An EKG, or electrocardiogram, is a testing procedure that uses your heart's electrical output to check for signs of certain heart-related ailments. In some circumstances, this testing may be part of a procedure called an exercise stress test, which measures your heart's response to controlled physical exertion. Doctors use your heart rate to help determine when to stop stress testing.
Basics
An EKG machine monitors your heart's electrical output through a series of wired devices called electrodes, which are attached to your body at points on your chest, torso and arms. Information from an EKG machine is displayed in the form of waves on graph paper, which a doctor or trained specialist can examine and interpret. An EKG machine can only reveal heart abnormalities that occur during testing, and some heart problems won't typically appear during a resting EKG procedure. To overcome this limitation, your doctor may use an exercise stress test, which uses physical exertion to help reveal hidden abnormalities.
Target Heart Rate
During exercise stress testing, your doctor will attach you to an EKG machine and blood pressure monitor, then ask you to exercise on a treadmill or stationary bicycle. If you have problems using these devices, you may alternatively use a cranking device you can turn with your hands. As your test proceeds, your doctor will monitor both your heart rate and blood pressure. When your heart rate reaches a target output, typically 85 percent of your maximum safe pumping capacity, your doctor will end the procedure and review the EKG results.
Testing Accuracy
If you reach your target heart rate, an EKG stress test can uncover signs of a heart ailment called coronary artery disease roughly 67 percent of the time, according to HeartSite.com. If you have narrowing of a single coronary artery, a stress test can reveal your condition roughly 50 percent of the time. If you have narrowing in all three of your major coronary arteries, a stress test can reveal your condition roughly 80 percent of the time.
Considerations
If you can't perform any sort or exercise, your doctor can mimic the effects of an exercise stress test with certain medications, according to the National Heart Lung and Blood Institute. During all forms of stress testing, your doctor or a technician will ask you to report your responses to the procedure. If you're having difficulties, your test may end before you reach your target heart rate. Signs and symptoms that typically lead to an end of testing include dizziness, significant shortness of breath, the onset of moderate or severe chest pain, development of abnormally high or low blood pressure and irregular heartbeat.
