What Is a Cardiac Stress Test?

What to expect when undergoing this test

Cardiac Stress Test
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A cardiac stress test (also known as a cardiac exercise test) is an in-office exam used to measure the heart's response to physical exertion in a controlled environment. Performed commonly on a treadmill or a stationary cycle, the test is useful in diagnosing coronary artery disease (CAD), a condition often missed when a person is at rest.

Purpose of Test

The cardiac stress test is used to evaluate the status of your cardiovascular system, which comprises both your heart and blood vessels. It does so by comparing your circulation at rest with the same measurements taken at maximum exertion. While the primary aim of the test is to detect abnormalities suggestive of CAD, it can also be used to monitor the health of people with other forms of heart disease.

Test Aims

CAD occurs when the walls of a coronary artery (an artery that feeds the heart) begin to harden, thicken, and accumulate plaque. This is a condition known as atherosclerosis. Over time, the blockage can impede blood flow and may eventually lead to a heart attack or stroke.

The challenge with CAD is that, even with a partial blockage, the heart may still receive an ample supply of blood while at rest. It is only when the heart is placed under stress that the effects of the blockage may be seen and felt.

The cardiac stress test involves several elements, which can help reveal a blockage in several ways:

  • Blood oxygen level monitoring: When the blood flow is obstructed (a condition known as ischemia), the amount of oxygen delivered to the heart and carried from the lungs is decreased.
  • Pulse and blood pressure monitoring: When the blood flow is partially obstructed by plaque, the heart has to work harder to pump blood through the narrowed vessels.
  • Electrocardiogram (ECG): These same effects alter not only the heart rate but the heart rhythm as well. With CAD, the changes are characteristic and may be identified with an ECG.

In addition to diagnosing CAD, a stress test can often tell us how significant the blockage is (referred to as a functional capacity evaluation). For instance, if signs of ischemia develop with little exercise, the blockage is likely significant and in need of aggressive intervention. Ischemia occurring at higher levels of exercise is usually less significant and may alter the approach to treatment.

Periodic stress tests can also be used to monitor the progression of congestive heart failure (where the heart is not pumping blood as it should) or assess how well you are recovering from a heart attack. 

Test Limitations

It is important to note that, while useful in detecting blockages, a cardiac stress test cannot tell how much an artery has hardened or thickened. The test is only a generalized measure of blood flow, which doctors can use to detect areas of restriction or diagnose the severity of CAD.

To pinpoint the location of the arterial obstruction, your cardiologist may need to perform a computed tomography (CT) coronary angiogram in which a contrast dye is injected into your vein to generate images of your coronary arteries.

The cardiac stress test is also unable to predict how stable an arterial plaque may be or if and when a person may have a heart attack.

In terms of accuracy, a cardiac stress test is often open to interpretation, and results can vary based on the equipment used, the experience of the technician, and other factors that can change from day to day (such as whether a characteristic symptom occur during the test or not).

According to research from the American College of Cardiology, the sensitivity of a cardiac stress test without imaging is 68 percent, while its specificity is 77 percent. (Sensitivity refers to a test's ability to render a correct positive diagnosis, while specificity refers to its ability to render a correct negative diagnosis).

Clinical experience, therefore, plays a huge role in how accurately a test result is rendered.

Risks and Contraindications

While the cardiac stress test is a relatively safe and controlled procedure, it may pose risks to people with advanced heart disease, including fainting, chest pains (angina), irregular heartbeat (arrhythmia), and heart attack.

The general risk of the test is considered low if your doctor deems the test appropriate for you. For safety reasons, a cardiac stress test would not be used if you have any of the following conditions:

If and when these conditions are controlled, stress testing may be considered.

An inability to use your legs does not preclude you from getting a cardiac stress test; a bicycle-like crank that you turn with your arms may be provided instead of a treadmill.

Others unable to exercise because of a physical disability may be given a short-acting drug called dobutamine, which can simulate the effects of exercise on the heart.

Before the Test

While the preparations for a cardiac stress test are relatively minimal, there are a few things you should know before you arrive for the exam.

Timing

When scheduling a cardiac stress test, be prepared to set aside no less than 90 minutes of your day. While the test itself takes only around six to 15 minutes, it requires preparation and time afterward to cool down. There may also be delays to account for.

Try to arrive 30 minutes in advance of your appointment so that you can sign in, relax, and not feel rushed.

Location

A cardiac stress test is most commonly performed in a cardiologist’s office. If more specialized equipment is needed—such as an echocardiogram sometimes used to support the test—you may be asked to go to a hospital. The room itself is called a stress lab.

The equipment set-up is relatively straightforward and usually involves:

  • A treadmill with an adjustable incline (or other pieces of appropriate equipment, if needed)
  • An ECG machine with electrodes
  • A blood pressure unit (sphygmomanometer)
  • A pulse oximeter to measure blood oxygen levels

The test will be overseen by a doctor, nurse, or a trained technician.

What to Wear

Be sure to wear a pair of comfortable pair of walking shoes and a loose two-piece outfit when arriving for your appointment. You should also be prepared to remove your shirt or blouse so that the EEG electrodes can be attached to your chest.

While the office may have lockers to store your wallet and cell phone, it is best to leave jewelry and other valuables at home.

Food and Drink

You will need to stop smoking and avoid eating or drinking anything with caffeine 24 hours prior to the test. This includes coffee, tea, energy drinks, chocolate, and certain energy bars.

Only plain water should be consumed in the four hours before the test. If you have diabetes or take medications for a chronic illness with meals (such a certain HIV drugs), you may want to schedule your test later in the day so that you eat when needed and still adhere to the four-hour restriction. Be sure to advise your doctor of any such need. 

Medications

When scheduling the stress test, advise your cardiologist about any medications you may be taking, whether they be prescription, over-the-counter, homeopathic, traditional, or nutritional. In some cases, the drugs may interfere with the accuracy of the test.

These include any medications containing caffeine, which can increase your heart rate and blood pressure. Examples include weight loss pills, alertness tablets such as No-Doz or Vivarin, and caffeine-bolstered pain relievers like Anacin or Excedrin.

Chronic heart medications and nitrate drugs used to treat angina also need to be stopped 24 hours before the test. (With that being said, do not stop any drug without direct instructions from your doctor.) 

If you take insulin to control your blood sugar, ask your cardiologist how much you should take on the day of your test. Oftentimes, the insulin dose will need to be decreased and any oral medications delayed until after the test is completed.

On the other hand, if you use an inhaler for asthma or COPD, be sure to bring it with you just in case. If you use a glucose monitor, you should also bring that along to test your blood sugar after you’ve completed the test.

Cost and Health Insurance

The cost of a cardiac stress test with ECG can run anywhere from a couple of hundred dollars to $1,000 depending on the provider and where the test is performed. If imaging tests are included, such as an echocardiogram or a nuclear imaging test, the price can easily run into the thousands of dollars.

To this end, it is important to know the cost of the test in advance and to find how much health insurance, if you have it, will cover and what your deductible and out-of-pocket costs will be. With rare exception, the test will require insurance pre-authorization, which the administrator of the cardiology office can usually submit on your behalf.

If you are denied coverage for any reason, ask your insurer for a written reason for the denial. You can then take the letter to your state insurance consumer protection office and ask for help. Your cardiologist should also intervene and provide additional motivation as to why the test is essential.

What to Bring

You may want to bring a towel, water bottle, and a change of clothing, as well as anything else you might need to freshen up after exercising.

Other Considerations

While a cardiac stress test may leave you momentarily winded, it shouldn’t interfere with your ability to drive home. With that being said, if you are older and/or unaccustomed to exercise or experience frequent lightheadedness, angina, or acute respiratory symptoms, you may want to bring a driving companion just in case.

During the Test

On the day of your test, after signing in and confirming your insurance information, you may be asked to provide emergency contact information and to sign a liability form stating that you are aware of the purpose and risks of the test.

You are then taken to the stress lab. The test itself is performed by a lab technician or an attending physician.

Pre-Test

Before the test, you will need to remove your shirt so that 10 individual electrodes from the ECG machine can be attached to your chest with a sticky adhesive. If your chest is hairy, parts may need to be shaved. A modesty gown may be provided once the electrodes are securely in place.

A blood pressure cuff is then wrapped on your arm, while a clothespin-like sensor is clipped to your finger to connect you to the pulse oximeter.

Before the exercise portion of the test begins, the technician will record your ECG, pulse, blood pressure, and blood oxygen level at rest. These serve as baselines that your other results will be compared to.

Throughout the Testing

After the resting results are obtained, the exercise portion of the test begins. The exercise is graded, meaning that the intensity is increased every three minutes by raising the speed of the machine and/or adjusting its resistance or incline.

At each three-minute interval, your pulse, blood pressure, blood oxygen, and ECG are recorded along with any symptoms you may be experiencing. Do not grab tightly onto the handrails or handlebars as this may affect the results.

During the test, you may breathe heavily, sweat, and feel your heart racing, but should not feel any overt pain or distress. If you do, tell the technician. Your ECG will be monitored throughout the procedure so that the technician can see if you are reaching your maximum heart rate (MHR) or approaching any real trouble.

Depending on the aims of the test, you may undergo what is called a maximal stress test or a submaximal stress test. By definition:

  • Maximal stress testing involves increasing the intensity level until you can no longer keep up, either because you are winded or the ECG indicates this there is a cardiac problem. The goal of maximal testing is to provide evidence of CAD. The test can last from six to 15 minutes, sometimes less, depending on your cardiovascular fitness level.
  • Submaximal stress testing involves continuing exercise only until you reach 85 percent of your MHR. The test is commonly used for people recovering from a heart attack to determine how much exercise they can safely perform. The maximum time for this test is 27 minutes. Most people will reach eight to 10 minutes, according to research from the Cleveland Clinic Journal of Medicine.

You may stop the test at any time if you feel moderate to severe chest pain, severe shortness of breath, dizziness, or fatigue. Similarly, the test will be stopped prematurely if the ECG indicates arrhythmia or your blood pressure is abnormally high or low.

Post-Test

Once the stress test is complete and the requisite measures obtained, you will cool down gradually by continuing to walk or cycle at a slower pace for two to three minutes. After that, the test is officially over. You will be given some water and asked to lie down for 10 to 15 minutes.

After the lab technician has determined that your pulse and blood pressure has normalized, the blood pressure cuff, pulse oximeter, and ECG leads would be removed. You can then change back into your clothes and freshen up in the restroom.

If you have diabetes, this is the time to use your glucose meter to measure your blood sugar level. If it is abnormal, advise the technician, nurse, or attending physician.

Similarly, if you do not feel well for whatever reason, do not leave the office. Tell someone on the medical staff and let them check you out to ensure that you are okay.

After the Test

Generally speaking, there will be no adverse symptoms or lingering side effects if your vital signs checked out after the stress test. If you are not used to exercise or live a sedentary lifestyle, you may feel exhausted or experience muscle or joint pain a day or two following the exam. This is normal. Even the burning sensation in your legs (caused by the build-up of lactic acid) will gradually subside.

However, you need to call 911 or go to your nearest emergency room if you experience the following after returning home from a stress test:

  • Chest tightness or pain that lasts for a few minutes or keeps returning
  • Pain in your jaw, neck, back, stomach, or one or both of your arms
  • Trouble breathing
  • A sudden cold sweat, often accompanied by lightheadedness or dizziness

Interpreting Results

A few days after the test is performed, your doctor will review the results with you. The results are sometimes confusing to understand but are based on an evaluation of the following factors:

  • A basic interpretation of your ECG reading
  • Changes in ECG during exercise (particularly the ST-segment)
  • Blood pressure changes (especially severe hypotension)
  • Symptoms reported during testing
  • The development of arrhythmia during exercise
  • The reasons for ending the test prematurely, if applicable
  • Your estimated exercise capacity based on metabolic equivalents (METS)

The combination of specific values and subjective interpretations will form the basis of the diagnosis, classified as being either positive, negative, equivocal (ambiguous), or inconclusive.

Follow-Up

If the results of the test are normal (negative), meaning that the none of diagnostic values are suggestive of CAD, you may require no further testing.

If the results are abnormal (positive), meaning that there is evidence of CAD, your doctor will want to speak with you about treatment options. Depending on what the tests say, further testing may be recommended, including a coronary angiogram to pinpoint the exact location of the blockage.

However, if the results are normal or inconclusive but your cardiac symptoms persist, your cardiologist may recommend a more sophisticated form of stress testing, such as an echocardiogram stress test or a nuclear perfusion study, in which a radioactive tracer is injected into your vein during exercise to locate the blockage using a specialized camera. 

Other Considerations

It is important to remember that a cardiac stress test is open to interpretation and may only suggest rather than confirm a CAD diagnosis.

To this end, you should speak freely and openly with your doctor if the test results don’t make sense to you. This is especially true if you’re experiencing cardiovascular symptoms, but the tests say you are fine. In the end, your symptoms may not be related to CAD but still warrant investigation.

Also, do not hesitate to get a second opinion if you are not getting the answers you need, or to ask your cardiologist to forward your records to another specialist. You can also request a copy of the results for yourself, which can usually be delivered in a digital format. 

A Word From Verywell

A cardiac stress test is a valuable tool for diagnosis. Despite its limitations, it can offer important insights that may lead to the early diagnosis and treatment of CAD and atherosclerosis. Moreover, it is a relatively affordable test to which you are neither exposed to radiation nor chemicals.

To better ensure test accuracy, always follow your doctor's instructions without exception. Moreover, try to find dedicated cardiology practice with its own stress lab or a hospital with a dedicated cardiology unit. And, finally, never be afraid to ask questions about a prospective doctor's background and experience; it is your right to know.

In the end, when it comes to cardiac stress testing, experience and expertise do matter.

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