What is Fractional Flow Reserve?

Myocardial fractional flow reserve (FFR) is a new index of the functional severity of a coronary stenosis that is calculated from pressure measurements made during coronary arteriography. This new approach enables an "on the spot" diagnosis as to what extent a given stenosis (coronary blockage) contributes to reversible myocardial ischemia and the decision whether revascularization of the stenosis is warranted.

How does FFR work?

• Fractional flow reserve (FFR) closely relates distal coronary pressure to myocardial blood flow during maximum arteriolar vasodilatation.
• The functional state of a patient with a coronary artery stenosis is determined by the maximum blood flow that can reach the heart muscle. As soon as maximum achievable blood flow, at a given level of exercise, is no longer sufficient to match oxygen demand, myocardial ischemia and angina will occur.

Simplified illustration of a coronary artery and the dependent myocardial bed. If that system is studied under conditions of maximum arteriolar vasodilatation, myocardial resistance will be minimal and equal to Rmin. Under such circumstances the flow limiting effect of the epicardial stenosis is maximal, as is the pressure drop across the lesion, expressed as the ratio of driving pressure to resistance, maximum attainable blood flow through the myocardium equals the ratio of the perfusion pressure across the myocardium (distal coronary pressure minus central venous pressure) and the resistance Rmin. If there is no epicardial stenosis, the perfusion pressure across the myocardium equals Pa  Pv where Pa is mean aortic pressure and Pv is central venous pressure. In the presence of a coronary stenosis, the perfusion pressure across the myocardium has decreased to Pd  Pv, where Pd represents hyperaemic coronary pressure distal to the stenosis.

How are FFR Measurements Performed?

• FFR can be measured during a routine cardiac catheterization
• The stenosis is crossed with an 0.014" pressure guidewire for recording the trans-stenotic pressure, and administering a maximum hyperaemic stimulus. (intracoronary adenosine -12 to 20 µg or intravenous adenosine- 140 µg/kg/min infused into the femoral vein).

What do the FFR values mean?

FFR value < 0.75 discriminates functionally significant lesions

• FFR > 0.75 means the blockage is not severe enough to limit blood flow to the heart
• FFR < 0.75 means that the blockage is severe enough to limit blood flow to the heart and should be opened if possible.

What are the Benefits of FFR?

• FFR is a specific index for the epicardial stenosis and therefore better indicates to what degree a patient can be helped by revascularization.
• FFR has a normal value of 1.0 in every patient and every coronary artery
• FFR is independent of changes in heart rate, blood pressure, and contractility
• FFR takes into account the contribution of the collateral flow
• FFR can be applied in multivessel disease and for serial lesions within one vessel

How are FFR Measurements Performed?

• FFR can be measured during a routine cardiac catheterization
• The stenosis is crossed with an 0.014" pressure guidewire for recording the trans-stenotic pressure, and administering a maximum hyperaemic stimulus. (intracoronary adenosine -12 to 20 µg or intravenous adenosine- 140 µg/kg/min infused into the femoral vein).

When is FFR used?

• FFR is used as a diagnostic tool to determine whether a particular coronary stenosis, found at angiography, is responsible for reversible ischaemia (and consequently should be dilated or bypassed if medical treatment fails).
  • Specifically in respect to intermediate stenosis
  • identification of the culprit lesion in case of multivessel disease
  • Justification to perform (or avoid) angioplasty in a patient without documented evidence of ischemia at non-invasive testing
  • To indicate the exact location of a lesion in case of overprojection and other situations where the angiographic image is unclear.
    
    
• Coronary Intervention
  • A high value of FFR after regular balloon angioplasty is associated with a favorable long term outcome.
    
    
• Coronary Stenting
  • Evaluation of optimum stent deployment.