Diagnostic performance of resting full-cycle ratio in identifying coronary lesions causing myocardial ischaemia: a meta-analysis

BACKGROUND

The resting full-cycle ratio (RFR), a new non-congestive resting index, is commonly used for physiological evaluations of coronary arteries.

AIMS

This study aims to evaluate the accuracy of RFR in detecting coronary artery stenosis with hemodynamic significance using fractional flow reserve (FFR) as the reference standard.

METHODS

Using 'RFR, resting full-cycle ratio' as the search term, we searched PubMed, Embase, Cochrane Library, and Web of Science databases, screening the literature according to the inclusion and exclusion criteria. By applying FFR ≤ 0.80 and RFR ≤ 0.89 as the diagnostic criteria for ischaemia, we analysed the synthetic sensitivity, specificity, and corresponding 95% confidence intervals, then synthesised the summary receiver operating characteristic curve (SROC).

RESULTS

Three studies were included in this meta-analysis, comprising 1,084 patients with 1,312 lesions. When we used FFR ≤ 0.80 as the reference standard, the synthesised sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (LR+), and negative likelihood ratio (LR-) of RFR in the diagnosis of coronary ischaemia were 73%, 81%, 67%, 85%, 3.95, and 0.33, respectively. Besides, the area under the curve (AUC) was 0.8276.

CONCLUSION

Using FFR as the reference standard, RFR has good diagnostic accuracy in detecting coronary ischaemic lesions and may be an effective alternative to FFR in the future, to some extent.

Prognostic impact of resting full-cycle ratio and diastolic non-hyperemic pressure ratios in patients with deferred revascularization

BACKGROUND

Non-hyperemic pressure ratios (NHPRs) like resting full-cycle ratio (RFR), diastolic pressure ratio during entire diastole (dPR[entire]) and diastolic pressure ratio during wave-free period (dPR[WFP]) are increasingly used to guide revascularization. The effect of NHPRs on mid-term prognosis has not been well established.

OBJECTIVE

We investigated the prognostic implications of NHRPs in patients whose revascularization was deferred based on fractional flow reserve (FFR) in a single-centre population.

METHODS

NHPRs and FFR were calculated offline from pressure tracings by an independent core laboratory. Follow-up data were acquired through records of hospital visits or telephone interviews. The primary outcome was a vessel-oriented composite outcome (VOCO) (a composite of cardiac death, vessel-related myocardial infarction, and ischemia-driven revascularization) in deferred vessels at 2 years.

RESULTS

316 patients with 377 deferred lesions were analysed. Discordance of NHPRs and FFR was found in 13.0-18.3% of lesions. The correlation coefficient between NHPRs was 0.99 (95% confidence interval 0.99-1.00). At 2 years, VOCO occurred in 19 lesions (5.0%). Estimated glomerular filtration rate < 30 mL/min/1.73 m2 [hazard ratio (HR) 5.7, p = 0.002], previous myocardial infarction (HR 3.3, p = 0.018), diabetes (HR 2.7, p = 0.042), RFR ≤ 0.89 (HR 2.7, p = 0.041) and dPR[WFP] ≤ 0.89 (HR 2.7, p = 0.049) were associated with higher incidence of VOCO at 2 years in the univariable analysis. A non-significant trend was found for dPR[entire] (HR 1.9, p = 0.26).

CONCLUSION

A positive RFR or dPR[WFP] were associated with a worse prognosis in deferred lesions, suggesting that the use of NHPRs in addition to FFR may improve risk estimation.

The reliability and utility of on-site CT-derived fractional flow reserve (FFR) based on fluid structure interactions: comparison with FFRCT based on computational fluid dynamics, invasive FFR, and resting full-cycle ratio

Fractional flow reserve (FFR) derived off-site by coronary computed tomography angiography (CCTA) (FFRCT) is obtained by applying the principles of computational fluid dynamics. This study aimed to validate the overall reliability of on-site CCTA-derived FFR based on fluid structure interactions (CT-FFR) and assess its clinical utility compared with FFRCT, invasive FFR, and resting full-cycle ratio (RFR). We calculated the CT-FFR for 924 coronary vessels in 308 patients who underwent CCTA for clinically suspected coronary artery disease. Of these patients, 35 patients with at least one obstructive stenosis (> 50%) detected on CCTA underwent both CT-FFR and FFRCT for further investigation. Furthermore, 24 and 20 patients underwent invasive FFR and RFR in addition to CT-FFR, respectively. The inter-observer correlation (r) of CT-FFR was 0.93 (95% confidence interval [CI] 0.85-0.97, P < 0.0001) with a mean absolute difference of - 0.0042 (limits of agreement - 0.073, 0.064); 97.3% of coronary arteries without obstructive lesions on CCTA had negative results for ischemia on CT-FFR (> 0.80). The correlation coefficient between CT-FFR and FFRCT for 105 coronary vessels was 0.87 (95% CI 0.82-0.91, P < 0.0001) with a mean absolute difference of - 0.012 (limits of agreement - 0.12, 0.10). CT-FFR correlated well with both invasive FFR (r = 0.66, 95% CI 0.36-0.84, P = 0.0003) and RFR (r = 0.78, 95% CI 0.51-0.91, P < 0.0001). These data suggest that CT-FFR can potentially substitute for FFRCT and correlates closely with invasive FFR and RFR with high reproducibility. Our findings should be proven by further clinical investigation in a larger cohort.

Impact of Left Ventricular Outflow Tract Obstruction on Coronary Physiological Assessment

Hypertrophic cardiomyopathy which is known to occasionally have coronary artery disease as concomitant disease may require coronary physiological assessment (Okayama et al., 2015; Shin et al., 2019 [1,2]). However, no study clarified the impact of left ventricular outflow tract obstruction on coronary physiological assessment. Herein, a case of hypertrophic obstructive cardiomyopathy concomitant with moderate coronary lesion was reported, in which dynamic change of physiological values was observed during pharmacological intervention. Specifically, fractional flow reserve (FFR) and resting full-cycle ratio (RFR) changed in an opposite fashion when the left ventricular outflow tract pressure gradient was decreased by intravenous propranolol and cibenzoline: in FFR from 0.83 to 0.79 and in RFR from 0.73 to 0.91. Cardiologists should pay attention to the presence of concomitant cardiovascular disorders in interpreting coronary physiological data.

Comparison of vessel fractional flow reserve with invasive resting full-cycle ratio in patients with intermediate coronary lesions

BACKGROUND

Vessel fractional flow reserve (vFFR) is a novel angiography-derived index for the assessment of myocardial ischemia without the need for pressure wires and hyperemic agents. vFFR has demonstrated very good diagnostic performance compared with the hyperemic index fractional flow reserve (FFR). The aim of this study was to compare vFFR to the non-hyperemic pressure ratio resting full-cycle ratio (RFR).

METHODS

This was a retrospective, observational, single-center study of an all-comer cohort undergoing RFR assessment. Invasive coronary angiography was obtained without a dedicated vFFR acquisition protocol, and vFFR calculation was attempted in all vessels interrogated by RFR (1483 lesions of 1030 patients).

RESULTS

vFFR could be analyzed in 986 lesions from 705 patients. Median diameter stenosis was 37% (interquartile range (IQR): 30.0-44.0%), vFFR 0.86 (IQR: 0.81-0.91) and RFR 0.94 (IQR: (0.90-0.97). The correlation between vFFR and RFR was strong (r = 0.70, 95% confidence interval (CI): 0.66-0.74, p < 0.001). Using RFR ≤0.89 as reference, the sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy for vFFR were 77%, 93%, 77%, and 92% and 89%. vFFR yielded a high area under the curve (AUC) of 0.92 (95% CI: 0.90-0.94). The good diagnostic performance of vFFR was confirmed among subgroups of patients with diabetes, severe aortic stenosis, female gender and lesions located in the left anterior descending artery.

CONCLUSION

vFFR has a high diagnostic performance taking RFR as the reference standard for evaluating the functional significance of coronary stenoses.

Going under the bridge: unmasking ischaemia and endothelial dysfunction of myocardial bridging: a case report

Background

Physiological assessment of myocardial bridging prevents unnecessary interventions. Non-invasive workup or visual coronary artery compression may underestimate the underlying ischaemia associated with myocardial bridging in symptomatic patients.

Case summary

A 74-year-old male presented to the outpatient clinic with chest pain and shortness of breath on exertion. He underwent coronary artery calcium scan showing an elevated calcium score of 404. On follow-up, he endorsed progressive worsening of symptoms with chest pain and decreased exercise tolerance. He was then referred for coronary angiography that revealed mid-left anterior descending myocardial bridging with initial normal resting full-cycle ratio of 0.92. Further workup after ruling out coronary microvascular disease demonstrated abnormal hyperaemic full-cycle ratio of 0.80 with a diffuse rise across the myocardial bridging segment on pullback. Our patient also had increased spastic response to hyperaemia on angiography, supporting the presence of underlying endothelial dysfunction and ischaemia, likely contributing to his exertional symptomology. The patient was started on beta-blocker therapy with improvement in symptoms and resolution of chest pain on follow-up.

Conclusion

Our case highlights the importance of thorough workup of myocardial bridging in symptomatic patients to better understand the underlying physiology and endothelial function after ruling out microvascular disease and consideration of hyperaemic testing if symptoms are suggestive of ischaemia.

Diagnostic performance of quantitative flow ratio versus fractional flow reserve and resting full-cycle ratio in intermediate coronary lesions

BACKGROUND

Quantitative flow ratio (QFR) is a novel angiography-derived index aimed to assess the functional relevance of coronary stenoses without pressure wires and adenosine. Good diagnostic yield with the hyperemic fractional flow reserve (FFR) have been reported, while data on the comparison of QFR to non-hyperemic pressure ratios (NHPR) are scarce.

METHODS

In this retrospective, observational and single-center study with a large population representative of the real practice, we assessed and compared the diagnostic performance of contrast flow (cQFR) and fixed flow (fQFR) QFR against the NHPR resting full-cyle ratio (RFR) using FFR as reference standard.

RESULTS

A total of 626 lesions from 544 patients were investigated. Mean diameter stenosis, FFR, cQFR, fQFR and RFR were 44.8%, 0.842, 0.847, 0.857 and 0.912, respectively. The correlation between cQFR and FFR was stronger (r = 0.830, P < 0.001) compared to that between FFR and RFR (r = 0.777, P < 0.001) and between cQFR and RFR (r = 0.687, P < 0.001). Using FFR ≤0.80 as reference, the sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy for cQFR were 82%, 95%, 87%, 92%, and 91%, respectively. cQFR displayed a higher area under the curve (AUC) than fQFR and RFR (0.938 vs. 0.891 vs. 0.869, P < 0.01). The good diagnostic yield of cQFR appeared to be maintained in different clinical subsets including female gender, aortic valve stenosis and atrial fibrillation, and in different anatomical subsets including focal and non-focal lesions.

CONCLUSION

cQFR has a high and better diagnostic performance than the NHPR RFR in predicting FFR-based functional significance of coronary stenoses.

Independent predictors of discordance between the resting full-cycle ratio and fractional flow reserve

The resting full-cycle ratio (RFR), a novel resting index, is well correlated with and shows good diagnostic accuracy to the fractional flow reserve (FFR). However, discordance results between the RFR and FFR have been observed to occur in about 20% of cases. This study aimed to clarify the prevalence and factors of discordant results between the RFR and FFR through a direct comparison of these values in daily clinical practice. A total of 220 intermediate coronary lesions of 156 consecutive patients with RFR and FFR measurements were allocated to four groups according to RFR and FFR cutoff values. We compared the angiographic, clinical, and hemodynamic variables among the groups. Discordant results between the RFR and FFR were observed in 19.6% of vessels, and the proportion of discordant results was significantly higher in the left main trunk and left anterior descending artery (LM + LAD) than in non-LAD vessels (25.2% vs. 12.3%, p = 0.006). In the multivariable regression analysis, LM + LAD location, hemodialysis, and peripheral artery disease were associated with a low RFR among patients with a high FFR. Conversely, the absence of diabetes mellitus and the presence of higher hemoglobin levels were associated with a higher RFR among patients with a low FFR. Specific angiographic and clinical characteristics such as LM + LAD location, hemodialysis, peripheral artery disease, and absence of diabetes mellitus and anemia can be independent predictors of physiologic discordance between the RFR and FFR.

Predictors of discordance between fractional flow reserve and resting full-cycle ratio in patients with coronary artery disease: Evidence from clinical practice

BACKGROUND

Fractional flow reserve (FFR) is an established method for assessing functional myocardial ischemia. Recently, the resting full-cycle ratio (RFR) has been introduced as a non-hyperemic index of functional coronary stenosis. However, the effects of clinical characteristics on discordance between RFR and FFR have not been fully evaluated. We aimed to identify clinical characteristics that influence FFR-RFR concordance.

METHODS

We included 410 patients with 573 intermediate coronary lesions who underwent clinically indicated invasive coronary angiography, as well as assessments of FFR and RFR. Receiver-operating characteristic (ROC) curves were created to assess the optimal cut-off values of RFR for predicting FFR ≤0.80.

RESULTS

RFR exhibited a strong correlation with FFR (r = 0.66, p < 0.0001). ROC analysis identified an optimal RFR cut-off value of 0.92 for categorization based on an FFR cut-off value of 0.8. The discordance of FFR >0.8 and RFR ≤0.92 (high FFR/low RFR) was observed in 112 lesions (20.9%), whereas the discordance of FFR ≤0.8 and RFR >0.92 (low FFR/high RFR) was observed in 35 lesions (6.5%). Higher rate of hemodialysis and lower hemoglobin levels were observed in the high FFR/low RFR group. Multivariate analyses identified female sex, left anterior descending artery (LAD) lesions, and hemodialysis as significant predictors of high FFR/low RFR. Conversely, body surface area and non-LAD lesions were significantly associated with low FFR/high RFR. Hemodialysis [odds ratio (OR): 2.41, 95% confidence interval (CI) 1.31-4.41; p = 0.005] and LAD lesions (OR: 1.86, 95% CI: 1.25-2.79; p = 0.002) were identified as independent predictors of overall FFR-RFR discordance.

CONCLUSIONS

RFR exhibited good diagnostic performance in the identification of functionally significant stenosis. However, RFR may overestimate functional severity in patients undergoing hemodialysis or in those with LAD lesions. Further prospective trials are required to demonstrate the non-inferiority of RFR to FFR.

All Resting Physiological Indices May Not Be Equivalent - Comparison Between the Diastolic Pressure Ratio and Resting Full-Cycle Ratio

BACKGROUND

Differences between resting full-cycle ratio (RFR) and diastolic pressure ratio (dPR) have not been sufficiently discussed. This study aimed to investigate if there is a difference in diagnostic performance between RFR and dPR for the functional lesion assessment and to assess if there are specific characteristics for discordant revascularization decision-makings between RFR and dPR.Methods and Results:A total of 936 intermediate lesions in 776 patients who underwent measurements of fractional flow reserve (FFR), coronary flow reserve (CFR), and the index of microcirculatory resistance (IMR) were retrospectively studied. Physiological indices were measured from anonymized pressure recordings at an independent core laboratory. Both RFR and dPR measures were highly correlated (r=0.997, P<0.001), with equivalent diagnostic performance relative to FFR-based decision-makings measured by using a dichotomous threshold of 0.80 (accuracy, 79.7% vs. 80.1%, respectively, P=0.960). The rate of diagnostic discordance was 4.7% (44/936), with no RFR-/dPR+ lesions observed. An overall significant difference in FFR and CFR values were detected among RFR/dPR-based classifications. The prevalence of positive studies was significantly higher for RFR than dPR (54.3% vs. 49.6%, respectively, P=0.047) when using the cut-off value of 0.89.

CONCLUSIONS

Both RFR and dPR were highly correlated, but the prevalence of positive studies was significantly different. The revascularization rate may differ significantly according to the resting index used.

Clinical feasibility of resting full-cycle ratio as a unique non-hyperemic index of invasive functional lesion assessment

The resting full-cycle ratio (RFR) is a new physiologic index to assess myocardial ischemia. RFR and fractional flow reserve (FFR), the conventionally used index, have not been directly compared in evaluating the entire cardiac cycle. Accordingly, we aimed to compare the diagnostic performance of RFR directly with FFR and clarify the clinical feasibility of RFR as a unique non-hyperemic index in evaluating the cardiac cycle. The diagnostic performance of RFR was compared with FFR using an automated online calculation software. A total of 156 consecutive patients with 220 intermediate lesions were enrolled. RFR showed significant correlation with FFR (r = 0.774, p < 0.001). RFR systole and RFR diastole did also with FFR (r = 0.918, p < 0.001, and r = 0.733, p < 0.001, respectively). With FFR < 0.80 as a reference standard, RFR showed good diagnostic accuracy (DA: 80.5%), similar DA between RFR systole and RFR diastole (79.6% and 87.5%, p = 0.58, respectively), and good DA in any lesion locations, especially in non-left anterior descending coronary artery (LAD) lesions (73.7% and 87.6% for LAD vs. non-LAD, p < 0.05, respectively). RFR is a feasible and reliable non-hyperemic index regardless of the difference in cardiac cycle in evaluating physiological lesion severity in daily practice.

Resting Full-Cycle Ratio (RFR) in the Assessment of Left Main Coronary Disease: Caution Required

Hyperaemia-free indices have been gaining traction in recent times due to the practical advantages they offer over the fractional flow reserve (FFR) in the evaluation of angiographically intermediate coronary lesions. More recently, a new hyperaemia-free index, the resting full-cycle ratio (RFR), was described and found to correlate closely with the instantaneous wave-free ratio (iFR). The comparison between FFR and these hyperaemia-free indices, however, is nuanced and remains an ongoing area of debate and investigation. Herein, we highlight one of the important differences between the RFR and FFR, specifically in relation to the assessment of left main coronary lesion. We contend that the interchangeability of these indices cannot always be assumed and clinicians need to be aware of these limitations in their clinical practice.

Intravascular ultrasound or optical coherence tomography-defined anatomic severity and hemodynamic severity assessed by coronary physiologic indices

INTRODUCTION AND OBJECTIVES

Fractional flow reserve or instantaneous wave-free ratio has become a standard criterion for revascularization. We sought to evaluate the association between intravascular ultrasound (IVUS) or optical coherence tomography (OCT)-derived quantitative plaque characteristics and the severity of physiologic stenosis.

METHODS

A total of 365 stenoses from 330 patients were evaluated. The association between IVUS or OCT-derived parameters and resting physiologic indices (instantaneous wave-free ratio, resting full-cycle ratio, and diastolic pressure ratio) and fractional flow reserve were explored.

RESULTS

Among the total number of lesions, 50.7% and 58.1% showed an instantaneous wave-free ratio ≤ 0.89 and fractional flow reserve ≤ 0.80, respectively. IVUS or OCT-derived parameters showed significant correlations with resting physiologic indices (P values <.005). The best cutoff values of IVUS minimum lumen area (MLA), plaque burden, OCT-MLA, and OCT-area stenosis to predict functional significance were the same (IVUS-MLA: 3.4 mm², plaque burden: 72.0%, OCT-MLA: 2.0 mm², OCT-area stenosis: 68.0%) for all resting physiologic indices (instantaneous wave-free ratio, resting full-cycle ratio, and diastolic pressure ratio). The best cutoff values for fractional flow reserve were an IVUS-MLA of 3.8 mm², plaque burden of 70.0%, OCT-MLA of 2.3 mm², and OCT-area stenosis of 65.0%. Regardless of IVUS or OCT-derived parameters, the overall diagnostic accuracies of the parameters were lower than 70% and discrimination indices were less than 0.75 for resting physiologic indices or fractional flow reserve.

CONCLUSIONS

The resting physiologic indices showed an identical relationship with IVUS or OCT-defined quantitative plaque characteristics. The diagnostic accuracy and discrimination ability of anatomical parameters were modest in predicting functional significance defined by resting and hyperemic invasive physiologic indices. This trial is registered at ClinicalTrials.gov (Identifier: NCT03795714).

Clinical Outcome of Lesions With Discordant Results Among Different Invasive Physiologic Indices - Resting Distal Coronary to Aortic Pressure Ratio, Resting Full-Cycle Ratio, Diastolic Pressure Ratio, Instantaneous Wave-Free Ratio, and Fractional Flow Reserve

BACKGROUND

We evaluated the 2-year clinical outcomes of deferred lesions with discordant results between resting and hyperemic pressure-derived physiologic indices, including resting distal to aortic coronary pressure (resting Pd/Pa), instantaneous wave-free ratio (iFR), resting full-cycle ratio (RFR), diastolic pressure ratio (dPR), and fractional flow reserve (FFR).Methods and Results:The 2-year clinical outcomes of 1,024 vessels (435 patients) with available resting Pd/Pa, iFR, RFR, dPR, and FFR data were analyzed according to a 4-group classification using known cutoff values (resting Pd/Pa ≤0.92, iFR/RFR/dPR ≤0.89, and FFR ≤0.80): Group 1 (concordant normal), Group 2 (high resting index and low FFR), Group 3 (low resting index and high FFR), and Group 4 (concordance abnormal). The primary outcome was vessel-oriented composite outcomes (VOCO) in deferred vessels at 2 years. In the comparison of VOCO risk among 4 groups classified according to FFR and 4 resting physiologic indices, Group 4 consistently showed a significantly higher risk of VOCO than Group 1. Comparison of VOCO risk among 4 groups classified according to iFR and other resting physiologic indices also showed the same results. The presence of discordance, either between hyperemic and resting indices or among resting indices, was not an independent predictor for VOCO.

CONCLUSIONS

Discordant results between resting physiologic indices and FFR and among the resting indices were not associated with increased risk of VOCO in deferred lesions.