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Specialized Circulations in Susceptible Tissues
Published in Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos, McDonald's Blood Flow in Arteries, 2022
The notion of instantaneous wave-free ratio (iFR) arose out of analysis of ascending aortic waveforms by Kim Parker, biomedical engineer at Imperial College in London and was first published in 1990 (Parker and Jones, 1990). This compared forward and backward pressure and flow wave using the Method of Characteristics, which had been introduced by the well respected authorities in hydrodynamics Streeter, Keitzer and Bohr in 1963 (Streeter et al., 1963); see also Streeter’s textbook Fluid Mechanics (Streeter, 1951). Streeter’s work was undertaken around the time that McDonald and Taylor’s work on vascular impedance was first published, expressing pressure and flow relationships in the arterial tree. Streeter and colleagues did not pursue the work on Characteristics in the cardiovascular field, and neither did McDonald, Taylor or their colleagues, but Kim Parker, Alan Hughes and Justin Davies applied the method to analysis of pressure waves recorded in the ascending aorta. This approach was highly controversial and still is. Westerhof et al. (2018) summarized this method and other concepts arising from it in a booklet Snapshots of Hemodynamics. Other concepts included the “reservoir-wave concept”, a “wave-free period” (in diastole) and concepts of coronary “compressions” and “suction” waves at the beginning and end of systole. Considerable controversy resulted (Westerhof et al., 2015; Smolich and Mynard, 2016). The approach appears to violate the Laws of Newton relating movement of blood to amplitude and direction of applied force.
Physiological assessment of coronary lesion severity
Published in John Edward Boland, David W. M. Muller, Interventional Cardiology and Cardiac Catheterisation, 2019
Usaid Allahwala, Ravinay Bhindi
The instantaneous wave-free ratio (iFR) is a resting index used to assess severity of an intracoronary stenosis. It measures the ratio of Pd to the Pa during an isolated period of diastole (the ‘wave-free period’). A cut-off value of 0.89 has been identified as a marker of ischaemia. It is an attractive alternative to FFR because it does not require hyperemia, and therefore has a lower incidence of patient discomfort, side effects, and shorter procedural time. In the DEFINE-FLAIR3 and iFR-SWEDEHEART14 trials, iFR was found to be non-inferior to FFR for guiding revascularisation with respect to MACE.
Validity and correlation of quantitative flow ratio with fractional flow reserve for assessment of intermediate coronary lesions
Published in Acta Cardiologica, 2023
Ganesh Kasinadhuni, Akash Batta, Atit A. Gawalkar, Sudhanshu Budakoty, Ankush Gupta, Rajesh Vijayvergiya
Coronary angiography is the gold standard to establish for the diagnosis and extent of coronary artery disease (CAD). A percentage diameter stenosis (%DS) of >50% as assessed by quantitative coronary angiography (QCA) is considered a significant lesion for further intervention [1]. However, QCA cannot assess the functional significance of an intermediate lesion of 50–90%DS. Various hyperaemic and non-hyperaemic physiological indices are in practice to assess the functional significance of these intermediate lesions. It includes invasive pressure wire-based techniques such as fractional flow reserve (FFR), instantaneous wave-free ratio (iFR) and resting full-cycle ratio (RFR) [2]. FFR remains the gold standard among them; however, it is underutilised due to its invasive technique and adenosine related side effects [2–4]. Non-hyperaemic pressure wire-based ratios (NHPR) [5] such as iFR and RFR eliminates the use of adenosine, reduces the procedural time and the cost, but is similar to FFR in their invasive approach. There are few angiography derived ratios such as quantitative flow ratio (QFR: Medis Medical Imaging Systems, Leiden, the Netherlands), FFRangio (CathWorks, Kfar-Saba, Israel), vFFR (Pie Medical Imaging, Maastricht, the Netherlands), which do not require pressure wire and their results are also comparable with FFR [6]. In the present study, we correlate and validate the angiography based QFR with FFR in patients with intermediate coronary lesions.
Functional assessment of coronary stenosis: an overview of available techniques. Is quantitative flow ratio a step to the future?
Published in Expert Review of Cardiovascular Therapy, 2018
Arturo Cesaro, Felice Gragnano, Domenico Di Girolamo, Elisabetta Moscarella, Vincenzo Diana, Ivana Pariggiano, Alfonso Alfieri, Rocco Perrotta, Pasquale Golino, Francesco Cesaro, Giuseppe Mercone, Gianluca Campo, Paolo Calabrò
In the VERification of Instantaneous Wave-Free Ratio and FFR for the Assessment of Coronary Artery Stenosis Severity in EverydaY Practice (VERIFY) study [58], and in the VERIFY 2 Study [60] the results affirmed that there was no diagnostic advantage to utilizing an iFR-guided revascularization strategy compared with FFR. This initial studies did not give the expected results, probably because the number of patients was not sufficient. The most important results derived from the iFR-SWEDEHEART [61] and the Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularisation (DEFINE-FLAIR) studies [62] that aimed to investigate whether iFR was non-inferior to FFR concerning clinical outcomes between patients who have an indication for assessment of coronary artery stenosis [63,64]. The iFR-SWEDEHEART study showed that there was no difference respect to the rate of MACE at 12 months in patients with stable angina or an acute coronary syndrome, with iFR-guided revascularization strategy compared with an FFR-guided revascularization strategy. In the same direction were the results of the DEFINE-FLAIR study [62]. Also, in this case, coronary revascularization guided by iFR was non-inferior to revascularization guided by FFR concerning the risk of MACE at 1 year. However, based on these results, iFR stands as a safe tool and usable for i.c. functional assessment when the administration of adenosine is not desirable (Table 1).
Endothelial dysfunction assessed by digital tonometry and discrepancy between fraction flow reserve and instantaneous wave free ratio
Published in Acta Cardiologica, 2020
Stepan Jerabek, David Zemanek, Jan Pudil, Kristyna Bayerova, Ales Kral, Karel Kopriva, Yoshiaki Kawase, Hiroyuki Omori, Toru Tanigaki, Zhi Chen, Alexandra Vodzinska, Marian Branny, Hitoshi Matsuo, Martin Mates, Milan Sonka, Tomas Kovarnik
Fractional flow reserve (FFR) and instantaneous wave free ratio (iFR) are methods for determining of the hemodynamic significance of a coronary stenosis, which are labeled as IA in current guidelines for revascularization [1]. Both indexes measure the pressure gradient across the stenosis. FFR represents the hyperemic index, because it measures the pressure gradient across the stenosis during hyperemia [2]. Instantaneous wave free ratio is called a resting index and measures the pressure gradient during the resting condition in the middle part of the diastoly [3]. The correlation between FFR and iFR was found to be around 80% [4]. However, this correlation is much worse when we compare only measurements close to cut-off points for FFR and iFR examinations [4].