How is your heart's 'supply'? Let's talk about Coronary Flow Reserve (CFR)!

Have you ever wondered if your heart is getting the extra blood it needs when it is stressed, like when you exercise? Our heart is an amazing organ. It needs a good blood supply to function properly. That's what we're going to talk about today, and it says a lot about the health of your heart: `Coronary Flow Reserve` or `CFR`. Don't worry, these words may sound a bit complicated, but let's keep it simple.

What is `Coronary Flow Reserve (CFR)`? Simply put...

Think of your heart as a car engine. When it's running normally, the engine needs a certain amount of fuel. But when you're going up a hill, or going fast, the engine needs more fuel, right? That's how our heart is. When we're at rest, the heart needs a certain amount of blood. But when we exercise, run, jump, lift weights, or are under stress, the heart needs more oxygen and nutrients . To meet this increased demand, the blood supply to the heart needs to increase.

The main blood vessels that carry blood to the heart are called the coronary arteries . Coronary Flow Reserve (CFR) is a measure of how much your coronary arteries can increase their blood supply when the heart needs more blood. It's like looking at the heart's 'supply' reserve.

This is also called `Myocardial blood flow reserve`. Because blood flows from these coronary arteries to your heart muscle, that is, to the heart muscle `(Myocardium)` . So through this CFR value, doctors can assess whether your heart muscle is getting enough blood when it needs it.

How is this CFR value calculated?

This is a very simple calculation. But it requires special tests to do this. Simply put, the CFR is the maximum blood flow that can flow through your coronary arteries , divided by the normal blood flow that flows through you when you are at rest, without any exertion .

For example, when you are at rest, your heart pumps X milliliters of blood per minute. When you are at maximum exertion (or when that condition is artificially induced), your heart pumps Y milliliters of blood. Then CFR = Y / X.

This is how much more blood your heart can pump than normal.

In what cases is a CFR test performed?

There are several reasons why a doctor might recommend a CFR test for you:

• Find out if you have coronary artery disease (CAD): Sometimes chest pain (angina), difficulty breathingWhen symptoms such as these occur, this test helps to confirm whether the cause is a blockage in the coronary arteries.
• Assess the severity of CAD: This is important to understand how much of the arteries are affected and how much blood flow is obstructed in someone who already has CAD.
• Predict future heart attack risk : As the CFR value decreases, the risk of having a heart attack or other heart disease in the future may increase.
• Measure the success of treatments: This test can also be used to see if blood supply to the heart has been restored after certain treatments (e.g. angioplasty, bypass surgery).

What is an average CFR value?

A healthy person's CFR is usually between 2.0 and 2.5 or higher . This means that when you are working hard, your heart receives at least twice as much blood flow as when you are resting. A healthy person can have this value as high as 3. This means that they have the ability to increase their blood supply threefold.

One study found that people with a CFR greater than 2 had a better six-month recovery after a heart attack. A CFR less than 2 indicates a higher risk of heart disease.

But it's important to understand that this "normal" value can change with age. A healthy young person may have a CFR of 5 or 6. But even a healthy 80-year-old may have a CFR of less than 2. Also, a child who has had surgery for a congenital heart defect may have a lower CFR. Therefore, your doctor will decide whether your CFR is normal or not, based on your overall health and other factors.

How to take the CFR test? How to prepare for it?

There are two main methods for measuring CFR. One is an invasive method , which involves inserting something into the body. This involves something called `Cardiac Catheterization`. The other is a non-invasive method , which involves using a special `Nuclear Stress Test`, which is a `Rubidium-82 Positron Emission Tomography (PET) scan`. Rarely, a `Magnetic Resonance Imaging (MRI) scan` can also be used for this purpose.

Now let's see how to prepare for this test and what happens on the day of the test.

Things you need to know before the test

• Tell your doctor about the medications you are taking: including prescription medications, over-the-counter medications, and vitamins.You should also tell your doctor about any herbal products you are taking, as some medications can affect blood circulation.
• Tell us about your allergies: If you have any allergies to any medications, contrast dye used in tests, or latex, let us know in advance.
• Food and Drink Advice: If you are having a cardiac catheterization or PET scan, ask your doctor how many hours before the test you should stop eating or drinking. Typically, you will not be allowed to eat or drink anything for 6 to 8 hours before the test.

What to expect on test day?

• For an MRI scan: You should not have any metal objects (such as jewelry or hairpins) in your body. Some medical devices (such as pacemakers) may not be compatible with MRI. So if you have such a device, ask your doctor beforehand to make sure it is safe for MRI.
• Cardiac Catheterization: In this procedure, a very thin tube (catheter) is inserted through a blood vessel in your neck, groin, or arm into the coronary arteries of your heart. You will be given a mild sedative to make you feel less uncomfortable.
• An IV line: Regardless of the test method, an ``Intravenous line (IV)`` will be connected to a vein in your arm. This IV is where medication (vasodilator) is given to maximize blood flow to the heart and sometimes a ``Contrast dye`` to make the coronary arteries more visible. If you are having a ``PET scan``, a radioactive substance ``Radiotracer`` is also given through this IV.

Let me explain a little more about how CFR is measured...

Your doctor will use various imaging techniques to measure blood flow in your coronary arteries at rest and during peak exertion. The main ones are:

• `PET scan`: In this, when a `Radiotracer` given through an IV reaches the heart, the signals emitted by it are captured by a special camera, and with the help of a computer, clear images of the blood flow in the heart are obtained.
• ` Cardiac MRI` : This is also an imaging method. However, it is used less frequently to measure CFR.

It is very important that you remain still during this scan, otherwise the images obtained may not be clear.

The `Cardiac Catheterization` method is a little different. It involves:

1. After the catheter is inserted into the coronary artery, a special wire is passed through it. At the tip of this wire is an `Ultrasound transducer` (a small device that emits and receives ultrasound waves). This can measure the speed of blood flowing inside the coronary artery.

2. During this process, a medicine called `Heparin` is given through the IV to prevent blood clotting.

3. There are other types of wires that measure blood flow using two temperature sensors and a saline injection.

What exactly happens during the test?

During your examination, the medical team will do the following:

1. First, blood flow in your coronary arteries is measured while you are at rest .

2. Then, a `Vasodilator` type of medicine (such as `Adenosine (Adenocard® or Adenoscan®)`) is given through your IV, which increases heart rate and blood flow. This medicine increases blood flow by four to five times compared to when you are at rest. It takes a short time, about two to three minutes, for this medicine to take effect. This is called `Cardiac Catheterization`, and sometimes this medicine may be given through the catheter instead of the IV.

3. After the drug is given, the blood flow in the coronary arteries is measured again. This is the maximum blood flow.

4. Finally, your `Coronary Flow Reserve (CFR)` value is calculated by comparing this maximum blood flow and your resting blood flow .

What happens after the test?

• If you have a catheter inserted (especially in the groin or arm), you will need to keep the incision site upright for an hour or more to prevent bleeding.
• Your doctor may tell you to drink more water to help flush the contrast dye out of your body.
• If you have been given a sedative, you will not be able to drive for that day. So you will need to bring someone home with you .

What are the risks and side effects of this CFR test?

A CFR test is generally a safe procedure, but like any medical procedure, there are some minor risks.

• Because catheters and wires are inserted into the coronary arteries, very rarely a blood clot, spasm of the arteries, or bleeding may occur.
• There is a very small risk of blood vessel damage. If this happens, surgery may be needed to repair it, very rarely.

When given the drug `Adenosine`, some people may experience the following side effects, which last only a few seconds:

• Abnormal heart rhythm
• Low blood pressure (Hypotension)
• Shortness of breath
• Chest discomfort

Important: This `Adenosine` medicine is not given to people with asthma. Because it can cause bronchospasms. In such cases, the doctor may use an alternative IV medicine like `Dobutamine`.

What are the results like? What do they tell us?

Your CFR test gives you a number. This number tells you how much your coronary arteries can increase blood flow during exertion.

As we've discussed before, this value can decrease with age. A healthy young person might have a CFR of 5 or 6. But a healthy older person might have a CFR of less than 2.

Reduced blood flow (i.e., a risk factor) can occur at any CFR value between 1.6 and 3.3. What is normal for one person may not be normal for another. Therefore, only your doctor can accurately interpret your results. He or she will take into account many factors, such as your age, health status, and symptoms, to arrive at a conclusion.

How long does it take to know the results?

It may take a few days for your doctor to analyze the results of your CFR test and let you know. If your results are borderline, your doctor may want to discuss them with other doctors. If your results indicate a risk of heart disease, your doctor will also talk to you about a plan to reduce your risk.

When should I contact the doctor?

If you have any questions before the CFR test begins, ask your doctor. Also, if you experience any unusual symptoms, side effects, or discomfort after the test , notify your doctor immediately.

Take-Home Message

A `Coronary Flow Reserve (CFR)` test is a test that provides valuable information about the health of the coronary arteries that supply blood to your heart. It can check whether your heart is getting the extra blood it needs when it is working hard.

A low CFR value can be a sign of coronary artery disease. It can also give an idea of ​​your future risk of heart attack.

If there's anything you don't understand about this test, don't be afraid to ask your doctor. They'll explain everything to you and help you make the test as comfortable as possible. Remember, taking care of your heart is very important!

`Heart disease, coronary arteries, blood supply, CFR test, heart attack, heart health, medical tests