A computed tomographic fractional flow reserve (FFR) is a noninvasive test used to measure how much blood flow is being restricted by a blockage in an artery. An FFR is one of several tests used to diagnose a heart attack.
In a healthy heart artery, the pressure at the end of the artery is the same as at the beginning of the artery (where it comes off of the aorta). But when a blockage reduces flow through the heart artery, the pressure at the end is reduced proportionately to the restriction. The greater the restriction, the lower the pressure downstream because the flow is reduced. When the FFR guidewire is placed across the blockage, it measures the pressure in front of and beyond the blockage. If the blood pressure in the artery or beyond the blockage is found to be significantly reduced, then that blockage may be a good candidate for angioplasty and stenting to clear the blockage and prop the artery open.