Current use of fractional flow reserve: a nationwide survey

Non-invasive Angiographic-based Fractional Flow Reserve: Technical Development, Clinical Implications, and Future Perspectives

New non- and less-invasive techniques have been developed to overcome the procedural and operator related burden of the fractional flow reserve (FFR) for the assessment of potentially significant stenosis in the coronary arteries. Virtual FFR-techniques can obviate the need for the additional flow or pressure wires as used for FFR measurements. This review provides an overview of the developments and validation of the virtual FFR-algorithms, states the challenges, discusses the upcoming clinical trials, and postulates the future role of virtual FFR in the clinical practice.

Coronary Flow Rate Adds Predictive Capability for FFR Assessment

A non-invasive risk assessment tool capable of stratifying coronary artery stenosis into high and low risk would reduce the number of patients who undergo invasive FFR, the current gold standard procedure for assessing coronary artery disease. Current statistic-based models that predict if FFR is above or below the threshold for physiological significance rely completely on anatomical parameters, such as percent diameter stenosis (%DS), resulting in models not accurate enough for clinical application. The inclusion of coronary artery flow rate (CFR) was added to an anatomical-only logistic regression model to quantify added predictive value. Initial hypothesis testing on a cohort of 96 coronary artery segments with some degree of stenosis found higher mean CFR in a group with low FFR < 0.8 (μ = 2.37 ml/s) compared to a group with high FFR > 0.8 (μ = 1.85 ml/s) (p-value = 0.046). Logistic regression modeling using both %DS and CFR (AUC = 0.78) outperformed logistic regression models using either only %DS (AUC = 0.71) or only CFR (AUC = 0.62). Including physiological parameters in addition to anatomical parameters are necessary to improve statistical based models for assessing high or low FFR.

Non-Invasive Quantification of Fraction Flow Reserve Based on Steady-State Geometric Multiscale Models

Background: The underuse of invasive fraction flow reserve (FFR) in clinical practice has motivated research towards its non-invasive prediction. The early attempts relied on solving the incompressible three-dimensional Navier–Stokes equations in segmented coronary arteries. However, transient boundary condition has a high resource intensity in terms of computational time. Herein, a method for calculating FFR based on steady-state geometric multiscale (FFR_SS) is proposed.

Methods: A total of 154 moderately stenotic vessels (40–80% diameter stenosis) from 136 patients with stable angina were included in this study to validate the clinical diagnostic performance of FFR_SS. The method was based on the coronary artery model segmented from the patient’s coronary CTA image. The average pressure was used as the boundary condition for the inlet, and the microcirculation resistance calculated by the coronary flow was used as the boundary condition for the outlet to calculate the patient-specific coronary hyperemia. Then, the flow velocity and pressure distribution and the FFRss of each coronary artery branch were calculated to evaluate the degree of myocardial ischemia caused by coronary stenosis. Also, the FFR_SS and FFR_CT of all patients were calculated, and the clinically measured FFR was used as the “gold standard” to verify the diagnostic performance of FFR_SS and to compare the correlation between FFR_SS and FFR_CT.

Results: According to the FFR_SS calculation results of all patients, FFR_SS and FFR have a good correlation (r = 0.68, p < 0.001). Similarly, the correlation of FFR_SS and FFR_CT demonstrated an r of 0.75 (95%CI: 0.67–0.72) (p < 0.001). On receiver-operating characteristic analysis, the optimal FFR_SS cut point for FFR≤0.80 was 0.80 (AUC:0.85 [95% confidence interval: 0.79 to 0.90]; overall accuracy:88.3%). The overall sensitivity, specificity, PPV, and NPV for FFR_SS ≤0.80 versus FFR ≤0.80 was 68.18% (95% CI: 52.4–81.4), 93.64% (95% CI: 87.3–97.4), 82.9%, and 91.1%, respectively.

Conclusion: FFR_SS is a reliable diagnostic index for myocardial ischemia. This method was similar to the closed-loop geometric multiscale calculation of FFR accuracy but improved the calculation efficiency. It also improved the clinical applicability of the non-invasive computational FFR model, helped the clinicians diagnose myocardial ischemia, and guided percutaneous coronary intervention.

The association between provider characteristics and post-catheterization interventions

Objectives

To examine whether the demographics of providers’ prior year patient cohorts, providers’ historic degree of catheter-based fractional flow reserve (FFR) utilization, and other provider characteristics were associated with post-catheterization performance of percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG).

Study design

A retrospective, observational analysis of outpatient claims data was performed.

Methods

All 2018 outpatient catheterization claims from a national organization offering commercial and Medicare Advantage health plans were examined. Claims were excluded if the patient had a prior catheterization in 2018, had any indications of CABG or valvular heart disease in the prior year of claims, or if the provider had ≤10 catheterization claims in 2017. Downstream PCI and CABG were determined by examining claims 0–30 days post-catheterization. Using multivariate mixed effects logistic regression with provider identity random effects, the association between post-catheterization procedures and provider characteristics was assessed, controlling for patient characteristics.

Results

The sample consisted of 31,920 catheterization claims pertaining to procedures performed by 964 providers. Among the catheterization claims, 8,554 (26.8%) were followed by PCI and 1,779 (5.6%) were followed by CABG. Catheterizations performed by providers with older prior year patient cohorts were associated with higher adjusted odds of PCI (1.78; CI: 1.26–2.53), even after controlling for patient age. Catheterizations performed by providers with greater historic use of FFR had significantly higher adjusted odds of being followed by PCI (1.73; CI: 1.26–2.37).

Conclusion

Provider characteristics may impact whether patients receive a procedure post-catheterization. Further research is needed to characterize this relationship.

Adoption and patterns of use of invasive physiological assessment of coronary artery disease in a large cohort of 40821 real-world procedures over a 12-year period

INTRODUCTION AND OBJECTIVES

Use of invasive physiological assessment in patients with coronary artery disease varies widely and is perceived to be low. We aimed to examine adoption rates as well as patterns and determinants of use in an unselected population undergoing invasive coronary angiography over a long time frame.

METHODS

We retrospectively determined the per-procedure prevalence of physiological assessment in 40821 coronary cases performed between 2007 and 2018 in two large-volume centers. Adoption was examined according to procedure type and patient- and operator-related variables. Its association with relevant scientific landmarks, such as the release of clinical trial results and practice guidelines, was also assessed.

RESULTS

Overall adoption was low, ranging from 0.6% in patients undergoing invasive coronary angiography due to underlying valve disease, to 6% in the setting of stable coronary artery disease (CAD); it was 3.1% in patients sustaining an acute coronary syndrome. Of scientific landmarks, FAME 1, the long-term results of FAME 2 and the 2014 European myocardial revascularization guidelines were associated with changes in practice. Publication of instantaneous wave-free ratio (iFR) trials had no influence on adoption rates, except for a higher proportion of iFR use. In 42.9% of stable CAD patients undergoing percutaneous coronary intervention there was no objective non-invasive evidence of ischemia, nor was physiological assessment performed. Younger operator age (4.5% vs. 4.0% vs. 0.9% for ages <40, 40-55 and >55 years, respectively; p<0.001) and later time of procedure during the day (2.9% between 6 and 8 p.m. vs. 4.4% at other times) were independent correlates of use of invasive physiology.

CONCLUSIONS

Our study confirms the low use of invasive physiology in routine practice. The availability of resting indices did not increase adoption. Strategies are warranted to promote guideline implementation and to improve patient care and clinical outcomes.

Adoption and patterns of use of invasive physiological assessment of coronary artery disease in a large cohort of 40821 real-world procedures over a 12-year period

INTRODUCTION AND OBJECTIVES

Use of invasive physiological assessment in patients with coronary artery disease varies widely and is perceived to be low. We aimed to examine adoption rates as well as patterns and determinants of use in an unselected population undergoing invasive coronary angiography over a long time frame.

METHODS

We retrospectively determined the per-procedure prevalence of physiological assessment in 40821 coronary cases performed between 2007 and 2018 in two large-volume centers. Adoption was examined according to procedure type and patient- and operator-related variables. Its association with relevant scientific landmarks, such as the release of clinical trial results and practice guidelines, was also assessed.

RESULTS

Overall adoption was low, ranging from 0.6% in patients undergoing invasive coronary angiography due to underlying valve disease, to 6% in the setting of stable coronary artery disease (CAD); it was 3.1% in patients sustaining an acute coronary syndrome. Of scientific landmarks, FAME 1, the long-term results of FAME 2 and the 2014 European myocardial revascularization guidelines were associated with changes in practice. Publication of instantaneous wave-free ratio (iFR) trials had no influence on adoption rates, except for a higher proportion of iFR use. In 42.9% of stable CAD patients undergoing percutaneous coronary intervention there was no objective non-invasive evidence of ischemia, nor was physiological assessment performed. Younger operator age (4.5% vs. 4.0% vs. 0.9% for ages <40, 40-55 and >55 years, respectively; p<0.001) and later time of procedure during the day (2.9% between 6 and 8 p.m. vs. 4.4% at other times) were independent correlates of use of invasive physiology.

CONCLUSIONS

Our study confirms the low use of invasive physiology in routine practice. The availability of resting indices did not increase adoption. Strategies are warranted to promote guideline implementation and to improve patient care and clinical outcomes.

The relationship between coronary stenosis morphology and fractional flow reserve: a computational fluid dynamics modelling study

Aims

International guidelines mandate the use of fractional flow reserve (FFR) and/or non-hyperaemic pressure ratios to assess the physiological significance of moderate coronary artery lesions to guide revascularization decisions. However, they remain underused such that visual estimation of lesion severity continues to be the predominant decision-making tool. It would be pragmatic to have an improved understanding of the relationship between lesion morphology and haemodynamics. The aim of this study was to compute virtual FFR (vFFR) in idealized coronary artery geometries with a variety of stenosis and vessel characteristics.

Methods and results

Coronary artery geometries were modelled, based upon physiologically realistic branched arteries. Common stenosis characteristics were studied, including % narrowing, length, eccentricity, shape, number, position relative to branch, and distal (myocardial) resistance. Computational fluid dynamics modelling was used to calculate vFFRs using the VIRTUheart™ system. Percentage lesion severity had the greatest effect upon FFR. Any ≥80% diameter stenosis in two views (i.e. concentric) was physiologically significant (FFR ≤ 0.80), irrespective of length, shape, or vessel diameter. Almost all eccentric stenoses and all 50% concentric stenoses were physiologically non-significant, whilst 70% uniform concentric stenoses about 10 mm long straddled the ischaemic threshold (FFR 0.80). A low microvascular resistance (MVR) reduced FFR on average by 0.05, and a high MVR increased it by 0.03.

Conclusion

Using computational modelling, we have produced an analysis of vFFR that relates stenosis characteristics to haemodynamic significance. The strongest predictor of a positive vFFR was a concentric, ≥80% diameter stenosis. The importance of MVR was quantified. Other lesion characteristics have a limited impact.

Behavioural determinants impacting the adoption rate of coronary physiology

BACKGROUND

Despite international revascularisation guidelines strongly recommending functional assessment of coronary artery stenosis using pressure-wire derived indices, the adoption rate of coronary physiology remains low.

METHODS

An online questionnaire was designed to evaluate behavioural determinants impacting the adoption rate of coronary physiology. Factor analysis was performed to combine multiple items of a common behavioural domain into one explanatory factor. Regression analysis was performed to evaluate the influence of resulting factors on the variance of the coronary physiology adoption rate. Additionally, the influence of experience, demographics and provider structures was assessed.

RESULTS

104 interventional cardiologists, from 21 countries, completed the questionnaire. Mean adoption rate of coronary physiology was 26.9%. Regression analysis revealed that factors ease-of-use (Coefficient = 0.58, p = 0.01), financial and/or time constraints (Coefficient = -0.22, p = 0.01) and knowledge about guideline recommendations (Coefficient = 0.21, p = 0.06) had the greatest influence on coronary physiology adoption rate variance (R² = 0.3, p < 0.001), with ease-of-use and guideline recommendations positively influencing greater uptake and constraints influencing lesser uptake of adoption of coronary physiology.

CONCLUSION

Ease-of-use, financial and/or time constraints, and knowledge about guideline recommendations were the most relevant behavioural factors impacting the adoption rate of coronary physiology. Ease-of-use was identified as the most influential factor, highlighting the importance of cardiac catheterisation laboratory teams being adequately trained to perform coronary physiology assessment seamlessly.

Physiology over Angiography to Determine Lesion Severity: the FAME Trials

The "Achilles heel" of invasive coronary angiography is its inability to accurately localize which stenoses induce ischemia and warrant treatment. Fractional flow reserve (FFR) is a coronary wire-based physiologic index that measures the functional significance of epicardial stenoses, thereby overcoming this limitation. Over the past decade, the landmark FAME (Fractional Flow Reserve vs Angiography for Multivessel Evaluation) trials demonstrated the clinical utility of an FFR-guided strategy for percutaneous coronary intervention (PCI) compared with angiography-only PCI or medical therapy alone in patients with predominantly stable ischemic heart disease. These trials have spurred the current era of coronary-physiology-guided revascularization.

Coronary Angiography With Pressure Wire and Fractional Flow Reserve

BACKGROUND

Approximately 800 000 coronary angiography procedures are per- formed in Germany each year, mainly in order to identify coronary artery stenoses. As a rule, revascularization is indicated only when coronary artery stenoses cause relevant ischemia, but this cannot be determined unequivocally by angiography alone. Pressure wire measurement and the measurement of fractional flow reserve (FFR) enable direct evaluation of the hemodynamic relevance of coronary artery stenoses during diagnostic coronary angiography.

METHODS

This review is based on publications retrieved by a selective search in PubMed focusing especially on large randomized trials, registry studies, and meta- analyses on either pressure wire measurement or FFR.

RESULTS

According to a registry study from France, the hemodynamic evaluation of a stenosis during coronary angiography affected decisions about revascularization in 43% of cases. Randomized multicenter trials have shown that a combined end- point consisting of death, myocardial infarction, or revascularization arose signifi- cantly less commonly in the FFR group than in the group receiving angiography without FFR (13.2% versus 18.3%; p = 0.02), and that patients with one or more hemodynamically significant coronary artery stenoses (FFR ≤ 0.80) benefited more from revascularization than from medical management alone (event rate, 8.1% versus 19.5%; p <0.001). It was also shown that revascularization yields no benefit if relevant ischemia has been ruled out, even if the angiogram shows high-grade coronary artery stenoses.

CONCLUSION

All cardiac catheter laboratories should be capable of performing pres- sure wire measurements and measurements of FFR and should do so regularly if ischemia due to coronary artery stenosis cannot be demonstrated non-invasively. A pathological FFR measurement is an indication for revascularization.

Fractional flow reserve use during elective coronary angiography among elderly patients in the US

Fractional flow reserve (FFR) is a physiologic measurement of coronary artery perfusion. Studies have demonstrated its benefit in lowering cost and improving outcomes in patients undergoing elective coronary angiography, though follow-up surveys have demonstrated low usage nationwide. We sought to investigate the actual usage in elderly patients undergoing elective coronary angiography. Overall utilization of FFR for elective coronary angiography was 6.3%. Age, sex, race, prior stress testing and region of the country were all statistically significant predictors for FFR use. There still exist many barriers to widespread adoption of this modality, which require further exploration.

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.

Temporal Trends in Fractional Flow Reserve Use in Patients Undergoing Coronary Angiography: A Population-Based Study

Background

Invasive fractional flow reserve (FFR) has emerged as an important tool to identify a subset of patients in whom coronary revascularization may be beneficial. Our objective was to evaluate temporal trends in FFR use.

Methods

We identified all coronary angiograms in the CorHealth Ontario Cardiac Registry between the years 2010 and 2015. The primary and secondary outcomes were the age- and sex-adjusted monthly rate of FFR per 100,000 population and per 100 angiograms, respectively. Piecewise regression analyses were used to evaluate the temporal trends in FFR use for the entire cohort, and then stratified by indication (stable coronary artery disease [CAD]) vs acute coronary syndrome [ACS]).

Results

The study cohort included 379,688 angiograms, of which 122,571 were for stable CAD (32%) and 134,769 were for ACS (36%). Monthly age- and sex-adjusted FFR use rates increased significantly over the study period, from 0.4 to 2.3 per 100,000 people per month. The monthly FFR use rate per 100 angiograms increased from 0.9 to 4.9 per 100 angiograms per month; however, the proportion of positive FFR (< 0.8) results was relatively constant at 28%. There was a more dramatic increase in the use of FFR in the population with stable CAD (1.1 to 8.0 per 100 angiograms/month) compared with the population with ACS (0.6 to 4.5 per 100 angiograms/month).

Conclusions

There was a > 5-fold increase in the use of FFR in patients across Ontario, which was predominantly driven by use in stable CAD. Case selection for FFR use was relatively unchanged with approximately one-quarter of FFR cases being positive over time.

Uncertainty Quantification and Sensitivity Analysis for Computational FFR Estimation in Stable Coronary Artery Disease

PURPOSE

The main objectives of this study are to validate a reduced-order model for the estimation of the fractional flow reserve (FFR) index based on blood flow simulations that incorporate clinical imaging and patient-specific characteristics, and to assess the uncertainty of FFR predictions with respect to input data on a per patient basis.

METHODS

We consider 13 patients with symptoms of stable coronary artery disease for which 24 invasive FFR measurements are available. We perform an extensive sensitivity analysis on the parameters related to the construction of a reduced-order (hybrid 1D-0D) model for FFR predictions. Next we define an optimal setting by comparing reduced-order model predictions with solutions based on the 3D incompressible Navier-Stokes equations. Finally, we characterize prediction uncertainty with respect to input data and identify the most influential inputs by means of sensitivity analysis.

RESULTS

Agreement between FFR computed by the reduced-order model and by the full 3D model was satisfactory, with a bias ([Formula: see text]) of [Formula: see text] at the 24 measured locations. Moreover, the uncertainty related to the factor by which peripheral resistance is reduced from baseline to hyperemic conditions proved to be the most influential parameter for FFR predictions, whereas uncertainty in stenosis geometry had greater effect in cases with low FFR.

CONCLUSION

Model errors related to solving a simplified reduced-order model rather than a full 3D problem were small compared with uncertainty related to input data. Improved measurement of coronary blood flow has the potential to reduce uncertainty in computational FFR predictions significantly.

Fractional Flow Reserve and Cardiac Events in Coronary Artery Disease: Data From a Prospective IRIS-FFR Registry (Interventional Cardiology Research Incooperation Society Fractional Flow Reserve)

BACKGROUND

We evaluated the prognosis of deferred and revascularized coronary stenoses after fractional flow reserve (FFR) measurement to assess its revascularization threshold in clinical practice.

METHODS

The IRIS-FFR registry (Interventional Cardiology Research In-cooperation Society Fractional Flow Reserve) prospectively enrolled 5846 patients with ≥1coronary lesion with FFR measurement. Revascularization was deferred in 6468 lesions and performed in 2165 lesions after FFR assessment. The primary end point was major adverse cardiac events (cardiac death, myocardial infarction, and repeat revascularization) at a median follow-up of 1.9 years and analyzed on a per-lesion basis. A marginal Cox model accounted for correlated data in patients with multiple lesions, and a model to predict per-lesion outcomes was adjusted for confounding factors.

RESULTS

For deferred lesions, the risk of major adverse cardiac events demonstrated a significant, inverse relationship with FFR (adjusted hazard ratio, 1.06; 95% confidence interval, 1.05-1.08; P<0.001). However, this relationship was not observed in revascularized lesions (adjusted hazard ratio, 1.00; 95% confidence interval, 0.98-1.02; P=0.70). For lesions with FFR ≥0.76, the risk of major adverse cardiac events was not significantly different between deferred and revascularized lesions. Conversely, in lesions with FFR ≤0.75, the risk of major adverse cardiac events was significantly lower in revascularized lesions than in deferred lesions (for FFR 0.71-0.75, adjusted hazard ratio, 0.47; 95% confidence interval, 0.24-0.89; P=0.021; for FFR ≤0.70, adjusted hazard ratio 0.47; 95% confidence interval, 0.26-0.84; P=0.012).

CONCLUSIONS

This large, prospective registry showed that the FFR value was linearly associated with the risk of cardiac events in deferred lesions. In addition, revascularization for coronary artery stenosis with a low FFR (≤0.75) was associated with better outcomes than the deferral, whereas for a stenosis with a high FFR (≥0.76), medical treatment would be a reasonable and safe treatment strategy.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01366404.

Prediction of fractional flow reserve with angiographic DILEMMA score

Objective:

Angiographic assessment of stenosis has limited predictive value for functionally significant lesions compared with fractional flow reserve (FFR). The recently developed angiographic DILEMMA score, which consists of minimal lumen diameter (MLD), lesion length (LL) and Bypass Angioplasty Revascularization Investigation (BARI) Myocardial Jeopardy Index (MJI) was found to have diagnostic value in predicting FFR ≤0.80. The present study was an investigation of prediction of FFR ≤0.80 using DILEMMA score and its relationship to resting distal coronary artery pressure/aortic pressure (Pd/Pa).

Methods:

Records of consecutive patients who underwent coronary angiography and FFR were retrospectively analyzed. Assessment of MLD and LL was performed using quantitative coronary angiography. BARI MJI was calculated using angiographic calculation index.

Results:

A total of 185 pressure wire analysis data sets from 150 patients were analyzed retrospectively. There were 82 lesions in FFR >0.80 group and 103 lesions in FFR ≤0.80 group. Negative correlation was found between FFR and DILEMMA score (r=-0.494; p<0.001), FFR and BARI-MJI (r=-0.378; p<0.001), and between FFR and LL (r=-0.314; p<0.001). Positive correlation was found between FFR and baseline Pd/Pa (r=0.713; p<0.001), and between FFR and MLD (r=0.415; p<0.001). DILEMMA score had negative correlation with resting Pd/Pa (r=-0.389; p<0.001). In receiver operating characteristic analysis for diagnosing FFR≤0.80, area under curve values of resting Pd/Pa, DILEMMA score, MLD, BARI-MJI, and LL were 0.862, 0.793, 0.780, 0.728, and 0.686, respectively.

Conclusion:

DILEMMA score had moderately strong correlation with FFR and good accuracy in diagnosing significant FFR, but it had weak correlation with resting Pd/Pa. (Anatol J Cardiol 2017; 17: 285-92)