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How Does Exercise Affect EKG Results?

The electrocardiogram (EKG), a test that provides a readout of the heart's electrical activity, is often performed to check for abnormal heart rates or rhythms, heart attacks and causes of symptoms such as chest discomfort, dizziness or shortness of breath. Even if the EKG is normal during a rest period, it may reveal abnormalities during physical activity. For this reason, a health-care provider may perform an EKG during exercise, commonly called a stress test, to determine the heart's condition with exertion.

  1. Heart Rate

    • As a person increases the intensity of exercise, the EKG should show a steadily increasing heart rate. During a stress test, the health-care provider will gradually increase the speed and incline of the treadmill to confirm this normal change. If the heart rate goes up too quickly during or after exercise, it may indicate an abnormally fast rhythm called a tachyarrhythmia. If the EKG shows the heart rate failing to rise or increasing too slowly, a problem with the electrical conduction pathway in the heart may be to blame. However, certain cardiac medications such as beta-blockers may also keep the heart rate down, even during vigorous exercise.

    Heart Rhythm

    • Despite the changes in the heart rate during exercise, the EKG rhythm should remain regular throughout physical activity. This means that, although the complexes on the EKG may appear more narrow and the intervals between them shorter, they should be evenly spaced and occur consistently. If the complexes have an irregular pattern, it may suggest an arrhythmia such as atrial fibrillation. During exercise, the EKG may also detect a short interruption of a normal rhythm caused by a skipped or extra heart beat.

    Ischemic Changes

    • Changes in the EKG during exercise can indicate that there is an area of the heart that is not receiving adequate blood flow. Each part, or lead, of the EKG corresponds to a specific wall of the heart. If, during exercise, there is depression of the ST-segment in one or more leads of the EKG, it could mean there is a partial or complete blockage of one or more arteries in the heart. A normal exercise EKG will not show this change.

    Variable Factors

    • Although the exercise EKG can be a useful tool in cardiac testing, it is not always accurate in detecting the presence of heart disease. According to a 2009 issue of the "Netherlands Heart Journal," downward-slopping ST-segments in an exercise EKG only have 68 percent sensitivity for the detection of coronary artery disease. The percentage is even lower in women, who may also have a false-positive reading. It is recommended that other tests, such as MRI or nuclear imaging, which visualize the heart muscle, be used in conjunction with the EKG.

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