Fractional flow reserve
Fractional flow reserve
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Fractional flow reserve

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Fractional flow reserve

Fractional flow reserve (FFR) is a diagnostic technique used in coronary catheterization. FFR measures pressure differences across a coronary artery stenosis (narrowing, usually due to atherosclerosis) to determine the likelihood that the stenosis impedes oxygen delivery to the heart muscle (myocardial ischemia).

Fractional flow reserve is defined as the pressure after (distal to) a stenosis relative to the pressure before the stenosis. The result is an absolute number; an FFR of 0.80 means that a given stenosis causes a 20% drop in blood pressure. In other words, FFR expresses the maximal flow down a vessel in the presence of a stenosis compared to the maximal flow in the hypothetical absence of the stenosis.

During coronary catheterization, a catheter is inserted into the femoral (groin) or radial arteries (wrist) using a sheath and guidewire. FFR uses a small sensor on the tip of the wire (commonly a transducer) to measure pressure, temperature and flow to determine the exact severity of the lesion. This is done during maximal blood flow (hyperemia), which can be induced by injecting products such as adenosine or papaverine. A pullback of the pressure wire is performed, and pressures are recorded across the vessel.

When interpreting FFR measurements, higher values indicate a non-significant stenosis, whereas lower values indicate a significant lesion. There is no absolute cut-off point at which an FFR measurement is considered abnormal. However, reviews of clinical trials show a cut-off range between 0.75 and 0.80 has been used when determining significance.

Fractional flow reserve (FFR) is the ratio of maximum blood flow distal to a stenotic lesion to normal maximum flow in the same vessel. It is calculated using the pressure ratio

where is the pressure distal to the lesion, and is the pressure proximal to the lesion.

The decision to perform a percutaneous coronary intervention (PCI) is usually based on angiographic results alone. Angiography can be used for visual evaluation of the inner diameter of a vessel. In ischemic heart disease, deciding which narrowing is the culprit lesion is not always clear-cut. Fractional flow reserve can provide a functional evaluation by measuring the pressure decline caused by a vessel narrowing.

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