Hemodynamic and Lesion Characteristics Associated with Discordance between the Instantaneous Wave-Free Ratio and Fractional Flow Reserve

Hyperemic vs non-hyperemic indexes discordance: Role of epicardial and microvascular resistance (HyperDisco Study)

BACKGROUND

Literature reports a 20 % discordance between hyperemic (FFR) and non-hyperemic indexes (NHi) of coronary stenosis lesions. This work aims to develop and test clinically, a formula relating FFR and NHi (including iFR, RFR and Pd/Pa) to study their discordance.

METHODS

We conducted a prospective, single-center, clinical study enrolling all patients undergoing full coronary physiology assessment with Coroventis CoroFlow Cardiovascular System (Abbott Vascular, St. Paul, Minnesota) to validate the developed formula: [Formula: see text] where IMR(BMR) is the hyperemic (basal) microvascular resistance and HSR(BSR) is the hyperemic (basal) stenosis resistance.

RESULTS

A total of 51 patients were enrolled, 72 % male, average age 67.4 ± 8.9. Mean hemodynamic data were: FFR 0.87 ± 0.07, iFR 0.93 ± 0.05, RFR 0.91 ± 0.05, Pd/Pa 0.92 ± 0.05, BMR 76.6 ± 51.6 mmHg*s, IMR 28.4 ± 22.8 mmHg*s, BSR 5.5 ± 4.7 mmHg, HSR 3.8 ± 2.9 mmHg*s, coronary flow reserve (CFR) 2.9 ± 1.6, resistive reserve ratio (RRR) 3.3 ± 2.0. Lin's Concordance and Bland Altman analysis showed an optimal correlation between measured and estimated data. Sensitivity analysis showed that: (1) FFR can underestimate epicardial stenosis severity leading to FFR- vs NHi + discordance in case of elevated IMR, (2) NHi can overestimate epicardial stenosis severity leading to FFR- vs NHi + in the case of low BMR, (3) if BSR > HSR, FFR- vs NHi + discordance can occur, while if BSR < HSR, FFR+ vs NHi- discordance can occur.

CONCLUSION

(1) NHi can be more reliable in case of elevated IMR; (2) FFR-CFR combination can be more reliable for low BMR occurring to compensate an epicardial stenosis; (3) NHi-CFR combination can be more reliable when BSR > HSR, while FFR-CFR combination can be more reliable when BSR < HSR. The combination between pressure and flow indexes (FFR-CFR or NHi-CFR) is more reliable when compensatory mechanisms occur.

The role of gender in resting full-cycle ratio (RFR) guided coronary revascularization

BACKGROUND

Gender-based differences in clinical outcomes of patients undergoing fractional flow reserved (FFR) guided coronary revascularization is well documented. This study aimed to compare resting full-cycle ratio (RFR) values between men and women and whether this translated into difference in clinical outcomes in patients who underwent RFR-guided coronary revascularization.

METHODS

This was a retrospective single-centre study of consecutive patients who underwent RFR-guided revascularization for coronary lesions with intermediate degree of stenosis. The primary endpoint was a composite of all-cause mortality, myocardial infarction (MI), unplanned revascularization, and unstable angina requiring hospital admission at one year.

RESULTS

In 373 consecutive patients (510 lesions, 26% women) there was no statistically significant difference in RFR value between men and women (0.90 ± 10 versus 0.90 ± 11, P = 0.95). There was no statistically significant difference between men and women in the primary endpoint, even after adjustment to the imbalance between the two groups [3.7% vs. 3.0%; HR 1.43, 95% CI (0.46 to 4.43), P = 0.54]; or its individual components of death (1.1% vs 0.8%, P = 0.76), MI (1.9% vs 0.8%, P = 0.38) or unplanned revascularization, including unstable angina admissions (2.6% vs 2.3%, P = 0.82). The comparable clinical outcomes were consistent across all different subgroups, including clinical presentation, diabetes status, left ventricle systolic function, kidney function, and the interrogated coronary artery.

CONCLUSION

Our study suggests no significant gender-based difference in the value of RFR or 1-year clinical outcomes in patients undergoing resting physiology guided coronary revascularization.

Cardiovascular events in patients with deferred lesions and chronic kidney disease

No study has reported the association between the worsening of chronic kidney disease (CKD) and cardiovascular events in patients with deferred coronary artery lesions. We included patients with deferred lesions, defined as a fractional flow reserve (FFR) value > 0.80 treated with conservative medical therapy. Patients were divided into three groups: group 1, CKD stages 1-2; group 2, CKD stages 3-5; and group 3, CKD stage 5D (hemodialysis), with the clinical outcomes compared. The primary endpoint was the first occurrence of target vessel myocardial infarction, ischemia-driven target-vessel revascularization, or all-cause death. The primary endpoint was noted in 17, 25, and 36 patients in groups 1, 2, and 3, respectively. Within the three groups, the incidence rate of deferred lesions was 7.0%, 10.4%, and 32.4%, respectively. No difference was observed in the incidence of the primary endpoint between groups 1 and 2 (log-rank p = 0.16). However, the patients in group 3 had a significantly higher risk for the primary endpoint than those in groups 1 and 2 (log-rank p < 0.0001). In the multivariate Cox proportional hazards model, the patients in group 3 exhibited a higher incidence of the primary endpoint than those in group 1 (HR: 2.14; 95% CI 1.02-4.49; p < 0.01). Careful management is needed in patients undergoing hemodialysis, even if coronary artery stenosis is considered a deferred lesion.

Outcomes of deferred revascularisation following negative fractional flow reserve in diabetic and non-diabetic patients: a meta-analysis

BACKGROUND

Fractional Flow Reserve (FFR) is a widely applied invasive physiological assessment, endorsed by major guidelines to aid in the decision to perform or defer revascularisation. While a threshold of  > 0.8 has been applied universally, clinical outcomes may be affected by numerous factors, including the presence of diabetes. This meta-analysis aims to investigate the outcomes of diabetic versus non-diabetic patients in whom revascularisation was deferred based on negative FFR.

METHODS

We performed a meta-analysis investigating the outcomes of diabetic and non-diabetic patients in whom revascularisation was deferred based on negative FFR. A search was performed on MEDLINE, PubMed and EMBASE, and peer-reviewed studies that reported MACE for diabetic and non-diabetic patients with deferred revascularisation based on FFR  > 0.8 were included. The primary end point was MACE.

RESULTS

The meta-analysis included 7 studies in which 4275 patients had revascularisation deferred based on FFR > 0.8 (1250 diabetic). Follow up occurred over a mean of 3.2 years. Diabetes was associated with a higher odds of MACE (OR = 1.66, 95% CI 1.35-2.04, p =  < 0.001), unplanned revascularisation (OR = 1.48, 95% CI 1.06-2.06, p = 0.02), all-cause mortality (OR = 1.74, 95% CI 1.20-2.52, p = 0.004) and cardiovascular mortality (OR = 2.08, 95% CI 1.07-4.05, p = 0.03).

CONCLUSIONS

For patients with stable coronary syndromes and deferred revascularisation based on FFR > 0.8, the presence of diabetes portends an increased long-term risk of MACE compared to non-diabetic patients. Trail registration URL:  https://www.crd.york.ac.uk/PROSPERO/ ; Unique identifier: CRD42022367312.

Fractional Flow Reserve Versus Instantaneous Wave-Free Ratio in Assessment of Lesion Hemodynamic Significance and Explanation of their Discrepancies. International, Multicenter and Prospective Trial: The FiGARO Study

Background

The FiGARO (FFR versus iFR in Assessment of Hemodynamic Lesion Significance, and an Explanation of Their Discrepancies) trial is a prospective registry searching for predictors of fractional flow reserve/instantaneous wave‐free ratio (FFR/iFR) discrepancy.

Methods and Results

FFR/iFR were analyzed using a Verrata wire, and coronary flow reserve was analyzed using a Combomap machine (both Philips‐Volcano). The risk polymorphisms for endothelial nitric oxide synthase and for heme oxygenase‐1 were analyzed. In total, 1884 FFR/iFR measurements from 1564 patients were included. The FFR/iFR discrepancy occurred in 393 measurements (20.9%): FFRp (positive)/iFRn (negative) type (264 lesions, 14.0%) and FFRn/iFRp (129 lesions, 6.8%) type. Coronary flow reserve was measured in 343 lesions, correlating better with iFR (R=0.56, P<0.0001) than FFR (R=0.36, P<0.0001). The coronary flow reserve value in FFRp/iFRn lesions (2.24±0.7) was significantly higher compared with both FFRp/iFRp (1.39±0.36), and FFRn/iFRn lesions (1.8±0.64, P<0.0001). Multivariable logistic regression analysis confirmed (1) sex, age, and lesion location in the right coronary artery as predictors for FFRp/iFRn discrepancy; and (2) hemoglobin level, smoking, and renal insufficiency as predictors for FFRn/iFRp discrepancy. The FFRn/iFRp type of discrepancy was significantly more frequent in patients with both risk types of polymorphisms (endothelial nitric oxide synthase_r+heme oxygenase‐1_r): 8 patients (24.2%) compared with FFRp/iFRn type of discrepancy: 2 patients (5.9%), P=0.03.

Conclusions

Predictors for FFRp/iFRn discrepancy were sex, age, and location in the right coronary artery. Predictors for FFRn/iFRp were hemoglobin level, smoking, and renal insufficiency. The risk type of polymorphism in endothelial nitric oxide synthase and heme oxygenase‐1 genes was more frequently found in patients with FFRn/iFRp type of discrepancy.

Registration

URL: https://clinicaltrials.gov; Unique identifier: NCT03033810.

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.

Comparison of Resting Full-Cycle Ratio and Fractional Flow Reserve in a German Real-World Cohort

Objective: The aim of this study was to evaluate non-hyperemic resting pressure ratios (NHPRs), especially the novel “resting full-cycle ratio” (RFR; lowest pressure distal to the stenosis/aortic pressure during the entire cardiac cycle), compared to the gold standard fractional flow reserve (FFR) in a “real-world” setting.

Methods: The study included patients undergoing coronary pressure wire studies at one German University Hospital. No patients were excluded based on any baseline or procedural characteristics, except for insufficient quality of traces. The diagnostic performance of four NHPRs vs. FFR ≤ 0.80 was tested. Morphological characteristics of stenoses were analyzed by quantitative coronary angiography.

Results: 617 patients with 712 coronary lesions were included. RFR showed a significant correlation with FFR (r = 0.766, p < 0.01). Diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of RFR were 78% (95% confidence interval = 75; 81), 72% (65; 78), 81% (77; 84), 63% (57; 69), and 86% (83; 89). Relevant predictors for discordance of RFR ≤ 0.89/FFR > 0.8 were LAD lesions, peripheral artery disease, age, female sex and non-focal stenoses. Predictors for discordance of RFR > 0.89/FFR ≤ 0.8 included non-LCX lesions, percent diameter stenosis and previous percutaneous coronary intervention in the target vessel. RFR and all other NHPRs were highly correlated with each other.

Conclusion: All NHPRs have a similar correlation with the gold standard FFR and may facilitate the acceptance and implementation of physiological assessments of lesion severity. However, we found ~20% discordant results between NHPRs and FFR in our “all-comers” German cohort.

The stability of flow velocity and intracoronary resistance in the intracoronary electrocardiogram-triggered pressure ratio

Assessment of coronary artery lesions using the fractional flow reserve and instantaneous flow reserve (iFR) measurements has been found to reduce the incidence of further cardiovascular events. Here, we investigated differences in terms of coronary flow velocity and resistance within the analysis interval between the iFR and the intracoronary electrocardiogram (IC-ECG)-triggered distal/aortic pressure (Pd/Pa) ratio (ICE-T). We enrolled 23 consecutive patients (n = 33 stenoses) who required coronary flow measurements. ICE-T was defined as the average Pd/Pa ratio in the period corresponding to the isoelectric line of the IC-ECG. We compared the index value, flow velocity, and intracoronary resistance during the analysis intervals of the iFR and the ICE-T, both at rest and under hyperemia. ICE-T values and ICE-T intracoronary resistance were both found to be significantly lower, whereas flow velocity was significantly higher than those of the iFR at both rest and under hyperemia (P < 0.001), and all fluctuations in ICE-T values were also significantly smaller than those in the iFR. In conclusion, the ICE-T appears theoretically superior to pressure-dependent indices for analyzing phases with low and stable resistance, without an increase in invasiveness.

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.

Non-hyperaemic pressure ratios to guide percutaneous coronary intervention

The use of fractional flow reserve (FFR) in guiding revascularisation improves patient outcomes and has been well-established in clinical guidelines. Despite this, the uptake of FFR has been limited, likely attributable to the perceived increase in procedural time and use of hyperaemic agents that can cause patient discomfort. This has led to the development of instantaneous wave-free ratio (iFR), an alternative non-hyperaemic pressure ratio (NHPR). Since its inception, the use of iFR has been supported by an increasing body of evidence and is now guideline recommended. More recently, other commercially available NHPRs including diastolic hyperaemia-free ratio and resting full-cycle ratio have emerged. Studies have demonstrated that these indices, in addition to mean distal coronary artery pressure to mean aortic pressure ratio, are mathematically analogous (with specific nuances) to iFR. Additionally, there is increasing data demonstrating the equivalent diagnostic performance of alternative NHPRs in comparison with iFR and FFR. These NHPRs are now integral within most current pressure wire systems and are commonly available in the catheter laboratory. It is therefore key to understand the fundamental differences and evidence for NHPRs to guide appropriate clinical decision-making.