Invasive physiological assessment of coronary disease: non-hyperaemic indices (iFR)

Summary

Non-hyperaemic pressure indices (NHPI), also known as resting pressure indices, constitute a new approach to functional stenosis assessment using intracoronary pressure guidewires. The instantaneous wave free ratio (iFR) was the first NHPI developed to circumvent the dependence of fractional flow reserve (FFR) on maximal coronary hyperaemia, which was associated with patient discomfort and increased procedural costs and time. Upon demonstration of the benefits of iFR, other NHPI have been recently developed. In this chapter we will review the basic principles behind iFR, as well as the validation studies and the results of clinical outcome studies that have established iFR as an evidence-based tool for the assessment of intermediate coronary stenoses recognized in the revascularization guidelines. Data about the use of iFR in special clinical indications such as tandem stenosis, multivessel disease, left main stenosis location, acute coronary syndromes and aortic stenosis will be discussed. Further, we will review the value of iFR to assess disease pattern within a vessel and guide interventions, the co-registration of iFR with coronary angiography, and the assessment of functional PCI results. Other NHPI recently developed will be also discussed.

Introduction

Over the last 20 years the evidence supporting the value of functional assessment of...