Coronary Flow Reserve

What is coronary flow reserve?

Coronary flow reserve (CFR) is how much your blood flow to your coronary arteries can increase under stress (exertion). It tells a provider how well your heart can increase blood flow when its need for oxygen goes up. For example, you need more oxygen when you’re exercising.

Coronary flow reserve is also known as myocardial blood flow reserve. Blood that goes through your two coronary arteries goes to your myocardium, or heart muscle.

Using an invasive or noninvasive method, a provider can detect coronary artery disease and identify people at risk of cardiac events (such as a heart attack) in the future. A provider can use coronary flow reserve to make a diagnosis and/or prognosis in people who have (or may have) coronary artery disease.

How is coronary flow reserve calculated?

To calculate your coronary flow reserve, divide your coronary artery’s maximum blood flow by your at-rest blood flow.

When is coronary flow reserve performed?

A provider can use coronary flow reserve to determine the presence and/or severity of coronary artery disease. They may use a coronary flow reserve test to predict whether you’re at risk of a future heart issue.

What is a normal coronary flow reserve?

The normal value for coronary flow reserve is greater than 2 to 2.5. This means that under stress (exertion), you have double the amount of blood flow to your heart that you have while at rest. A healthy person can have a coronary flow reserve of 3, which means they have three times the blood flow they have while at rest.

A study found that people with a coronary flow reserve higher than 2 had a better recovery six months after a heart attack. A coronary flow reserve lower than 2 means you have a higher risk of a cardiac issue.

How does a coronary flow reserve test work?

There are two popular methods to measure coronary flow reserve. One is an invasive method that requires a cardiac catheterization of your coronary artery. Another is a noninvasive method that uses a specific type of nuclear stress test — a Rubidium-82 positron emission tomography (PET).

Rarely, a provider may use a magnetic resonance imaging (MRI) scan to measure coronary flow reserve.

A provider uses one of these methods to check the blood flow in each coronary artery. They compare the difference between your maximum blood flow and your blood flow at rest.

How do I prepare for a coronary flow reserve test?

A provider will want to know what medications you’re taking. This includes any over-the-counter medicines that you buy without a prescription that could affect your blood flow. Also, they’ll want to know about any allergies you have to medicines, dyes or latex.

If a provider is doing your test with cardiac catheterization or positron emission tomography (PET) scan, ask what time you should stop eating and drinking. In most cases, you shouldn’t eat or drink anything six to eight hours before your procedure.

What should I expect on the date of the coronary flow reserve test?

If you’re having an MRI scan, you’ll need to make sure you don’t have any metal on or in your body. Certain medical devices may be OK. Check with a provider to make sure your device is safe for an MRI.

For methods that use cardiac catheterization, a provider will put a catheter (very small tube) into your neck, groin or arm. They’ll work it through blood vessels until it reaches your coronary artery. You’ll receive a mild sedative to help you relax.

No matter which type of procedure you have, you’ll need an intravenous line (IV). A provider will give you medicine through an IV to create maximum blood flow. In some cases, you’ll also get a contrast dye in your IV to make images of your coronary artery clearer. For a PET scan, you’ll get a radiotracer in your IV.

How is coronary flow reserve measured?

A provider can use imaging methods to measure your maximum and resting blood flow in your coronary artery. These include:

• PET.
• Cardiac MRI (not as common).

You’ll need to keep still during scans so the images aren’t blurry.

Another way to have this test is an invasive method using cardiac catheterization. A provider puts a guide catheter into your coronary artery and uses a diagnostic wire that has an ultrasound transducer. This transducer measures coronary blood flow velocity in your coronary arteries. You need heparin in an IV during this procedure to prevent blood clots.

Another type of wire uses two temperature sensors and a saline injection to measure blood flow.

What can I expect during the coronary flow reserve test?

During your test, a provider will:

1. Measure your coronary artery’s blood flow while you’re at rest.
2. Give you a vasodilator like adenosine (Adenocard® or Adenoscan®) in your IV to increase your coronary flow to four or five times what it was at rest. It takes two to three minutes for it to work. If you’re having a cardiac catheterization, a provider can put the medicine through the guide catheter instead of your IV.
3. Check your coronary artery’s blood flow again.
4. Compare your maximum blood flow to your resting blood flow (what it was before receiving the vasodilator). This comparison is how they figure out your coronary blood flow reserve.

What to expect after the coronary flow reserve test

If you had a catheter, you’ll need to keep your arm or leg (where the incision was) straight for an hour or more to prevent bleeding.

A provider may recommend drinking fluids to clear the contrast dye out of your body.

If you had a sedative, you’ll need someone to drive you home.

What are the risks and side effects of a coronary flow reserve test?

A coronary flow reserve test is a safe procedure. However, catheters and wires in your coronary artery have a risk of a blood clot, spasm and bleeding. There’s also a risk of injury to blood vessels, which in very rare cases requires surgery to fix.

Adenosine can cause side effects that last a few seconds. These include:

• Abnormal heart rhythm.
• Hypotension.
• Shortness of breath.
• Discomfort in your chest.

People with asthma shouldn’t have this test because adenosine can cause bronchospasms. In some cases, a provider can use an alternative IV medication, such as dobutamine.

What type of results do you get and what do the results mean?

Your coronary flow reserve is a number that tells how much your coronary blood flow can increase under exertion.

The number goes down as you age. A coronary flow reserve of 5 or 6 is normal for a young person in good health. However, someone in their 80s who’s healthy can have a coronary flow reserve below 2.

Depending on the person, reduced blood flow could happen below a coronary flow reserve ranging anywhere from 1.6 to 3.3. What’s normal for one person may not be normal for another.

After surgery for a congenital (since birth) heart defect, a child can have a lower coronary flow reserve.

When should I know the results of my coronary flow reserve test?

A provider may need a few days to review the results of your coronary blood flow reserve test. They may want to talk with colleagues if you have borderline results. If your results show a risk of cardiac issues, they may make a plan for you to follow to lessen your risk.

When should I call my doctor?

Ask a provider any questions you have about your coronary flow reserve test before it starts. Also, contact them if you have any reactions or side effects after your test.

A note from Cleveland Clinic

A coronary flow reserve test can provide valuable information about the health of your coronary arteries. These are the arteries that supply blood to your heart muscle. Finding out your coronary flow reserve score can help a provider know if you need treatment for coronary artery disease. Don’t be afraid to ask questions if there’s anything you don’t understand about your test. They should be able to make your test comfortable for you.