(Exercise ECG, Exercise EKG, Stress Test)
What is an exercise electrocardiogram?
An electrocardiogram (ECG or EKG) is one of the simplest and fastest procedures used to evaluate the heart. Electrodes (small, plastic patches) are placed at certain locations on the chest, arms, and legs. When the electrodes are connected to an ECG machine by lead wires, the electrical activity of the heart is measured, interpreted, and printed out for the physician's information and further interpretation.
An exercise ECG is performed to assess the heart's response to stress or exercise. The ECG is monitored while a person is exercising on a treadmill or stationary bike. While this procedure is seldom used for young children, it may be very useful in evaluating adolescents and young adults.
An ECG tracing will be taken at certain points during the test in order to compare the effects of increasing stress on the heart. Periodically, the incline and treadmill speed will be increased in order to make exercise more difficult for the person being tested. If the person is riding a bicycle, he/she will pedal faster against increased resistance. In either circumstance, the person will exercise until reaching a target heart rate (determined by the physician based on age and physical status) or until unable to continue due to fatigue, shortness of breath, chest pain, or other symptoms.
Other related procedures that may be used to assess the heart include resting electrocardiogram (ECG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest x-ray, computed tomography (CT scan) of the chest, echocardiography, electrophysiological studies, magnetic resonance imaging (MRI) of the heart, myocardial perfusion scans, radionuclide angiography, and ultrafast CT scan. Please see these procedures for additional information.
The heart's electrical conduction system:
The heart is, in the simplest terms, a pump made up of muscle tissue. Like all pumps, the heart requires a source of energy in order to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.
An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber) of the heart.
The sinus node generates an electrical stimulus regularly at 60 to 100 times per minute under normal conditions. This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's lower chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart).
The electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), where impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles.
This electrical activity of the heart is measured by an electrocardiogram. By placing electrodes at specific locations on the body (chest, arms, and legs), a graphic representation, or tracing, of the electrical activity can be obtained. Changes in an EKG from the normal tracing may indicate one or more of several heart-related conditions.
Reasons for the Procedure
Reasons for your physician to request an exercise ECG include, but are not limited to , the following:
to determine limits for safe exercise in patients who are entering a cardiac rehabilitation program and/or those who are recovering from a cardiac event, such as a heart attack (myocardial infarction, or MI) or heart surgery
to assess leg pain with exercise (also called intermittent claudication) in patients with suspected occlusion in the legs' circulatory system
to evaluate blood pressure during exercise
to assess stress or exercise tolerance in patients with known or suspected coronary artery disease