Application of the DILEMMA score to improve lesion selection for invasive physiological assessment

Coronary Flow Rate Adds Predictive Capability for FFR Assessment

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

Functional Coronary Artery Assessment: a Systematic Literature Review

Cardiovascular diseases represent the number one cause of death in the world, including the most common disorders in the heart's health, namely coronary artery disease (CAD). CAD is mainly caused by fat accumulated in the arteries' internal walls, creating an atherosclerotic plaque that impacts the blood flow functional behavior. Anatomical plaque characteristics are essential but not sufficient for a complete functional assessment of CAD. In fact, plaque analysis and visual inspection alone have proven insufficient to determine the lesion severity and hemodynamic repercussion. Furthermore, the fractional flow reserve (FFR) exam, which is considered the gold standard for stenosis functional impair determination, is invasive and contains several limitations. Such a panorama evidences the need for new techniques applied to image exams to improve CAD functional assessment. In this article, we perform a systematic literature review on emerging methods determining CAD significance, thus delivering a unique base for comparing these methods, qualitatively and quantitatively. Our goal is to guide further studies with evidence from the most promising methods, highlighting the benefits from both areas. We summarize benchmarks, metrics for evaluation, and challenges already faced, thus shedding light on the requirements for a valid, meaningful, and accepted technique for functional assessment evaluation. We create a base of comparison based on quantitative and qualitative indicators and highlight the most relevant geometrical metrics that correlate with lesion significance. Finally, we point out future benchmarks based on recent literature.

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).

Impact of diabetes mellitus on the relationship between a Poiseuille-based index and fractional flow reserve in intermediate coronary lesions

BACKGROUND

The ratio of lesion length (LL) to the fourth power of minimal lumen diameter (MLD) (LL/MLD4) is a Poiseuille-based index with good diagnostic accuracy for the detection of coronary lesions with abnormal fractional flow reserve (FFR). We aimed to evaluate the impact of diabetes mellitus (DM) on its performance in intermediate coronary stenoses.

METHODS

We performed quantitative coronary angiography and simultaneous FFR measurement in 324 patients (234 non-DM and 90 DM) with 335 coronary lesions. The area under the receiver-operating characteristic curve (AUC) for angiographic parameters was determined, using an FFR value ≤0.80 to indicate the physiological significance of coronary stenoses.

RESULTS

In the non-DM group, FFR was significantly related to percent diameter stenosis (%DS) (R = -0.238) and LL/MLD4 ratio (R = -0.301; P < 0.001 for both). In the DM group, there was no correlation between %DS and FFR, whereas a close-to-threshold correlation was observed for the LL/MLD4 ratio (R = -0.205; P = 0.048). The AUC of LL/MLD4 ratio was significantly different between non-diabetic and diabetic subjects (0.738 vs. 0.540; P = 0.024). Moreover, the LL/MLD4 ratio showed higher AUCs than %DS (0.738 vs. 0.635; P = 0.017) and LL (0.738 vs. 0.634; P = 0.024) in non-diabetic population but this superiority did not exist in diabetic population.

CONCLUSION

We showed good diagnostic accuracy of LL/MLD4 ratio for identifying ischemic lesions in patients without DM. However, there was an impaired performance in diabetic patients and thus FFR measurement is essential to determine their hemodynamic status.

Feasibility and Validity of Computed Tomography-Derived Fractional Flow Reserve in Patients With Severe Aortic Stenosis: The CAST-FFR Study

BACKGROUND

Coronary artery disease is common in patients with severe aortic stenosis. Computed tomography-derived fractional flow reserve (CT-FFR) is a clinically used modality for assessing coronary artery disease, however, its use has not been validated in patients with severe aortic stenosis. This study assesses the safety, feasibility, and validity of CT-FFR in patients with severe aortic stenosis.

METHODS

Prospectively recruited patients underwent standard-protocol invasive FFR and coronary CT angiography (CTA). CTA images were analyzed by central core laboratory (HeartFlow, Inc) for independent evaluation of CT-FFR. CT-FFR data were compared with FFR (ischemia defined as FFR ≤0.80).

RESULTS

Forty-two patients (68 vessels) underwent FFR and CTA; 39 patients (92.3%) and 60 vessels (88.2%) had interpretable CTA enabling CT-FFR computation. Mean age was 76.2±6.7 years (71.8% male). No patients incurred complications relating to premedication, CTA, or FFR protocol. Mean FFR and CT-FFR were 0.83±0.10 and 0.77±0.14, respectively. CT calcium score was 1373.3±1392.9 Agatston units. On per vessel analysis, there was positive correlation between FFR and CT-FFR (Pearson correlation coefficient, R=0.64, P<0.0001). Sensitivity, specificity, positive predictive value, and negative predictive values were 73.9%, 78.4%, 68.0%, and 82.9%, respectively, with 76.7% diagnostic accuracy. The area under the receiver-operating characteristic curve for CT-FFR was 0.83 (0.72-0.93, P<0.0001), which was higher than that of CTA and quantitative coronary angiography (P=0.01 and P<0.001, respectively). Bland-Altman plot showed mean bias between FFR and CT-FFR as 0.059±0.110. On per patient analysis, the sensitivity, specificity, positive predictive, and negative predictive values were 76.5%, 77.3%, 72.2%, and 81.0% with 76.9% diagnostic accuracy. The per patient area under the receiver-operating characteristic curve analysis was 0.81 (0.67-0.95, P<0.0001).

CONCLUSIONS

CT-FFR is safe and feasible in patients with severe aortic stenosis. Our data suggests that the diagnostic accuracy of CT-FFR in this cohort potentially enables its use in clinical practice and provides the foundation for future research into the use of CT-FFR for coronary evaluation pre-aortic valve replacement.

Feasibility and Validity of Computed Tomography-Derived Fractional Flow Reserve in Patients With Severe Aortic Stenosis: The CAST-FFR Study

BACKGROUND

Coronary artery disease is common in patients with severe aortic stenosis. Computed tomography-derived fractional flow reserve (CT-FFR) is a clinically used modality for assessing coronary artery disease, however, its use has not been validated in patients with severe aortic stenosis. This study assesses the safety, feasibility, and validity of CT-FFR in patients with severe aortic stenosis.

METHODS

Prospectively recruited patients underwent standard-protocol invasive FFR and coronary CT angiography (CTA). CTA images were analyzed by central core laboratory (HeartFlow, Inc) for independent evaluation of CT-FFR. CT-FFR data were compared with FFR (ischemia defined as FFR ≤0.80).

RESULTS

Forty-two patients (68 vessels) underwent FFR and CTA; 39 patients (92.3%) and 60 vessels (88.2%) had interpretable CTA enabling CT-FFR computation. Mean age was 76.2±6.7 years (71.8% male). No patients incurred complications relating to premedication, CTA, or FFR protocol. Mean FFR and CT-FFR were 0.83±0.10 and 0.77±0.14, respectively. CT calcium score was 1373.3±1392.9 Agatston units. On per vessel analysis, there was positive correlation between FFR and CT-FFR (Pearson correlation coefficient, R=0.64, P<0.0001). Sensitivity, specificity, positive predictive value, and negative predictive values were 73.9%, 78.4%, 68.0%, and 82.9%, respectively, with 76.7% diagnostic accuracy. The area under the receiver-operating characteristic curve for CT-FFR was 0.83 (0.72-0.93, P<0.0001), which was higher than that of CTA and quantitative coronary angiography (P=0.01 and P<0.001, respectively). Bland-Altman plot showed mean bias between FFR and CT-FFR as 0.059±0.110. On per patient analysis, the sensitivity, specificity, positive predictive, and negative predictive values were 76.5%, 77.3%, 72.2%, and 81.0% with 76.9% diagnostic accuracy. The per patient area under the receiver-operating characteristic curve analysis was 0.81 (0.67-0.95, P<0.0001).

CONCLUSIONS

CT-FFR is safe and feasible in patients with severe aortic stenosis. Our data suggests that the diagnostic accuracy of CT-FFR in this cohort potentially enables its use in clinical practice and provides the foundation for future research into the use of CT-FFR for coronary evaluation pre-aortic valve replacement.

Comparison of diagnostic performance between quantitative flow ratio, non-hyperemic pressure indices and fractional flow reserve

Background

Quantitative flow ratio (QFR) is an estimate of fractional flow reserve (FFR) and is derived from 3-dimensional quantitative coronary angiography. The DILEMMA score is an angiographic technique developed to predict FFR. Unlike other diastolic indices such as instantaneous wave-free ratio (iFR), diastolic pressure ratio (dPR) and dPR_25-75, neither QFR nor DILEMMA score require pressure wires. This study sought to compare the diagnostic performance of QFR, diastolic indices and DILEMMA score to predict FFR.

Methods

Between January 2010 and December 2013, patients who underwent invasive coronary angiography and FFR assessments were retrospectively studied. iFR and dPR were derived from FFR pressure tracings. QFR was computed using commercial software.

Results

Eighty-five lesions (25% FFR significant) were included in this study. Median FFR was 0.88 (0.81-0.92). QFR (r_s=0.801), iFR (r_s=0.710), dPR (r_s=0.716), dPR_25-75 (r_s=0.715) and DILEMMA score (r_s=-0.623) significantly correlated with FFR (P<0.001). QFR ≤0.8 had a specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) of 95%, 86%, 86% and 95% respectively of predicting significant FFR (P<0.001). Receiver-operating characteristic (ROC) analysis revealed the AUC to predict significant FFR for QFR (0.947), iFR (0.880), dPR (0.883), dPR_25-75 (0.880) and DILEMMA score (0.916) were not significantly different. However, QFR was a better predictor of FFR than iFR (0.947 vs. 0.770, P<0.01).

Conclusions

QFR had excellent correlation and accuracy as measured against FFR. When compared to other diastolic indices and DILEMMA score, QFR performed at least as well as the other indices. QFR predicts FFR better than it predicts iFR. QFR is a convenient tool to assess significance of coronary stenosis and a reliable alternative to pressure-wire based indices. Prospective studies are required to investigate the performance and cost-effectiveness of QFR when independently used to guide clinical decision making.

Fractional Flow Reserve following Percutaneous Coronary Intervention

Fractional flow reserve (FFR) is routinely used to determine lesion severity prior to percutaneous coronary intervention (PCI). However, there is an increasing recognition that FFR may also be useful following PCI to identify mechanisms leading to restenosis and the need for repeat revascularization. Post-PCI FFR is associated with the presence and severity of stent under-expansion and may help identify peri-stent-related complications. FFR pullback may also unmask other functionally significant lesions within the target vessel that were not appreciable on angiography. Recent studies have confirmed the prognostic utility of performing routine post-PCI FFR and suggest possible interventional targets that would improve stent durability. In this review, we detail the theoretical basis underlying post-PCI FFR, provide practical tips to facilitate measurement, and discuss the growing evidence supporting its use.

Angiographic Functional Scoring of Coronary Artery Disease Predicts Mortality in Patients With Severe Aortic Stenosis Undergoing TAVR

BACKGROUND/PURPOSE

Coronary artery disease (CAD) is common in patients undergoing transcatheter aortic valve replacement (TAVR), although its prognostic significance is questionable. Significant CAD stratified using SYNTAX score (SS) has been associated with greater mortality, yet it is unknown whether the functional impact of CAD also impacts outcomes in this cohort. DILEMMA score (DS) is a validated angiographic functional scoring tool that correlates with fractional flow reserve and instantaneous wave-free ratio. This study sought to assess the functional impact of CAD on outcomes in patients undergoing TAVR for severe aortic stenosis (AS).

METHODS/MATERIALS

229 patients were included in this analysis. Patients underwent angiographic DS and SS and were classified using predefined values. The primary endpoint was one-year all-cause mortality, with secondary endpoints of 30-day major adverse cardiac and cerebrovascular events (MACCE).

RESULTS

The mean age was 83.9 ± 0.5 years (55.0% female), with 11.8% all-cause mortality. CAD defined by ≥30% stenosis in any vessel was not associated with adverse outcomes (HR = 1.08, p = 0.84). However, the risk of one-year mortality was greater in patients with either SS > 9 (20.8% vs. 9.4%, HR 2.34, p = 0.03) or DS > 2 (18.4% vs. 8.5%, HR = 2.28, p = 0.03). Both scoring systems were also associated with 30-day MACCE (both p < 0.05). After multivariate adjustment, independent predictors of one-year mortality were DS > 2 (HR = 2.29, p = 0.04), left ventricular ejection fraction <50% (HR 2.66, p = 0.04) and COPD (HR 2.43, p = 0.04).

CONCLUSION

Our results demonstrate that angiographic functional scoring is independently predictive of both 12-month mortality and 30-day MACCE following TAVR.

Beyond patency: Functional assessment of adequacy using internal mammary artery grafting to the left anterior descending artery

INTRODUCTION

Arterial graft physiology influences the long-term outcome of coronary artery bypass grafting (CABG). We studied factors that can affect the overall resistance to flow using internal mammary artery grafting to the left anterior descending artery.

METHODS

This was a prospective, nonrandomized observational study of 100 consecutive patients who underwent elective on-pump isolated or combined valve surgery and CABG. Coronary stenoses were assessed using conventional and quantitative coronary angiography assessment. The flow and pulsatility index (PI) of the grafts were assessed by transit-time flowmetry during cardioplegic arrest and at the end of the operation. Fractional polynomials were used to explore linearity, followed by multivariable regression analysis.

RESULTS

Univariate analysis demonstrated higher flows at the end of the operation in patients who had higher flows with the cross-clamp on (P < .001), in males (P = .004), in patients with a low PI at the end of the operation (P = .04), and in patients with a larger size of the recipient artery (P = .005). Multivariable regression analysis showed that the graft flow at the end of the operation was significantly associated with the mean flow with the cross-clamp on (P < .001), sex (P = .003), and PI at the end of the operation (P = .003). Concomitant valve surgery did not influence flows. Male patients had 18 mL/min higher flow.

CONCLUSIONS

The graft flow at the end of the operation can be determined by the flow with the cross-clamp on, the PI with the cross-clamp off and coronary artery. We reported differences in the graft flows between sexes, and for first the time, we introduced the concepts of "adequate flow" and "resistance-to-forward-flow" for patent coronary grafts.