Instantaneous wave-free ratio (iFR) is a physiological index that can be obtained at rest without hyperaemic stimulation. iFR is conceptually different from fractional flow reserve (FFR), leading to lively scientific debate about this index.1 Until recently, no data were available on the impact of iFR on clinical outcomes; there still are scarce data on the significance of the situation when these measurements (iFR and FFR) give different results.2,3 Therefore, this poses a fundamental question: what should we do when one index is negative and the other one is positive? The aim of this study was to analyse the correlation between iFR and FFR measurements and its impact on long-term outcome.
We prospectively enrolled patients with stable coronary artery disease who qualified for FFR performance between January and August 2015. Patients had ≥50% stenosis in at least one coronary artery. FFR measurement was performed with the use of adenosine given in intracoronary (IC) boluses (120 µg, 240 µg, or 480 µg) or in intravenous infusion (140 µg/kg/min). Additionally, prior to FFR measurement, iFR measurement was performed. FFR and iFR measurements were performed with Verrata™ Pressure Guide Wire (Philips Volcano, Amsterdam, Netherlands). Clinical follow-up was planned at 12 months.
We enrolled 112 patients, in whom 267 iFR/FFR measurements were performed. The mean age of the population was 67±8 years. Diabetes mellitus was present in 31.25% of patients, hypertension in 62.5%, and 26.7% had a history of prior myocardial infarction. Most measurements were performed in the left anterior descending artery and its branches (71.4%), followed by the left circumflex artery (48.2%), right coronary artery (44.6%), and left main artery (20.5%). One-vessel disease (1-VD) was found in 13.4% of patients, 2-VD in 61.6%, and 3-VD in 25%. Adenosine was given as IC boluses in 87.5% of cases.
Regarding the lesion severity, the correlation between iFR and FFR measurements was r=0.84 (p<0.01), r=0.82 (p<0.01), and r=0.79 (p<0.01) for 50–60%, 61–70%, and 71–89% of lesions, respectively. When analysing the advancement of the disease, the aforementioned correlation was as follows: r=0.85 (p<0.01), r=0.84 (p<0.01), and r=0.58 (p<0.01) for 1-VD, 2-VD, and 3-VD, respectively. Interestingly, we also found differences in correlation regarding the dose of adenosine given: r=0.83 (p<0.01), r=0.82 (p<0.01), and r=0.39 (p<0.01) for 120 µg IC, 240 µg IC, and 480 µg IC, respectively.
In our study, ~35% of procedures ended with percutaneous coronary intervention/coronary artery bypass grafting. At 12 months, the major adverse cardiovascular events (MACE) rate was 6.5%, and the target lesion revascularisation rate was 4.7%. In logistic regression, patients had the best prognosis when both indexes were in agreement (both positive or both negative), and the worst prognosis was in the group with positive FFR and negative iFR, with an odds ratio of 2.93 for MACE.
Why are the results of this study important for physicians and patients? Firstly, this study shows that the use of high doses of adenosine is not necessary, and that further management based on such results does not improve the prognosis. Additionally, higher doses of adenosine are associated with an increased rate of adverse events. In terms of the possibility of changing medical practice, the results showed that stenting with positive FFR when other indexes (e.g. IFR) show no ischaemia is not always necessary.