INSTANTANEOUS WAVE-FREE RATIO (IFR)-AN EMERGING TECHNIQUE

Abstract

The advent of fractional flow reserve (FFR)changed the landscape of viewing andinterpreting coronary artery lesions, particularly intermediate ones.¹ FFR isdefined as ratio of the pressure distal to a stenosis (Pd) relative to the pressureproximal to the stenosis (Pa). For FFR to be accurate intra-coronary resistancemust be constant and minimal so that the change in pressure across a lesion isproportional to change in blood flow, this requires hyperemia induced by avasodilating agent typically adenosine. The use of coronary physiology to guiderevascularization has been found to improve patient outcomes and defer stentingof nonischemic lesions compared with angio-graphic assessment.

National Cardiovascular Data Registry (NCDR), FFR evaluation across US was being performed in only 6% of intermediatelesions. The lack of utilization primarily stems from the cost and administration of adenosine. Adenosine is contraindicated inpatients with asthma, severe COPD, bradycardia and hypotension. Additionally, it may require central venous access.

In IFR-SWEDEHEART, 2,037 patients were enrolled at 15 centers in Sweden, Denmark and Iceland. A total of 2,019 patients inthis study were treated according to protocol, with 1,012 patients receiving iFR and 1,007 receiving FFR. This documented asubstantial reduction in patient discomfort, with just 3 % of iFR reporting discomfort compared to 68 % of FFR. A primary endpointevent occurred in 68 patients (6.7%) in iFR group and in 61 patients (6.1%) in FFR group (95% confidence interval [CI],−1.5 to 2.8; p=0.007 for noninferiority; hazard ratio, 1.12; 95% CI, 0.79 to 1.58; p=0.53). The rates of myocardial infarction,target-lesion revascularization, restenosis, and stent thrombosis did not differ significantly between the two groups. Asignificantly higher proportion of patients in the FFR group than in the iFR group reported chest discomfort during the procedure.Significant lesions were found in 29.2 percent of patients undergoing iFR and 36.8 percent undergoing FFR.

To conclude, if there is a significant lesion that strongly correlates with stress tests, then one should go ahead and revascularizethe indicated lesion. However, if the lesion is not absolutely correlating, then one should opt for iFR/FFR evaluation. With reducedprocedure length, requirement of fewer stents and elimination of need for a vasodilator drug should translate into significant costsavings iFR appears to be more promising technology.