Resting Indices of Coronary Lesion Severity: Not Always as Simple as It Seems.

Abstract

Physiological guided percutaneous coronary intervention (PCI) has been demonstrated to result in a better clinical outcome compared with angiographic guidance alone.1 Pressure and Doppler-tipped guide wires that can be used for intracoronary physiological assessment were introduced >2 decades ago. Fractional flow reserve (FFR) has emerged as the most widely used physiological index in current clinical practice. This pressure-only index estimates the functional significance of a coronary stenosis by quantifying the trans-stenotic pressure ratio under hyperemic conditions2 and has been well validated throughout the years.3 However, the prerequisite of inducing stable hyperemia is considered the main practical limitation of FFR measurements that has hampered its embedment in clinical practice. See Article by Cook et al More recently, nonhyperemic pressure-derived indices were introduced to accommodate the need to further simplify physiological assessment; instantaneous wave-free ratio (iFR) and whole-cycle distal to proximal pressure ratio (Pd/Pa). Both indices make use of a trans-stenotic pressure gradient across a stenosis during resting conditions, obtained with conventional pressure wires and, in case of iFR, appropriate software. iFR assesses the pressure ratio in a particular part of the diastole, the wave-free period, where microvascular resistance is constant and minimal.4 Thereby, it relies on the same theoretical framework as FFR. Both iFR and whole-cycle Pd/Pa are shown to have equivalent diagnostic accuracy for the detection of ischemia-generating coronary stenoses when compared with FFR.5 These nonhyperemic pressure-derived indices rely on smaller differences in trans-stenotic pressure than FFR and are thereby more vulnerable to technical and procedural errors affecting distal and aortic pressure. These errors result in pressure drift that in general becomes overt at the end of the procedure when equality …