Definition and Overview
A treadmill stress test, also called cardiac stress test, is a diagnostic cardiovascular test used to determine how well the heart is working and responding to external stress. It evaluates how well the heart handles activity or exertion that is more than the normal level it is used to. This type of test is highly effective in detecting cardiovascular diseases and in evaluating a person’s risk or likelihood of falling prey to chronic heart disease.
This is just one of many types of cardiac stress tests and falls under the category of an exercise stress test. Exercise-based tests vary depending on the type of activity that the patient is asked to do. For example, for a treadmill test, the patient is asked to walk on a treadmill, but patients can also be asked to use a stationary bike or do other forms of exercises. On the other hand, there are also cardiac tests that do not use exercise; instead, in order to increase the level of heart activity, the patient can take medications or can be given a radioactive substance intravenously to trigger a stronger heart response.
Who Should Undergo and Expected Results
A treadmill stress test is helpful for patients who:
- Are suspected of having a cardiovascular issue due to the presence of some symptoms
- Have a family history of chronic heart diseases, i.e. patients with a medium risk of coronary heart disease
- Chronic or long-time smokers
- Are taking heart medications
- Have an existing heart condition
- Have hypertension, high cholesterol problems, and diabetes
The following symptoms may cause a doctor to suggest a stress test:
- Chest pain
- Irregular or abnormal heartbeat
- Difficulty breathing
The test is expected to:
Determine if blood flow to the heart, which is expected to increase in proportion to a person’s activity level, is adequate
Assess if medications being taken for existing heart conditions, such as medications for ischemia and angina, are working properly
Check whether previous treatments for existing heart conditions are effective, e.g. whether a person with coronary heart disease now receives adequate blood supply within the heart vessels during times of increased activity
Detect any abnormalities in heart rhythm or the presence of an arrhythmia
Check the health and proper function of heart valves
Determine if other tests are necessary
Determine the ideal level of activity a person should pursue or are allowed to reach during workouts
Evaluate a person’s heart condition after suffering from a heart attack (or myocardial infarction)
A treadmill stress test is known to have 73 to 90 percent sensitivity and a specificity of 50 to 74 percent. In comparison, a nuclear stress test, which is another type of cardiac stress test wherein heart function is increased by the injection of a radioactive substance, has 81 percent sensitivity and 85 to 95 percent specificity. Sensitivity refers to the percentage of correctly identified diseases, whereas specificity refers to the percentage of healthy people who have successfully been identified as not having a heart condition through a stress test.
How Does the Procedure Work?
A treadmill stress test is performed by a doctor, cardiologist, or a trained technician. The procedure starts by placing electrodes on the chest, which is first cleaned to ensure direct contact. These electrodes measure electrical activity in the heart, sending the results to an attached electrocardiograph monitor. The test is often done in conjunction with an ECG to accurately diagnose any cardiovascular disease. It is also most often used for the diagnosis and treatment of coronary artery disease or ischemic heart disease.
Before the test, patients are given clear instructions on how to prepare for it. For example, they are advised against consuming any food or beverage with caffeine or taking heart medications so that the results will not be influenced by other factors. Also, right before the test begins, the patient’s cardiac statistics are recorded so the doctors can compare the results before and after the exam.
During the test, as the patient walks on the treadmill at an increasingly faster rate, his heart rate, blood pressure, and electrocardiogram are all monitored, and any changes as an effect of his increased activity and body stress level are recorded. The level of activity exerted by the patient during the test will thus increase as the treadmill moves faster and becomes steeper. At some points during the test, the doctor may ask the patient to breathe into a tube for some time to measure the amount of air he or she is able to breathe out during the activity. Although patients are asked to continue exercising for as long as he can, it is important to inform the technician or doctor if any abnormal symptoms such as chest pain, arm pain, or dizziness arise. The test facilitator will also stop the test if deemed necessary based on the results.
Once the patient stops exercising, he will be asked to rest by sitting or lying down. At this point, his heart rate and blood pressure will again be recorded.
Patients should allot at least 60 minutes for a treadmill cardiac test appointment. The test itself will take less than 12 minutes or as fast as 7 minutes, but there are preparations made prior to it that may take some time. Just to be sure, patients should avoid scheduling other commitments hours before and after the test.
Possible Complications and Risks
Since a treadmill stress test measures the effects of treadmill exercise on your body, risks are very minimal. Its effects are similar to doing other exercises such as running uphill or walking at a fast pace, which may include shortness of breath. The only risk is for the activity to be too much for a patient to handle, given an existing heart condition. This is why patients are told to stop the test any time they feel the need to, such as when they feel they cannot handle the exercise anymore or when chest pain, nausea, fatigue, or palpitations are felt.
A treadmill test also poses fewer risks than other types of stress tests. Medication-based tests are known to cause mild hypotension due to the medications used, while radioactive tracers used for nuclear tests cannot be used frequently and for monitoring purposes due to their risk of causing cancer, although the chances are very small.
To make sure no complications occur while the test is ongoing, technicians who facilitate stress tests must be highly trained and medical professionals are made available to respond to any complications and emergencies that may arise.
Balady GJ, Morise AP. Exercise stress testing. In: Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 10th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 13.
Boden WE. Angina pectoris and stable ischemic heart disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 71.