[Fractional flow reserve in diabetics: does it have an expiry date?].

Assessing the clinical importance of intermediate coronary stenosis, defined as a luminal obstruction of 40% to 70%, is a challenge for the interventional cardiologist. Coronary angiography correlates poorly with the functional importance of epicardial coronary disease, especially in patients with stenosis at the threshold of significance. Post-mortem studies have demonstrated that the coronary lumen area only decreases when atherosclerotic plaque values are above 40%. This event is due to the vessel undergoing positive remodeling during the atherosclerotic process.1 Another potential source of error lies in the actual methodology used in calculating the severity of coronary stenosis. Thus, the percentage of stenosis is normally calculated as the ratio between the minimum luminal diameter at the site of obstruction and a reference diameter considered “normal,” that is, without disease.2 Obviously, in the case of diffuse disease, it is very difficult to establish a disease-free reference diameter, which can lead to underestimating the degree of coronary obstruction. Other sources of error are stenosis in tortuous arteries, in bifurcations, with overlapping branches, or highly focal “diaphragm-like” stenosis. This is compounded by the not inconsiderable degree of variation between observers in the qualitative calculation of the degree of obstruction. The calculation of the fractional flow reserve (FFR) has helped to resolve many of these limitations. The FFR is defined as the ratio between the peak coronary flow in the stenotic artery and the peak coronary flow in the same vessel in the theoretical absence of obstruction.3,4 This should be calculated during maximum arteriolar vasodilation, which establishes the minimum myocardial resistance in the area under study. This is usually achieved by the Fractional Flow Reserve in Diabetics: Does It Have an Expiry Date?