What is FFR (Fractional Flow Reserve)?

FFR is a measurement used to assess the functional significance of coronary artery stenosis (narrowing or blockage). It involves measuring the pressure difference across a coronary artery stenosis during the administration of a vasodilator (such as adenosine) that dilates the coronary arteries.

• FFR Measurement:
  • A special pressure wire is passed through a catheter into the coronary artery to measure the pressure before and after the blockage.
  • FFR value is calculated by dividing the pressure distal (downstream) to the blockage by the pressure proximal (upstream) to the blockage during induced hyperemia (increased blood flow caused by the vasodilator).
  • The normal FFR value is typically 1.0.
  • If the FFR is less than 0.80, it typically indicates that the blockage is functionally significant and is reducing blood flow to the heart muscle, and thus treatment (stenting or surgery) is recommended.

The Role of FFR in Stenting or Bypass Surgery Decisions:

FFR-guided decisions are primarily used to help decide whether a coronary artery blockage requires treatment with stenting (PCI) or whether a patient should undergo coronary artery bypass grafting (CABG). The use of FFR helps make more informed decisions by providing a better understanding of which blockages are causing significant reductions in blood flow and which ones are less likely to be harmful.

FFR-Guided Approach to Stenting (Percutaneous Coronary Intervention – PCI):

• Stenting involves the insertion of a small mesh-like tube (stent) into a narrowed artery to keep it open and restore blood flow.
• FFR in PCI Decision-Making:
  • If the FFR value is significantly less than 1.0 (usually less than 0.80), it indicates a flow-limiting blockage that is causing significant ischemia (lack of oxygen) to the heart muscle. In such cases, PCI with stenting is often recommended.
  • FFR helps avoid unnecessary stenting. For example, if a coronary artery has a mild blockage but the FFR value is high (near 1.0), it means the blockage is not reducing blood flow significantly, and PCI may not be necessary. This reduces unnecessary interventions and their associated risks.

FFR-Guided Approach to Bypass Surgery (CABG):

• CABG surgery involves creating new pathways for blood to flow to the heart by grafting healthy blood vessels to bypass the blocked coronary arteries.
• FFR in CABG Decision-Making:
  • FFR is especially helpful in multivessel disease where multiple coronary arteries are narrowed or blocked.
  • In cases where there is extensive disease with multiple blockages but the FFR values in those arteries are low (i.e., significantly reducing blood flow), CABG may be preferred over PCI, as it may offer better long-term outcomes for complex cases, especially if there’s a need to bypass several major arteries.
  • FFR helps identify which blockages are critical to blood flow and which are less significant, allowing for more tailored surgical planning.
  • For some patients with multivessel disease, FFR-guided assessment can determine which lesions need bypass grafting and which can be safely treated with PCI.

FFR and Treatment Personalization:

The main advantage of FFR-guided decision-making is its ability to personalize treatment for each patient. By assessing the physiological impact of blockages (rather than just their anatomical severity), FFR allows clinicians to prioritize interventions based on the functional significance of the stenosis, rather than solely on the appearance of the artery.

Benefits of FFR-Guided Decision Making:

1. Reduced Unnecessary Interventions: By measuring the actual impact of a blockage on blood flow, FFR can help avoid unnecessary stenting or surgery for lesions that do not significantly affect the heart’s function.
2. Improved Outcomes: FFR-guided treatment has been shown to improve clinical outcomes, reduce complications, and lower healthcare costs by targeting only the most severe blockages.
3. Optimized Resource Allocation: FFR helps physicians focus on the blockages that need treatment, reducing the number of unnecessary procedures and resources used.
4. Better Patient Selection: FFR-guided decisions can help determine the most appropriate strategy (stenting vs. surgery), especially in patients with complex coronary artery disease or those with multiple blockages.
5. Lower Risk of Over-Treatment: In patients with stable CAD but low FFR values, PCI or CABG can be performed, whereas in those with minimal symptoms and high FFR values, conservative management might be sufficient.

Clinical Evidence Supporting FFR-Guided Decisions:

Multiple clinical studies have demonstrated the benefits of FFR-guided decisions for treatment strategies:

• FAME (Fractional Flow Reserve Versus Angiography in Multivessel Evaluation) trials have shown that FFR-guided PCI in patients with multivessel coronary artery disease leads to better clinical outcomes (lower rates of death, heart attack, and repeat revascularization) compared to angiography-guided PCI.
• DEFER (Deferral of Intervention in Patients With Stable Coronary Artery Disease) trial demonstrated that patients with lesions with an FFR above 0.75 did not benefit from PCI, showing the importance of functional assessment in decision-making.

Indications for FFR Assessment:

FFR is particularly useful in the following situations:

1. Patients with moderate coronary artery disease (when it’s unclear whether to treat with PCI or CABG).
2. Patients with multivessel disease (helping determine which arteries should be treated surgically and which can be treated with PCI).
3. Patients with intermediate lesions (when angiography alone does not provide enough information on the significance of a blockage).
4. Assessing the need for revascularization in cases of stable angina or non-ST elevation myocardial infarction (NSTEMI).

Risks and Limitations of FFR:

• Invasive Procedure: FFR requires the insertion of a catheter and pressure wire into the coronary arteries, which involves some degree of risk, such as vascular complications or arrhythmias.
• Not Suitable for All Patients: FFR may not be suitable for patients with very small coronary arteries or severe disease that cannot be accurately assessed through FFR measurement.
• Limited in Severe Calcification: In arteries with heavy calcification, the pressure wire used for FFR measurement may not provide accurate results.