The pressure wire in practice.

Fractional flow reserve (FFR) is increasingly used to evaluate the functional significance of epicardial coronary disease. When compared with non-invasive techniques this index has superior sensitivity and specificity, is largely independent of prevailing haemodynamic conditions and has an unequivocal normal value. Furthermore, it can be used at the time of invasive coronary assessment. FFR measurements are invaluable for evaluation of intermediate coronary lesions but clinical decisions must be based on accurate measurements and an understanding of the limitations of the data supporting its use. This article identifies procedural and clinical issues pertaining to measurement of FFR and identifies potential pitfalls and situations where interpretation can be difficult; for example, the presence of serial stenoses and left main stem disease, its use in specific conditions such as diffuse epicardial disease, microvascular abnormalities, left ventricular dysfunction and acute coronary syndromes.