Search

Background: Myocardial ischaemia results from insufficient coronary blood flow. Computed virtual fractional flow reserve (vFFR) allows quantification of proportional flow loss without the need for invasive pressure-wire testing. In the current study, we describe a novel, conductivity model of side branch flow, referred to as 'leak'. This leak model is a function of taper and local pressure, the latter of which may change radically when focal disease is present. This builds upon previous techniques, which either ignore side branch flow, or rely purely on anatomical factors. This study aimed to describe a new, conductivity model of side branch flow and compare this with established anatomical models., Methods and Results: The novel technique was used to quantify vFFR, distal absolute flow (Qd) and microvascular resistance (CMVR) in 325 idealised 1D models of coronary arteries, modelled from invasive clinical data. Outputs were compared to an established anatomical model of flow. The conductivity model correlated and agreed with the reference model for vFFR (r = 0.895, p < 0.0001; ＋0.02, 95% CI 0.00 to ＋ 0.22), Qd (r = 0.959, p < 0.0001; -5.2 mL/min, 95% CI -52.2 to ＋13.0) and CMVR (r = 0.624, p < 0.0001; ＋50 Woods Units, 95% CI -325 to ＋2549)., Conclusion: Agreement between the two techniques was closest for vFFR, with greater proportional differences seen for Qd and CMVR. The conductivity function assumes vessel taper was optimised for the healthy state and that CMVR was not affected by local disease. The latter may be addressed with further refinement of the technique or inferred from complementary image data. The conductivity technique may represent a refinement of current techniques for modelling coronary side-branch flow. Further work is needed to validate the technique against invasive clinical data., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. This independent research was carried out at the National Institute for Health and Care Research (NIHR) Sheffield Biomedical Research Centre (BRC). The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care., (Crown Copyright © 2024. Published by Elsevier Ltd. All rights reserved.)

Background: Determining the functional significance of each individual coronary lesion in patients with serial coronary stenoses is challenging. It has been proposed that nonhyperemic pressure ratios, such as the instantaneous wave free ratio (iFR) and the ratio of resting distal to proximal coronary pressure (Pd/Pa) are more accurate than fractional flow reserve (FFR) because autoregulation should maintain stable resting coronary flow and avoid hemodynamic interdependence (cross-talk) that occurs during hyperemia. This study aimed to measure the degree of hemodynamic interdependence of iFR, resting Pd/Pa, and FFR in a porcine model of serial coronary stenosis., Methods: In 6 anesthetized female swine, 381 serial coronary stenoses were created in the left anterior descending artery using 2 balloon catheters. The degree of hemodynamic interdependence was calculated by measuring the absolute changes in iFR, resting Pd/Pa, and FFR across the fixed stenosis as the severity of the other stenosis varied., Results: The hemodynamic interdependence of iFR, resting Pd/Pa, and FFR was 0.039±0.048, 0.021±0.026, and 0.034±0.034, respectively (all P <0.001). When the functional significance of serial stenoses was less severe (0.70-0.90 for each index), the hemodynamic interdependence was 0.009±0.020, 0.007±0.013, and 0.017±0.022 for iFR, resting Pd/Pa, and FFR, respectively (all P <0.001). However, in more severe serial coronary stenoses (<0.60 for each index), hemodynamic interdependence was 0.060±0.050, 0.037±0.030, and 0.051±0.037 for iFR, resting Pd/Pa, and FFR, respectively (all P <0.001)., Conclusions: When assessing serial coronary stenoses, nonhyperemic pressure ratios are affected by hemodynamic interdependence. When the functional significance of serial coronary stenoses is severe, the effect is similar to that which is seen with FFR.

Background: The treatment of a coronary bifurcation with a single stent (the provisional stenting technique) is associated with a good outcome in most cases. In the majority of cases, after provisional stenting technique, a residual significant angiographic stenosis is associated with the absence of ischemia when fractional flow reserve (FFR) is measured. Jailing an optical pressure guidewire in the side branch (SB) could potentially reduce unnecessary SB interventions after provisional stenting technique. The aim of this study was to compare distal pressure to aortic pressure ratio (Pd/Pa) measurements between 2 second-generation optical pressure guidewires in bifurcation treatment-a jailed wire (JW) and a second free-floating wire (FW) advanced into the SB after stenting., Methods: In an in vitro bifurcation hydrodynamic model with pressure sensors, a JW was advanced into the SB and the FW into the main branch. Bifurcation stenting is performed with the proximal optimization technique (POT)-side-POT technique using a 3.0 x 22-mm stent, a 4.0 x 12-mm noncompliant balloon for the POT, and a 2.5 x 12-mm semicompliant balloon for the SB opening. The same steps were performed in a second model where a surgical clamp was placed in the main vessel to lower overall absolute values pressures., Results: A strong correlation was found between JW and FW values (Pearson's coefficient, r=0.91). All wires could be safely retrieved., Conclusion: In bifurcation stenting, the Pd/Pa value of a second-generation optical pressure guidewire jailed in the SB is reliable compared with a FW inserted after stent implantation.

Aims: Several invasive techniques are available in clinical practice to assess coronary flow. Nevertheless, the test-retest repeatability of these techniques in a controlled setting has not been reported. Therefore, we sought to evaluate fractional flow reserve (FFR), coronary flow reserve (CFR), index of microvascular resistance (IMR), and absolute coronary blood flow (ABF) with absolute microvascular resistance (AMR) test-retest repeatability using a coronary flow simulator., Methods and Results: Using a coronary flow simulator (FFR WetLab version 2.0; Abbott Vascular, Santa Clara, CA), we created stenoses ranging from 0% to 70%, with 10% increments. Three different flows were established with their hyperemic phases, and two consecutive measurements were obtained, evaluating the following indices: FFR, CFR, IMR, ABF, and AMR, using a pressure/temperature wire and an infusion catheter. One hundred and thirty-eight pairs of measurements were performed. Test-retest reliability was compared in 48 FFR, 18 CFR, 24 IMR, 24 ABF, and 24 AMR. Test-retest repeatability showed excellent reproducibility for FFR, ABF, and AMR; respectively 0.98 (0.97-0.99), 0.92 (0.81-0.97) and 0.91 (0.79-0.96) (P < 0.0001 for all). However, test-retest repeatability was weaker for IMR and poor for CFR; respectively 0.53 (0.16-0.77) (P = 0.006) and 0.27 (-0.26-0.67) (P = 0.30)., Conclusions: Using a coronary flow simulator, FFR and ABF with AMR had excellent test-retest reliability. IMR and CFR demonstrated weaker test-retest reliability., (© 2019 Wiley Periodicals, Inc.)

Background: Pressure measurement for the duration of the wave-free period (WFP) is considered essential for resting-state physiological assessment of coronary stenosis severity using the instantaneous wave-free ratio (iFR)., Objectives: The aim of this study was to compare other diastolic resting indexes to iFR., Methods: In the population of the VERIFY2 (Pd/Pa vs iFR in an Unselected Population Referred for Invasive Angiography) study, iFR calculated by proprietary software (Volcano Harvest, Volcano Corporation, Rancho Cordova, California) was compared with the ratio of resting distal coronary pressure and aortic pressure during the complete duration of diastole (dPR), 25% to 75% of diastole (dPR 25-75 ), and midpoint of diastole (dPR mid ), along with Matlab calculated iFR (iFR matlab ) and iFR-like indexes shortening the length of the WFP by 50 and 100 ms (iFR -50ms and iFR -100ms ), respectively. Mutual differences, Spearman correlations, area under the curve values from receiver-operating characteristic analyses, and diagnostic performance with respect to iFR and fractional flow reserve (FFR) were calculated for all indexes., Results: Median iFR in 197 patients with 257 vessels was 0.91 with an interquartile range of 0.87 to 0.95. The mutual differences (± SD) with iFR were 0.006 ± 0.011 (dPR), 0.001 ± 0.007 (dPR 25-75 ), 0.001 ± 0.008 (dPR mid ), 0.005 ± 0.009 (iFR matlab ), 0.003 ± 0.008 (iFR -50ms ), and 0.001 ± 0.009 (iFR -100ms ). Correlations for all indexes with iFR were >0.99 (p < 0.001 for all). Area under the curve values for predicting iFR were >0.99 for all indexes as well. Diagnostic accuracy compared with FFR was 76% to 77% for all indexes including iFR., Conclusions: All diastolic resting indexes tested were identical to iFR, both numerically and with respect to their agreement with FFR. A numerically equal value to iFR can be determined without restriction to the WFP. Cutoff values, guidelines, and clinical recommendations for iFR can therefore be extended to these other indexes. (Pd/Pa vs iFR in an Unselected Population Referred for Invasive Angiography [VERIFY2]; NCT02377310)., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Objectives: The purpose of this study was to investigate the relationship between angiographic and functional severity of coronary artery stenoses in the FAME (Fractional Flow Reserve Versus Angiography in Multivessel Evaluation) study., Background: It can be difficult to determine on the coronary angiogram which lesions cause ischemia. Revascularization of coronary stenoses that induce ischemia improves a patient's functional status and outcome. For stenoses that do not induce ischemia, however, the benefit of revascularization is less clear., Methods: In the FAME study, routine measurement of the fractional flow reserve (FFR) was compared with angiography for guiding percutaneous coronary intervention in patients with multivessel coronary artery disease. The use of the FFR in addition to angiography significantly reduced the rate of all major adverse cardiac events at 1 year. Of the 1,414 lesions (509 patients) in the FFR-guided arm of the FAME study, 1,329 were successfully assessed by the FFR and are included in this analysis., Results: Before FFR measurement, these lesions were categorized into 50% to 70% (47% of all lesions), 71% to 90% (39% of all lesions), and 91% to 99% (15% of all lesions) diameter stenosis by visual assessment. In the category 50% to 70% stenosis, 35% were functionally significant (FFR 0.80). In the category 71% to 90% stenosis, 80% were functionally significant and 20% were not. In the category of subtotal stenoses, 96% were functionally significant. Of all 509 patients with angiographically defined multivessel disease, only 235 (46%) had functional multivessel disease (>or=2 coronary arteries with an FFR

Objectives: This study sought to validate a new method for direct volumetric blood flow measurement in coronary arteries in animals and in conscious humans during cardiac catheterization., Background: Direct volumetric measurement of blood flow in selective coronary arteries would be useful for studying the coronary circulation., Methods: Based on the principle of thermodilution with continuous low-rate infusion of saline at room temperature, we designed an instrumental setup for direct flow measurement during cardiac catheterization. A 2.8-F infusion catheter and a standard 0.014-inch sensor-tipped pressure/temperature guidewire were used to calculate absolute flow (Q(thermo)) in a coronary artery from the infusion rate of saline, temperature of the saline at the tip of the infusion catheter, and distal blood temperature during infusion. The method was tested over a wide range of flow rates in 5 chronically instrumented dogs and in 35 patients referred for physiological assessment of a coronary stenosis or for percutaneous coronary intervention., Results: Thermodilution-derived flow corresponded well with true flow (Q) in all dogs (Q(thermo) = 0.73 Q + 42 ml/min; R(2) = 0.72). Reproducibility was excellent (Q(thermo,)(1) = 0.96 x Q(thermo,)(2) + 3 ml/min; R(2) = 0.89). The measurements were independent of infusion rate and sensor position as predicted by theory. In the humans, a good agreement was found between increase of thermodilution-derived volumetric blood flow after percutaneous coronary intervention and increase of fractional flow reserve (R(2) = 0.84); reproducibility of the measurements was excellent (Q(thermo,)(1) = 1.0 Q(thermo,)(2) + 0.9 ml/min, R(2) = 0.97), and the measurements were independent of infusion rate and sensor position., Conclusions: Using a suitable infusion catheter and a 0.014-inch sensor-tipped guidewire for measurement of coronary pressure and temperature, volumetric blood flow can be directly measured in selective coronary arteries during cardiac catheterization.

Objectives: The objective of this study was to investigate the underlying stenosis severity of the culprit lesion in acute myocardial infarction., Background: It is widely believed that myocardial infarction often occurs in angiographically mild luminal stenosis. This, however, is in contradiction with experience from interventional practice in primary PCI., Methods: We performed quantitative coronary angiography (QCA) in 250 consecutive patients referred for acute percutaneous coronary intervention (PCI) because of acute myocardial infarction (AMI). Fundamental for analysis was that a realistic estimate of underlying luminal narrowing before the infarction could be made angiographically that QCA could be performed and that one of two criteria was met: (1) spontaneous reflow allowing assessment of the lumen proximal and distal to the culprit lesion, or (2) coronary artery closed at arrival but reflow after uncomplicated wiring allowing assessment of the lumen proximal and distal to the culprit lesion., Results: Of 250 consecutive patients (mean age 61.7 +/- 12.7 years, 48 women) referred for acute PCI, 156 patients (62%) fulfilled at least one of the above criteria for reliable QCA. In 151 of these patients (96%) the severity of the underlying stenosis was >50% and in 103 (66%) it was >70%. There were no differences in stenosis severity between the left anterior descending [LAD, (72 +/- 13)%, n = 57], left circumflex [Cx, (74 +/- 10)%, n = 20], and right coronary artery territory [RCA, (74 +/- 12)%, n = 76] (ANOVA, P = 0.76). There were no differences in stenosis severity between women [(73 +/- 13)%, n = 36] and men [(75 +/- 11)%, n = 120; P = 0.35]., Conclusion: In contrast to what is often believed, the majority of myocardial infarctions occurs in significant stenosis., (Copyright 2007 Wiley-Liss, Inc.)

Objectives: The purpose of this study was to investigate the appropriateness of stenting a functionally nonsignificant stenosis., Background: Percutaneous coronary intervention (PCI) of an intermediate stenosis without evidence of ischemia is often performed, but its benefit is unproven. Coronary pressure-derived fractional flow reserve (FFR) is an invasive index used to identify a stenosis responsible for reversible ischemia., Methods: In 325 patients scheduled for PCI of an intermediate stenosis, FFR was measured just before the planned intervention. If FFR was >or =0.75, patients were randomly assigned to deferral (Defer group; n = 91) or performance (Perform group; n = 90) of PCI. If FFR was <0.75, PCI was performed as planned (Reference group; n = 144). Clinical follow-up was 5 years., Results: There were no differences in baseline clinical characteristics between the 3 groups. Complete follow-up was obtained in 98% of the patients. Event-free survival was not different between the Defer and Perform groups (80% and 73%, respectively; p = 0.52), but was significantly worse in the Reference group (63%; p = 0.03). The composite rate of cardiac death and acute myocardial infarction in the Defer, Perform, and Reference groups was 3.3%, 7.9%, and 15.7%, respectively (p = 0.21 for Defer vs. Perform group; p = 0.003 for the Reference vs. both other groups). The percentage of patients free from chest pain at follow-up was not different between the Defer and Perform groups., Conclusions: Five-year outcome after deferral of PCI of an intermediate coronary stenosis based on FFR >/=0.75 is excellent. The risk of cardiac death or myocardial infarction related to this stenosis is <1% per year and not decreased by stenting.

Aims: The aim of this study was to investigate the physiologic parameters: fractional flow reserve (FFR), hyperaemic trans-stent gradient (HTG), and wall shear stress (WSS) at implantation and at 6-month follow-up in the drug-eluting sirolimus stent and in its bare metal counterpart implanted in pairs within the same patient., Methods and Results: Twenty patients, accepted for percutaneous coronary intervention of at least two coronary arteries with comparable vessel and stenosis characteristics, received at random one sirolimus-eluting stent and one bare metal stent (BMS). Coronary pressure, FFR, HTG, and WSS were measured just after stent implantation and at 6-month follow-up. At 6-month follow-up, FFR was significantly higher in the sirolimus group compared with the bare metal group (0.91+/-0.05 vs. 0.83+/-0.10, P=0.027) and HTG was significantly lower (1.2+/-1.2 vs. 7.5+/-8.1 mmHg, P<0.001). In-stent WSS at 6 months remained normal in the sirolimus group but was elevated in the bare metal group (1.6+/-0.7 vs 3.9+/-3.1 Pa, respectively, P=0.003)., Conclusion: The physiologic characteristics of the drug-eluting sirolimus stents were superior to those of the equivalent BMS. Six months after implantation, FFR was significantly higher, HTG was significantly lower in arteries treated by a sirolimus stent, and normal WSS was maintained within the drug-eluting stent.