Overview of Instantaneous Wave-Free Ratio
Coronary artery disease (or CAD for short) is a relatively common condition that affects more than 15 million Americans every year. It is actually the leading cause of death for both men and women. CAD happens when, usually because of a disease called atherosclerosis, the arteries that supply blood to your heart get narrowed or blocked. If your heart gets less blood than it needs, because of these blockages, then it can get damaged. This damage can lead to severe chest pain (also known as angina), or even a heart attack.
Doctors often use a test called cardiac catheterization with angiography to look at the heart’s blood vessels. It’s a procedure where a small tube is inserted into an artery in your leg or wrist and navigated to your heart. A special dye that can be seen with an X-ray is then injected, allowing your doctor to see any blockages. Once this is done, your doctor will look at the images taken to see if there are blockages (also known as lesions) in your arteries.
A study from 2018, based on test results from China, showed that doctors’ visual estimations of how severe these blockages are can be quite different from computer-based measurements. The study also showed that there was a lot of variability among test results from different hospitals and doctors. This reaffirms the usefulness of additional tests.
Blockages that have narrowed the heart’s arteries by more than 70% are considered significant. These can be treated with techniques such as balloon angioplasty (a procedure where a balloon is inflated to open up the blocked artery) or the placement of a stents, a metal tube that is permanently placed in the artery to keep it open. Less significant blockages, narrowing less than 40% of the heart’s blood vessels, are usually treated with medication.
What to do with blockages that are milder, causing the 40% to 70% narrowing, has been a subject of debate. A clinical study in 2007 found that medication was just as effective as a procedure to open up these types of blockages.
Doctors now use additional ways to study arteries, such as fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR). FFR is a technique where doctors can precisely measure blood pressure and flow through a blockage using a thin wire. Medical research has shown that blockages with an FFR value of less than 0.75 can cause symptoms like chest pain and should be treated with a procedure, while those with values higher than 0.75 can be managed with medication.
iFR, a newer test, works similarly to FFR but doesn’t require a medication to increase blood flow during the measurement. A study in 2017 found that both iFR and FFR were equally good at predicting which blockages could lead to chest pain or a heart attack. Other studies also found that treating patients based on iFR readings was just as good as treating based on FFR. In iFR, blockages with a certain cut-off value are considered significant. However, as this is a new technique, some doctors may prefer to use FFR for certain cases.
Anatomy and Physiology of Instantaneous Wave-Free Ratio
During iFR, a procedure used to measure blood pressure and flow in the coronary arteries, only a small portion of the body’s anatomy is needed. However, understanding the structure of the coronary arteries – the blood vessels supplying the heart muscle – is crucial for the procedure. This detailed knowledge is covered in other resources.
Why do People Need Instantaneous Wave-Free Ratio
If you have a stable form of coronary artery disease (CAD), a condition that involves the narrowing of the heart’s arteries due to plaque build-up, then your doctor may recommend a medical procedure known as iFR (Instantaneous wave-Free Ratio). This procedure is particularly beneficial if you have lesions or damaged patches in your arteries that are difficult to interpret. It’s mainly used when stenosis (a condition in which the artery narrows) is in the range of 40% to 70%.
When a Person Should Avoid Instantaneous Wave-Free Ratio
At the moment, there are no reasons why someone couldn’t have an Instantaneous Wave-Free Ratio (iFR) test. However, it’s important to note that current guidelines do not recommend this test for people with Acute Coronary Syndrome (ACS), which is a medical term for a sudden, reduced blood flow to the heart.
Equipment used for Instantaneous Wave-Free Ratio
iFR, which stands for instant wave-Free Ratio, is a process that needs a special kind of wire. This wire can sense the pressure and speed of blood flow. To get the iFR values, a computer program is used which can do these calculations accurately. Other tools used in iFR, such as the heart catheters, vascular sheath (a device that keeps the blood vessel open), and imaging tools, are the same as those used in a routine heart catheterization procedure, which is a test to check the heart’s function and blood supply.
Who is needed to perform Instantaneous Wave-Free Ratio?
The Instantaneous Wave-free Ratio (iFR), a test that checks how well blood flows through your heart, should only be carried out by cardiologists. These are specialist heart doctors who have officially been trained in ‘interventional cardiac catheterization,’ or using a thin tube to access the heart and treat any problems. They have been recognized by a board of doctors as being experts in this area.
Preparing for Instantaneous Wave-Free Ratio
Once the special computer software needed to work out the iFR (instantaneous wave-free ratio) value is installed, and the necessary tubes are ready, very little extra preparations are required compared to a standard heart catheterization. Catheterization is a procedure where a thin, flexible tube called a catheter is inserted into a large blood vessel that leads to your heart. It’s done to diagnose and treat heart conditions.
How is Instantaneous Wave-Free Ratio performed
Instantaneous wave-free ratio (iFR) is a method used by doctors to measure the blood flow in your heart, particularly around a narrow or blocked part of your artery (this is what’s referred to as a ‘stenotic lesion’). In this process, they use special devices (known as ‘pressure wires’) which are moved to a spot located beyond the affected area of your artery.
The iFR procedure takes place during a certain part of your heart’s beating motion, known as the ‘wave-free period’, when your heart is not actively contracting (this is referred to as ‘diastole’). During this time, there is minimal influence from the blood flow in your artery, making it easier to get accurate measurements.
The calculations during this test are based on comparing two pressures. One is the pressure at the place in your artery that is beyond the blocked or narrowed spot (referred to as the distal coronary artery, or Pd). The other is the pressure in the part of your heart that pushes out blood to your body (known as the aortic outflow tract, or Pa). The iFR method calculates the ratio of these two pressures (Pd to Pa).
This measurement helps your doctor understand how the blockage or narrowing is affecting your heart’s function and informs the best treatment strategies for you.
Possible Complications of Instantaneous Wave-Free Ratio
The procedure known as iFR (instantaneous wave-free ratio), used to evaluate heart health, generally has very few complications. However, it’s important to note that the ones that do occur are the same as those from more typical heart checks, such as an angiography and PCI (Percutaneous Coronary Intervention). These could include:
Bleeding: This is any kind of bleeding that can happen after the procedure.
Access site hematoma and pseudoaneurysm: These terms refer to swelling or growth within the blood vessels in the area where your doctor performed the procedure, which could cause some discomfort or pain.
Acute kidney injury caused by the contrast agent: This is when your kidneys get hurt by the dye that’s used to make your heart and blood vessels show up on the X-ray.
Anaphylaxis caused by the contrast agent: This is a severe allergic reaction that can happen due to the dye used in the procedure.
Coronary artery dissection: A rare complication where the layers of the wall of a coronary artery (the blood vessels that provide oxygen and nutrients to the heart itself) separate or tear. It can cause chest pain or even a heart attack.
Remember, your doctor will always weigh the risks against the benefits to make sure that this the best choice of procedure for you.
What Else Should I Know About Instantaneous Wave-Free Ratio?
iFR, or instant wave-free ratio, is a non-invasive test that doctors use to assess the severity of blockages in heart arteries which could be causing chest pain or other symptoms. This test assists doctors in deciding whether a patient needs a procedure called PCI (Percutaneous Coronary Intervention) or medication-based therapy to treat their heart condition.
If someone is experiencing symptoms like chest pain, and their iFR value is 0.89 or less, it typically suggests that the heart muscle isn’t getting enough blood due to a significant blockage in a heart artery. These patients might need a procedure called PCI, which involves inserting a small tube to open up the blocked artery and restore normal blood flow to the heart.
On the other hand, if a patient’s iFR value is more than 0.93, the blockage in their heart is typically not severe enough to be causing their symptoms. In such cases, the patient usually receives a treatment plan that includes medications and lifestyle changes to manage their heart health, also known as optimization of medical therapy (OMT).
However, patients with iFR values between 0.90 and 0.93 need additional testing using a method called FFR (Fractional Flow Reserve) to make a more accurate decision about their treatment. Similarly, if a patient doesn’t have symptoms typical of heart disease, but their iFR value is less than 0.86, they might require PCI, while patients with iFR values between 0.86 and 0.89 are also recommended for FFR testing to confirm the need for treatment.
Summing up, the iFR value is important in determining the best course of treatment, helping doctors to decide whether a heart procedure or medication-based therapies are more suitable for the patient.
