Fractional flow reserve (FFR) is a technique to evaluate the hemodynamic relevance of coronary artery stenoses 1-3.
It is defined as "the ratio of maximal flow achievable in the stenotic coronary artery to the maximal flow achievable in the same coronary artery if it was normal" 1.
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Clinical applications
Fractional flow reserve has become the gold standard method for assessing coronary lesion severity during invasive coronary angiography (ICA) by facilitating the identification of specific coronary lesions that cause myocardial ischemia and can be targeted for revascularization.
While coronary stenoses can be detected very well during invasive coronary angiography, the hemodynamic relevance of these stenoses still poses a challenge especially those in the significant moderate range of 50-69% diameter stenoses or calculated 80-90% area stenoses.
Coronary guidewire sensor technology enables interventional cardiologists to measure coronary blood pressure, flow velocity, and resistance to assess lesion-level ischemia, coronary collateral supply and other parameters of vascular function.
Several prospective multicenter studies have demonstrated that fractional flow reserve during ICA with interventional revascularization improves the event-free survival rate and also leads to cost reduction of the procedures as only a fraction of detected coronary stenoses show a relevant obstruction of blood flow as determined by fractional flow reserve, especially since FFR also includes collateral blood flow distal to a stenosis 4.
Technique
A pressure wire is placed across the stenosis during coronary catheterization. To induce maximal flow in the coronary vessel, hyperemia is induced by intravenous/intra-arterial injection of adenosine and the pressure gradient across the stenosis is measured.
Fractional flow reserve is calculated as the ratio of maximal blood flow distal to the stenosis divided by maximal flow proximal to the stenosis. This translesional pressure ratio at maximum flow expresses the 'functional significance' of a coronary lesion.
Interpretation
Several studies have shown that an FFR <0.8 is a reliable cut-off for hemodynamically relevant stenoses 3,4.
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