Stress tests for the heart: What happens after exercise just as important as what happens during
An exercise stress test measures how the heart responds to and copes with increasing amounts of activity. It can warn of impending heart trouble or monitor the aftermath of a heart attack.
Research suggests that checking not only how the heart does during exercise, but also how the heart recovers from it adds an extra dimension to the test. During a cool-down period, the heart should slow toward its normal rate with a steady pattern of regular, healthy electrical activity. But sometimes the heart may take too long to slow down or may beat irregularly — signs of possible trouble ahead.
Stress test basics
An exercise stress test gauges how exercise affects blood pressure, the heart rate, and its electrical activity.
The basic idea behind the test is that making the heart work harder reveals problems lurking in the background. For example, cholesterol can block an artery and make it harder for the blood to flow to the heart. In severe cases, this can cause a heart attack. But enough blood may get through a cholesterol-narrowed artery when the heart beats at its normal pace, and only fail to keep up during exercise. This would show up on a stress test as electrical irregularities or a drop in blood pressure.
This test employs a blood pressure cuff, an electrocardiograph to record the heart's electrical activity, and a treadmill or stationary bicycle.
The post-exercise heart
Doctors never used to be as interested in what happened in the heart after the treadmill stopped. Then a team from the Cleveland Clinic reviewed the results of almost 35,000 exercise stress tests. The researchers were especially interested in abnormal heart rhythms that occurred in the ventricles (the heart's lower chambers) during exercise and during the recovery period. These rhythms ranged from harmless premature ventricular beats to the potentially deadly ventricular fibrillation.
Abnormal ventricular beats that occurred only during the exercise phase of the test didn't seem to pose any long-term problems. But abnormal beats did signal trouble ahead when they occurred only during recovery. Eleven percent of people who had this problem died during a five-year follow-up period, compared to 5% of those who didn't. The report appeared in the Feb. 27, 2003, New England Journal of Medicine.
Two weeks later, a report in the American Journal of Cardiology showed the same thing among more than 200 heart attack survivors who took stress tests before leaving the hospital. Those whose hearts took longer than normal to recover were four times more likely to have died over the next three years.
These findings suggest that the 5 to 10 minutes after the exercise part of the test should be included in a stress test.
If irregular rhythms do show up during the cool-down period, your doctor may be more aggressive about controlling risk factors for heart attack and stroke, such as high blood pressure, high cholesterol, high blood sugar, high weight, and smoking. In the Cleveland Clinic study, people who had abnormal ventricular heartbeats during recovery from exercise often had less forceful contractions of the ventricles, an early warning sign of heart failure. So your doctor may also suggest an echocardiogram to examine your left ventricle in action.
December 2003 Update
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