Performing and Interpreting Fractional Flow Reserve Measurements in Clinical Practice: An Expert Consensus Document

Use of coronary physiology to guide revascularization in clinical practice: results of the F(FR)2 registry

BACKGROUND

Despite the recommendation of coronary physiology to guide revascularization in angiographically intermediate stenoses without established correlation to ischemia, its uptake in clinical practice is slow.

AIMS

This study aimed to analyze the use of coronary physiology in clinical practice.

METHODS

Based on a multicenter registry (Fractional Flow Reserve Fax Registry, F(FR)2, ClinicalTrials.gov identifier NCT03055910), clinical use, consequences, and complications of coronary physiology were systematically analyzed.

RESULTS

F(FR)2 enrolled 2,000 patients with 3,378 intracoronary pressure measurements. Most measurements (96.8%) were performed in angiographically intermediate stenoses. Out of 3,238 lesions in which coronary physiology was used to guide revascularization, revascularization was deferred in 2,643 (78.2%) cases. Fractional flow reserve (FFR) was the most common pressure index used (87.6%), with hyperemia induced by an intracoronary bolus of adenosine in 2,556 lesions (86.4%) and intravenous adenosine used for 384 measurements (13.0%). The route of adenosine administration did not influence FFR results (change-in-estimate -3.1% for regression model predicting FFR from diameter stenosis). Agreement with the subsequent revascularization decision was 93.4% for intravenous and 95.0% for intracoronary adenosine (p = 0.261). Coronary artery occlusion caused by the pressure wire was reported in two cases (0.1%) and dissection in three cases (0.2%), which was fatal once (0.1%).

CONCLUSIONS

In clinical practice, intracoronary pressure measurements are mostly used to guide revascularization decisions in angiographically intermediate stenoses. Intracoronary and intravenous administration of adenosine seem equally suited. While the rate of serious complications of wire-based intracoronary pressure measurements in clinical practice seems to be low, it is not negligible.

Agreement of Fractional Flow Reserve Estimated by Computed Tomography With Invasively Measured Fractional Flow Reserve: A Systematic Review and Meta-Analysis

BACKGROUND

Fractional flow reserve (FFR) is the ratio of blood pressure measured distal to a stenosis and pressure proximal to a stenosis. FFR can be estimated noninvasively using computed tomography (CT) although the usefulness of this technique remains controversial. This meta-analysis evaluated the agreement of FFR estimated by CT (FFR-CT) with invasively measured FFR. The study also evaluated the diagnostic accuracy of FFR-CT, defined as the ability of FFR-CT to classify lesions as hemodynamically significant (invasive FFR ≤0.8) or insignificant (invasive FFR >0.8).

METHODS AND RESULTS

Forty-three studies reporting on 7291 blood vessels from 5236 patients were included. A moderate positive linear relationship between FFR-CT and invasively measured FFR was observed (Spearman correlation coefficient: 0.67). Agreement between the 2 measures increased as invasively measured FFR values approached 1. The overall diagnostic accuracy, sensitivity and specificity of FFR-CT were 82.2%, 80.9%, and 83.1%, respectively. Diagnostic accuracy of 90% could be demonstrated for FFR-CT values >0.90 and <0.49. The diagnostic accuracy of off-site tools was 79.4% and the diagnostic accuracy of on-site tools was 84.1%.

CONCLUSIONS

The agreement between FFR-CT and invasive FFR is moderate although agreement is highest in vessels with FFR-CT >0.9. Diagnostic accuracy varies widely with FFR-CT value but is above 90% for FFR-CT values >0.90 and <0.49. Furthermore, on-site and off-site tools have similar performance. Ultimately, FFR-CT may be a useful adjunct to CT coronary angiography as a gatekeeper for invasive coronary angiogram.

Association between vessel-specific coronary Aggregated plaque burden, Agatston score and hemodynamic significance of coronary disease (The CAPTivAte study)

Background

CT coronary angiography (CTCA) is a guideline-endorsed assessment for patients with stable angina and suspected coronary disease. Although associated with excellent negative predictive value in ruling out obstructive coronary disease, there are limitations in the ability of CTCA to predict hemodynamically significant coronary disease. The CAPTivAte study aims to assess the utility of Aggregated Plaque Burden (APB) in predicting ischemia based on Fractional Flow Reserve (FFR).

Methods

In this retrospective study, patients who had a CTCA and invasive FFR of the LAD were included. The entire length of the LAD was analyzed using semi-automated software which characterized total plaque burden and plaque morphological subtype (including Low Attenuation Plaque (LAP), Non-calcific plaque (NCP) and Calcific Plaque (CP). Aggregated Plaque Burden (APB) was calculated. Univariate and multivariate analysis were performed to assess the association between these CT-derived parameters and invasive FFR.

Results

There were 145 patients included in this study. 84.8 % of patients were referred with stable angina. There was a significant linear association between APB and FFR in both univariate and multivariate analysis (Adjusted R-squared = 0.0469; p = 0.035). Mean Agatston scores are higher in FFR positive vessels compared to FFR negative vessels (371.6 (±443.8) vs 251.9 (±283.5, p = 0.0493).

Conclusion

CTCA-derived APB is a reliable predictor of ischemia assessed using invasive FFR and may aid clinicians in rationalizing invasive vs non-invasive management strategies. Vessel-specific Agatston scores are significantly higher in FFR-positive vessels than in FFR-negative vessels. Associations between HU-derived plaque subtype and invasive FFR were inconclusive in this study.

Impact of vessel morphology on CT-derived fractional-flow-reserve in non-obstructive coronary artery disease in right coronary artery

OBJECTIVES

Computed tomography (CT)-derived fractional flow reserve (FFRCT) decreases continuously from proximal to distal segments of the vessel due to the influence of various factors even in non-obstructive coronary artery disease (NOCAD). It is known that FFRCT is dependent on vessel-length, but the relationship with other vessel morphologies remains to be explained.

PURPOSE

To investigate morphological aspects of the vessels that influence FFRCT in NOCAD in the right coronary artery (RCA).

METHODS

A total of 443 patients who underwent both FFRCT and invasive coronary angiography, with < 50% RCA stenosis, were evaluated. Enrolled RCA vessels were classified into two groups according to distal FFRCT: FFRCT ≤ 0.80 (n = 60) and FFRCT > 0.80 (n = 383). Vessel morphology (vessel length, lumen diameter, lumen volume, and plaque volume) and left-ventricular mass were assessed. The ratio of lumen volume and vessel length was defined as V/L ratio.

RESULTS

Whereas vessel-length was almost the same between FFRCT ≤ 0.80 and > 0.80, lumen volume and V/L ratio were significantly lower in FFRCT ≤ 0.80. Distal FFRCT correlated with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). Among all vessel-related parameters, V/L ratio showed the highest correlation with distal FFRCT (r = 0.61, p < 0.0001). Multivariable analysis showed that calcified plaque volume was the strongest predictor of distal FFRCT, followed by V/L ratio (β-coefficient = 0.48, p = 0.03). V/L ratio was the strongest predictor of a distal FFRCT ≤ 0.80 (cut-off 8.1 mm3/mm, AUC 0.88, sensitivity 90.0%, specificity 76.7%, 95% CI 0.84-0.93, p < 0.0001).

CONCLUSIONS

Our study suggests that V/L ratio can be a measure to predict subclinical coronary perfusion disturbance.

CLINICAL RELEVANCE STATEMENT

A novel marker of the ratio of lumen volume to vessel length (V/L ratio) is the strongest predictor of a distal CT-derived fractional flow reserve (FFRCT) and may have the potential to improve the diagnostic accuracy of FFRCT.

KEY POINTS

• Physiological FFRCT decline depends not only on vessel length but also on the lumen volume in non-obstructive coronary artery disease in the right coronary artery. • FFRCT correlates with plaque-related parameters (low-attenuation plaque, intermediate-attenuation plaque, and calcified plaque) and vessel-related parameters (proximal and distal vessel diameter, vessel length, lumen volume, and V/L ratio). • Of vessel-related parameters, V/L ratio is the strongest predictor of a distal FFRCT and an optimal cut-off value of 8.1 mm3/mm.

Multimodality OCT, IVUS and FFR evaluation of coronary intermediate grade lesions in women vs. men

Background

The pathophysiology of atherosclerotic plaque formation and its vulnerability seem to differ between genders due to contrasting risk profiles and sex hormones, however this process is still insufficiently understood. The aim of the study was to compare the differences between sexes regarding the optical coherence tomography (OCT), intravascular ultrasound (IVUS) and fractional flow reserve (FFR)-derived coronary plaque indices.

Methods

In this single-center multimodality imaging study patients with intermediate grade coronary stenoses identified in coronary angiogram (CAG) were evaluated using OCT, IVUS and FFR. Stenoses were considered significant when the FFR value was ≤0.8. Minimal lumen area (MLA), was analyzed by OCT in addition to plaque stratification into fibrotic, calcific, lipidic and thin-cap fibroatheroma (TCFA). IVUS was used for evaluation of lumen-, plaque- and vessel volume, as well as plaque burden.

Results

A total of 112 patients (88 men and 24 women) with chronic coronary syndromes (CCS), who underwent CAG were enrolled. No significant differences in baseline characteristics were present between the study groups. The mean FFR was 0.76 (0.73-0.86) in women and 0.78 ± 0.12 in men (p = 0.695). OCT evaluation showed a higher prevalence of calcific plaques among women than men p = 0.002 whereas lipid plaques were more frequent in men (p = 0.04). No significant differences regarding minimal lumen diameter and minimal lumen area were found between the sexes. In IVUS analysis women presented with significantly smaller vessel area, plaque area, plaque volume, vessel volume (11.1 ± 3.3 mm² vs. 15.0 ± 4.6 mm² p = 0.001, 6.04 ± 1.7 mm² vs. 9.24 ± 2.89 mm² p < 0.001, 59.8 ± 35.2 mm³ vs. 96.3 (52.5-159.1) mm³ p = 0.005, 106.9 ± 59.8 mm³ vs. 153.3 (103-253.4) mm³ p = 0.015 respectively). At MLA site plaque burden was significantly greater for men than women (61.50 ± 7.7% vs. 55.5 ± 8.0% p = 0.005). Survival did not differ significantly between women and men (94.6 ± 41.9 months and 103.51 ± 36.7 months respectively; p = 0.187).

Conclusion

The presented study did not demonstrate significant differences in FFR values between women and men, yet a higher prevalence of calcific plaques by OCT and lower plaque burden at the MLA site by IVUS was found in women vs. men.

The Controversies of Coronary Artery Disease in End-Stage Kidney Disease Patients: A Narrative Review

Cardiovascular disease (CVD) accounts for more than 50% of deaths among patients with end-stage kidney disease (ESKD). Approximately 40-50% of ESKD patients have clinically significant coronary artery disease (CAD) due to atherosclerosis which accounts for a significant proportion of CVD risk. However, other CVD pathologies including myocardial fibrosis, vascular calcification and arterial stiffening play important contributory roles. The pathophysiology of CAD in ESKD is distinct from the general population. ESKD patients is typically have diffuse multi-vessel involvement with increased calcification that involves both intimal and medial layers of the arterial wall. There is a complex interplay between an increased burden of traditional Framingham risk factors and exposure to non-traditional risk factors including chronic inflammation and dialysis per se. Established treatments for CAD risk factors including cholesterol lowering with statin therapy have attenuated effects and ESKD patients also have worse outcomes after revascularisation. Recent trials such as the Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS) have established that direct modulation of inflammation improves CVD outcomes in the general population, which may prove to be a potential attractive therapeutic target in ESKD patients. Multiple retrospective observational studies comparing mortality outcomes between haemodialysis (HD) and peritoneal dialysis (PD) patients have been inconclusive. Randomised trials on this issue of clinical equipoise are clearly warranted but are unlikely to be feasible. Screening for stable CAD in asymptomatic ESKD patients remains a clinical dilemma which is unique to chronic dialysis patients being assessed for kidney transplantation. This has become particularly relevant in light of the recent ISCHEMIA-CKD trial which demonstrated no difference between optimal medical therapy and revascularisation upon CVD outcomes or mortality. The optimal strategy for screening is currently being investigated in the ongoing large international multi-centre CARSK trial. Here we discuss the pathophysiology, risk modification, treatment, screening and future directions of CAD in ESKD.

Fractional myocardial blood volume by ferumoxytol-enhanced MRI: Estimation of ischemic burden

PURPOSE

To investigate model-fitted fractional myocardial blood volume (fMBV) derived from ferumoxytol-enhanced MRI as a measure of myocardial tissue hypoperfusion at rest.

METHODS

We artificially induced moderate to severe focal coronary stenosis in the left anterior descending artery of 19 swine by percutaneous delivery of a 3D-printed coronary implant. Using the MOLLI pulse sequence, we acquired T1 maps at 3 T after multiple incremental ferumoxytol doses (0.0-4.0 mg/kg). We computed pixel-wise fMBV using a multi-compartmental modeling approach in 19 ischemic swine and 4 healthy swine.

RESULTS

Ischemic myocardial segments showed a mean MRI-fMBV of 11.72 ± 3.00%, compared with 8.23 ± 2.12% in remote segments and 8.38 ± 2.23% in normal segments. Ischemic segments showed a restricted transvascular water-exchange rate (ki  = 15.32 ± 8.69 s-1 ) relative to remote segments (ki  = 17.78 [11.60, 26.36] s-1 ). A mixed-effects model found significant difference in fMBV (p = 0.002) and water-exchange rate (p < 0.001) between ischemic and remote myocardial regions after adjusting for biological sex and slice location. Analysis of fMBV as a predictor of impaired myocardial contractility using receiver operating characteristics showed an area under the curve of 0.89 (95% confidence interval [CI] 0.80, 0.95). An MRI-fMBV threshold of 9.60% has a specificity of 90.0% (95% CI 76.3, 97.2) and a sensitivity of 72.5% (95% CI 56.1, 83.4) for prediction of impaired myocardial contractility.

CONCLUSIONS

Model-fitted fMBV derived from ferumoxytol-enhanced MRI can distinguish regions of ischemia from remote myocardium in a swine model of myocardial hypoperfusion.

Combination of coronary CT angiography, FFRCT , and risk factors in the prediction of major adverse cardiovascular events in patients suspected CAD

BACKGROUND

To examine the utility of fractional flow reserve by coronary computed tomography (CT) angiography (FFR_CT ) for predicting major adverse cardiovascular events (MACE) in patients with suspected coronary artery disease (CAD).

METHODS

This was a nationwide multicenter prospective cohort study including consecutive 1187 patients aged 50-74 years with suspected CAD and had available coronary CT angiography (CCTA). In patients with ≥50% coronary artery stenosis (CAS), FFR_CT was further analyzed. The Cox proportional hazards model was used to examine the association of FFR_CT and cardiovascular risk factors with incident MACE within 2 years.

RESULTS

Among 933 patients with available information on MACE within 2 years after enrollment, the incidence rate of MACE was higher in 281 patients with CAS than in those without CAS (6.11 vs. 1.16 per 100 patient-year). In 241 patients with CAS, the Cox proportional hazards analysis showed that FFR_CT as well as diabetes mellitus and low high-density lipoprotein cholesterol level were independently associated with incident MACE. Moreover, the hazard ratio was significantly higher in patients harboring all three factors compared to those harboring 0-2 of the three factors (6.01; 95% confidence interval: 2.77-13.03).

CONCLUSIONS

Combinatorial assessment using CCTA for stenosis, FFR_CT , and risk factors was useful for more accurate prediction of MACE in patients with suspected CAD. Among patients with CAS, those with lower FFR_CT , diabetes mellitus, and low high-density lipoprotein cholesterol level were at highest risk for MACE during the 2-year period following enrollment.

Is it the Time to Move Towards Coronary Computed Tomography Angiography-Derived Fractional Flow Reserve Guided Percutaneous Coronary Intervention? The Pros and Cons

Coronary artery disease is the leading cause of mortality worldwide. Diagnosis is conventionally performed by direct visualization of the arteries by invasive coronary angiography (ICA), which has inherent limitations and risks. Measurement of fractional flow reserve (FFR) has been suggested for a more accurate assessment of ischemia in the coronary artery with high accuracy for determining the severity and decision on the necessity of intervention. Nevertheless, invasive coronary angiography-derived fractional flow reserve (ICA-FFR) is currently used in less than one-third of clinical practices because of the invasive nature of ICA and the need for additional equipment and experience, as well as the cost and extra time needed for the procedure. Recent technical advances have moved towards non-invasive high-quality imaging modalities, such as magnetic resonance, single-photon emission computed tomography, and coronary computed tomography (CT) scan; however, none had a definitive modality to confirm hemodynamically significant coronary artery stenosis. Coronary computed tomography angiography (CCTA) can provide accurate anatomic and hemodynamic data about the coronary lesion, especially calculating fractional flow reserve derived from CCTA (CCTA-FFR). Although growing evidence has been published regarding CCTA-FFR results being comparable to ICA-FFR, CCTA-FFR has not yet replaced the invasive conventional angiography, pending additional studies to validate the advantages and disadvantages of each diagnostic method. Furthermore, it has to be identified whether revascularization of a stenotic lesion is plausible based on CCTA-FFR and if the therapeutic plan can be determined safely and accurately without confirmation from invasive methods. Therefore, in the present review, we will outline the pros and cons of using CCTA-FFR vs. ICA-FFR regarding diagnostic accuracy and treatment decision-making.

Impact of coronary bifurcation angle on computed tomography derived fractional flow reserve in coronary vessels with no apparent coronary artery disease

OBJECTIVES

Computed tomography (CT) derived fractional flow reserve (FFR_CT) decreases from the proximal to the distal part due to a variety of factors. The energy loss due to the bifurcation angle may potentially contribute to a progressive decline in FFR_CT. However, the association of the bifurcation angle with FFR_CT is still not entirely understood. This study aimed to investigate the impact of various bifurcation angles on FFR_CT decline below the clinically crucial relevance of 0.80 in vessels with no apparent coronary artery disease (CAD).

METHODS

A total of 83 patients who underwent both CT angiography including FFR_CT and invasive coronary angiography, exhibiting no apparent CAD were evaluated. ΔFFR_CT was defined as the change in FFR_CT from the proximal to the distal in the left anterior descending artery (LAD) and left circumflex artery (LCX). The bifurcation angle was calculated from three-dimensional volume rendered images. Vessel morphology and plaque characteristics were also assessed.

RESULTS

ΔFFR_CT significantly correlated with the bifurcation angle (LAD angle, r = 0.35, p = 0.001; LCX angle, r = 0.26, p = 0.02) and vessel length (LAD angle, r = 0.30, p = 0.005; LCX angle, r = 0.49, p < 0.0001). In LAD, vessel length was the strongest predictor for distal FFR_CT of ≤ 0.80 (β-coefficient = 0.55, p = 0.0003), immediately followed by the bifurcation angle (β-coefficient = 0.24, p = 0.02). The bifurcation angle was a good predictor for a distal FFR_CT ≤ 0.80 (LAD angle, cut-off 31.0°, AUC 0.70, sensitivity 74%, specificity 68%; LCX angle, cut-off 52.6°, AUC 0.86, sensitivity 88%, specificity 85%).

CONCLUSIONS

In vessels with no apparent CAD, vessel length was the most influential factor on FFR_CT, directly followed by the bifurcation angle.

KEY POINTS

• Both LAD and LCX bifurcation angles are factors influencing FFR _CT. • Bifurcation angle is one of the predictors of a distal FFR_CT of ≤ 0.80 and an optimal cut-off value of 31.0° for the LAD and 52.6° for the LCX. • Bifurcation angle should be taken into consideration when interpreting numerical values of FFR_CT.

Influence of multiple stenoses on thrombosis formation: an in vitro study

Multiple lesions in the same vessel is one of the most common situations found in patients suffering from cardiovascular diseases, this complicates not only the assessment of the severity of each one but also their treatment. To date, the effect of multiple stenoses on different parameters has been simulated by numerical studies. Few others have implemented in vitro platforms for their investigation. However, visualization of thrombosis formation in this kind of lesion is still needed. This in vitro study monitors the formation of thrombus inside microchannels having one, two, and three stenoses. Whole blood was perfused through each channel at high shear rates (> 12,000 s−1), generating thrombosis. Flow changes across each lesion as well as the final percentage of aggregations were monitored. Thus, the location where total occlusion could be produced was found to be the first stenosis for all the cases. Less flow reaching the second and third stenoses was observed which demonstrates that aggregations were growing at the first one. This was verified by measuring the percentage of aggregations at the end of the test.

Impact of machine-learning-based coronary computed tomography angiography-derived fractional flow reserve on decision-making in patients with severe aortic stenosis undergoing transcatheter aortic valve replacement

OBJECTIVES

To evaluate feasibility and diagnostic performance of coronary CT angiography (CCTA)-derived fractional flow reserve (CT-FFR) for detection of significant coronary artery disease (CAD) and decision-making in patients with severe aortic stenosis (AS) undergoing transcatheter aortic valve replacement (TAVR) to potentially avoid additional pre-TAVR invasive coronary angiography (ICA).

METHODS

Consecutive patients with severe AS (n = 95, 78.6 ± 8.8 years, 53% female) undergoing pre-procedural TAVR-CT followed by ICA with quantitative coronary angiography were retrospectively analyzed. CCTA datasets were evaluated using CAD Reporting and Data System (CAD-RADS) classification. CT-FFR measurements were computed using an on-site machine-learning algorithm. A combined algorithm was developed for decision-making to determine if ICA is needed based on pre-TAVR CCTA: [1] all patients with CAD-RADS ≥ 4 are referred for ICA; [2] patients with CAD-RADS 2 and 3 are evaluated utilizing CT-FFR and sent to ICA if CT-FFR ≤ 0.80; [3] patients with CAD-RADS < 2 or CAD-RADS 2-3 and normal CT-FFR are not referred for ICA.

RESULTS

Twelve patients (13%) had significant CAD (≥ 70% stenosis) on ICA and were treated with PCI. Twenty-eight patients (30%) showed CT-FFR ≤ 0.80 and 24 (86%) of those were reported to have a maximum stenosis ≥ 50% during ICA. Using the proposed algorithm, significant CAD could be identified with a sensitivity, specificity, and positive and negative predictive value of 100%, 78%, 40%, and 100%, respectively, potentially decreasing the number of necessary ICAs by 65 (68%).

CONCLUSION

Combination of CT-FFR and CAD-RADS is able to identify significant CAD pre-TAVR and bears potential to significantly reduce the number of needed ICAs.

KEY POINTS

• Coronary CT angiography-derived fractional flow reserve (CT-FFR) using machine learning together with the CAD Reporting and Data System (CAD-RADS) classification safely identifies significant coronary artery disease based on quantitative coronary angiography in patients prior to transcatheter aortic valve replacement. • The combination of CT-FFR and CAD-RADS enables decision-making and bears the potential to significantly reduce the number of needed invasive coronary angiographies.

Myocardial deformation indices for detection of the functional significance of intermediate left anterior descending coronary artery stenosis: FFR guided study

This study aimed to investigate the diagnostic performance of non-invasive resting myocardial deformation indices in identifying functional significance of intermediate stenosis of the left anterior descending (LAD) artery. Patients with 50–70% LAD stenosis upon coronary angiography were enrolled and divided into group I with fractional flow reserve (FFR) > 0.8 and group II with FFR ≤ 0.8. Patients were subjected to conventional and speckle tracking echocardiography with measurement of myocardial deformation indices including regional peak longitudinal strain (PLS), global longitudinal strain (GLS), Post-systolic strain index (PSI), and time interval between Aortic valve closure (AVC) and PLS. The current study included 200 patients. Group II patients had significantly lower absolute mean values of regional (PLS) and (GLS) compared to group I (− 14.98 ± 5.05 and − 18.73 ± 3.92 vs. − 17.59 ± 3.62 and − 19.20 ± 2.61, p = 0.001 and 0.02, respectively). The FFR values of LAD correlated significantly and negatively with the time interval between AVC and regional PLS (r = − 0.201, p = 0.004) as well as PSI (r = − 0.257, p < 0.001). For identifying cases with FFR ≤ 0.8, the optimal cut-off value of the time interval between AVC and PLS was 76 ms with 77.8% sensitivity and 93.8% specificity. The best cut-off value of PSI was 13%, yielding 50% sensitivity and 87.5% specificity. In patients with intermediate 50–70% LAD coronary artery stenotic lesions, the PSI and the duration between AVC and regional PLS enabled the identification of functionally significant lesions with reasonable diagnostic accuracy.

Trial registration ZU-IRB#3199-20-11-2015 Registered 20 November 2015, IRB_123@medicine.zu.edu.eg.

Comparison of adenosine-independent pressure indices to fractional flow reserve in stent-jailed bifurcation side branches

OBJECTIVES AND BACKGROUND

This study aims to evaluate whether the high correlation and classification agreement of the instantaneous wave-free ratio (iFR) and the resting distal coronary to aortic pressure ratio (P_d /P_a ) with the fractional flow reserve (FFR) can be confirmed in stent-jailed side branches (J-SB).

METHODS

Consecutive patients (n = 49) undergoing provisional stenting were prospectively enrolled and a physiological assessment of the J-SB (n = 51) was performed. FFR, iFR, and P_d /P_a were measured and the hemodynamic relevance was determined using cutoff values of ≤0.80, ≤0.89, and ≤0.92, respectively.

RESULTS

Both iFR (r = 0.75) and P_d /P_a (r = 0.77) correlated closely with FFR. Classification agreement with FFR was 78% for iFR (81% sensitivity, 77% specificity) and 75% for P_d /P_a (63% sensitivity and 80% specificity). However, angiographic diameter stenosis and pressure indices correlated poorly. For a threshold of ≥70% stenosis, agreement concerning hemodynamic relevance was found in 59% for FFR, 69% for iFR, and 61% for P_d /P_a .

CONCLUSION

As reported for other lesion types, FFR and the adenosine-independent pressure indices iFR and P_d /P_a show close correlation and a high classification agreement of approximately 75%-80% in J-SB. Therefore, iFR can be regarded as a recommendable alternative to FFR for the guidance of provisional stenting in bifurcation lesions.

Coronary Artery and Cardiac Disease in Patients With Type 2 Myocardial Infarction: A Prospective Cohort Study

BACKGROUND

Type 2 myocardial infarction is caused by myocardial oxygen supply-demand imbalance, and its diagnosis is increasingly common with the advent of high-sensitivity cardiac troponin assays. Although this diagnosis is associated with poor outcomes, widespread uncertainty and confusion remain among clinicians as to how to investigate and manage this heterogeneous group of patients with type 2 myocardial infarction.

METHODS

In a prospective cohort study, 8064 consecutive patients with increased cardiac troponin concentrations were screened to identify patients with type 2 myocardial infarction. We excluded patients with frailty or renal or hepatic failure. All study participants underwent coronary (invasive or computed tomography angiography) and cardiac (magnetic resonance or echocardiography) imaging, and the underlying causes of infarction were independently adjudicated. The primary outcome was the prevalence of coronary artery disease.

RESULTS

In 100 patients with a provisional diagnosis of type 2 myocardial infarction (median age, 65 years [interquartile range, 55-74 years]; 43% women), coronary and cardiac imaging reclassified the diagnosis in 7 patients: type 1 or 4b myocardial infarction in 5 and acute myocardial injury in 2 patients. In those with type 2 myocardial infarction, median cardiac troponin I concentrations were 195 ng/L (interquartile range, 62-760 ng/L) at presentation and 1165 ng/L (interquartile range, 277-3782 ng/L) on repeat testing. The prevalence of coronary artery disease was 68% (63 of 93), which was obstructive in 30% (28 of 93). Infarct-pattern late gadolinium enhancement or regional wall motion abnormalities were observed in 42% (39 of 93), and left ventricular systolic dysfunction was seen in 34% (32 of 93). Only 10 patients had both normal coronary and normal cardiac imaging. Coronary artery disease and left ventricular systolic dysfunction were previously unrecognized in 60% (38 of 63) and 84% (27 of 32), respectively, with only 33% (21 of 63) and 19% (6 of 32) on evidence-based treatments.

CONCLUSIONS

Systematic coronary and cardiac imaging of patients with type 2 myocardial infarction identified coronary artery disease in two-thirds and left ventricular systolic dysfunction in one-third of patients. Unrecognized and untreated coronary or cardiac disease is seen in most patients with type 2 myocardial infarction, presenting opportunities for initiation of evidence-based treatments with major potential to improve clinical outcomes.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03338504.

Fractional Flow Reserve: Patient Selection and Perspectives

The aim of this review was to discuss the current practice and patient selection for invasive FFR, new techniques to estimate invasive FFR and future of coronary physiology tests. We elaborate on the indication and application of FFR and on the contraindications and concerns in certain patient populations.

Effect of guidewire insertion in fractional flow reserve procedure for real geometry using computational fluid dynamics

BACKGROUND

Coronary artery disease is an abnormal contraction of the heart supply blood vessel. It limits the oxygenated blood flow to the heart. Thus, diagnosing its severity helps physicians to select the appropriate treatment plan. Fractional flow reserve (FFR) is the most accurate method to pinpoint the stenosis severity. However, inserting the guidewire across stenosis may cause a false overestimation of severity.

METHODS

To estimate the errors due to guidewire insertion, reconstructed three-dimensional coronary artery geometry from a patient-specific scan is used. A comprehensive three-dimensional blood flow model is developed. Blood is considered non-Newtonian and the flow is pulsatile. The model is numerically simulated using realistic boundary conditions.

RESULTS

The FFR value is calculated and compared with the actual flow ratio. Additionally, the ratio between pressure drop and distal dynamic pressure (CDP) is studied. The obtained results for each case are compared and analyzed with the case without a guidewire. It was found that placing the guidewire leads to overestimating the severity of moderate stenosis. It reduces the FFR value from 0.43 to 0.33 with a 23.26% error compared to 0.44 actual flow ratio and the CDP increases from 5.31 to 7.2 with a 35.6% error. FFR value in mild stenosis does not have a significant change due to placing the guidewire. The FFR value decreases from 0.83 to 0.82 compared to the 0.83 actual flow ratio.

CONCLUSION

Consequently, physicians should consider these errors while deciding the treatment plan.

Non-invasive characterization of complex coronary lesions

Conventional invasive diagnostic imaging techniques do not adequately resolve complex Type B and C coronary lesions, which present unique challenges, require personalized treatment and result in worsened patient outcomes. These lesions are often excluded from large-scale non-invasive clinical trials and there does not exist a validated approach to characterize hemodynamic quantities and guide percutaneous intervention for such lesions. This work identifies key biomarkers that differentiate complex Type B and C lesions from simple Type A lesions by introducing and validating a coronary angiography-based computational fluid dynamic (CFD-CA) framework for intracoronary assessment in complex lesions at ultrahigh resolution. Among 14 patients selected in this study, 7 patients with Type B and C lesions were included in the complex lesion group including ostial, bifurcation, serial lesions and lesion where flow was supplied by collateral bed. Simple lesion group included 7 patients with lesions that were discrete, [Formula: see text] long and readily accessible. Intracoronary assessment was performed using CFD-CA framework and validated by comparing to clinically measured pressure-based index, such as FFR. Local pressure, endothelial shear stress (ESS) and velocity profiles were derived for all patients. We validates the accuracy of our CFD-CA framework and report excellent agreement with invasive measurements ([Formula: see text]). Ultra-high resolution achieved by the model enable physiological assessment in complex lesions and quantify hemodynamic metrics in all vessels up to 1mm in diameter. Importantly, we demonstrate that in contrast to traditional pressure-based metrics, there is a significant difference in the intracoronary hemodynamic forces, such as ESS, in complex lesions compared to simple lesions at both resting and hyperemic physiological states [n = 14, [Formula: see text]]. Higher ESS was observed in the complex lesion group ([Formula: see text] Pa) than in simple lesion group ([Formula: see text] Pa). Complex coronary lesions have higher ESS compared to simple lesions, such differential hemodynamic evaluation can provide much the needed insight into the increase in adverse outcomes for such patients and has incremental prognostic value over traditional pressure-based indices, such as FFR.

The absence of evidence is not the evidence of absence: A case report on the challenges in diagnosing ostial left main stenosis

Because left main (LM) coronary artery stenosis is known to have higher mortality and morbidity compared to lesions in other territories, an early diagnosis and management are crucial to prevent worse outcomes. Due to limitations of coronary angiography (CA), the diagnosis of ostial LM stenosis solely based on CA may result in underdiagnosis of such lesions. Therefore, additional testing is often needed either by pressure wire or intravascular ultrasound (IVUS) to make appropriate diagnosis. We, hereby, present a case of left main ostial stenosis in a 56-year-old male that was missed on multiple coronary angiograms, and highlights many of the considerations in the diagnosis of LM disease.

Usefulness of the Hybrid RFR-FFR Approach: Results of a Prospective and Multicenter Analysis of Diagnostic Agreement between RFR and FFR-The RECOPA (REsting Full-Cycle Ratio Comparation versus Fractional Flow Reserve (A Prospective Validation)) Study

Background

The resting full‐cycle ratio (RFR) is a novel resting index which in contrast to the gold standard (fractional flow reserve (FFR)) does not require maximum hyperemia induction. The objectives of this study were to evaluate the agreement between RFR and FFR with the currently recommended thresholds and to design a hybrid RFR-FFR ischemia detection strategy, allowing a reduction of coronary vasodilator use.

Materials and Methods

Patients subjected to invasive physiological study in 9 Spanish centers were prospectively recruited between April 2019 and March 2020. Sensitivity and specificity studies were made to assess diagnostic accuracy between the recommended levels of RFR ≤0.89 and FFR ≤0.80 (primary objective) and to determine the RFR “grey zone” in order to define a hybrid strategy with FFR affording 95% global agreement compared with FFR alone (secondary objective).

Results

A total of 380 lesions were evaluated in 311 patients. Significant correlation was observed (R² = 0.81; P < 0.001) between the two techniques, with 79% agreement between RFR ≤ 0.89 and FFR ≤ 0.80 (positive predictive value, 68%, and negative predictive value, 80%). The hybrid RFR-FFR strategy, administering only adenosine in the “grey zone” (RFR: 0.86 to 0.92), exhibited an agreement of over 95% with FFR, with high predictive values (positive predictive value, 91%, and negative predictive value, 92%), reducing the need for vasodilators by 58%.

Conclusions

Dichotomous agreement between RFR and FFR with the recommended thresholds is significant but limited. The adoption of a hybrid RFR-FFR strategy affords very high agreement, with minimization of vasodilator use.

Coronary Computed Tomographic Angiography Imaging as a Prognostic Indicator for Coronary Artery Disease: Data from a Lebanese Tertiary Center

Background:

Coronary artery disease (CAD) is a major cause of death and disability worldwide. Coronary computed tomographic angiography (CCTA) is a noninvasive imaging technique with a high negative predictive value (NPV). Most studies were done in developed countries, where the prevalence of CAD does not reflect the actual disease burden in developing countries, such as Lebanon.

Methods:

We retrospectively evaluated the prognostic value of CCTA in predicting acute myocardial events (AMEs) in 200 Lebanese patients. We determined if specific medical and radiological characteristics are linked with AME and looked for any association between the patient's medical risk factors and the type/location of detected atheromatous plaques. Patients' records were reviewed, and the follow-up period of 5–8 years ensued. Chi-square/Fisher test and Student's t-test were used, in addition to multinomial logistic regression to adjust for the confounding variables. P <0.05 was considered statistically significant.

Results:

Our study showed that CCTA had a NPV that reaches 97.9% in asymptomatic patients, a positive predictive value (PPV) of 76.4% for symptomatic patients, a sensitivity of 88.9%, and a specificity of 52.5%. AMEs were significantly increased in patients with a mixed plaque type and/or a moderate-to-severe lumen reduction on CCTA.

Conclusions:

CCTA is a sensitive modality for plaque detection and is found to have a remarkably high NPV for asymptomatic patients. A CCTA, along with a low pretest clinical probability of CAD, can be sufficient to rule out an AME for up to 8 years.

Meta-Analysis of Complete versus Culprit-Only Revascularization in Patients with ST-Segment Elevation Myocardial Infarction and Multivessel Coronary Disease

Approximately half of patients with ST-segment elevation myocardial infarction (STEMI) present with noninfarct related multivessel coronary artery disease (CAD) during primary percutaneous coronary intervention (PCI). However, questions remain concerning whether patients with STEMI and multivessel CAD should routinely undergo complete revascularization. Our objective was to compare the risks of major cardiovascular outcomes and procedural complications in patients with STEMI and multivessel CAD randomized to complete revascularization versus culprit-only PCI. We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) comparing complete revascularization to culprit-only PCI. RCTs were identified via a systematic search of MEDLINE, Embase, and Cochrane CENTRAL. Count data were pooled using DerSimonian and Laird random-effects models with inverse variance weighting to obtain relative risks (RRs) and 95% confidence intervals (CIs). A total of 9 RCTs (n = 6,751) were included, with mean/median follow-up times ranging from 6 to 36 months. Compared with culprit-only PCI, complete revascularization was associated with a substantial reduction in major adverse cardiovascular events (13.1% vs 22.1%; RR: 0.54; 95%CI: 0.43 to 0.66), repeat myocardial infarction (4.9% vs 6.8%; RR: 0.64; 95%CI: 0.48 to 0.84), and repeat revascularization (3.7% vs 12.3%; RR: 0.33; 95%CI: 0.25 to 0.44). Complete revascularization may have beneficial effects on all-cause and cardiovascular mortality, but 95%CIs were wide. Findings for stroke, major bleeding, and contrast-induced acute kidney injury were inconclusive. In conclusion, complete coronary artery revascularization appears to confer benefit over culprit-only PCI in patients with STEMI and multivessel CAD, and should be considered a first-line strategy in these patients.

Sex Differences in Coronary Computed Tomography Angiography-Derived Fractional Flow Reserve: Lessons From ADVANCE

OBJECTIVES

This study is to determine the management and clinical outcomes of patients investigated with coronary computed tomography angiography (CCTA)-derived fractional flow reserve (FFR_CT) according to sex.

BACKGROUND

Women are underdiagnosed with conventional ischemia testing, have lower rates of obstructive coronary artery disease (CAD) at invasive coronary angiography (ICA), yet higher mortality compared to men. Whether FFR_CT improves sex-based patient management decisions compared to CCTA alone is unknown.

METHODS

Subjects with symptoms and CAD on CCTA were enrolled (2015 to 2017). Demographics, symptom status, CCTA anatomy, coronary volume to myocardial mass ratio (V/M), lowest FFR_CT values, and management plans were captured. Endpoints included reclassification rate between CCTA and FFR_CT management plans, incidence of ICA demonstrating obstructive CAD (≥50% stenosis) and revascularization rates.

RESULTS

A total of 4,737 patients (n = 1,603 females, 33.8%) underwent CCTA and FFR_CT. Women were older (age 68 ± 10 years vs. 65 ± 10 years; p < 0.0001) with more atypical symptoms (41.5% vs. 33.9%; p < 0.0001). Women had less obstructive CAD (65.4% vs. 74.7%; p < 0.0001) at CCTA, higher FFR_CT (0.76 ± 0.10 vs. 0.73 ± 0.10; p < 0.0001), and lower likelihood of positive FFR_CT ≤ 0.80 for the same degree stenosis (p < 0.0001). A positive FFR_CT ≤0.80 resulted in equal referral to ICA (n = 510 [54.5%] vs. n = 1,249 [56.5%]; p = 0.31), but more nonobstructive CAD (n = 208 [32.1%] vs. n = 354 [24.5%]; p = 0.0003) and less revascularization (n = 294 [31.4%] vs. n = 800 [36.2%]; p < 0.0001) in women, unless the FFR_CT was ≤0.75 where revascularization rates were similar (n = 253 [41.9%] vs. n = 715 [46.4%]; p = 0.06). Women have a higher V/M ratio (26.17 ± 7.58 mm³/g vs. 24.76 ± 7.22 mm³/g; p < 0.0001) that is associated with higher FFR_CT independent of degree stenosis (p < 0.001). Predictors of revascularization included stenosis severity, FFR_CT, symptoms, and V/M ratio (p < 0.001) but not female sex (p = 0.284).

CONCLUSIONS

FFR_CT differs between the sexes, as women have a higher FFR_CT for the same degree of stenosis. In FFR_CT-positive CAD, women have less obstructive CAD at ICA and less revascularization, which is associated with higher V/M ratio. The findings suggest that CAD and FFR_CT variations by sex need specific interpretation as these differences may affect therapeutic decision making and clinical outcomes. (Assessing Diagnostic Value of Non-invasive FFRCT in Coronary Care [ADVANCE]; NCT02499679).

Analysis of the effect of guidewire position on stenosis diagnosis using computational fluid dynamics

BACKGROUND

Fractional flow reserve is an accurate method for diagnosing stenosis. The difficulty in using this procedure lies in placing the guidewire precisely at the blood vessel centerline. Owing to the long distance between the insertion point and the stenosis, a guidewire inclination can occur. Therefore, the main objective of this study is to investigate how the measured pressure in a blood vessel varies with the guidewire position.

METHODS

A three-dimensional model of blood flow is developed and numerically simulated. Two positions and two inclination angles from the blood vessel centerline and three throat diameters are investigated. The predicted results are validated using the available experimental data. The predicted results and actual measurements are observed to agree well with each other.

RESULTS

The pressure drop coefficient (CDP) increases because of guidewire insertion. When the guidewire is placed at inclined positions in moderate stenosis, the values of CDP are 66 and 68, depending on the inclination angle; the errors in CDP are 69% and 76%, respectively. At a high flow rate, the errors are reduced to 67% and 70%, respectively. The error in the CDP ranges from 42% to 61% when the guidewire is placed parallel to the centerline. For severe stenosis, the CDP is nearly the same at all positions and varies between 240 and 250; without a guidewire, the CDP is 163.

CONCLUSIONS

The findings confirmed that practitioners should be aware of the guidewire position during the operation. The displacement of the guidewire should be estimated, and the corresponding error must be considered.

Feasibility and accuracy of SPECT myocardial perfusion imaging in end-stage lung disease

BACKGROUND

Coronary artery disease (CAD) is associated with increased mortality in patients with chronic lung disease. However, non-invasive diagnostic of CAD is difficult, especially in patients with more advanced disease. Therefore, we aimed to assess the feasibility and accuracy of SPECT-myocardial perfusion imaging (MPI) stress testing with regadenoson in patients with end-stage lung disease (ELD) undergoing assessment of stable CAD.

METHODS

Between January 2012 and May 2018, 102 patients with ELD, who were referred to our institution for lung transplant evaluation, were assessed retrospectively. All patients underwent both stress SPECT-MPI as well as coronary angiography.

RESULTS

The mean age in our population was 57±6 years. All patients had severe pulmonary function impairment. During stress SPECT-MPI 14 patients (14%) reported regadenoson-related symptoms, but only 2 patients (2%) required medical treatment. Coronary angiography revealed obstructive CAD in 20 patients (20%). Among those, 5 patients had abnormal SPECT-MPI and PCI was performed in 3 patients accordingly. In 14 patients with obstructive CAD, revascularization was deferred based on normal SPECT-MPI findings.

CONCLUSIONS

SPECT-MPI using regadenoson is well tolerated in patients with ELD and can help to make decisions about coronary revascularization before lung transplant.

Cardiac magnetic resonance for asymptomatic patients with type 2 diabetes and cardiovascular high risk (CATCH): a pilot study

Background

Stress cardiovascular magnetic resonance (CMR) to screen for silent myocardial ischaemia in asymptomatic high risk patients with type 2 diabetes mellitus (DM) has never been performed, and its effectiveness is unknown. Our aim was to determine the feasibility of a screening programme using stress CMR by obtaining preliminary data on the prevalence of silent ischaemia caused by obstructive coronary artery disease (CAD) and quantify myocardial perfusion in asymptomatic high risk patients with type 2 diabetes.

Methods

In this prospective cohort study, we recruited 63 asymptomatic DM patients (mean age 66 years ± 4.4 years; 77.8% male); with Framingham risk score ≥ 20% from 3 sites from June 2017 to August 2018. Normal volunteers were recruited to determine normal global myocardial perfusion reserve index (MPRI). Adenosine stress CMR and global MPRI was performed and measured in all subjects. Positive stress CMR cases were referred for catheter coronary angiography (CCA) with/without fractional flow reserve (FFR) measurements. Positive CCA was defined as an FFR ≤ 0.8 or coronary narrowing ≥ 70%. Patients were followed up for major adverse cardiovascular events. Prevalence is presented as patient numbers and percentage. Mann–Whitney U test was used to compare global MPRI between patients and normal volunteers.

Results

13 patients had positive stress CMR with positive CCA (20.6% of patient population), while 9 patients with positive stress CMR examinations had a negative CCA. 5 patients (7.9%) had infarcts detected of which 2 patients had no stress perfusion defects. 12 patients had coronary artery stents inserted, whilst 1 patient declined stent placement. DM patients had lower global MPRI than normal volunteers (n = 7) (1.43 ± 0.27 vs 1.83 ± 0.31 respectively; p < 0.01). After a median follow-up of 653 days, there was no death, heart failure, acute coronary syndrome hospitalisation or stroke.

Conclusion

20.6% of asymptomatic DM patients (with Framingham risk ≥ 20%) had silent obstructive CAD. Furthermore, asymptomatic patients have reduced global MPRI than normal volunteers.

Trial Registration: ClinicalTrials.gov Registration Number: NCT03263728 on 28th August 2017; https://clinicaltrials.gov/ct2/show/NCT03263728.

Feasibility of coronary angiogram-derived vessel fractional flow reserve in the setting of standard of care percutaneous coronary intervention and its correlation with invasive FFR

BACKGROUND

Vessel Fractional Flow Reserve (vFFR), a new angiography-derived method for the functional assessment of coronaries, was recently shown to have good correlation with invasive wire-derived FFR, when vFFR-specific image acquisition requirements were followed. We sought to investigate the feasibility of vFFR analysis and its correlation with FFR in the situation where angiography is completed in routine fashion, without intention for virtual analysis.

METHODS

Utilizing an anonymized database maintained at our Cardiovascular Imaging Core Laboratory, we included angiographic images from patients that underwent pre- and post-PCI FFR. CAAS Workstation 8.1 software (Pie Medical Imaging) was used for vFFR evaluation.

RESULTS

Out of 624 angiograms (312 pre-PCI and 312 post-PCI), vFFR was successfully analyzed in 219 (35.1%) (115 pre-PCI and 104 post-PCI). Reasons for vFFR analysis failure were: <2 angiographic projections (42.5%), table movement while acquisition (25.7%) and resolution incompatibility (15%). From 115 patients with analyzable pre-PCI vFFR, 74 (64.3%) showed agreement with the respective FFR results in terms of positive (≤0.80) vs negative (>0.80) FFR. Pearson's correlation coefficient between them was 0.449 (p < 0.0001). From 104 lesions with analyzable post-PCI vFFR, 94 had availability of FFR, 74 (78.7%) of which showed agreement between the vFFR and FFR. Pearson's correlation between the values was 0.115 (p = 0.2703).

CONCLUSION

vFFR could be analyzed in about one-third of previously completed angiographies and a weak correlation was seen between vFFR and FFR. Our results show the importance of following the pre-specified requirements for vFFR analysis. Further studies are needed to validate the software in different settings.

Diagnostic Performance of Machine Learning Based CT-FFR in Detecting Ischemia in Myocardial Bridging and Concomitant Proximal Atherosclerotic Disease

BACKGROUND

The diagnostic performance of coronary computed tomography angiography-derived fractional flow reserve (CT-FFR) in detecting ischemia in myocardial bridging (MB) has not been investigated to date.

METHODS

This retrospective multicentre study included 104 patients with left anterior descending MBs. MB was classified as either superficial or deep, short, or long, whereas all MB vessels were further divided into <50%, 50% to 69%, and ≥70% groups, according to proximal lumen stenosis on invasive coronary angiography. Diagnostic performance and receiver operating characteristics (ROC) of CT-FFR to detect lesion-specific ischemia was assessed on a per-vessel level, using invasive FFR as reference standard. Intraclass correlation coefficient (ICC) and Bland-Altman plots were used for agreement measurement.

RESULTS

Forty-eight MB vessels (46.2%) showed ischemia by invasive FFR (≤0.80). Sensitivity, specificity, and accuracy of CT-FFR to detect functional ischemia were 0.96 (0.85 to 0.99), 0.84 (0.71 to 0.92), and 0.89 (0.81 to 0.94), respectively, in all MB vessels. There were no differences in diagnostic performance between superficial and deep MB or between short and long MB (all P > 0.05). The accuracy of CT-FFR was 0.96 (0.85 to 0.99) in ≥70% stenosis, 0.82 (0.67 to 0.91) in 50% to 69% stenosis, and 0.89 (0.51 to 0.99) in <50% stenosis (P = 0.081). Bland-Altman analysis showed a slight mean difference between CT-FFR and invasive FFR of 0.014 (95% limit of agreement, -0.117 to 0.145). The ICC was 0.775 (95% confidence interval, 0.685-0.842, P < 0.001).

CONCLUSIONS

CT-FFR demonstrated high diagnostic performance for identifying functional ischemia in vessels with MB and concomitant proximal atherosclerotic disease when compared with invasive FFR. However, the clinical use of CT-FFR in patients with MB needs further study for stronger and more robust results.

Impact of Inflow Boundary Conditions on the Calculation of CT-Based FFR

Background: Calculation of fractional flow reserve (FFR) using computed tomography (CT)-based 3D anatomical models and computational fluid dynamics (CFD) has become a common method to non-invasively assess the functional severity of atherosclerotic narrowing in coronary arteries. We examined the impact of various inflow boundary conditions on computation of FFR to shed light on the requirements for inflow boundary conditions to ensure model representation. Methods: Three-dimensional anatomical models of coronary arteries for four patients with mild to severe stenosis were reconstructed from CT images. FFR and its commonly-used alternatives were derived using the models and CFD. A combination of four types of inflow boundary conditions (BC) was employed: pulsatile, steady, patient-specific and population average. Results: The maximum difference of FFR between pulsatile and steady inflow conditions was 0.02 (2.4%), approximately at a level similar to a reported uncertainty level of clinical FFR measurement (3–4%). The flow with steady BC appeared to represent well the diastolic phase of pulsatile flow, where FFR is measured. Though the difference between patient-specific and population average BCs affected the flow more, the maximum discrepancy of FFR was 0.07 (8.3%), despite the patient-specific inflow of one patient being nearly twice as the population average. Conclusions: In the patients investigated, the type of inflow boundary condition, especially flow pulsatility, does not have a significant impact on computed FFRs in narrowed coronary arteries.