Have a stress test coming up? Here's what to expect

By Richard N. Fogoros, MD 

 Medically reviewed by Anthony Pearson, MD

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. It can also be used to monitor the health of people with other forms of heart disease.¹

This article explains the types and purpose of stress tests, and how they are done. It offers a step-by-step guide on what to expect, as well as information about interpreting stress test results.

Purpose of a Stress Test

The purpose of a stress test is to evaluate the status of your cardiovascular system, which comprises both your heart and blood vessels.² It does so by comparing your circulation at rest with the same measurements taken at maximum exertion.

Test Aims

Plaque build up in the coronary arteries causes no symptoms until the plaque is large enough to obstruct blood flow. The first symptoms often occur with exercise when the heart calls on the coronary arteries to provide more blood flow. Blockages great than around 70% restrict this needed increase in flow to the heart muscle during exertion.

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

• Blood oxygen level monitoring: When blood flow is obstructed (a condition known as ischemia), the amount of oxygen delivered to the heart muscles is reduced.³

• Pulse and blood pressure monitoring: These measures help doctors determine whether the heart is working too hard to pump blood through narrowed vessels.⁴

• Electrocardiogram (ECG): As heart rate and blood pressure increase with exercise the inadequate supply of blood to the heart muscle (ischemia) changes its electrical and mechanical function. The electrical changes result in depression of the ST segment of the ECG.

The stress tests, especially when combined with imaging, also yield information on how severe the ischemia is which can help determine optimal treatment..⁵

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

Stress tests have both false negatives (test is normal despite having significant blockage) and false positives (test is positive when coronary arteries don't havre significant blockages).

In addition, the stress test is a physiologic test of the adequacy of blood flow. If your doctor wants an anatomic test to look at the coronary arteries he may follow the stress test with a another noninvasive test like coronary CT angiography or an invasive test like cardiac catheterization.

In terms of accuracy, a cardiac stress test is often open to interpretation. 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 occurs 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%, while its specificity is 77%.⁶ 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.

When imaging is used during a stress test, sensitivity and specificity are close to 90%. Clinical experience, therefore, plays a huge role in how accurately a test result is rendered.

Stress Test Risks and Contraindications

Cardiac stress tests are relatively safe and controlled procedures, but they 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 healthcare provider 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:

• Unstable angina not yet stabilized with medication⁷

• Severe pulmonary hypertension

• Uncontrolled arrhythmia

• Inadequately controlled congestive heart failure⁷

• Pulmonary embolism (a clot in the arteries of a lung)

• Aortic dissection (a tear in the aorta)⁷

• An acute illness of any sort

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

Modified and Chemical Stress Tests

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. Stress test by injection may be used if you are unable to exercise because of a physical disability. A short-acting drug, usually regadenoson or adenosine, can simulate the effects of exercise on the heart.⁸

Before the Stress 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.

How Long Does a Stress Test Usually Take?

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 about 10 to 20 minutes, it requires preparation and time afterward to cool down.⁹ 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.

Where Stress Tests Are Done

A cardiac stress test is most commonly performed in a cardiologist’s office.⁹ 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)⁹

• 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 healthcare provider, nurse, or a trained technician.

What to Wear

Be sure to wear a pair of comfortable 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.⁹

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 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 healthcare provider 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 before the test.¹⁰ (With that being said, do not stop any drug without direct instructions from your healthcare provider.) 

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 for safety's sake. 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.¹¹ With rare exceptions, 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 to ask for help.¹² Your cardiologist should also intervene and provide additional support for 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.

While a cardiac stress test may leave you momentarily winded, it shouldn’t interfere with your ability to drive home. However, if you are older, unaccustomed to exercise, or experience frequent lightheadedness, angina, or acute respiratory symptoms, bring a driving companion.¹³

During the Stress 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 healthcare provider.¹⁴

Pre-Test

Before the test, you will need to remove your shirt so that electrodes from the ECG machine can be attached to your chest, arms, and legs with a sticky adhesive. If your chest is hairy, parts may need to be shaved.¹⁵ A modesty gown may be provided once the electrodes are securely in place.

A blood pressure cuff is then wrapped around your arm, while a clothespin-like sensor is clipped to your finger to connect you to the pulse oximeter.⁹

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.⁵

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.¹

Different Types of Stress Tests

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 there is a cardiac problem. A maximal stress test also requires the heart rate to reach at least 85% of the maximum predicted heart rate. The goal of maximal testing is to provide evidence of CAD.⁵ 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% of your MHR.¹⁶ 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.

You will be asked to stop the test at any time if you feel moderate to severe chest pain, severe shortness of breath, dizziness, or fatigue.¹⁵ 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.¹⁴ After that, the test is officially over. You will be given some water and will usually be monitored for at least six minutes after the conclusion of the stress test.

After the lab technician has determined that your pulse and blood pressure have normalized, the blood pressure cuff, pulse oximeter, and ECG leads will 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 healthcare provider.

After the stress test, 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 you can safely go home.

After the Stress Test

Cardiac stress tests don't usually cause adverse symptoms or lingering side effects.

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.

When to Seek Medical Attention

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 pressure, tightness, or pain that lasts for a few minutes or keeps returning¹⁷

• Pain in your jaw, neck, back, shoulders, stomach, or one or both arms

• Trouble breathing¹⁸

• Fatigue or weakness

• A sudden cold sweat, often accompanied by lightheadedness or dizziness

Interpreting Results

Stress test results are usually back a few days after the test is performed, and your healthcare provider 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 none of the 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 healthcare provider 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.¹⁹

Your cardiologist may recommend a more sophisticated form of stress testing, such as an echocardiogram stress test or a nuclear perfusion study, which involves a radioactive tracer injected into your vein during exercise to locate the blockage using a specialized camera.¹⁵

Other Considerations

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. 

Summary

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 that doesn't expose you to radiation or chemicals.

To better ensure test accuracy, always follow your healthcare provider's instructions without exception. Moreover, try to find a dedicated cardiology practice with its own stress lab or a hospital with a dedicated cardiology unit.

When it comes to cardiac stress testing, experience and expertise do matter. Don't 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.