ABC | Volume 114, Nº2, February 2020

Short Editorial Invasive Physiological Assessment: From Binary to Continuous Daniel Chamié 1, 2 and Alexandre Abizaid 1,2,3 Invasive Cardiology Department, Instituto Dante Pazzanese de Cardiololgia, 1 São Paulo, SP – Brazil Invasive Cardiology Department, Hospital do Coração, 2 São Paulo, SP – Brazil Invasive Cardiology Department, Hospital Sírio Libanês, 3 São Paulo, SP – Brazil Short Editorial related to the article: Evaluation of Myocardial Ischemia with iFR (Instantaneous Wave-Free Ratio in the Catheterization Laboratory: A Pilot Study Mailing Address: Daniel Chamié • Invasive Cardiology Department, Instituto Dante Pazzanese de Cardiologia. Avenida Dr. Dante Pazzanese, 500, Ibirapuera. Postal Code 04012-180, São Paulo, SP – Brazil E-mail: daniel.chamie@gmail.com Keywords Myocardial Ischemia; Fractional Flow Reserve; Myocardial Coronary Artery Disease; Coronary Stenosis; Risk Factors; Percutaneous Coronary Intervention. DOI: https://doi.org/10.36660/abc.20200054 Described by Pijls et al., in 1993, and based on extensive validation and robust clinical data, fractional flow reserve (FFR) was incorporated into the guidelines of myocardial revascularization to guide the need for revascularization of angiographically intermediate stenosis in patients with stable coronary artery disease (CAD). 1-3 The broadest arguments for this decision were: (1) by depicting a complex tridimensional structure as a planar silhouette coronary angiography suffers from well-known limitations, it presents large variability in estimating coronary stenosis severity, and it has low ability in predicting the functional significance of epicardial coronary stenoses, and (2) revascularization in stable coronary artery disease based solely on the severity of luminal narrowing, as determined by coronary angiography, does not improve clinical outcomes as compared to optimized medical treatment 8 or versus revascularization of only physiologically significant lesions. 9-11 The central premise of invasive assessment of coronary physiology is to identify myocardial ischemia with superior spatial resolution (per vessel) compared to non-invasive methods (per territory), aiding in the identification of lesions (and, therefore, patients) that are more likely to benefit from revascularization. However, despite the clinical benefits and guideline recommendations, the FFR uptake in clinical practice remains low (<10%) inmost catheterization laboratories around the globe. Costs, time added to procedures, patient discomfort to hyperemic stimulus or contraindications to adenosine use, as well as difficulties in interpretation of physiological traces in certain anatomic situations (e.g., serial/diffuse stenosis), are some of the reasons for FFR underutilization. Recently, the introduction of instantaneous wave‑free ratio (iFR) led to renewed interest in the use of invasive physiology. The iFR is measured at rest – without the need to achieve maximal hyperemia –, which simplifies the use of coronary physiology in several anatomic scenarios, with shorter procedure time and fewer adverse symptoms for the patient. Seven years after its initial description by Sen et al., 12 two large randomized studies documented the non‑inferiority of iFR compared with FFR on the occurrence of adverse clinical outcomes when they were used to guide revascularization of coronary stenoses. 13,14 These results were achieved despite a classification mismatch between FFR and iFR in approximately 20% of the cases. 15 In this issue of the Arquivos Brasileiros de Cardiologia , Vieira et al 16 describe their initial experience with the use of iFR to guide coronary revascularization decision-making in 96 lesions from 52 patients, accumulated for over four years. Out of these, 56 stenoses (58.3%) were graded as intermediate (between 41% and 70%), and 40 (41.7%) were classified as severe (between 71% and 90%), as determined by visual assessment of coronary angiography. In agreement with extensive previous validation, the authors used a cut-off value of iFR of ≤0.89 15 to classify stenoses as hemodynamically significant and decide upon the need for revascularization. Percutaneous coronary intervention (PCI) with stent implantation was the primary outcome used, which was performed in 32% of all studied lesions. However, the median and the interquartile range of iFR observed in intermediate (0.92 [0.82 to 0.94]) and severe (0.79 [0.61 to 1.00]) lesions draw our attention to the fact that a non‑negligible proportion of lesions were treated with stent despite the absence of physiological significance as per the iFR evaluations – particularly those of intermediate severity (Figure 4, Vieira et al. 16 ). These findings corroborate the idea that physiological information is just one (important) piece of the decision-making puzzle, which should take into account other equally important factors, such as clinical presentation, presence, type and frequency of anginal symptoms, target lesion location, left ventricular function and perspective of long-term prognosis. Although relieving significant stenosis through mechanical intervention improves anginal symptoms more effectively than optimal medical treatment, 17,18 this practice does not result in major significant reductions of hard clinical events such as death and myocardial infarction. 8 It is noteworthy that about half the patients with a positive FFR have a favorable long‑term prognosis when maintained on optimal medical therapy alone. 19,20 Thus, there is a significant opportunity for medical optimization of some stable patients regardless of the physiological significance of the lesion under investigation, particularly in asymptomatic or oligosymptomatic individuals with lesions that produce minimal physiological impact. These arguments leave room for disagreements with the outcome adopted by Vieira et al, 16 which was the performance of PCI or not. On the contrary, a much more complex and thorough assessment (including the physiological evaluation) should support the revascularization decision than simply the “positive” or “negative” value of a diagnostic index. 265