Cardiac stress tests are used to detect possible problems with the circulatory system that could otherwise go undiscovered. A stress test, so named because it involves activity levels that subject the heart to "stress" or work, determines whether a person has signs of blockages in the arteries and, if so, to what extent the individual’s health is affected by these blockages. The test provides a doctor with the necessary information to prescribe treatment to prevent a heart attack or other problems, while also gauging the patient’s overall fitness level.
The American Heart Association recommends the cardiac stress test for anyone with risk factors like hypertension, family history of heart disease, high cholesterol, smoking or diabetes. Sub-maximal stress testing is also used to diagnose the extent of arterial blockage in patients known to have coronary heart disease.
How Cardiac Stress Tests Work
A cardiac stress test measures heart activity and blood pressure while a patient is active. Baseline readings are taken with an ECG (electrocardiogram) and a blood pressure cuff while at rest, and then again during exercise on a treadmill or stationary bicycle. Some stress tests also use a sensor that attaches to a finger and measures blood oxygen levels, while others involve injection of a mildly radioactive chemical to observe the flow of blood into the heart muscle.
The stress test starts slow, at a gentle walking pace, with the activity level increasing every three minutes while information is collected on heart rate, blood pressure, and any symptoms a patient might experience. After the test, monitoring continues until all readings have returned to baseline levels.
In some cases, a person may be unable to perform physical exercise due to muscle weakness, fragility, obesity or other factors. These patients are given a pharmacological stress test, using medication to stimulate the heart as if the person were exercising. The same observations are noted as in a physical stress test.
Types of Cardiac Stress Tests
There are two types of cardiac stress tests, maximal and sub-maximal.
In a maximal stress test, activity level is increased until the patient is exhausted or until ECG readings or symptoms (such as shortness of breath, chest pain or lightheadedness) indicate a problem.
In a sub-maximal stress test, activity level is capped at a certain point for safety reasons, and the stress test ends when that level is reached. This type of stress test is typically used to examine patients with known heart disease.
Cardiac Stress Test Results
Stress tests are useful in detecting blockages in the arteries that partly obstruct the healthy flow of blood. A resting ECG may not detect any problem because at rest, the body obtains all the blood and oxygen it needs in spite of any blockages. At higher levels of activity, however, the effect of arterial blockage on heart rate and blood pressure can more easily be noted in symptoms like irregular heart rhythm, abnormal blood pressure or angina (chest pain).
A stress test can also indicate cardiac arrhythmia, irregularities that tend to occur when adrenaline levels are high (such as during stressful situations or while exercising).
In patients with known coronary arterial disease or congestive heart failure, the cardiac stress test can be used to determine the progression of the disease over time and to track the effectiveness of treatment. Doctors often prescribe cardiac stress tests in cases of recent heart attack, bypass surgery or other heart surgery to observe how heart function may have changed.
Preparing for Testing
Patients are advised to wear comfortable, loose-fitting clothing that they would feel comfortable exercising in, including rubber-soled shoes and a bra for women. Caffeine, alcohol, and cigarettes should be avoided on the day of the test, but a light meal can be eaten about two hours beforehand.
There is a very small risk of heart incidents, such as myocardial infarction, but this is very rare. The stress test is about as dangerous as a brisk walk or a walk uphill, and should anything untoward happen, a physician is on hand to provide quick and effective care.