Park SH & Koo BK. Clinical application of FFR in bifurcation lesions 279 Figure 1. Concept and measurement of fractional flow reserve (FFR). QSmax: hyperaemic myocardial blood flow in the presence N of a stenosis; Q max: normal hyperaemic myocardial blood flow; Pd: distal coronary pressure; Pa: aortic pressure; Pv: venous pressure; R: hyperaemic myocardial resistance. FFR was < 1% per year.[14] In patients with multivessel dis- ease, an FFR-guided revascularization strategy improved the outcomes of patients and saved cost compared to an angiography-guided strategy.[13,15,16] Therefore, FFR-guided PCI was graded as a class I (level of evidence A) indication in 2010 European Society of Cardiology/European Asso- ciation for Cardio-Thoracic Surgery (ESC/EACTS) guide- lines when objective evidence of vessel-related ischemia was not available.[17] 3 FFR before bifurcation intervention Best clinical practice suggests that revascularization procedures should be based not only on the coronary anatomy but also on the presence of myocardial ischemia.[18,19] Angiographic assessment of the severity of a bifurcation lesion is sometimes difficult due to the inherent limitations of angiography such as vessel overlap, angulation and foreshortening.[20] Therefore, visual estimation of the bifurcation lesion by angiography can be inaccurate to predict the true anatomical or functional significance of the bifurcation lesion. Other invasive anatomical assessment tools such as intravascular ultrasound (IVUS) and optical coherence tomo- graphy can provide detailed anatomical information, but they still have limitations in assessment of the functional significance of a stenosis.[21–24] Previous studies showed that there can be discrepancies between anatomical parameters and functional significance in ostial lesions.[20,25] When FFR and IVUS parameters were compared in pure SB ostial lesions in a study by Koh, et al.,[25] an IVUS minimal luminal area (1.8 mm2) and percent plaque burden (56%) had negative predictive values of 82% and 89% to determine the functional significance, but their positive predictive values were only 50% and 44%, respectively. This limitation of anatomical evaluation seems to be natural considering the variability in vessel size or myocardial territory of SB and the influence of vessel remodeling. In contrast, the functional significance of a bifurcation lesion and the need for revascularization can be reliably assessed by FFR as this physiologic parameter reflects the interaction between the anatomic stenosis and the area of perfusion. Current pressure wires have a similar handling profile to conventional angioplasty guidewires; therefore, FFR can be easily measured in bifurcation lesions both before and after the intervention. However, when FFR of a SB lesion is measured, the influence of proximal and distal stenotic lesions should be taken into account. If a significant stenosis exists at the proximal main branch (MB), SB FFR overestimates the functional severity of the SB lesion due to pressure decrease by the proximal stenosis. On the contrary, if a significant stenosis exists distal to a SB ostial lesion and FFR was measured before that stenosis, FFR underestimates the lesion severity by submaximal flow through the SB ostial lesion by the distal lesion.[26] Therefore, when pre- intervention SB FFR is measured and is significant, the pullback pressure recording during sustained hyperemia should be performed along the length of a coronary artery to assess the functional significance of the SB lesion and to determine the necessity for intervention (Figure 2). In a pure SB ostial lesion, significant pressure step-up occurs only at the SB ostium. However, when SB plaque is connected to the plaque of a proximal MB, it is impossible to discriminate the influence of the MB lesion on SB FFR. Therefore, when SB FFR was measured, the following aspects need to be considered: clinical relevance of a SB compared to a MB, influence of MB plaque and distal SB plaque and the in- ability of pre-intervention SB FFR to predict jailed SB FFR. 4 FFR after MB stenting A SB ostial lesion is generally aggravated after MB stenting (SB jailing). This phenomenon occurs due to the combination of spasm, thrombus, stent struts, plaque shift and carina shift.[27–30] However, there is no validated criterion for SB intervention after MB stenting. Previous bifurcation studies used different angiographic and flow criteria for jailed SB intervention, and resulted in different portions of SB angioplasty (Figure 3). However, angiographic assessment for jailed SB ostial lesion is difficult due to stent radiopacity, image filtering and edge enhancement by digital angiography, along with incomplete mixing of blood and contrast medium because of turbulence, contributing to impaired visualization.[31] http://www.jgc301.com; jgc@mail.sciencep.com | Journal of Geriatric Cardiology