The use of physiology to guide revascularisation in patients with coronary disease has been demonstrated to improve clinical outcomes and reduce costs.1,2 Despite this, its adoption into clinical practice is very low,3 moreover, when it is employed it is used simplistically – only to determine if the vessel is ischaemic or not.
Recently, several new indices of stenosis severity have been introduced that aim to improve adoption by addressing some of the major limitations of the existing clinical standard – fractional flow reserve (FFR).4,5 The most validated of these indices is the instantaneous wave-free ratio (iFR).4 This review will highlight the clinical problem in terms of hyperaemia-based indices, the physiological background of iFR, overview its validation studies and discuss the potential of ongoing clinical outcome studies.
Finally, the unique potential of hyperaemia-free indices will be discussed; to determine if they can fundamentally transform the use of physiology from a tool that can only ascertain if revascularisation is required into a tool that can also guide how the revascularisation procedure should be performed.