The Exercise Stress Test
61Severe chest pain (angina pectoris) or even a heart attack can sometimes be the first sign of coronary artery problems. Indications of previously undiagnosed heart disease can be detected in a gradually increased exercise challenge known as a stress test. Narrowed coronary arteries may be able to supply the blood you need for sedentary pursuits, but during exercise the oxygen needs of heart muscle go up, and electrocardiographic abnormalities or physical symptoms may indicate a problem.
A physician uses a progressive ECG-monitored exercise test as a diagnostic tool to identify or verify the presence of heart disease, as a pre-exercise test to reduce risks or set limits, as a postcoronary test to indicate the extent of damage and subsequent progress in therapeutic programs, or after a coronary bypass or angioplasty procedure to establish extent of recovery as well as work and activitylimits. Although most stress tests are conducted on the treadmill, arm testing (cranking) may be required for individuals returning to jobs that require strenuous use of the upper body.
Maximal or near-maximal workloads may be needed to elicit the symptoms of previously undiagnosed heart disease. Many physicians, however, terminate the stress test when the heart rate reaches some percentage of the age-adjusted maximal heart rate, reasoning that it is unnecessary to risk a maximal test. Unfortunately, there is such variability in maximal heart rates that the test may be too strenuous for some and too easy for others.
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The stress test should be terminated when the subject cannot continue or has symptoms of exertional intolerance (chest pain, intolerable fatigue) or distress (staggering, dizziness, confusion, pallor, labored breathing, or nausea), when there are significant electrocardiographic changes, or when blood pressure drops in spite of an increasing workload. Termination of the test at some predetermined percentage of the assumed maximal heart rate, on the other hand, risks missing important signs or symptoms. The maximal heart rate is highly variable. Using an age-related maximal heart rate (e.g., 220 beats per minute minus age equals the predicted maximal heart rate) can lead to substantial errors. For example, the maximal heart rate for 40-year-old patients may average 180 beats per minute (bpm) (220 minus 40 equals 180), but the range goes from below!44 to above 216. So a test terminated at 85 percent of the predicted maximal heart rate (.85 times 180 equals 153 bpm) may be too strenuous for a few and much
