heart scan. |
