Basing on the machine learning model to analyse the coronary calcification score and the coronary flow reserve score to evaluate the degree of coronary artery stenosis

AIM

To obtain the coronary artery calcium score (CACS) for each branch in coronary artery computed tomography angiography (CCTA) examination combined with the flow fraction reserve (FFR) of each branch in the coronary artery detected by CT and apply a machine learning model (ML) to analyse and predict the severity of coronary artery stenosis.

METHODS

All patients who underwent coronary computed tomography angiography (CCTA) from January 2019 to April 2022 in the HOSPITAL (T.C.M) AFFILIATED TO SOUTHWEST MEDICAL UNIVERSITY) were retrospectively screened, and their sex, age, characteristics of lipid-containing lesions, coronary calcium score (CACS) and CT-FFR values were collected. Five machine learning models, random forest (RF), k-nearest neighbour algorithm (KNN), kernel logistic regression, support vector machine (SVM) and radial basis function neural network (RBFNN), were used as predictive models to evaluate the severity of coronary stenosis.

RESULTS

Among the five machine learning models, the SVM model achieved the best prediction performance, and the prediction accuracy of mild stenosis was up to 90%. Second, age and male sex were important influencing factors of increasing CACS and decreasing CT-FFR. Moreover, the critical CACS value of myocardial ischemia >200.70 was calculated.

CONCLUSION

Through computer machine learning model analysis, we prove the importance of CACS and FFR in predicting coronary stenosis, especially the prominent vector machine model, which promotes the application of artificial intelligence computer learning methods in the field of medical analysis.

Utility of FFRCT in Patients with Chest Pain

PURPOSE OF REVIEW

The goal of this article is to review the data supporting the use of fractional flow reserve derived from coronary computed tomography angiography (FFRCT) in patients with chest pain.

REVIEW FINDINGS

Numerous clinical trials have demonstrated that the diagnostic accuracy of coronary computed tomography angiography (CCTA) can be improved with the use of FFRCT, primarily due to its superior specificity when compared to CCTA alone. This promising development may help reduce the need for invasive angiography in patients presenting with chest pain. Furthermore, some studies have indicated that incorporating FFRCT into decision-making is safe, with an FFRCT value of ≥ 0.8 being associated with favorable outcomes. While FFRCT has been shown to be feasible in patients with acute chest pain, further large-scale studies are warranted to confirm its utility. The emergence of FFRCT as a tool for the management of patients with chest pain is promising. However, potential limitations require the interpretation of FFRCT in conjunction with clinical context.

Long-Term Outcomes of Revascularization Compared to Deferral in Stable Coronary Artery Disease: a Review

PURPOSE OF REVIEW

The aim of this study is assessing the long-term outcomes of revascularization compared to deferral in stable coronary artery disease with available literature.

RECENT FINDINGS

The overall safety of stable coronary artery disease using IFR has been well established. There have been very few studies that have examined the safety of deferral of revascularization vs revascularization. As seen in listed literature, there appears to be no difference between revascularization compared to deferral in stable coronary artery disease.

Cost-effectiveness analysis of fractional flow reserve versus angiography among patients with coronary artery disease undergoing borderline coronary lesions treatment in Iran

BACKGROUND

The present study aimed to examine the cost-effectiveness of fractional flow reserve (FFR) versus angiography in treating borderline coronary lesions in patients with coronary artery stenosis in Iran. Cardiovascular disease is a leading cause of morbidity, mortality, readmission and the most important cause of disability in many countries, including Iran.

METHODS

This was a cost-effectiveness study conducted from the perspective of the Ministry of Health in 2019. The effectiveness was determined using four indicators: Quality Adjusted Life Years (QALYs), major adverse cardiac events (MACE), angina, and number of used stents (mean). Only direct medical costs (DMC) were estimated. To evaluate the cost-effectiveness of FFR versus angiography, A decision tree model was built by patient's level data.To coping with uncertainty Probabilistic sensitivity analysis (PSA) was performed.

RESULTS

Totally, 98 cases of FFR and 238 cases of angiography were included in the analysis. The average of QALY in FFR and angiography were 0.853 and 0.787, respectively. The cost of these methods were $6128 and $8388, correspondingly. Therefore, FFR was dominant compared to angiography. Results of the scatter plots and acceptability curve showed that FFR was more cost-effective than angiography in 94% and 96% of simulations for a threshold lower than $11,000 PPP. The PSA analysis confirmed the robustness of the study results.

CONCLUSION

The results indicated that FFR was more cost-effective than angiography in the cases studied in Iran. Consequently, FFR can be used as a high-priority diagnostic method and it is recommendable to be included in insurance coverage.

Comparison of coronary CT angiography-based and invasive coronary angiography-based quantitative flow ratio for functional assessment of coronary stenosis: A multicenter retrospective analysis

BACKGROUND

The aim of this study was to evaluate the diagnostic performance of coronary CT angiography (CTA)-based quantitative flow ratio (QFR), namely CT-QFR, and compare it with invasive coronary angiography (ICA)-based Murray law QFR (μQFR), using fractional flow reserve (FFR) as the reference standard.

METHODS

Patients who underwent coronary CTA, ICA and pressure wire-based FFR assessment within two months were retrospectively analyzed. CT-QFR and μQFR were computed in blinded fashion and compared with FFR, all applying the same cut-off value of ≤0.80 to identify hemodynamically significant stenosis.

RESULTS

Paired comparison between CT-QFR and μQFR was performed in 191 vessels from 167 patients. Average FFR was 0.81 ​± ​0.10 and 42.4% vessels had an FFR ≤0.80. CT-QFR had a slightly lower correlation with FFR compared with μQFR, although statistically non-significant (r ​= ​0.87 versus 0.90, p ​= ​0.110). The vessel-level diagnostic performance of CT-QFR was slightly lower but without statistical significance than μQFR (AUC ​= ​0.94 versus 0.97, difference: -0.03 [95%CI: -0.00-0.06], p ​= ​0.095), and substantially higher than diameter stenosis by CTA (AUC difference: 0.17 [95%CI: -0.10-0.23], p ​< ​0.001). The patient-level diagnostic accuracy, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio and negative likelihood ratio for CT-QFR to identify FFR value ​≤ ​0.80 was 88%, 90%, 86%, 86%, 91%, 6.59 and 0.12, respectively. The diagnostic accuracy of CT-QFR was 84% in extensively calcified lesions, while in vessels with no or less calcification, CT-QFR showed a comparable diagnostic accuracy with μQFR (91% versus 92%, p ​= ​0.595). Intra- and inter-observer variability in CT-QFR analysis was -0.00 ​± ​0.04 and 0.00 ​± ​0.04, respectively.

CONCLUSIONS

Performance in diagnosis of hemodynamically significant coronary stenosis by CT-QFR was slightly lower but without statistical significance than μQFR, and substantially higher than CTA-derived diameter stenosis. Extensively calcified lesions reduced the diagnostic accuracy of CT-QFR.

Synergistic prognostic value of coronary distensibility index and fractional flow reserve based cCTA for major adverse cardiac events in patients with Coronary artery disease

BACKGROUND

Coronary distensibility index (CDI), as an early predictor of cardiovascular diseases, has the potential to complement coronary computed tomography angiography (cCTA)-derived fractional flow reserve (CT-FFR) for predicting major adverse cardiac events (MACEs). Thus, the prognostic value of CT-FFR combined with CDI for MACEs is worth exploring.

METHODS

Patients with a moderate or severe single left anterior descending coronary artery stenosis were included and underwent FFR and CDI analysis based on cCTA, followed up at least 1 year, and recorded MACEs. Multivariate logistic regression analysis was performed to determine independent predictors of MACEs. The area under of receiver operating characteristic (ROC) curve was used to evaluated evaluate the diagnostic performance of CT-FFR, CDI, and a combination of the two.

RESULTS

All the vessel-specific data were from LAD. 150 patients were analysed. 55 (37%) patients experienced MACEs during follow-up. Patients with CT-FFR ≤ 0.8 had higher percentage of MACEs compared with CT-FFR > 0.8 (56.3% vs.7.3%, p < 0.05). Patients' CDI was significantly decreased in MACEs group compared with non-MACEs group (p < 0.05). Multivariate analysis revealed that diabetes (p = 0.025), triglyceride (p = 0.015), CT-FFR ≤ 0.80 (p = 0.038), and CDI (p < 0.001) are independent predictors of MACEs. According to ROC curve analysis, CT-FFR combined CDI showed incremental diagnostic performance over CT-FFR alone for prediction of MACEs (AUC = 0.831 vs. 0.656, p = 0.0002).

CONCLUSION

Our study provides initial evidence that combining CDI with CT-FFR shows incremental discriminatory power for MACEs over CT-FFR alone, independent of clinical risk factors. Diabetes and triglyceride are also associated with MACEs.

Diagnostic performance of deep learning and computational fluid dynamics-based instantaneous wave-free ratio derived from computed tomography angiography

BACKGROUND AND OBJECTIVES

Both fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are widely used to evaluate ischemia-causing coronary lesions. A new method of CT-iFR, namely AccuiFRct, for calculating iFR based on deep learning and computational fluid dynamics (CFD) using coronary computed tomography angiography (CCTA) has been proposed. In this study, the diagnostic performance of AccuiFRct was thoroughly assessed using iFR as the reference standard.

METHODS

Data of a total of 36 consecutive patients with 36 vessels from a single-center who underwent CCTA, invasive FFR, and iFR were retrospectively analyzed. The CT-derived iFR values were computed using a novel deep learning and CFD-based model.

RESULTS

Mean values of FFR and iFR were 0.80 ± 0.10 and 0.91 ± 0.06, respectively. AccuiFRct was well correlated with FFR and iFR (correlation coefficients, 0.67 and 0.68, respectively). The diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of AccuiFRct ≤ 0.89 for predicting FFR ≤ 0.80 were 78%, 73%, 81%, 73%, and 81%, respectively. Those of AccuiFRct ≤ 0.89 for predicting iFR ≤ 0.89 were 81%, 73%, 86%, 79%, and 82%, respectively. AccuiFRct showed a similar discriminant function when FFR or iFR were used as reference standards.

CONCLUSION

AccuiFRct could be a promising noninvasive tool for detection of ischemia-causing coronary stenosis, as well as facilitating in making reliable clinical decisions.

Trans-lesional fractional flow reserve gradient as derived from coronary CT improves patient management: ADVANCE registry

BACKGROUND

The role of change in fractional flow reserve derived from CT (FFRCT) across coronary stenoses (ΔFFRCT) in guiding downstream testing in patients with stable coronary artery disease (CAD) is unknown.

OBJECTIVES

To investigate the incremental value of ΔFFRCT in predicting early revascularization and improving efficiency of catheter laboratory utilization.

MATERIALS

Patients with CAD on coronary CT angiography (CCTA) were enrolled in an international multicenter registry. Stenosis severity was assessed as per CAD-Reporting and Data System (CAD-RADS), and lesion-specific FFRCT was measured 2 ​cm distal to stenosis. ΔFFRCT was manually measured as the difference of FFRCT across visible stenosis.

RESULTS

Of 4730 patients (66 ​± ​10 years; 34% female), 42.7% underwent ICA and 24.7% underwent early revascularization. ΔFFRCT remained an independent predictor for early revascularization (odds ratio per 0.05 increase [95% confidence interval], 1.31 [1.26-1.35]; p ​< ​0.001) after adjusting for risk factors, stenosis features, and lesion-specific FFRCT. Among the 3 models (model 1: risk factors ​+ ​stenosis type and location ​+ ​CAD-RADS; model 2: model 1 ​+ ​FFRCT; model 3: model 2 ​+ ​ΔFFRCT), model 3 improved discrimination compared to model 2 (area under the curve, 0.87 [0.86-0.88] vs 0.85 [0.84-0.86]; p ​< ​0.001), with the greatest incremental value for FFRCT 0.71-0.80. ΔFFRCT of 0.13 was the optimal cut-off as determined by the Youden index. In patients with CAD-RADS ≥3 and lesion-specific FFRCT ≤0.8, a diagnostic strategy incorporating ΔFFRCT >0.13, would potentially reduce ICA by 32.2% (1638-1110, p ​< ​0.001) and improve the revascularization to ICA ratio from 65.2% to 73.1%.

CONCLUSIONS

ΔFFRCT improves the discrimination of patients who underwent early revascularization compared to a standard diagnostic strategy of CCTA with FFRCT, particularly for those with FFRCT 0.71-0.80. ΔFFRCT has the potential to aid decision-making for ICA referral and improve efficiency of catheter laboratory utilization.

Verification of Coronary Computed Tomography-Derived Fractional Flow Reserve Measurement Site for Detection of Significant Coronary Artery Disease

Background: The optimal site for measuring computed tomography (CT)-derived fractional flow reserve (FFR_CT) to detect significant coronary artery disease (CAD) remains unknown. We investigated how diagnostic performance changes with FFR_CT measurement site. Methods and Results: The diagnostic performance of FFR_CT, measured 1-2 cm distal to the stenosis vs. a far-distal site, in detecting significant CAD with invasive fractional flow reserve ≤0.8 was evaluated in 254 diseased vessels from 146 patients with stable or suspected CAD diagnosed by coronary CT angiography. Receiver operating characteristic curve analysis revealed a significantly larger area under the curve for FFR_CT measured 1-2 cm distal to the stenosis than at a far-distal site (0.829 vs. 0.791, respectively; P=0.0305). The rate of reclassification of positive FFR_CT was 19% for measurements made 1-2 cm distal to the stenosis, and diagnostic accuracy for FFR_CT 0.71-0.80 improved from 36% to 58% (P=0.0052). Vessel-based diagnostic accuracy of FFR_CT 1-2 cm distal to the stenosis and at a far-distal site was 75% and 65%, respectively (P<0.0001), with corresponding sensitivity of 87% and 94% (P=0.0039), specificity of 60% and 29% (P<0.0001), a positive predictive value of 73% and 62% (P=0.028), and a negative predictive value of 78% and 79% (P=0.958). Conclusions: Our data suggest measuring FFR_CT 1-2 cm distal to the stenosis has better diagnostic performance for detecting physiologically significant CAD.

Case report: Dobutamine stress intracoronary physiology and imaging to examine the functional and dynamic properties of an apparent malignant intra-arterial right coronary artery

Background

We present a case concerning a 64-year-old female with complaints of palpitations, chest pain, and an anomalous right coronary artery (RCA) from the opposite sinus (R-ACAOS) with a suspected malignant trajectory on computed tomography. She was referred to our clinic for a second opinion to re-assess the suggested treatment of coronary surgery.

Case summary

A coronary angiogram was performed demonstrating a RCA with a tapered ostium typical for an inter-arterial course. Dobutamine and adenosine stress test during simultaneous intracoronary flow, pressure, and ultrasound assessment, was performed to determine the functional significance. After 120 mcg adenosine, intracoronary baseline flow velocity increased from 14 cm/s to a peak flow velocity of 37 cm/s, demonstrating a sufficient coronary flow velocity reserve (CFVR) of 2.6. No intracoronary pressure drop during maximal hyperaemia was found. After maximum dobutamine stress, CFVR was measured 2.5. Fractional flow reserve measured 0.99. Cross-sectional area measurement through intravascular ultrasound demonstrated a diameter reduction from 14.6 mm² to 8.5 mm². Therefore, we concluded this aberrant trajectory was not of any functional relevance and should be considered non-malignant.

Discussion

There are several anatomic coronary anomalies which may contribute to coronary compression during exercise and are therefore correlated with sudden cardiac death. Right coronary artery from the opposite sinus is correlated with a low mortality rate of 0.2% in comparison to left-ACAOS at 6.3% over 20 years in participants of competitive sport. Therefore, strong evidence of ischaemia must be present before opting for surgery. Our pragmatic approach provided in our opinion enough evidence for a conservative treatment strategy.

Diagnostic performance of CT-derived resting distal to aortic pressure ratio (resting Pd/Pa) vs. CT-derived fractional flow reserve (CT-FFR) in coronary lesion severity assessment

Background

Computed tomography-derived fractional flow reserve (CT-FFR) has emerged as a promising non-invasive substitute for fractional flow reserve (FFR) measurement. Normally, CT-FFR providing functional significance of coronary artery disease (CAD) by using a simplified total coronary resistance index (TCRI) model. Yet the error or discrepancy caused by this simplified model remains unclear.

Methods

A total of 20 consecutive patients with suspected CAD who underwent CTA and invasive FFR measurement were retrospectively analyzed. CT-FFR and CT-(Pd/Pa)_rest values derived from the coronary CTA images. The diagnostic performance of CT-FFR and CT-(Pd/Pa)_rest were evaluated on a per-vessel level using C statistics with invasive FFR<0.80 as the reference standard.

Results

Of the 25 vessels eventually analyzed, the prevalence of functionally significant CAD were 64%. The Youden index of the ROC curve indicated that the best cutoff value of invasive resting Pd/Pa was 0.945 for identifying functionally significant lesions. Sensitivity, specificity, negative predictive value, positive predictive value and accuracy were 85%, 91%, 92%, 83% and 88% for CT-(Pd/Pa)_rest and 85%, 58% 69%, 78% and 72% for CT-FFR. Area under the receiver-operating characteristic curve (AUC) to detect functionally significant stenoses of CT-(Pd/Pa)_rest and CT-FFR were 0.87 and 0.90.

Conclusions

In this study, the results suggest CT-derived resting Pd/Pa has a potential advantage over CT-FFR in triaging patients for revascularization.

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.

Closed-loop geometric multi-scale heart-coronary artery model for the numerical calculation of fractional flow reserve

BACKGROUND AND OBJECTIVES

Fractional flow reserve (FFR) is considered to be the "gold standard" for the clinical diagnosis of functional myocardial ischemia. With the development of medical imaging and computational fluid dynamics (CFD), noninvasive computation of FFR has been developed. The most representative calculation method is the noninvasive FFR derived from coronary CT angiography (FFR_CT), but it cannot thoroughly simulate the real physiological structure of the cardiovascular system. In this study, we propose a noninvasive closed-loop FFR derived from coronary CT angiography (FFR_CCT).

METHODS

The closed-loop multi-scale model includes three parts: the heart module, the coronary artery module with microcirculation structure and the systemic circulation module. The proposed structure was formed by coupling a lumped parameter model (0D) with a 3D model, such that the 0D model provides the boundary conditions for the 3D model. We enrolled 100 patients through a prospective multi-center clinical trial and calculated their FFR_CCT. Then, we extracted the pressure and flow waveforms of the coronary stenosis vessels through closed-loop geometric multi-scale CFD calculations. We evaluated the accuracy of FFR_CCT in diagnosing myocardial ischemia using the clinical measurement of FFR as the standard.

RESULTS

The results of FFR_CCT calculation in all patients showed a good correlation between FFR_CCT and FFR (r = 0.64, p < 0.05). The AUC (95% CI) of FFR_CCT was 0.819 [0.72, 0.91]. The accuracy, specificity, sensitivity, positive predictive value and negative predictive value of FFR_CCT were 86%, 95%, 62%, 86% and 83%, respectively.

CONCLUSIONS

The closed-loop multi-scale model proposed in this study can simulate the physiological cycle in a more realistic way. FFR_CCT is a reliable diagnostic index for myocardial ischemia.

Total versus staged versus functional revascularization in NSTEACS patients with multivessel disease

Background

The optimal strategy for revascularization in patients with NSTEACS who had multivessel coronary artery disease. A lack of evidence exists about the role of complete coronary revascularization by PCI in patients with non-ST segment elevation acute coronary syndrome (NSTEACS). Till now, ACC/AHA and ESC guidelines are not clear regarding the optimal strategy for revascularization in NSTEACS patients with multivessel coronary artery disease. In this setting, identification of the culprit lesion by angiography only could be challenging. The objective is to compare the hospital and short-term (6 months) outcomes of 3 different coronary revascularization strategies in NSTEACS patients with and multivessel coronary artery disease.

Results

Our study was a prospective study that included 90 patients who presented with acute chest pain and were diagnosed with NSTEACS. The patients were divided into 3 groups according to the plan of management: total revascularization group (total group), staged revascularization group (staged group), and functional revascularization group using FFR (FFR group). We studied the effect of demographic data, risk factors, and angiographic and procedural criteria on hospital and short-term outcomes. No significant statistical difference was seen among the three groups regarding the hospital outcome (in-stent thrombosis, unstable angina, and renal impairment). Also, the short-term (after 6 months) outcome regarding myocardial infarction, hospitalization, stroke, and cardiac death did not differ significantly between the three groups.

Conclusions

Considering NSTEACS patients with multivessel disease, different coronary revascularization strategies (total, staged, or FFR) are comparable regarding immediate and short-term (6 months) clinical follow-up. FFR can change the preplanned management, and less number of stents per patient is needed when FFR is utilized.

Clinical prediction models of fractional flow reserve: an exploration of the current evidence and appraisal of model performance

Background

Invasive fractional flow reserve (FFR) is a standard indicator of coronary stenoses' hemodynamic severity. Clinical prediction models (CPMs) may help differentiate ischemic from non-ischemic lesions without using a pressure wire but by integrating related variables. This approach differs from that of physics-based models. However, it is not yet known which CPMs are the most reliable at detecting hemodynamic significance.

Methods

A systematic review was performed of relevant publications that developed or validated any FFR CPMs from inception to April 2019 in the PubMed, EMBASE, and Cochrane Library databases by two independent authors. The risk of bias and applicability were assessed using the prediction model risk of the bias assessment tool (PROBAST).

Results

A total of 11 unique CPMs and 5 subsequent external validation studies were identified. The prevalence of hemodynamically significant lesions (FFR ≤0.80) across the studies had a median of 37.1% (range: 20.7-68.0%). Lesion length, percent diameter stenosis, and minimal lumen diameter were the three most frequently used variables in the CPMs. Of the 11 FFR CPMs, 9 (82%) exhibited strong discrimination [area under the curve (AUC) >0.75], and 5 (45%) had been subject to external validation; however, calibration was only available for 3 models (27%). There was a high degree of applicability; however, none of the studies was assessed as having a low risk of bias. A CPM was identified that had undergone rigorous validation and calibration: the DILEMMA score (three validations; median AUC, 0.83).

Conclusions

Almost half of the existing FFR CPMs had been externally validated. Due to their good discrimination abilities, these FFR CPMs are useful tools that could reduce the need for invasive hemodynamic measurements. Future research that adheres to methodological guidelines should be undertaken to develop high-quality models in this setting. (PROSPERO registration number: CRD42019125011).

The association between the extent of lipidic burden and delta-fractional flow reserve: analysis from coronary physiological and near-infrared spectroscopic measures

Background

Vulnerable plaque features including lipidic plaque have been shown to affect fractional flow reserve (FFR). Given that formation and propagation of lipid plaque is accompanied by endothelial dysfunction which impairs vascular tone, the degree of lipidic burden may affect vasoreactivity during hyperemia, potentially leading to reduced FFR. Our aim is to elucidate the relationship of the extent of lipidic plaque burden with coronary physiological vasoreactivity measure.

Methods

We analyzed 89 subjects requeuing PCI due to angiographically intermediate coronary stenosis with FFR ≤0.80. Near-infrared spectroscopy (NIRS) and intravascular ultrasound were used to evaluate lipid-core burden index (LCBI) and atheroma volume at both target lesion (maxLCBI_4mm; maximum value of LCBI within any 4 mm segments) and entire target vessel (LCBI_vessel: LCBI within entire vessel). In addition to FFR, delta-FFR was measured by difference of distal coronary artery pressure/aortic pressure (Pd/Pa) between baseline and hyperemic state.

Results

The averaged FFR and delta-FFR was 0.74 (0.69-0.77), and 0.17±0.05, respectively. On target lesion-based analysis, maxLCBI_4mm was negatively correlated to FFR (ρ=-0.213, P=0.040), and it was positively correlated to delta-FFR (ρ=0.313, P=0.002). Furthermore, target vessel-based analysis demonstrated similar relationship of LCBI_vessel with FFR (ρ=-0.302, P=0.003) and delta-FFR (ρ=0.369, P<0.001). Even after adjusting clinical characteristics and lesion/vessel features, delta-FFR (by 0.10 increase) was independently associated with maxLCBI_4mm (β=57.2, P=0.027) and LCBI_vessel (β=24.8, P=0.007) by mixed linear model analyses.

Conclusions

A greater amount of lipidic plaque burden at not only "target lesion" alone but "entire target vessel" was associated with a greater delta-FFR. The accumulation of lipidic plaque materials at both local site and entire vessel may impair hyperemia-induced vasoreactivity, which causes a reduced FFR.

The reasons why fractional flow reserve and instantaneous wave-free ratio are similar using wave separation analysis

Background and objectives

Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are the two most commonly used coronary indices of physiological stenosis severity based on pressure. To minimize the effect of wedge pressure (P_wedge), FFR is measured during hyperemia conditions, and iFR is calculated as the ratio of distal and aortic pressures (P_d/P_a) in the wave-free period. The goal of this study was to predict P_wedge using the backward wave (P_back) through wave separation analysis (WSA) and to reflect the effect of P_wedge on FFR and iFR to identify the relationship between the two indices.

Methods

An in vitro circulation system was constructed to calculate P_wedge. The measurements were performed in cases with stenosis percentages of 48, 71, and 88% and with hydrostatic pressures of 10 and 30 mmHg. Then, the correlation between P_back by WSA and P_wedge was calculated. In vivo coronary flow and pressure were simultaneously measured for 11 vessels in all patients. The FFR and iFR values were reconstructed as the ratios of forward wave at distal and proximal sites during hyperemia and at rest, respectively.

Results

Based on the in vitro results, the correlation between P_back and P_wedge was high (r = 0.990, p < 0.0001). In vivo results showed high correlations between FFR and reconstructed FFR (r = 0.992, p < 0.001) and between iFR and reconstructed iFR (r = 0.930, p < 0.001).

Conclusions

Reconstructed FFR and iFR were in good agreement with conventional FFR and iFR. FFR and iFR can be expressed as the variation of trans-stenotic forward pressure, indicating that the two values are inferred from the same formula under different conditions.

Relationship Between Coronary Fractional Flow Reserve and Computational Fluid Dynamics Analysis in Moderate Stenosis of the Coronary Artery

Background: Fractional flow reserve (FFR) is used to evaluate the need for percutaneous coronary intervention (PCI) in cases of moderate stenosis of the coronary artery. Recently, diagnostic imaging support with computational fluid dynamics (CFD) analysis has been garnering attention. This study defines the relationship between FFR conducted for cardiac catheterization and CFD analyses conducted using coronary computed tomography (CT) for moderate stenosis, in addition to considering whether wall pressure (WP) and wall shear stress (WSS) can be used to evaluate ischemia.

Methods and Results: Cases in which FFR was measured via coronary CT and cardiac catheterization was performed within 3 months were collected retrospectively. In the CFD analysis, WP and WSS were calculated and compared with FFR. Three groups were created to compare results of CFD analysis and FFR values according to the location of the stenosis: the right coronary artery, the left anterior descending artery, and the left circumflex artery. There was a correlation between FFR and WSS according to CFD analysis for moderate stenosis of the coronary artery, with a cut-off value for treatment able to be calculated.

Conclusions: The results of this study suggest that ischemia can be evaluated by conducting CFD analysis (WSS) using coronary CT.

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.

Physiologic assessment of moderate coronary lesions: a step towards complete revascularization in coronary artery bypass grafting

Background

An accurate diagnostic assessment of coronary artery disease is crucial for patients undergoing coronary artery bypass grafting (CABG). Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) to guide complete revascularization have not been adequately studied in patients prior to CABG. We compared an anatomic to a physiologic assessment of moderate coronary lesions (40-70% stenosis) in patients referred for CABG.

Methods

We retrospectively reviewed 109 medical records of patients who underwent CABG at Tulane Medical Center from 2014 to 2016. Patients were divided into an FFR/iFR-guided and an angiography-guided group. Clinical characteristics, procedural outcomes, and clinical outcomes for the two groups were compared over an 18-month follow-up period.

Results

There were significantly higher rates of three-vessel anastomoses (85.7% vs. 74.7%, P<0.05) and venous grafting (85.7% vs. 76.8%, P<0.05) in the FFR/iFR group. The FFR/iFR group had a lower rate of grafts placed to the left anterior descending artery (LAD) distribution than the angiography group (7.1% vs. 29.5%, P<0.05). The FFR/iFR group had a higher rate of grafts placed to the left circumflex (LCx) artery distribution than the angiography group (28.6% vs. 9.5%, P<0.05). We observed a trend toward reduction in major adverse cardiac events (MACEs) (7.1% vs. 11.6%, P=0.369) and angina (0.0% vs. 6.3%, P=0.429) in the FFR/iFR group compared to the angiography group over 18 months.

Conclusions

Physiologic assessment of coronary lesions can effectively guide complete revascularization in patients undergoing CABG. Moreover, FFR/iFR-guided CABG was associated with significantly higher rates of three-vessel anastomoses, venous grafting, and graft distribution to the circumflex system.

Computed Tomography Fractional Flow Reserve to Guide Coronary Angiography and Intervention

Computed tomography angiography (CTA) has played a significant role in evaluation of coronary artery disease in the last decade and has demonstrated high sensitivity and negative predictive values. However, the positive predictive value as compared with invasive fractional flow reserve (FFR) is limited. CT-FFR has emerged as a disruptive noninvasive technology with higher specificity and diagnostic accuracy for detection of hemodynamically significant coronary lesions as compared with invasive FFR than conventional coronary CTA. CT-FFR has been shown to be cost-effective as a gate-keeper to invasive coronary angiography and has the potential to limit unnecessary invasive angiography studies.

Changes in coronary atherosclerosis, composition, and fractional flow reserve evaluated by coronary computed tomography angiography in patients with type 2 diabetes

Background

The use of coronary computed tomography angiography (CCTA) for noninvasive anatomic detection of coronary artery disease is increasing. Recently, fractional flow reserve (FFR) assessment using routinely acquired CCTA datasets (FFR_CT) has been developed. However, there are no reports about changes in coronary atherosclerosis, composition, and FFR_CT in patients with type 2 diabetes.

Methods

This prospective, multicenter, observational trial evaluated changes in coronary atherosclerosis after alogliptin therapy in patients with type 2 diabetes. Fifty-one patients with type 2 diabetes who underwent CCTA examination and having intermediate coronary artery stenosis were treated with 25 mg of alogliptin. After 48 weeks, CCTA examination was repeated. The primary endpoint was changes in FFR_CT, and the secondary endpoint was changes in total atheroma volume (TAV) from the baseline to the 48-week follow-up.

Results

The FFR_CT decreased from the baseline to follow-up, but not significantly. A significant increase in TAV (from 658.5 mm³ to 668.9 mm³, p = 0.048) was observed. Vessel volume tended to increase, whereas percentage atheroma volume and lumen volume did not change. A significant negative correlation was observed between percentage change in TAV and change in FFR_CT (r = −0.185, p = 0.048). A significant increase in calcified plaques (p = 0.01) and a decrease in intermediate-attenuation plaques (p = 0.006) was observed.

Conclusions

In Japanese patients with diabetes and intermediate coronary artery stenosis, alogliptin could not improve FFR_CT or reduce atheroma volume, whereas the plaque composition changed. A progression of atheroma volume was associated with a reduction in FFR_CT.

The prognostic value of residual coronary stenoses after functionally complete revascularisation

Fractional flow reserve (FFR) has become the gold standard for functional assessment of coronary artery stenosis. Studies have confirmed the superiority of FFR guided percutaneous coronary intervention (PCI) compared to angiography guided PCI. Due to the high cost of FFR, it is not economically viable for FFR to be incorporated into every routine invasive coronary angiography. As a result, visual estimation of diameter stenosis on invasive coronary angiography still remains the cornerstone for decision making regarding revascularisation treatment for patients. This is despite recent studies questioning the "visual functional mismatch" between diameter stenosis and FFR in 57% of patients with non-left main stenosis. In patients with multivessel disease, complete revascularisation leads to improved long term outcomes. However, some lesions classified as significant by angiography may not be functionally significant. Kobayashi and colleagues demonstrated that after functionally complete revascularization with FFR guidance, residual angiographic lesions that are not functionally significant do not reflect residual ischemia or predict a worse outcome, supporting functionally complete, rather than angiographically complete, revascularization.

Fractional flow reserve to guide surgical coronary revascularization

Coronary angiography has traditionally been used as the final diagnostic tool in the evaluation of coronary artery disease (CAD). However, conventional angiography identifies anatomically obstructive coronary disease, but it is limited in its ability to identify hemodynamically significant lesions. The emergence of fractional flow reserve (FFR) technology, in conjunction with angiography, offers a functional, as well as anatomic, assessment of epicardial coronary obstructions. Several pivotal studies have demonstrated that FFR-guided coronary revascularization is a safe and effective in patients with single and multivessel CAD. There are emerging data to suggest that FFR may also play an integral role in planning surgical revascularization and in the evaluation of post-coronary artery bypass patients and their graft patency. This review will explore the physiologic underpinnings of FFR methodology, its clinical value and limitations, and its applications in coronary artery bypass grafting (CABG) surgery.

Stenotic flow reserve derived from quantitative coronary angiography has modest but incremental value in predicting functionally significant coronary stenosis as evaluated by fractional flow reserve

BACKGROUND

Stenotic flow reserve (SFR) derived from quantitative coronary angiography (QCA) has been correlated with myocardial ischaemia as determined by pharmacological stress echocardiography. However, the diagnostic accuracy of SFR in predicting functionally significant coronary stenosis as assessed by the gold standard, fractional flow reserve (FFR), has not been previously characterised.

METHODS

Patients who underwent coronary angiography and FFR assessment between January 2010 and February 2012 in a single tertiary centre were retrospectively assessed. QCA parameters such as minimal lumen diameter (MLD), lesion length, diameter stenosis (DS), SFR, turbulent resistance (TR) and Poiseuille resistance (PR) were assessed. Significant FFR was defined as FFR ≤0.8. The diagnostic accuracy of QCA parameters to predict significant FFR was assessed by independent t-test and receiver operator characteristic (ROC) curve. Statistical significance was defined as P value of <0.05.

RESULTS

The study included 272 patients (age: 64±11, 70% males) and 415 vessels. There were 180 (43%) vessels which were FFR significant. The mean FFR value for all vessels was 0.81±0.11. On comparison of AUC for predicting significant FFR, SFR (AUC =0.76) had the highest diagnostic accuracy compared to PR (AUC =0.75), % DS (AUC =0.73), TR (AUC =0.69), MLD (AUC =0.71) and DS >50% (AUC =0.64). Using a retrospectively determined optimal cut-off value of 3.51, the sensitivity of stenotic-flow-reserve was modest at 56% with good specificity of 81%. DS >50% had a sensitivity of 47% and specificity of 82% in predicting significant FFR. There was incremental predictive value when SFR was added to DS >50% on integrated discrimination improvement index (IDI =0.103, P<0.001) and net reclassification index (NRI =0.72, P<0.001).

CONCLUSIONS

SFR has modest diagnostic accuracy for predicting significant FFR but adds incremental predictive value to DS >50% for predicting significant FFR.

The instantaneous wave-free ratio (iFR) for evaluation of non-culprit lesions in patients with acute coronary syndrome and multivessel disease

BACKGROUND

Adenosine administration is currently required for evaluation of stenosis severity with fractional flow reserve (FFR). The instantaneous wave-free ratio (iFR) was recently introduced as an adenosine-free alternative in patients with stable CAD. The aim of the present study was to replicate the findings of previous iFR studies using an independent calculation algorithm and to evaluate the iFR for the assessment of non-culprit vessels in patients with acute coronary syndrome (ACS).

METHODS AND RESULTS

53 patients with ACS (65%) and at least one non-culprit intermediate lesion and 29 (35%) with stable CAD were included. A total of 123 stenoses were evaluated with both FFR and iFR. Classification match of iFR in ACS was not inferior to stable CAD (79.5% in ACS and 84.4% in CAD; p=0.497). Accordingly, no difference was observed in iFR/FFR correlation between ACS and stable CAD (r=0.66 in ACS vs. r=0.69 in CAD). Overall, a significant correlation was found between iFR and FFR (r=0.68; p<0.001) with a good diagnostic efficiency at ROC analysis (area under the curve: 0.87). In addition, neither the localization of the stenosis within the coronary tree (p=0.147) nor the time interval from the acute event (p=0.550) significantly influenced the concordance of iFR with FFR.

CONCLUSIONS

The iFR is a promising method for the assessment of non-culprit lesion severity in patients with acute coronary syndrome.

Measurement of the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography: Validation against fractional flow reserve

OBJECTIVES

The main objective of this study was to assess the blood flow rate and velocity in coronary artery stenosis using intracoronary frequency domain optical coherence tomography (FD-OCT). A correlation between fractional flow reserve (FFR) and FD-OCT derived blood flow velocity is also included in this study.

METHODS & RESULTS

A total of 20 coronary stenoses in 15 patients were assessed consecutively by quantitative coronary angiography (QCA), FFR and FD-OCT. A percutaneous coronary intervention (PCI) optimization system was used in this study which combines wireless FFR measurement and FD-OCT imaging in one platform. Stenoses were labelled severe if FFR ≤ 0.8. Blood flow rate and velocity in each stenosis segment were derived from the volumetric analysis of the FD-OCT pull back images. The FFR value was ≤ 0.80 in 5 stenoses (25%). The mean blood flow rate in severe coronary stenosis (n = 5) was 2.54 ± 0.55 ml/s as compared to 4.81 ± 1.95 ml/s in stenosis with FFR > 0.8 (n = 15). A good and significant correlation between FFR and FD-OCT blood flow velocity in coronary artery stenosis (r = 0.74, p < 0.001) was found.

CONCLUSION

The assessment of stenosis severity using FD-OCT derived blood flow rate and velocity has the ability to overcome many limitations of QCA and intravascular ultrasound (IVUS).

Fractional flow reserve guided revascularization in daily practice: clinical judgment does not always meet science

Measurement of the fractional flow reserve (FFR) during invasive coronary angiography is the accepted ''gold standard'' for assessing the functional significance of coronary artery lesions by determination of the characteristics of blood flow proximal and distal to a coronary stenosis during pharmacologically-mediated hyperemia. Abnormal FFR is associated with higher cardiac event rate if the coronary lesion is left untreated. On the other hand, it was shown that patients derived no clinical benefit from revascularization of angiographically obstructive lesions which were hemodynamically insignificant according to FFR (>0.8). This editorial comment refers to an observational cohort study which reported that in approximately 20% of real world patients the treatment strategy chosen was discordant with FFR findings. Our comment discusses these findings and concludes that while the standard of care is to treat patients in accordance with their FFR results (when available), it should be recognized that there are some clinical scenarios that may require a treatment strategy that is discordant with FFR result.

Fractional flow reserve application in everyday practice: adherence to clinical recommendations

Fractional flow reserve (FFR) is considered the gold standard for invasive assessment of functional, significant coronary stenosis. Nevertheless, its application and outcome in daily practice is rarely reported. We investigated whether decisions in clinical practice adhered to FFR-generated recommendations and whether FFR influenced cardiovascular outcomes. This retrospective, observational, cohort study included 189 patients that underwent FFR measurements during coronary angiography at our institution The median follow up was 27 months (range, 7-112 months). Clinical outcomes (up to 2 years) included all-cause mortality, cardiac-mortality, and major adverse cardiac events (MACE) which comprised cardiac mortality, non-fatal MI, target vessel revascularization, and coronary artery bypass graft (CABG). Patients most frequently presented with unstable angina (74.6%). Only 55 patients (29.1%) exhibited significant functional stenosis (FFR ≤0.8). Nevertheless, 68 patients (36%) underwent immediate coronary interventions; 64% were deferred from revascularization procedures and managed conservatively with optimal medical treatment. Thirty-five patients (18.5%) were treated in discordance with FFR results, but the overall MACE rate was similar to that of patients treated in concordance with FFR results (8.3% vs. 8.6%, P=0.41). In conclusion, in our everyday practice, the operator's decision was in discordance to the FFR measurements and indications in nearly 20% of cases. In these selected cases, the operator's subjective judgment may continue to play an important role.