A Look at Fractional Flow Reserve Measurements

Fractional Flow Reserve (otherwise known as FFR) is a technique utilised to measure the pressure differences on either side of a coronary artery stenosis. The main intention of this strategy is to determine if blood flow (and therefore oxygen) is being impeded due to a narrowing of the arteries. An FFR measurement is a rather common procedure and it can used to diagnose potential issues with the heart and therefore, to provide viable treatment options. Let us take a closer look at this concept in order to understand how and why it may be used within clinical settings. However, it is first wise to briefly examine what a stenosis is and the potential dangers.

Caas vFFR is an alternative to a FFR measurement. This software solution is less invasive and provides the FFR value and anatomical information based on two angiograms and the aortic root pressure of the patient.

What is a Coronary Stenosis and What Risks Can One Pose?

A coronary stenosis may be caused by injuries to a specific area which lead to an accumulation of fatty acids around the site. However, deposits within the heart containing cholesterol likewise play an important role.

Coronary stenoses are some of the most common causes of coronary heart disease (CAD). Not only can arteries within the heart begin to narrow due to an accumulation of plaque (known as atherosclerosis), but clots may form on occasion. This poses serious health threats such as a heart attack. There are other risks associated with a coronary stenosis including shortness of breath (especially when performing physical activities) and angina.

One of the concerns in regard to a coronary stenosis is that symptoms may not begin to appear until after a significant amount of damage has already occurred. This is when the use of modern treatments such as the administration of specific medications or surgery may be warranted.

What Does an FFR Procedure Involve?

Note that this is a slightly invasive procedure and therefore, patients will be provided with a general anaesthetic. An FFR cath lab will begin by inserting a small flexible tube through an incision made within the groin area. This tube is then navigated through various veins until it reaches the heart. Sensors inside this wire will measure both the blood flow as well as the blood pressure associated with a specific artery.

Such diagnostics are extremely useful, as low values may indicate that the patient is at a greater risk of developing a myocardial infraction (heart attack) or a similar cardiac issue. Thereafter, the correct preventative treatments can be put in place in order to avoid serious and potentially life-threatening situations.

What Measurements are Taken in an FFR Fractional Flow Reserve Test?

In technical terms, this type of examination is designed to measure two important variables:

• The blood pressure before a stenosis.
• The blood pressure immediately after (distal to) a stenosis.

The difference between these two figures is expressed as an absolute value from 0 to 100. In the event that an FFR reading of .80 is observed, this signifies that there is a 20 per cent drop in blood pressure on either side of the stenosis. Simply stated, this examination measures the real-time flow of blood in relation to the hypothetical flow of blood in the event that no stenosis is present (the artery itself is free from any issues).

When Might an FFR Procedure be Used?

There are several clinical scenarios which could warrant this procedure. Of course, the patient will first need to be examined by a cardiologist or similarly trained professional. Having said this, there are a handful of FFR guidelines that can be used to determine whether a catheter-based examination is required. Here are some situations:

• Acute coronary syndrome
• Multi-vessel disease
• Diffuse atherosclerosis
• The presence of bypass grafts
• Bifurcation and ostial branch stenoses
• Sequential stenoses

Note that this procedure is also the preferred method in the event that a percentage of stenosis between 50 and 70 per cent is present. It can also be used in conjunction with patients who have already been diagnosed with stable ischemic heart disease.

The FFR Procedure in Detail: What Can Patients Expect?

Before undergoing a procedure within an FFR cath lab, the patient will have to abstain from eating for eight hours. In many cases, a coronary angiography will be performed prior to the FFR itself. A vasodilator will then be administered, as this medication helps to ensure that internal veins and arteries are expanded (this is known as hyperaemia).

Note that during these procedures a local anaesthesia is used. However, The patient will normally remain awake and cognisant. The anaesthetic is simply utilised to provide a sense of relaxation and to abate any slight discomfort that may otherwise be experienced from the catheter.

A small incision will then be made around the groin area. The location of the incision is based upon the type of vasodilator employed as well as any specific health conditions of the patient. Radial (or wrist) access may also be used in the event that contraindications associated with the groin are present. A pressure wire is thereafter introduced followed by a flexible catheter. This catheter is guided through veins related to the heart (known as the "coronary tree"). In the vast majority of cases, a hyperaemic agent (normally adenosine) is administered intravenously in order to ensure that all veins and arteries are expanded to their maximum diameter.

Once the catheter reaches the suspected stenosis, it will take two separate pressure and flow readings:

• Aortic pressure (Pa)
• Distal pressure (Pd)

The FFR catheter is then removed via the same course that it took to reach the stenosis.

How Long Will it Take to Recover from an FFR Cardio Examination?

It is important to note that the majority of procedures can be completed within approximately 30 minutes. As an FFR is minimally invasive, recovery times should normally not present an issue. Depending upon the effects of the procedure, patients may be allowed to leave the same day or they may be required to remain overnight. In either case, another individual will be needed to drive (due to any potentially lingering effects of the anaesthesia as well as possible mobility issues resulting from the small incision).

How Will the Results of a Fractional Flow Reserve Measurement be Interpreted?

As mentioned previously, this test measures the differences associated with blood flow and pressure immediately before and after a stenosis. These values are measured in the form of a percentage. Here is a breakdown of how they are interpreted:

• A value of 1.0 indicates normal heart rate and blood pressure. In other words, no further intervention will be required.
• Values between .80 and 1.0 signify that the stenosis is not medically significant at the moment. Revascularisation is therefore not imminent.
• Values between .75 and .80 may be clinically significant. These will need to be examined by a cardiologist in order to determine if further medical steps are warranted.
• Values at or below .75 highlight that the stenosis is clinically significant. Therefore, some type of revascularisation will ne be necessary in order to prevent further cardiac complications.

Note that FFR values of below .75 indicate that ischemia is present. Therefore, it is important to take act sooner as opposed to later.

What are the Advantages of an FFR Heart Cath Procedure

As this method was initially developed in the 1990s, it is relatively new when compared to some other diagnostic techniques. Perhaps the main benefit involves the simple fact that it is easy to perform and in the majority of cases, it can be used as an outpatient procedure. Here are some other notable advantages of an FFR:

• An FFR can be used independently of a baseline flow.
• The resulting readings exhibit low variability.
• Measurements can be reproduced and they are effective when diagnosing up to 99 per cent of all arteries.
• The values themselves are not affected by sudden changes in heart rate or blood pressure.
• The technique can be used to discover the presence of a stenosis within an epicardial coronary artery.
• It can be used to identify the risks associated with a specific lesion; important when referring to conditions such as multi-vessel coronary artery disease.
• An FFR may be useful in the event that more invasive techniques such as branch vessel stenting are not recommended.
• Fractional flow reserve measurements are minimally invasive, less costly when compared to some other procedures and will not normally require extensive hospital stays.

It is now clear to appreciate why FFR procedures are some of the most common methods used when diagnosing potentially serious stenoses.

Are There Any Disadvantages Associated with an FFR?

Similar to any medical procedure, there are certain drawbacks which a clinician will consider. The two primary issues are:

• While the procedure is straightforward, it is nonetheless invasive (a potential issue for those with underlying health problems).
• The measurements themselves are extremely dependent upon achieving maximum levels of vasodilation.
• Other pathological factors may influence the outcome of an FFR reading.

This is why medical professionals will carefully examine the history of a patient, any medication he or she may be taking as well as addition al contraindications that could impact the outcome of a test.

While complications are rare (occurring in less than two per cent of patients), they should still be noted. Here is a breakdown of some possible risks and their relevant percentages:

• Transient bradycardia (1.7 per cent).
• Coronary spasms (2 per cent)
• Ventricular fibrillation (0.2 per cent).
• In rare cases, the guiding catheter may cause slight trauma to nearby blood vessels.

Once again, an FFR cardiology specialist will take all of these factors into account when determining whether such a procedure is warranted.

What Treatments May be Recommended after an FFR?

As we have already seen, fractional flow reserve measurement is used to detect, diagnose and determine the extent of a suspected stenosis. Assuming that an issue is found, there are several procedures which may be recommended.

Angioplasty

Angioplasty is a technique used to widen the diameter of an artery by removing the presence of any plaque that may be impeding blood flow to the heart and surrounding tissues. This will also help to balance the pressure before and after the affected area.

Coronary Artery Bypass Surgery

This is also referred to as coronary artery bypass graft (CABG) surgery. If an artery is almost completely blocked, it will simply be bypassed. A healthy blood vessel is obtained from the neck, arm or chest. This is essentially used to redirect the blood flow around an artery that is no longer functioning as it should. Bypass surgery has become increasingly common in recent times thanks to advancements in medical technology.

Artery Stenting

A stent may also be placed within the affected artery. A stent is a small mesh tube that widens its diameter and helps to restore a healthy flow of blood to the heart and nearby tissues.

Fractional Flow Reserve Measurements: Powerful Clinical Tools

It is now clear to see why this procedure is so effective in terms of detecting potentially serious stenoses. Not only will an FFR provide accurate results, but the entire process itself can often be performed on an outpatient basis. Similar to many issues associated with the heart, early diagnosis is essential in order to ensure an amenable outcome. This is why fractional flow reserve measurements have become common practice in modern times.

Would you like to learn more about what is involved with an FFR? Do you have additional questions that were not addressed within the above article? If so, please make it a point to contact one of our specialists. We will be more than happy to provide further assistance as well as to clarify any other concerns that you may have.