(Treadmill Stress Test or Exercise Stress Test)
Exercise stress testing, which is now widely available at a relatively low cost, is currently used most frequently to estimate prognosis and determine functional capacity, to assess the probability and extent of coronary disease, and to assess the effects of therapy. Ancillary techniques, such as metabolic gas analysis, radionuclide imaging (see the images below), and echocardiography, can provide further information that may be needed in selected patients, such as those with moderate or prior risk.
Cardiovascular exercise stress testing in conjunction with ECG has been established as one of the focal points in the diagnosis and prognosis of cardiovascular disease, specifically coronary artery disease (CAD).
A stress test can be used to test for heart disease. Stress tests are tests performed by a doctor and/or trained technician to determine the amount of stress that your heart can manage before developing either an abnormal rhythm or evidence of ischemia (not enough blood flow to the heart muscle). The most commonly performed stress test is the exercise stress test.
HOW THE TEST IS PERFORMED
This test is done at a medical center or health care provider’s office.
The technician will place 10 flat, sticky patches called electrodes on your chest. These patches are attached to an ECG monitor that follows the electrical activity of your heart during the test.
You will walk on a treadmill or pedal on an exercise bicycle. Slowly (about every 3 minutes), you will be asked to walk (or pedal) faster and on an incline. It is like walking fast or jogging up a hill.
While you exercise, the activity of your heart is measured with an electrocardiogram (ECG). Your blood pressure readings are also taken.
The test continues until:
- You reach a target heart rate.
- You develop chest pain or a change in your blood pressure that is concerning.
- ECG changes suggest that your heart muscle is not getting enough oxygen.
- You are too tired or have other symptoms, such as leg pain, that keep you from continuing.
You will be monitored for 10 – 15 minutes after exercising, or until your heart rate returns to baseline. The total time of the test is around 60 minutes.
WHY THE TEST IS PERFORMED
Reasons why an exercise stress test may be performed include:
- You are having chest pain (to check for coronary artery disease — narrowing of the arteries that feed the heart muscle).
- Your angina is getting worse or is happening more often.
- You have had a heart attack.
- You have had angioplasty or heart bypass surgery.
- You are going to start an exercise program and you have heart disease or certain risk factors, such as diabetes.
- To identify heart rhythm changes that may occur during exercise.
- To further test for a heart valve problem (such as aortic valve or mitral valve stenosis).
There may be other reasons why your health care provider asks for this test.
The initiation of dynamic exercise results in increases in ventricular heart rate, stroke volume, and cardiac output as a result of vagal withdrawal and sympathetic stimulation. Alveolar ventilation and venous return also increase as a consequence of sympathetic vasoconstriction. The overall hemodynamic response depends on the amount of muscle mass involved, exercise efficiency, conditioning, and exercise intensity.
In the initial phases of exercise in the upright position, cardiac output is increased by an augmentation in stroke volume mediated through the use of the Frank-Starling mechanism and heart rate. The increase in cardiac output in the later phases of exercise is due primarily to an increase in ventricular rate.
During strenuous exertion, sympathetic discharge is maximal and parasympathetic stimulation is withdrawn, resulting in autoregulation with generalized vasoconstriction, except in the vital organs (cerebral and coronary circulations).
Release of venous and arterial norepinephrine from sympathetic postganglionic nerve endings is increased, and epinephrine levels are increased at peak exertion, resulting in a rise in ventricular contractility. As exercise progresses, skeletal muscle blood flow increases; oxygen extraction increases as much as 3-fold; peripheral resistance decreases; and systolic blood pressure (SBP), mean arterial pressure, and pulse pressure usually increase. Diastolic blood pressure (DBP) remains unchanged or may increase or decrease by approximately 10 mm Hg.
The pulmonary vascular bed can accommodate as much as a 6-fold increase in cardiac output, with only modest increases in pulmonary arterial pressure, pulmonary capillary wedge pressure, and right atrial pressure; this is not a limiting determinant of peak exercise capacity in healthy subjects.
Maximum heart rate and cardiac output are decreased in older individuals, in part because of decreased beta-adrenergic responsiveness. Maximum heart rate can be calculated by subtracting the patient’s age (in years) from 220 (standard deviation, 10-12 beats/min).
The age-predicted maximum heart rate is a useful measurement for safety purposes and for estimating the adequacy of the stress to evoke inducible ischemia. A patient who reaches 80% of the age-predicted maximum is considered to have a good test result, and an age-predicted maximum of 90% or better is considered excellent.
In the postexercise phase, hemodynamics return to baseline within minutes after exercise is discontinued. The return of vagal stimulation is an important cardiac deceleration mechanism after exercise; it is more pronounced in well-trained athletes but is blunted in patients with chronic congestive heart failure.
Intense physical work or important cardiorespiratory impairment may interfere with achievement of a steady state, and an oxygen deficit occurs during exercise. The oxygen debt is the total oxygen uptake in excess of the resting oxygen uptake during the recovery period.
WHAT HAPPENS DURING THE EXERCISE STRESS TEST?
First, during a stress test, a technician will gently clean 10 small areas on your chest and place electrodes (small, flat, sticky patches) on these areas. The electrodes are attached to an electrocardiograph monitor (ECG or EKG) that charts your heart’s electrical activity during the test.
Before you start exercising, the technician will perform an EKG, to measure your heart rate at rest and will take your blood pressure.
You will begin to exercise by walking on a treadmill or pedaling a stationary bicycle. The rate of exercise, or degree of difficulty will gradually increase. You will be asked to exercise until you feel exhausted.
At regular intervals, the lab personnel will ask how you are feeling. Please tell them if you feel chest, arm or jaw pain or discomfort, short of breath, dizzy, lightheaded, or any other unusual symptoms. It is normal for your heart rate, blood pressure, breathing rate, and perspiration to increase during the test. The lab personnel will watch for any symptoms or changes on the ECG monitor that suggest the test should be stopped.
After the test you will walk or pedal slowly for a couple of minutes to cool down. Your heart rate, blood pressure and ECG will continue to be monitored until the levels begin returning to normal.
Although the appointment lasts about 60 minutes, the actual exercise time is usually between seven and 12 minutes.
The meaning of your test results depends on the reason for the test, your age, and your history of heart and other medical problems.
It may be hard to interpret the results of an exercise-only stress test in some patients.
WHAT ABNORMAL RESULTS MEAN
Abnormal results may be due to:
- Abnormal heart rhythms during exercise
- Changes in your ECG that may mean there is a blockage in the arteries that supply your heart (coronary artery disease)
When you have an abnormal exercise stress test, you may have other tests performed on your heart such as:
- Cardiac catheterization
- Nuclear stress test
- Stress echocardiography
Stress tests are generally safe. Some patients may have chest pain or may faint or collapse. A heart attack or dangerous irregular heart rhythm is rare.
People who are more likely to have such complications are often already known to have a weak heart, so they are not given this test.