Experimental basis of determining maximum coronary, myocardial, and collateral blood flow by pressure measurements for assessing functional stenosis severity before and after percutaneous transluminal coronary angioplasty

FFRCT and CT perfusion: A review on the evaluation of functional impact of coronary artery stenosis by cardiac CT

Coronary computed tomography angiography (CCTA) is at the frontline of the diagnostic strategies to detect coronary artery disease (CAD). Anatomical information have proven to be insufficient to detect hemodynamic significant epicardial stenosis. In the present invited review we discuss on FFR_CT and stress CTP, emerging technologies for an accurate and comprehensive evaluation of patients with suspected CAD, offering both anatomical (i.e. luminal and plaque) and functional assessment in one single technique.

Pressure Recovery in the Left Main Stenosis

A 76-year-old male patient with dyspnea was referred on a suspicion of coronary artery disease. A coronary computed tomography angiography (CTA) revealed a distal left main (LM) stenosis and in the right (right coronary artery [RCA]), left circumflex (LCX) and left anterior descending (LAD) coronary arteries stenosis could not be excluded. CTA-derived fractional flow reserve (FFRct) was 0.75, 0.72, 0.74, 0.86, and 0.94 in the LM, LAD, LCX, ramus, and RCA, respectively. Invasive coronary angiography confirmed a stenosis in the LM and LAD. FFR was 0.73 and 0.85 in the LCX and ramus, respectively. The patient was referred for coronary artery bypass surgery. The FFR and FFRct values in the ramus demonstrate the phenomenon of pressure recovery. This case shows that preserved FFR and FFRct cannot always be used to exclude the hemodynamic significance of upstream coronary lesions.

Feasibility and safety of jailed-pressure wire technique using durable optical fiber pressure wire for intervention of coronary bifurcation lesions

OBJECTIVES

The objective was to evaluate the safety, feasibility, and accuracy of the jailed-pressure wire technique using a durable optical fiber-based pressure wire with high-pressure dilatation using a non-compliant balloon after main vessel stenting.

BACKGROUND

Fractional flow reserve (FFR) information can help interventionists determine whether they should treat a jailed-side branch (SB). However, re-crossing a pressure wire into a jailed-SB is sometimes technically difficult.

METHODS

Fifty-one consecutive lesions from 48 patients who underwent the jailed-pressure wire technique were retrospectively investigated. The primary endpoint was complication rate and secondary endpoints included success rate of FFR measurement, incidence of wire disruption, and final drift rate. The usability of FFR for percutaneous coronary intervention of coronary bifurcation lesion was also evaluated.

RESULTS

Median age of the patients was 69 years and 80.4% were men. The most frequent underlying disease was stable angina (70.6%) and 68.6% were type B2 lesions. Our main findings were: the procedure was performed successfully in all cases without any complications or wire disruption, FFR could be measured without significant final drift in 95.9% of cases, and FFR measurements helped interventionists determine whether to perform a final kissing balloon dilatation in 49.0% cases.

CONCLUSIONS

The jailed-pressure wire technique using a durable optical fiber-based pressure wire with high-pressure post-dilatation maneuver was safe, feasible, and accurate.

The Human Coronary Collateral Circulation, Its Extracardiac Anastomoses and Their Therapeutic Promotion

Cardiovascular disease remains the leading global cause of death, and the number of patients with coronary artery disease (CAD) and exhausted therapeutic options (i.e., percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) and medical treatment) is on the rise. Therefore, the evaluation of new therapeutic approaches to offer an alternative treatment strategy for these patients is necessary. A promising research field is the promotion of the coronary collateral circulation, an arterio-arterial network able to prevent or reduce myocardial ischemia in CAD. This review summarizes the basic principles of the human coronary collateral circulation, its extracardiac anastomoses as well as the different therapeutic approaches, especially that of stimulating the extracardiac collateral circulation via permanent occlusion of the internal mammary arteries.

Methodology for Hemodynamic Assessment of a Three-Dimensional Printed Patient-Specific Vascular Test Device

Assessing hemodynamics in vasculature is important for the development of cardiovascular diagnostic parameters and evaluation of medical devices. Benchtop experiments are a safe and comprehensive preclinical method for testing new diagnostic endpoints and devices within a controlled environment. Recent advances in three-dimensional (3D) printing have enhanced benchtop tests by allowing generation of patient-specific and pathophysiologic conditions. We used 3D printing, coupled with image processing and computer-aided design (CAD), to develop a patient-specific vascular test device from clinical data. The proximal pulmonary artery (PA) tree including the main, left, and right pulmonary arteries, with a stenosis within the left PA was selected as a representative anatomy for developing the vascular test device. Three test devices representing clinically relevant stenosis severities, 90%, 80%, and 70% area stenosis, were evaluated at different cardiac outputs (COs). A mock circulatory loop (MCL) generating pathophysiologic pulmonary pressure and flow was used to evaluate the hemodynamics within the devices. The dimensionless pressure drop–velocity ratio characteristic curves for the three stenosis severities were obtained. At a fixed CO, the dimensionless pressure drop increased nonlinearly with an increase in (a) the velocity ratio for a fixed stenosis severity and (b) the stenosis severity at a specific velocity ratio. The dimensionless pressure drop observed in vivo was similar (within 1%) to that measured in moderate area stenosis of 70% because both flows were viscous dominated. The hemodynamics of the 3D printed test device can be used for evaluating diagnostic endpoints and medical devices in a preclinical setting under realistic conditions.

Applicability and Interpretation of Coronary Physiology in the Setting of a Chronic Total Occlusion

Concurrent coronary artery disease in a vessel remote from a chronic total occlusion (CTO) is common and presents a management dilemma. While the use of adjunctive coronary physiology to guide revascularization is now commonplace in the catheterization laboratory, the presence of a CTO provides a unique and specific situation whereby the physiological assessment is more complex and relies on theoretical assumptions. Broadly, the physiological assessment of a CTO relies on assessing the function and regression of collaterals, the assessment of the microcirculation, the impact of collateral steal as well as assessing the severity of a lesion in the donor vessel (the vessel supplying the majority of collaterals to the CTO). Recent studies have shown that physiological assessment of the donor vessel in the setting of a CTO may overestimate the severity of stenosis, and that after revascularization of a CTO, the index of ischemia may increase, potentially altering the need for revascularization. In this review article, we present the current literature on physiological assessment of patients with a CTO, management recommendations and identify areas for ongoing research.

Consensus document for invasive coronary physiologic assessment in Asia-Pacific countries

BACKGROUND

Currently, invasive physiologic assessment such as fractional flow reserve is widely used worldwide with different adoption rates around the globe. Patient characteristics and physician preferences often differ in the Asia-Pacific (APAC) region with respect to treatment strategy, techniques, lesion complexity, access to coronary physiology and imaging devices, as well as patient management. Thus, there is a need to construct a consensus document on recommendations for use of physiology-guided percutaneous coronary intervention (PCI) in APAC populations. This document serves as an overview of recommendations describing the best practices for APAC populations to achieve more consistent and optimal clinical outcomes.

METHODS AND RESULTS

A comprehensive multiple-choice questionnaire was provided to 20 interven- tional cardiologists from 10 countries in the APAC region. Clinical evidence, tips and techniques, and clinical situations for the use of physiology-guided PCI in APAC were reviewed and used to propose key recommendations. There are suggestions to continue to develop evidence for lesion and patient types that will benefit from physiology, develop directions for future research in health economics and local data, develop appropriate use criteria in different countries, and emphasize the importance of education of all stakeholders. A consensus recommendation to enhance the penetration of invasive physiology-based therapy was to adopt the 5E approach: Evidence, Education, Expand hardware, Economics and Expert consensus.

CONCLUSIONS

This consensus document and recommendations support interventional fellows and cardiologists, hospital administrators, patients, and medical device companies to build confidence and encourage wider implementation of invasive coronary physiology-guided therapy in the APAC region.

Association Between Physiological Stenosis Severity and Angina-Limited Exercise Time in Patients With Stable Coronary Artery Disease

Importance

Physiological stenosis assessment is recommended to guide percutaneous coronary intervention (PCI) in patients with stable angina.

Objective

To determine the association between all commonly used indices of physiological stenosis severity and angina-limited exercise time in patients with stable angina.

Design, Setting, and Participants

This cohort study included data (without follow-up) collected over 1 year from 2 cardiac hospitals. Selected patients with stable angina and physiologically severe single-vessel coronary artery disease presenting for clinically driven elective PCI were included.

Exposures

Fractional flow reserve (FFR), instantaneous wave-free ratio (iFR), hyperemic stenosis resistance (HSR), and coronary flow reserve (CFR) were measured invasively. Immediately after this, patients maximally exercised on a catheter-table-mounted supine ergometer until they developed rate-limiting angina. Subsequent PCI was performed in most patients, followed by repeat maximal supine exercise testing.

Main Outcomes and Measures

Associations between FFR, iFR, HSR, CFR, and angina-limited exercise time were assessed using linear regression and Pearson correlation coefficients. Additionally, the associations between the post-PCI increment in exercise time and baseline FFR, iFR, HSR, and CFR were assessed.

Results

Twenty-three patients (21 [91.3%] of whom were male; mean [SD] age, 60.6 [8.1] years) completed the pre-PCI component of the study protocol. Mean (SD) stenosis diameter was 74.6% (10.4%). Median (interquartile range [IQR]) values were 0.54 (0.44-0.72) for FFR, 0.53 (0.38-0.83) for iFR, 1.67 (0.84-3.16) for HSR, and 1.35 (1.11-1.63) for CFR. Mean (SD) angina-limited exercise time was 144 (77) seconds. Anatomical stenosis characteristics were not significantly associated with angina-limited exercise time. Conversely, FFR (R2 = 0.27; P = .01), iFR (R2 = 0.46; P < .001), HSR (R2 = 0.39; P < .01), and CFR (R2 = 0.16; P < .05) were all associated with angina-limited exercise time. Twenty-one patients (19 [90.5%] of whom were male; mean [SD] age, 60.1 [8.2] years) competed the full protocol of PCI, post-PCI physiological assessment, and post-PCI maximal exercise. After PCI, the median (IQR) FFR rose to 0.91 (0.85-0.96), median (IQR) iFR to 0.98 (0.94-0.99), and median (IQR) CFR to 2.73 (2.50-3.12), while the median (IQR) HSR fell to 0.16 (0.06-0.37) (P < .001 for all). The post-PCI increment in exercise time was most significantly associated with baseline iFR (R2 = 0.26; P = .02).

Conclusions and Relevance

In a selected group of patients with severe, single-vessel stable angina, FFR, iFR, HSR, and CFR were all modestly correlated with angina-limited exercise time to varying degrees. Notwithstanding the limited sample size, no clear association was demonstrated between anatomical stenosis severity and angina-limited exercise time.

Comparison of hyperemic efficacy between femoral and antecubital fossa vein adenosine infusion for fractional flow reserve assessment

Introduction

Intravenous infusion of adenosine via the femoral vein is commonly used to achieve maximum hyperemia for fractional flow reserve (FFR) assessment in the catheterization laboratory. In the era of transradial access for coronary interventions, obtaining additional venous access with sheath insertion in the groin is unpractical and may be associated with a higher risk of bleeding complications. In a vast majority of cases, patients scheduled for the catheterization laboratory are already equipped with peripheral vein access in antecubital fossa vein. However, only limited data exist to support non-central vein infusion of adenosine instead of the femoral vein for FFR assessment.

Aim

To compare infusion of adenosine via a central versus a peripheral vein for the assessment of peak FFR.

Material and methods

We enrolled 50 consecutive patients with 125 borderline coronary lesions that were assessed by FFR using adenosine femoral and antecubital vein infusion of 140 µg/kg/min.

Results

Physiological severity assessed with femoral vein adenosine infusion at 140 µg/kg/min was mean 0.82 ±0.09, and with antecubital vein adenosine infusion at 140 µg/kg/min was 0.82 ±0.09. The mean time from initiation of adenosine infusion to maximal stable hyperemia was significantly shorter for 140 µg/kg/min femoral vein infusion as compared to antecubital vein infusion (49 ±19 s vs. 68 ±23 s; p < 0.001). There was a strong correlation between FFR values obtained from 140 µg/kg/min femoral and antecubital vein infusion (r = 0.99; p < 0.001).

Conclusions

Antecubital vein adenosine infusion achieved FFR values are very similar to those obtained using femoral vein adenosine administration. However, time to maximal hyperemia is longer with infusion via the antecubital vein.

Effect of Tube Voltage on Diagnostic Performance of Fractional Flow Reserve Derived From Coronary CT Angiography With Machine Learning: Results From the MACHINE Registry

OBJECTIVE. Coronary CT angiography (CCTA)-based methods allow noninvasive estimation of fractional flow reserve (cFFR), recently through use of a machine learning (ML) algorithm (cFFR_ML). However, attenuation values vary according to the tube voltage used, and it has not been shown whether this significantly affects the diagnostic performance of cFFR and cFFR_ML. Therefore, the purpose of this study is to retrospectively evaluate the effect of tube voltage on the diagnostic performance of cFFR_ML. MATERIALS AND METHODS. A total of 525 coronary vessels in 351 patients identified in the MACHINE consortium registry were evaluated in terms of invasively measured FFR and cFFR_ML. CCTA examinations were performed with a tube voltage of 80, 100, or 120 kVp. For each tube voltage value, correlation (assessed by Spearman rank correlation coefficient), agreement (evaluated by intraclass correlation coefficient and Bland-Altman plot analysis), and diagnostic performance (based on ROC AUC value, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy) of the cFFR_ML in terms of detection of significant stenosis were calculated. RESULTS. For tube voltages of 80, 100, and 120 kVp, the Spearman correlation coefficient for cFFR_ML in relation to the invasively measured FFR value was ρ = 0.684, ρ = 0.622, and ρ = 0.669, respectively (p < 0.001 for all). The corresponding intraclass correlation coefficient was 0.78, 0.76, and 0.77, respectively (p < 0.001 for all). Sensitivity was 100.0%, 73.5%, and 85.0%, and specificity was 76.2%, 79.0%, and 72.8% for tube voltages of 80, 100, and 120 kVp, respectively. The ROC AUC value was 0.90, 0.82, and 0.80 for 80, 100, and 120 kVp, respectively (p < 0.001 for all). CONCLUSION. CCTA-derived cFFR_ML is a robust method, and its performance does not vary significantly between examinations performed using tube voltages of 100 kVp and 120 kVp. However, because of rapid advancements in CT and postprocessing technology, further research is needed.

Diastolic-systolic velocity ratio to detect coronary stenoses under physiological resting conditions: a mechanistic study

Objective

Diastolic-systolic velocity ratio (DSVR) is a resting index to assess stenoses in the left anterior descending artery (LAD). DSVR can be measured by echocardiographic or intracoronary Doppler flow velocity. The objective of this cohort study was to elucidate the fundamental rationale underlying the decreased DSVR in coronary stenoses.

Methods

In cohort 1, simultaneous measurements of intracoronary Doppler flow velocity and pressure were acquired in the LAD of 228 stable patients. Phasic stenosis resistance, microvascular resistance and total vascular resistance (defined as stenosis and microvascular resistance combined) were studied during physiological resting conditions. Stenoses were classified according to severity by strata of 0.10 fractional flow reserve (FFR) units.

Results

DSVR was decreased in stenoses with lower FFR. Stenosis resistance was equal in systole and diastole for every FFR stratum. Microvascular resistance was consistently higher during systole than diastole. In lower FFR strata, stenosis resistance as a percentage of the total vascular resistance increases both during systole and diastole. The difference between the stenosis resistance as a percentage of total vascular resistance during systole and diastole increases for lower FFR strata, with an accompanying rise in diastolic-systolic resistance ratio. A significant inverse correlation was observed between DSVR and the diastolic-systolic resistance ratio (r=0.91, p<0.001). In cohort 2 (n=23), DSVR was measured both invasively and non-invasively by transthoracic echocardiography, yielding a good correlation (r=0.82, p<0.001).

Conclusions

The rationale by which DSVR is decreased distal to coronary stenoses is dependent on a comparatively higher influence of the increased stenosis resistance on total vascular resistance during diastole than systole.

Meta-Analysis of Diagnostic Performance of Instantaneous Wave-Free Ratio versus Quantitative Flow Ratio for Detecting the Functional Significance of Coronary Stenosis

Background

Fractional flow reserve (FFR), as a functional measurement of coronary stenosis, is recommended for guiding revascularization in intermediate coronary lesions. However, it still remains underutilized for potential reasons including time consumption, costs, or contraindications associated with adenosine administration. Here we performed this meta-analysis to assess the diagnostic performance of two adenosine-free indices, instantaneous wave free-ratio (iFR), and quantitative flow ratio (QFR) in evaluating coronary stenosis severity with FFR as the reference standard.

Methods

PubMed, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) were searched to include relevant studies with the diagnostic accuracy of iFR or QFR referenced to FFR. A bivariate model was applied to pool diagnostic parameters. We used Cochran's Q test and I² index to assess heterogeneity and identify the potential source of heterogeneity by meta-regression.

Results

A total of 8213 lesions from 28 studies (19 for iFR and 9 for QFR) were included in this meta-analysis. The pooled sensitivity and specificity were 0.79 (95% CI, 0.75 to 0.83) and 0.85 (95% CI, 0.82 to 0.87) for iFR and 0.90 (95% CI, 0.84 to 0.93) and 0.88 (95% CI, 0.86 to 0.90) for QFR, respectively. Significantly higher sensitivity and specificity were observed in the bivariate analysis for QFR than for iFR (P < 0.001 for both). The area under summary receiver-operating curve of iFR and QFR was 0.89 (95% CI, 0.86 to 0.92) and 0.92 (95% CI, 0.89 to 0.94).

Conclusion

Evidence suggests that both of the two indices have good performance in detecting functional ischemia of coronary arteries and QFR might be a promising method without requiring the pressure wire. Further application of QFR may potentially provide important information to clinicians in the assessment of coronary lesions.

Coronary circulation: Pressure/flow parameters for assessment of ischemic heart disease

Both invasive and non-invasive parameters have been reported for assessment of the physiological status of the coronary circulation. Fractional flow reserve and coronary (or myocardial) flow reserve may be obtained by invasive or non-invasive means. These metrics of coronary stenosis severity have achieved wide clinical acceptance for guiding revascularization decisions and risk stratification. Other indices are obtained invasively (e.g., instantaneous wave-free ratio, iFR; hyperemic stenosis resistance) or non-invasively (e.g., PET absolute myocardial blood flow (mL/min/g)) and have been used for the same purposes. Both iFR, and whole-cycle distal coronary to aortic mean pressure (Pd/Pa) are measured under basal condition and used for assessment of hemodynamic stenosis severity as is index of basal stenosis resistance (BSR). These metrics typically are dichotomized at an empirically derived cut point into "normal" and "abnormal" categories for purposes of clinical decision making and data analysis. Once dichotomized the indices do not always point in the same direction and so confusion may arise. This review, therefore, will present basic principles relevant to understanding commonly employed metrics of the physiological status of the coronary circulation, potential strengths and weaknesses, and hopefully an improved appreciation of the clinical information provided by each.

Clinical Outcomes Data for Instantaneous Wave-Free Ratio-Guided Percutaneous Coronary Intervention

Instantaneous wave-free ratio (iFR) is a vasodilator-free index of coronary blood flow used for revascularization decision-making. iFR-based revascularization also had a decreased rate of adverse effects from vasodilators, shorter procedure times, and lower revascularization rates. iFR-pullback predicts post-percutaneous coronary intervention physiologic outcomes in tandem and diffuse coronary lesions. iFR may be particularly useful in patients with potential adenosine resistance, contraindications to adenosine, and multivessel or serial lesions. iFR is a useful tool both with and without fractional-flow reserve for revascularization planning.

Novel predictor of target vessel revascularization after coronary stent implantation: Intraluminal intensity of blood speckle on intravascular ultrasound

BACKGROUND

The difference in intraluminal intensity of blood speckle (IBS) on integrated backscatter-intravascular ultrasound (IB-IVUS) across the coronary artery stenosis (i.e., ΔIBS) has been reported to negatively correlate with fractional flow reserve. Fractional flow reserve after coronary stenting is known as a predictor of target vessel revascularization (TVR). However, the relation between ΔIBS and TVR is unclear.

METHODS

Seven hundred and three vessels which underwent percutaneous coronary intervention with stents were screened. Vessels without IVUS-guidance and follow-up information were excluded. Intraluminal IBS values were measured using IB-IVUS in cross-sections at the ostium of the target vessel and at the distal reference of implanted stent. ΔIBS was calculated as (distal IBS) - (ostium IBS).

RESULTS

A total of 393 vessels were included. Mean ΔIBS at postprocedure was 6.22 ± 5.65. During the follow-up period (11.2 ± 3.1 months), 24 cases (6.1%) had TVR. ΔIBS was significantly greater in the vessels with TVR than in those without (11.10 ± 5.93 vs. 5.90 ± 5.49, P <0.001). In receiver operating characteristic curve analysis, ΔIBS significantly predicted TVR (AUC 0.74, best cut-off value 8.24, P < 0.001). Multiple logistic regression analysis showed use of drug eluting stent and ΔIBS ≥ 8.24 as independent predictors of TVR.

CONCLUSIONS

ΔIBS at postprocedure was significantly associated with TVR. IVUS may be able to predict TVR by physiological assessment with measurement of ΔIBS.

Coronary Physiology in the Cardiac Catheterization Laboratory

Coronary angiography has been the principle modality for assessing the severity of atherosclerotic coronary artery disease for several decades. However, there is a complex relationship between angiographic coronary stenosis and the presence or absence of myocardial ischemia. Recent technological advances now allow for the assessment of coronary physiology in the catheterization laboratory at the time of diagnostic coronary angiography. Early studies focused on coronary flow reserve (CFR) but more recent work has demonstrated the physiologic accuracy and prognostic value of the fractional flow reserve (FFR) and instantaneous wave free ratio (iFR) for the assessment of coronary artery disease. These measurements have been validated in large multi-center clinical trials and have become indispensable tools for guiding revascularization in the cardiac catheterization laboratory. The physiological assessment of chest pain in the absence of epicardial coronary artery disease involves coronary thermodilution to obtain the index of microcirculatory resistance (IMR) or Doppler velocity measurement to determine the coronary flow velocity reserve (CFVR). Physiology-based coronary artery assessment brings "personalized medicine" to the catheterization laboratory and allows cardiologists and referring providers to make decisions based on objective findings and evidence-based treatment algorithms. The purpose of this review is to describe the theory, technical aspects, and relevant clinical trials related to coronary physiology assessment for an intended audience of general medical practitioners.

Qualitative resting coronary pressure wave form analysis to predict fractional flow reserve

AIMS

The aim of this study was to evaluate the predictability of resting distal coronary pressure wave forms for fractional flow reserve (FFR).

METHODS AND RESULTS

Resting coronary wave forms were qualitatively evaluated for the presence of (i) dicrotic notch, (ii) diastolic dipping, and (iii) ventricularisation. In a development cohort (n=88), a scoring system was developed that was then applied to a validation cohort (n=428) using a multivariable linear regression model to predict FFR and receiver operating characteristics (ROC) to predict FFR ≤0.8. In the development cohort, all three qualitative parameters were independent predictors of FFR. However, in a multivariable linear regression model in the validation cohort, qualitative wave form analysis did not further improve the ability of resting distal coronary to aortic pressure ratio (Pd/Pa) (p=0.80) or instantaneous wave-free ratio (iFR) (p=0.26) to predict FFR. Using ROC, the area under the curve of resting Pd/Pa (0.86 versus 0.86, p=0.08) and iFR (0.86 versus 0.86, p=0.26) did not improve by adding qualitative analysis.

CONCLUSIONS

Qualitative coronary wave form analysis showed moderate classification agreement in predicting FFR but did not add substantially to the resting pressure gradients Pd/Pa and iFR; however, when discrepancies between quantitative and qualitative analyses are observed, artefact or pressure drift should be considered.

Technical aspects and limitations of fractional flow reserve measurement

BACKGROUND

The only indication for coronary revascularization is elimination of ischaemia. Invasive hemodynamic methods (fractional flow reserve - FFR and instantaneous wave-free ratio (iFR) are superior to coronary angiography in detection of lesions causing myocardial ischaemia. Current European guidelines for myocardial revascularization recommend using of FFR for detection of functional assessment of lesions severity in category IA and number of these procedures increases. However, routine usage of these methods requires knowledge of technical requirements and limitations.

AIM

The aim of the study is to summarise good clinical practice for FFR and iFR measurements with explanation of possible technical challenges, that are necessary for increasing of measurement accuracy.

CONCLUSIONS

Authors describe frequent technical mistakes and malpractice during invasive assessment of lesion severity in coronary arteries.

Angiogram based fractional flow reserve in patients with dual/triple vessel coronary artery disease

OBJECTIVE

To assess the performance of angiography derived Fractional Flow Reserve (FFRangio) in multivessel disease (MVD) patients undergoing angiography.

BACKGROUND

FFR is the reference standard for physiologic assessment of coronary stenosis and guidance of revascularization, especially in patients with MVD, yet it remains grossly underutilized. The non-wire based FFRangio performs well in non-MVD patients, but its accuracy in MVD is unknown.

METHODS

A prospective clinical study was conducted at Gifu Heart Centre, Japan. Patients underwent physiologic assessment of all relevant coronary lesions using wire-based FFR (wbFFR) and FFRangio. Primary outcome was diagnostic performance (sensitivity, specificity, accuracy) for FFRangio with wbFFR as reference. Other outcomes were the correlation between wbFFR/FFRangio, time required for wbFFR/FFRangio measurements, and the effect of wbFFR/FFRangio on the reclassification of coronary disease severity.

RESULTS

Fifty patients (118 lesions in total) were included. Mean age was 72 ± 9 years, 72% were male, 36% had triple vessel disease and the average SYNTAX score was 13. The mean measurement of wbFFR and FFRangio were 0.83 ± 0.12 and 0.81 ± 0.11, respectively. Accuracy, sensitivity and specificity for FFRangio were 92.3% (95% CI 79.1-98.4%), 92.4% (95% CI 84.3-97.2%) and 92.4% (95% CI 87.4-97.3%), respectively. Pearson's r between wbFFR and FFRangio was 0.83. FFRangio measurement was faster than wbFFR (9.6 ± 3.4 vs. 15.0 ± 8.9 min, p < 0.001).

CONCLUSIONS

In patients with MVD, FFRangio shows good correlation and excellent diagnostic performance compared to wbFFR, and measuring FFRangio is faster than wbFFR. These results highlight the potential clinical benefits of utilizing FFRangio among patients with MVD.

Safety and efficacy of intracoronary sodium nitroprusside for the assessment of coronary fractional flow reserve

Background

Coronary fractional flow reserve (FFR) determination is a valuable tool for the assessment of stenosis significance in intermediate coronary obstructions. Maximal hyperemia is mandatory for this determination. Although intravenous (IV) Adenosine is the standard agent used, its use carries an elevated incidence of side effects. Intracoronary sodium nitroprusside (IC NTP) is a very well-known coronary vasodilator, but it is not routinely used for FFR determinations.

Objectives

The purpose of the present study was to compare FFR determinations and side effect profile of IC NTP with IV Adenosine.

Methods

We prospectively assessed FFR determinations in a total of 20 intermediate coronary artery stenotic lesions in 18 consecutive patients with the administration of IV Adenosine (140 μg/kg/min) and IC NTP (100 μg). The appearance of side effects was registered.

Results

The mean age was 55.5 ± 7.5 years. Fifteen (83%) of the patients were male. Mean FFR values with IC NTP were similar to those obtained with IV Adenosine (0.82 ± 0.07 vs 0.82 ± 0.06, respectively, r = 0.775, p < 0.0001). Intravenous Adenosine induced side effects in 45% of patients (shortness of breath 30%, flushing 5%, headache 5%, angina pectoris 5%, and transient conduction disturbances 10%). No side effects were reported with IC NTP.

Conclusions

IC NTP at a dose of 100 μg is as effective as IV Adenosine for FFR assessment. Besides, it is better tolerated and should be consider as a vasodilator agent in the assessment of FFR.

Clinical use of physiological lesion assessment using pressure guidewires: an expert consensus document of the Japanese Association of Cardiovascular Intervention and Therapeutics

In this document, the background, concept, and current evidence are briefly summarized. The focus is on the clinical application of physiological lesion assessment from a practical standpoint for facilities that do not have ample experience. Finally, the characteristics of new resting indexes are summarized.

Instantaneous wave-free ratio (iFR®) to determine hemodynamically significant coronary stenosis: A comprehensive review

Coronary angiography is considered to be the gold standard in the morphological evaluation of coronary artery stenosis. The morphological assessment of the severity of a coronary lesion is very subjective. Thus, the invasive fractional flow reserve (FFR) measurement represents the current standard for estimation of the hemodynamic significance of coronary artery stenosis. The FFR-guided revascularization strategy was initially classified as a Class-IA-recommendation in the 2014 European Society of Cardiology/European Association for Cardio-Thoracic Surgery guidelines on myocardial revascularization. Both the Deferral vs Performance of Percutaneous Coronary Intervention of Functionally Non-Significant Coronary Stenosis and Flow Reserve vs Angiography for Multivessel Evaluation studies showed no treatment advantage for hemodynamically insignificant stenoses. With the help of FFR (and targeted interventions), clinical results could be improved; however, the use in clinical practice is still limited due to the need of adenosine administration and a significant prolongation of the length of the procedure. Instantaneous wave-free ratio (iFR®) is a new innovative approach for the determination of the hemodynamic significance of coronary stenosis, which can be obtained at rest without the use of vasodilators. Regarding the periprocedural complications as well as prognosis, iFR® showed non-inferiority to FFR in the SWEDEHEART and DEFINE-FLAIR trials. Furthermore, iFR®, enhanced by iFR®-pullback, provides the possibility to display the iFR®-change over the course of the vessel to create a hemodynamic map.

Reduced order models for transstenotic pressure drop in the coronary arteries

The efficacy of reduced order modeling for transstenotic pressure drop in the coronary arteries is presented. Coronary artery disease is a leading cause of death worldwide and the computation of fractional flow reserve from computed tomography (FFRct) has become a standard for evaluating the functional significance of a coronary stenosis. FFRct uses 3D computational fluid dynamics to simulate coronary blood flow in order to compute transstenotic pressure drop during simulated hyperemia. In this study, we evaluate different fidelity hydrodynamic models and their ability to compute transstenotic pressure drop and FFRct in the coronary arteries. Models range from simple algebraic formulae to 1D, 2D and 3D time-dependent computational fluid dynamic simulations. Although several algebraic pressure-drop formulae have been proposed in the literature, these models were found to exhibit wide variation in predictions. Nonetheless, we demonstrate an algebraic formula that provides reliable predictions over a range of stenosis severity, morphology, location and flow rate when compared to the current standard for FFRct. The accounting of viscous dissipation, flow separation and pulsatile inertial effects were found to be the most significant contributions to accurate reduce order modeling of transstenotic coronary hemodynamics.

Network meta-analysis comparing iFR versus FFR versus coronary angiography to drive coronary revascularization

AIMS

Instantaneous free-wave ratio (iFR) has been recently demonstrated non-inferior to fractional flow reserve (FFR) to drive coronary revascularization; however, no study has compared iFR versus coronary angiography (CA). We performed a network meta-analysis to evaluate efficacy and safety of iFR- versus CA-guided strategy.

METHODS AND RESULTS

We searched for randomized trials and studies with propensity score matching in The Cochrane Collaboration Central Register of Controlled Trials, EMBASE, and MEDLINE/Pubmed. CA, FFR, and iFR were the three competitive arms, MACE (a composite endpoint of death, myocardial infarction [MI], and target vessel revascularization [TVR]) was the primary endpoint, while its single components the secondary ones. Subgroup analysis was performed for patients presenting with stable coronary artery disease. Eight studies were selected: 4126 patients were evaluated with FFR, 2160 with iFR, and 2214 with CA, acute coronary syndrome (ACS) was the most frequent admission diagnosis. After 12 months, rates of MACE and all-cause death did not differ between groups (respectively OR 1.04 and OR 0.86 for iFR vs FFR). Both FFR and iFR reduced TVR compared to CA (respectively OR 0.68 and OR 0.70). In patients with stable CAD both FFR and iFR reduced risk of subsequent MI compared to CA (respectively OR 0.66 and OR 0.79).

CONCLUSION

Compared to CA alone, both FFR and iFR are safe and effective in guiding coronary revascularization at 12 months. In patients with stable CAD, both FFR and iFR-guided revascularization reduce the risk of subsequent MI at 12 months.

Assessing the Haemodynamic Impact of Coronary Artery Stenoses: Intracoronary Flow Versus Pressure Measurements

Fractional flow reserve (FFR)-guided percutaneous coronary intervention results in better long-term clinical outcomes compared with coronary angiography alone in intermediate stenoses in stable coronary artery disease (CAD). Coronary physiology measurements have emerged for clinical decision making in interventional cardiology, but the focus lies mainly on epicardial vessels rather than the impact of these stenoses on the myocardial microcirculation. The latter can be quantified by measuring the coronary flow reserve (CFR), a combined pressure and flow index with a strong ability to predict clinical outcomes in CAD. However, combined pressure-flow measurements show 30-40 % discordance despite similar diagnostic accuracy between FFR and CFR, which is explained by the effect of microvascular resistance on both indices. Both epicardial and microcirculatory involvement has been acknowledged in ischaemic heart disease, but clinical implementation remains difficult as it requires individual proficiency. The recent introduced pressure-only index instantaneous wave-free ratio, a resting adenosine-free stenosis assessment, led to a revival of interest in coronary physiology measurements. This review focuses on elaborating the coronary physiological parameters and potential of combined pressure-flow measurements in daily clinical practice.

Comparison of sodium nitroprusside and adenosine for fractional flow reserve assessment: a systematic review and meta-analysis

BACKGROUND

Fractional flow reserve (FFR) has become a useful tool in the assessment of physiological significance of coronary artery stenosis (CAS), and Adenosine (ADE) is associated with a high incidence of transient side effects. Sodium nitroprusside (NPS) has been proposed as an alternative vasodilator agent. A meta-analysis of studies comparing ADE and NPS for FFR assessment in the same coronary lesions was performed.

METHODS

Authors searched for articles comparing NPS and ADE for FFR assessment in intermediate coronary lesions published through January 2018. The following keywords were used: 'fractional flow reserve' AND 'nitroprusside'. Data were summarized using weighted mean differences for paired data.

RESULTS

Seven studies were identified comprising 342 patients and 401 lesions. Four studies evaluated intravenous ADE and 3 studies intracoronary ADE administration. Weighted means FFR values obtained with ADE and NPS were 0.8411 and 0.8445, respectively (weighted mean difference: 0.00, 95% confidence interval (CI) -0.01 to 0.01, p = 0,548). Adverse events were significantly reduced with IC NPS (RR = 0.08, 95%CI 0.02-0.30, P < 0.0001).

CONCLUSIONS

NPS produces similar FFR measurements compared to ADE with a significant reduction in adverse effects. These results may support its use as a suitable alternative to ADE for FFR assessment.

The utility of high-sensitivity C-reactive protein levels in patients with moderate coronary lesions and gray-zone fractional flow reserve

OBJECTIVE

It remains controversial whether patients with fractional flow reserve (FFR) values of 0.75-0.80 (gray-zone) should be treated with percutaneous coronary intervention (PCI). This study aimed to evaluate the prediction of high-sensitivity C-reactive protein (hs-CRP) levels to guide treatment selection in gray-zone patients.

METHODS

This prospective interventional trial was conducted between January 2015 and March 2016. A total of 785 patients with stable angina and single-vessel stenosis with moderate coronary lesions were admitted to hospital in this period. After measurement of hs-CRP levels, coronary angiography, and FFR, gray-zone patients (n=308) were included in the study and were divided into four groups on the basis of a cutoff hs-CRP level of 3 mg/L and then on the basis of whether they underwent PCI or not. Patients in groups I (≥3 mg/L, n=70) and III (<3 mg/L, n=84) underwent PCI, whereas those in groups II (≥3 mg/L, n=70) and IV (<3 mg/L, n=84) were administered only drugs. Major adverse clinical events (MACEs) included cardiac death, nonfatal myocardial infarction (MI), target vessel revascularization (TVR), and PCI or coronary artery bypass grafting (CABG). These parameters were also evaluated during follow-up.

RESULTS

The total Kaplan-Meier curves showed macrodistribution differences among the four groups (p<0.05). There was a significantly increased MACE incidence in group II compared with group I or IV (p=0.039 or 0.006, respectively), and an increased incidence in group I compared with group III (p=0.028). However, there were no differences in MACE incidence between groups III and IV (p=0.095) despite the fact that these patients received different treatments.

CONCLUSION

Among FFR gray-zone patients, hs-CRP level was a predictor of MACE and risk stratification could guide treatment selection. Increased hs-CRP levels (≥3 mg/L) are an indication for urgent PCI whereas normal levels (<3 mg/L) are an indication for delayed PCI treatment. Patients with identical FFR values could require different treatment.

Comparison of coronary angiography and intracoronary imaging with fractional flow reserve for coronary artery disease evaluation: An anatomical-functional mismatch

Myocardial ischemia is a leading cause of death worldwide, and it corresponds to the imbalance between blood supply and myocardial demand. Epicardial coronary artery disease (CAD) is detected on the basis of coronary angiogram, whereas invasive detection of myocardial ischemia induced by coronary stenosis is commonly based on fractional flow reserve (FFR). The use of FFR for revascularization decision-making demonstrated clinical benefit and cost-effectiveness compared with that of angiographic indices. Discrepancies between anatomical metrics and physiological assessment of CAD are frequent, which lead to change in revascularization decision from angiography compared to functional evaluation of CAD. Despite several clinical studies and guidelines recommending with high level of evidence demonstrating that FFR should be adopted in stable CAD, revascularization decision-making is still based on coronary angiogram in current practice. Because of the unique coronary anatomy, coronary stenosis characteristics, risk factors profile, and microcirculation quality, the unique evaluation based on epicardial coronary stenosis threshold failed to be a landmark of ischemia compared with FFR. Furthermore, coronary angiogram can detect only epicardial vessels, which represent only 10% of the entire coronary vasculature; therefore, microcirculation is not seen and is poorly assessed in clinical practice. Thus, the role of microcirculation is of importance in myocardial ischemia and might impact these discrepancies between angiography and FFR evaluation of CAD. In this review, we aimed to describe the poor correlation between anatomical evaluation compared with physiological evaluation to detect myocardial ischemia induced by coronary stenosis as well as the clinical implications of this visual-functional mismatch.

Sex Differences in Adenosine-Free Coronary Pressure Indexes: A CONTRAST Substudy

OBJECTIVES

The goal of this study was to investigate sex differences in adenosine-free coronary pressure indexes.

BACKGROUND

Several adenosine-free coronary pressure wire indexes have been proposed to assess the functional significance of coronary artery lesions; however, there is a theoretical concern that sex differences may affect diagnostic performance because of differences in resting flow and distal myocardial mass.

METHODS

In this CONTRAST (Can Contrast Injection Better Approximate FFR Compared to Pure Resting Physiology?) substudy, contrast fractional flow reserve (cFFR), obtained during contrast-induced submaximal hyperemia, the instantaneous wave-free ratio (iFR), and distal/proximal coronary pressure ratio (Pd/Pa) were compared with fractional flow reserve (FFR) in 547 men and 216 women. Using FFR ≤0.8 as a reference, the diagnostic performance of each index was compared.

RESULTS

Men and women had similar diameter stenosis (p = 0.78), but women were less likely to have FFR ≤0.80 than men (42.5% vs. 51.5%, p = 0.04). Sensitivity was similar among cFFR, iFR, and Pd/Pa when comparing women and men, respectively (cFFR, 77.5% vs. 75.3%; p = 0.69; iFR, 84.9% vs. 79.4%; p = 0.30; Pd/Pa, 78.8% vs. 77.3%; p = 0.78). cFFR was more specific than iFR or Pd/Pa regardless of sex (cFFR, 94.3% vs. 95.8%; p = 0.56; iFR, 75.6% vs. 80.1%; p = 0.38; Pd/Pa, 80.6% vs. 78.7%; p = 0.69). By receiver-operating characteristic curve analysis, cFFR provided better diagnostic accuracy than resting indexes irrespective of sex (p ≤ 0.0001).

CONCLUSIONS

Despite the theoretical concern, the diagnostic sensitivity and specificity of cFFR, iFR, and Pd/Pa did not differ between the sexes. Irrespective of sex, cFFR provides the best diagnostic performance.