FFR and IFR in the Diagnosis and Treatment of Heart Disease

Introduction

Coronary artery disease is a leading cause of death in women and men around the world. An instantaneous wave-free ratio (IFR) can determine whether or coronary lesions are visualized angiographically and should undergo percutaneous intervention. The wave-free ratio used in the cardiac catheterization lab helps in determining the hemodynamic significance of the coronary lesions.

What Are FFR and IFR?

FFR - Fractional flow reserve is a minimally invasive procedure used to figure out how bad the stenosis (narrowing) is in the coronary arteries. The provider will check blood pressure as well as the flow of blood in the coronary arteries. In this procedure, a thin wire is threaded through the coronary arteries to measure the pressure drop across a stenotic lesion or narrowing of the artery. FFR is used to determine whether a stenotic lesion is actually causing a reduction in blood flow to the heart and can help guide decisions about whether to perform angioplasty or other interventions to treat the lesion.

IFR - Instantaneous wave-free ratio is an index used to assess the severity and intensity of coronary artery stenosis. This is tested against the fractional flow. IFR is a newer technique that also measures the pressure drop across a stenotic lesion, but does so during a specific period of the cardiac cycle known as the ‘wave-free period’. This period is thought to be less influenced by changes in the heart rate or contractility and therefore may provide a more accurate assessment of the significance of a stenotic lesion.

Both of these methods have high and similar diagnostic accuracy.

• IFR determines stenosis, causing a limitation of coronary arteries with subsequent ischemia. It is performed with high-fidelity pressure wires and is passed distally to coronary stenosis.

• Enhancement of FFR requires adenosine and can be time-consuming and costly, and contraindicated in certain individuals.

• IFR isolates a specific diastole known as the wave-free period.

• IFR can be calculated even using a single heartbeat, typically averaging five beats for normalization. It is measured at rest, and there is no need for any stressors or pharmacological vasodilators.

• Both of the trials are assessed with intracoronary nitroglycerin and administered prior to the lesion assessment.

• Coronary-pressure guidewires are used in measurement by IFR and FFR.

• Revascularization of an investigated vessel is mandated if IFR is 0.89 or lower, FFR is 0.80 or lower, and thresholds are indicated in the presence of hemodynamic stenosis.

• If IFR is higher than 0.89 or FFR is higher than 0.80, revascularization of the vessel is deferred.

Comparison between IFR and FFR -

IFR is comparable to FFR in producing a severity of coronary artery stenosis. IFR is strongly correlated with FFR, with a diagnostic accuracy of approximately 80 %. The instant wave-free ratio is calculated by measuring natural wave-free periods. The use of hyperemic reduces the potential side effects. IFR is preferred over FFR in elderly individuals with baseline sinus node dysfunction.

What Are the Indications of IFR and FFR?

Indications of IFR and FFR are in individuals with stable CAD (coronary artery disease) and indeterminate lesions, between 40 % to 70 % of stenosis.

What Are the Contraindications of IFR and FFR?

There are no contraindications at this time for IFR. Current recommendations for IFR do not include individuals with ACS (acute coronary syndrome).

What Is the Equipment Used for the Test?

IFR requires a specialized guidewire with flow and velocity sensing capabilities with computer software that allows an accurate calculation of IFR values. Along with other equipment, a vascular sheath, imaging modalities, and cardiac catheters are unchanged from traditional cardiac catheterization. A doctor with formal training in interventional cardiac catheterization should perform the procedure.

How Is the Test Performed?

In instant wave-free ratio, the pressure wires used in FFR are passed through a point distally to a stenotic lesion. A period of diastole is known as a ‘wave-free period.’ IFR calculated the ratio of the distal coronary artery pressure within the aortic outflow tract. The time frame for completing blood flow complicating the measurements is negligible. Percutaneous coronary intervention (PCI) and coronary artery bypass grafting are considered revascularization procedures for trial purposes.

What Are the Complications of the Test?

There are very minimal complications associated with IFR. They are the same as the standard cardiac catheterization with angiography and PCI:

• Coronary artery dissection.

• Pseudoaneurysm and access site hematoma.

• The contrast agent can potentially cause acute kidney injury.

• Bleeding.

• A contrast agent causes anaphylaxis.

What Are the Points to Remember About the Evolving Future of IFR and FFR?

The following points are to be remembered:

1. The use of coronary physiology revascularization has been found to improve individuals' outcomes and defer stenting of non-ischemic lesions compared with angiographic assessment.

2. FFR is defined as the pressure ratio of distal to stenosis relative to pressure proximal to stenosis during a hyperemia-inducing vasodilating agent, typically adenosine.

3. Potential reasons for the low adoption of FFR despite clinical benefits may include time consumption to perform FFR measurements, with adenosine, and in certain countries, it is due to patient-related discomfort, contraindication, and lack of reimbursement.

4. Renewed interest and development in the field of coronary physiology, the introduction of a new, non-hyperemic pressure-based index of stenosis severity.

5. FFR carries guiding revascularization in angiographically intermediate coronary stenosis with stable angina. FFR in coronary catheters has remained low.

6. IFR may be a superior prognostic tool compared to FFR for determining non-culprit lesions in individuals.

7. Fully-integrated physiological map of the coronary vessel under manual IFR is co-registered with an angiogram in real-time.

8. Real-time co-registered IFR pressure mapping with PCI may herald a new paradigm of functional lesion assessment.

Conclusion:

Technologies like FFR and IFR help with decision-making to improve individual health and reduce healthcare expenses. These technologies have led to immense changes within the organization. Thus, the healthcare administration can ultimately demand more guidelines and reimbursements for individual satisfaction, reduction in costly readmissions, and improved outcomes. The coronary pressure-based assessment using FFR provides benefits over coronary angiography for the guidance of coronary intervention.