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

Summary

Non-hyperaemic pressure indices (NHPI), also known as resting pressure indices, allow the evaluation of the functional impact of coronary stenosis using intracoronary pressure guidewires without the need for dedicated drug administration. 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 may be associated with patient discomfort and increased procedural costs and time. Upon demonstration of the efficacy of iFR, other NHPI have been 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 recognised in the revascularisation 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 developed after IFR introduction will be also discussed.

Introduction

Over the last...