Predictive factors of discordance between the instantaneous wave‐free ratio and fractional flow reserve

Impact of Kidney Function on Physiological Assessment of Coronary Circulation

Background

Diagnosing myocardial ischemia in chronic kidney disease (CKD) patients is crucial since coronary artery disease (CAD) forms the predominant cause of mortality in these patients. Thus, this study aimed to assess the impact of kidney function on the results of coronary circulation physiological assessment.

Methods

Data were collected from 279 consecutive patients admitted to the Clinical Department of Cardiology and Cardiovascular Interventions at the University Hospital in Krakow. A total of 417 vessels were assessed for fractional flow reserve (FFR) and non-hyperemic resting pressure ratios, such as instantaneous wave-free ratio (iFR) and resting full-cycle ratio (RFR). Patients were categorized into two groups: glomerular filtration rate (GFR)-L (estimated GFR (eGFR) <70 mL/min/1.73 m2) and GFR-H (eGFR ≥70 mL/min/1.73 m2).

Results

A total of 118 patients (42.3%) were included in the GFR-L group, while 161 patients (57.7%) were in the GFR-H group. The left anterior descending branch of the left coronary artery (LAD) was the assessed vessel in approximately 60% of procedures, the frequency of which was very similar in both study groups. Focusing solely on LAD assessments, both FFR metrics (continuous and binary) were comparable between the groups. In contrast, for non-LAD vessels, the GFR-H group revealed substantially reduced FFR values, with more vessels displaying significant constriction. Patients in the GFR-H group showed higher instances of FFR+ | iFR/RFR- discrepancies than their lower eGFR counterparts. An eGFR of 70 mL/min/1.73 m2 was the optimal cut-off to differentiate patients concerning the mentioned discrepancies.

Conclusions

Kidney function influenced the coronary circulation physiological assessment results. Patients with reduced eGFR tended to have negative hyperemic assessments, especially in non-LAD vessels.

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.

Understanding the Basis for Hyperemic and Nonhyperemic Coronary Pressure Assessment

Despite the now routine integration of invasive physiologic systems into coronary catheter laboratories worldwide, it remains critical that all operators maintain a sound understanding of the fundamental physiologic basis for coronary pressure assessment. More specifically, performing operators should be well informed regarding the basis for hyperemic (ie, fractional flow reserve) and nonhyperemic (ie, instantaneous wave-free ratio and other nonhyperemic pressure ratio) coronary pressure assessment. In this article, we provide readers a comprehensive history charting the inception, development, and validation of hyperemic and nonhyperemic coronary pressure assessment.

Hemodynamic Insights into Combined Fractional Flow Reserve and Instantaneous Wave-Free Ratio Assessment Through Quantitative [15O]H2O PET Myocardial Perfusion Imaging

In patients evaluated for obstructive coronary artery disease (CAD), guidelines recommend using either fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR) to guide coronary revascularization decision-making. The hemodynamic significance of lesions with discordant FFR and iFR measurements is debated. This study compared [15O]H2O PET-derived absolute myocardial perfusion between vessels with concordant and discordant FFR and iFR measurements. Methods: We included 197 patients suspected of obstructive CAD who had undergone [15O]H2O PET perfusion imaging and combined FFR/iFR interrogation in 468 vessels. Resting myocardial blood flow (MBF), hyperemic MBF, and coronary flow reserve (CFR) were compared among 4 groups: FFR low/iFR low (n = 79), FFR high/iFR low (n = 22), FFR low/iFR high (n = 22), and FFR high/iFR high (n = 345). Predefined [15O]H2O PET thresholds for ischemia were 2.3 mL·min-1·g-1 or less for hyperemic MBF and 2.5 or less for CFR. Results: Hyperemic MBF was lower in the concordant low (2.09 ± 0.67 mL·min-1·g-1), FFR high/iFR low (2.41 ± 0.80 mL·min-1·g-1), and FFR low/iFR high (2.40 ± 0.69 mL·min-1·g-1) groups compared with the concordant high group (2.91 ± 0.84 mL·min-1·g-1) (P < 0.001, P = 0.004, and P < 0.001, respectively). A lower CFR was observed in the concordant low (2.37 ± 0.76) and FFR high/iFR low (2.64 ± 0.84) groups compared with the concordant high group (3.35 ± 1.07, P < 0.01 for both). However, for vessels with either low FFR or low iFR, quantitative hyperemic MBF and CFR values exceeded the ischemic threshold in 38% and 49%, respectively. In addition, resting MBF exhibited a negative correlation with iFR (P < 0.001) and was associated with FFR low/iFR high discordance compared with concordant low FFR/low iFR measurements, independent of clinical and angiographic characteristics, as well as hyperemic MBF (odds ratio [OR], 0.41; 95% CI, 0.26-0.65; P < 0.001). Conclusion: We found reduced myocardial perfusion in vessels with concordant low and discordant FFR/iFR measurements. However, FFR/iFR combinations often inaccurately classified vessels as either ischemic or nonischemic when compared with hyperemic MBF and CFR. Furthermore, a lower resting MBF was associated with a higher iFR and the occurrence of FFR low/iFR high discordance. Our study showed that although combined FFR/iFR assessment can be useful to estimate the hemodynamic significance of coronary lesions, these pressure-derived indices provide a limited approximation of [15O]H2O PET-derived quantitative myocardial perfusion as the physiologic standard of CAD severity.

Impact of stenosis resistance and coronary flow capacity on fractional flow reserve and instantaneous wave-free ratio discordance: a combined analysis of DEFINE-FLOW and IDEAL

BACKGROUND

The pressure-derived parameters fractional flow reserve (FFR) and the emerging instantaneous wave-free ratio (iFR) are the most widely applied invasive coronary physiology indices to guide revascularisation. However, approximately 15-20% of intermediate stenoses show discordant FFR and iFR, and therapeutical consensus is lacking.

AIMS

We sought to associate hyperaemic stenosis resistance index, coronary flow reserve (CFR) and coronary flow capacity (CFC) to FFR/iFR discordance.

METHODS

We assessed pressure and flow measurements of 647 intermediate lesions (593 patients) of two multi-centre international studies.

RESULTS

FFR and iFR were discordant in 15% of all lesions (97 out of 647). FFR+/iFR- lesions had similar hyperaemic average peak velocity (hAPV), CFR and CFC as FFR-/iFR- lesions, whereas FFR-/iFR+ lesions had similar hAPV, CFR and CFC as FFR+/iFR+ lesions (p > 0.05 for all). FFR+/iFR- lesions were associated with lower baseline stenosis resistance, but not hyperaemic stenosis resistance, compared with FFR-/iFR+ lesions (p < 0.001).

CONCLUSIONS

Discordance with FFR+/iFR- is characterised by maximal flow values, CFR, and CFC patterns similar to FFR-/iFR- concordance that justifies conservative therapy. Discordance with FFR-/iFR+ on the other hand, is characterised by low flow values, CFR, and CFC patterns similar to iFR+/FFR+ concordance that may benefit from percutaneous coronary intervention.

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.

Impact of coronary disease patterns, anatomical factors, micro-vascular disease and non-coronary cardiac factors on invasive coronary physiology

Invasive coronary physiology has been applied by interventional cardiologists to guide the management of coronary artery disease (CAD), with well-defined thresholds applied to determine whether CAD should be managed with optimal medical therapy (OMT) alone or OMT and percutaneous coronary intervention (PCI). There are multiple modalities in clinical use, including hyperaemic and non-hyperaemic indices. Despite endorsement in the major guidelines, there are various factors which impact and confound the readings of invasive coronary physiology, both within the coronary tree and beyond. This review article aims to summarise the mechanisms by which these factors impact invasive coronary physiology, and distinguish factors that contribute to ischaemia from confounding factors. The potential for mis-classification of ischaemic status is highlighted. Lastly, the authors identify targets for future research to improve the precision of physiology-guided management of CAD.

Association of the severity of vascular damage with discordance between the fractional flow reserve and non-hyperemic pressure ratios

BACKGROUND

While there is a discordance between fractional flow reserve (FFR) and non-hyperemic pressure ratios (NHPRs) in some cases, the mechanisms underlying these discordances have not yet been fully clarified. We examined whether vascular damage as assessed by measurement of the brachial-ankle pulse wave velocity (baPWV), a marker of arterial stiffness, or ankle brachial pressure index (ABI), a marker of atherosclerotic arterial stenosis, might be associated with their discordances.

METHODS

FFR and NHPRs were measured in 283 consecutive patients (69 ± 10 years old). Based on previously established cut-off values of the two markers (i.e. +/- = FFR ≤/> 0.80 or =NHPRs ≤/> 0.89), the study participants were divided into four groups (the + and - signs denoting "predictive of significant stenosis" and "not predictive of significant stenosis," respectively): the FFR+/NHPRs+ group (n = 124), FFR-/NHPRs+ group (n = 16), FFR+/NHPRs- group(n = 65), and FFR-/NHPRs- group (n = 78). The baPWV and ABI were also measured in all the participants, and values of <2000 cm/s and ≥1.00 of the baPWV and ABI, respectively, were considered as representing relatively less advanced atherosclerotic systemic vascular damage.

RESULTS

The prevalence of subjects with ABI ≥1.00 was higher in the FFR+/NHPRs- group than in the FFR-/NHPRs- group (p < 0.05). When the study subjects were divided into 2 groups, namely, the FFR+/NHPRs- group and the combined group, the prevalence of ABI ≥1.00 and that of baPWV <2000 cm/s were higher in the FFR+/NHPRs- group as compared with those in the combined group (p < 0.05). The results of binary logistic regression analysis demonstrated that ABI ≥1.00 was associated with a significant odds ratio (2.34, p < 0.05) for the FFR+/NHPRs- discordance.

CONCLUSION

The FFR+/NHPRs- discordance appears to be observed in patients with relatively less advanced atherosclerotic systemic vascular damage. Thus, ABI ≥1.00 may be a marker of the presence of the FFR+/NHPRs- discordance.

Discordance between fractional flow reserve and instantaneous wave-free ratio in patients with severe aortic stenosis: A retrospective cohort study

BACKGROUND

Discordance between fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) occurs in approximately 20 % of cases. However, no studies have reported the discordance in patients with severe aortic stenosis (AS). We aimed to evaluate the diagnostic discordance between FFR and iFR in patients with severe AS.

METHODS

We examined 140 consecutive patients with severe AS (164 intermediate coronary artery stenosis vessels). FFR and iFR were calculated in four quadrants based on threshold FFR and iFR values of ≤0.8 and ≤0.89, respectively (Group 1: iFR >0.89, FFR >0.80; Group 2: iFR ≤0.89, FFR >0.80; Group 3: iFR >0.89, FFR ≤0.80; and Group 4: iFR ≤0.89, FFR ≤0.80). Concordant groups were Groups 1 and 4, and discordant groups were Groups 2 and 3. Positive and negative discordant groups were Groups 3 and 2, respectively.

RESULTS

The median (Q1, Q3) FFR and iFR were 0.84 (0.76, 0.88) and 0.85 (0.76, 0.91), respectively. Discordance was observed in 48 vessels (29.3 %). In the discordant group, negative discordance (Group 2: iFR ≤0.89 and FFR >0.80) was predominant (45 cases, 93.6 %). Multivariate analysis showed that the left anterior descending artery [odds ratio (OR), 3.88; 95 % confidence interval (CI): 1.54-9.79, p = 0.004] and peak velocity ≥5.0 m/s (OR, 3.21; 95%CI: 1.36-7.57, p = 0.008) were independently associated with negative discordance (FFR >0.8 and iFR ≤0.89).

CONCLUSIONS

In patients with severe AS, discordance between FFR and iFR was predominantly negative and observed in 29.3 % of vessels. The left anterior descending artery and peak velocity ≥5.0 m/s were independently associated with negative discordance.

Comparison of Fractional Flow Reserve with Resting Non-Hyperemic Indices in Patients with Coronary Artery Disease

Guidelines recommend using hyperemic (FFR) and non-hyperemic (iFR/RFR) methods of evaluating coronary artery stenoses in patients with coronary artery disease. However, in some cases, achieved results indicating significant ischemia may differ between those methods. Thus, we sought to identify predictors of such a discrepancy. Data were collected on all consecutive patients with chronic coronary syndrome hospitalized between 2020 and 2021. For 279 patients (417 vessels), results for both FFR and iFR/RFR were available. Values of ≤0.80 for FFR and ≤0.89 for iFR/RFR were considered positive for ischemia. Discordant measurements of FFR and iFR/RFR were observed in 80 (19.2%) patients. Atrial fibrillation was the only predictor of the overall FFR and iFR/RFR discordance - OR (95%CI) 1.90 (1.02-3.51); p = 0.040. The chance of positive FFR and negative iFR/RFR decreased independently with age - OR (95%CI) 0.96 (0.93-0.99); p = 0.024. On the contrary, insulin-treated diabetes mellitus was the predictor of negative FFR and positive iFR/RFR discrepancy - OR (95%CI) 4.61 (1.38-15.40); p = 0.013. In everyday clinical practice, iFR/FFR correlates well with FFR. However, discordance between these methods is quite common. Physicians should be aware of the risk of such discordance in patients with atrial fibrillation, advanced age, and insulin-treated diabetes mellitus.

Understanding the Basis for Hyperemic and Nonhyperemic Coronary Pressure Assessment

Despite the now routine integration of invasive physiologic systems into coronary catheter laboratories worldwide, it remains critical that all operators maintain a sound understanding of the fundamental physiologic basis for coronary pressure assessment. More specifically, performing operators should be well informed regarding the basis for hyperemic (ie, fractional flow reserve) and nonhyperemic (ie, instantaneous wave-free ratio and other nonhyperemic pressure ratio) coronary pressure assessment. In this article, we provide readers a comprehensive history charting the inception, development, and validation of hyperemic and nonhyperemic coronary pressure assessment.

Comparative study of fractional flow reserve and diastolic pressure ratio using a guidewire with a sensor for measuring intravascular pressure

PURPOSE

This study aimed to evaluate the correlation and diagnostic agreement between diastolic pressure ratio (dPR) and fractional flow reserve (FFR) in a Japanese real-world setting.

DESIGN

Prospective multicenter observational study.

METHODS

This study included 100 patients with intermediate coronary artery stenosis at 4 Japanese hospitals. For these lesions, FFR and dPR were measured using a guidewire with a sensor and a monitor to measure intravascular pressure. The correlation and diagnostic agreement between FFR and dPR were assessed. When both FFR and dPR were negative or positive, the results were considered to be concordant. When one was positive and the other was negative, the result was regarded as discordant (positive discordance, FFR > 0.80 and dPR ≤ 0.89; negative discordance, FFR ≤ 0.80 and dPR > 0.89).

RESULTS

Overall, the FFR and dPR were well-correlated (R = 0.841). FFR and dPR were concordant in 89% of cases (concordant normal, 43%; concordant abnormal, 46%) and discordant in 11% (positive discordance, 7%; negative discordance, 4%). No significant difference was observed in the rate of concordant results between patients with and without diabetes mellitus. The diagnostic concordance rate was significantly different among the 3 coronary arteries (right coronary artery, 93.3%; left anterior descending artery, 93.2%; and left circumflex artery, 58.3%; P = .001). Additionally, the rate of concordant results tended to be higher when using intravenous administration of adenosine than when using intracoronary bolus injection of nicorandil (adenosine, 95.1%; nicorandil, 84.7%; P = .103).

CONCLUSION

We found that dPR was highly correlated with FFR, and diagnostic discordance was observed in 11% of the lesions. Several factors, including lesion location and medication for hyperemia, may cause the diagnostic discordance between dPR and FFR.

Instantaneous Wave-Free Ratio for the Assessment of Intermediate Left Main Coronary Artery Stenosis: Correlations With Fractional Flow Reserve/Intravascular Ultrasound and Prognostic Implications: The iLITRO-EPIC07 Study

BACKGROUND

There is little information available on agreement between fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) in left main coronary artery (LMCA) intermediate stenosis. Besides, several meta-analyses support the use of FFR to guide LMCA revascularization, but limited information is available on iFR in this setting. Our aims were to establish the concordance between FFR and iFR in intermediate LMCA lesions, to evaluate with intravascular ultrasound (IVUS) in cases of FFR/iFR discordance, and to prospectively validate the safety of deferring revascularization based on a hybrid decision-making strategy combining iFR and IVUS.

METHODS

Prospective, observational, multicenter registry with 300 consecutive patients with intermediate LMCA stenosis who underwent FFR and iFR and, in case of discordance, IVUS and minimal lumen area measurements. Primary clinical end point was a composite of cardiovascular death, LMCA lesion-related nonfatal myocardial infarction, or unplanned LMCA revascularization.

RESULTS

FFR and iFR had an agreement of 80% (both positive in 67 and both negative in 167 patients); in case of disagreement (31 FFR+/iFR- and 29 FFR-/iFR+) minimal lumen area was ≥6 mm² in 8.7% of patients with FFR+ and 14.6% with iFR+. Among the 300 patients, 105 (35%) underwent revascularization and 181 (60%) were deferred according to iFR and IVUS. At a median follow-up of 20 months, major adverse cardiac events incidence was 8.3% in the defer group and 13.3% in the revascularization group (hazard ratio, 0.71 [95% CI 0.30-1.72]; P=0.45).

CONCLUSIONS

In patients with intermediate LMCA stenosis, a physiology-guided treatment decision is feasible either with FFR or iFR with moderate concordance between both indices. In case of disagreement, the use of IVUS may be useful to indicate revascularization. Deferral of revascularization based on iFR appears to be safe in terms of major adverse cardiac events.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT03767621.

Differential Impact of Renal Function on the Diagnostic Performance of Resting Full-Cycle Ratio in Patients With Renal Dysfunction

Background: Physiological assessments using fractional flow reserve (FFR) and resting full-cycle ratio (RFR) have been recommended for revascularization decision making. Previous studies have shown a 20% rate of discordance between FFR and RFR. In this context, the correlation between RFR and FFR in patients with renal dysfunction remains unclear. This study examined correlations between RFR and FFR according to renal function.

Methods and Results: In all, 263 consecutive patients with 370 intermediate lesions were enrolled in the study. Patients were classified into 3 groups according to renal function: Group 1, estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m²; Group 2, 30 mL/min/1.73 m²≤eGFR<60 mL/min/1.73 m²; Group 3, eGFR <30 mL/min/1.73 m². The discordance between FFR and RFR was assessed using known cut-off values for FFR (≤0.80) and RFR (≤0.89). Of the 370 lesions, functional significance with FFR was observed in 154 (41.6%). RFR was significantly correlated with FFR in all groups (Group 1, R²=0.62 [P<0.001]; Group 2, R²=0.67 [P<0.001]; Group 3, R²=0.46 [P<0.001]). The rate of discordance between RFR and FFR differed significantly among the 3 groups (Group 1, 18.8%; Group 2, 18.5%; Group 3, 42.9%; P=0.02).

Conclusions: The diagnostic performance of RFR differed based on renal function. A better understanding of the clinical factors contributing to FFR/RFR discordance, such as renal function, may facilitate the use of these indices.

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.

Myocardial Ischemia due to Rapid Atrial Fibrillation Revealed Using the Instantaneous Wave-Free Ratio

Instantaneous wave-free ratio (iFR) is a non-hyperemic coronary physiological index measured during the diastolic wave-free period. Although atrial fibrillation (AF) with beat-to-beat fluctuations can occur during diastole, the feasibility of iFR measurements during AF has previously been demonstrated. However, the effects of coronary circulation during AF on iFR measurements remain unknown. In addition, the pathophysiology of ischemia due to AF tachycardia requires further elucidation. We report a unique case of myocardial ischemia due to rapid AF, as indicated by the iFR pullback measurement and beat-to-beat analysis. When planning revascularization in patients with rapid AF, the ability of iFR to reflect ischemic stress due to AF tachycardia should be considered.

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 Role of Coronary Physiology in Contemporary Percutaneous Coronary Interventions

Invasive assessment of coronary physiology has radically changed the paradigm of myocardial revascularization in patients with coronary artery disease. Despite the prognostic improvement associated with ischemia-driven revascularization strategy, functional assessment of angiographic intermediate epicardial stenosis remains largely underused in clinical practice. Multiple tools have been developed or are under development in order to reduce the invasiveness, cost, and extra procedural time associated with the invasive assessment of coronary physiology. Besides epicardial stenosis, a growing body of evidence highlights the role of coronary microcirculation in regulating coronary flow with consequent pathophysiological and clinical and prognostic implications. Adequate assessment of coronary microcirculation function and integrity has then become another component of the decision-making algorithm for optimal diagnosis and treatment of coronary syndromes. This review aims at providing a comprehensive description of tools and techniques currently available in the catheterization laboratory to obtain a thorough and complete functional assessment of the entire coronary tree (both for the epicardial and microvascular compartments).

Reliability of Fractional Flow Reserve and Instantaneous Wave-Free Ratio in Assessing Intermediate Coronary Stenosis in Patients With Atrial Fibrillation

Despite the current use of fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) for guiding revascularization in atrial fibrillation (AF), there is a lack of studies evaluating their reliability in this particular population. This retrospective study aimed to investigate the reliability of FFR and iFR in patients with AF. This retrospective study included all patients with AF undergoing FFR measurements (n = 45 vessels from 36 patients) at Brugmann University Hospital, Brussels, Belgium, between 2012 and 2020 or iFR (n = 18 vessels from 13 patients) and a corresponding number of patients with sinus rhythm (SR) randomly selected from the same period, benefiting from iFR (n = 20 vessels from 17 patients) or FFR (n = 50 vessels from 37 patients). Our main findings indicate that there is an increased beat-to-beat variability of individual iFR measures in patients with AF, compared with SR. In addition, the reproducibility of iFR on test-retest is low in patients with AF, leading to increased lesion reclassification (53.8% of lesions reclassified on 2 consecutive iFR measurements in AF vs 6.6% lesions reclassified in SR, p <0.05). In contrast, FFR seems to be more robust in evaluating coronary lesions in AF in terms of equivalent variability, reproducibility, and lesion reclassification observed in the SR population. In conclusion, this is the first study to evaluate the reliability of iFR and FFR in AF. Our findings raise caution in using iFR to guide revascularization in patients with AF, whereas FFR seems to be more robust in this population.

Age and functional relevance of coronary stenosis: a post hoc analysis of the ADVISE II trial

BACKGROUND

The influence of age-dependent changes on fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR) and the response to pharmacological hyperaemia has not been investigated.

AIMS

We investigated the impact of age on these indices.

METHODS

This is a post hoc analysis of the ADVISE II trial, including a total of 690 pressure recordings (in 591 patients). Age-dependent correlations with FFR and iFR were calculated and adjusted for stenosis severity. Patients were stratified into three age terciles. The hyperaemic response to adenosine, calculated as the difference between resting and hyperaemic pressure ratios, and the prevalence of FFR-iFR discordance were assessed.

RESULTS

Age correlated positively with FFR (r=0.08, 95% CI: 0.01 to 0.15, p=0.015), but not with iFR (r=-0.03, 95% CI: -0.11 to 0.04, p=0.411). The hyperaemic response to adenosine decreased with patient age (0.12±0.07, 0.11±0.06, 0.09±0.05, for the 1st [33-58 years], 2nd [59-69 years] and 3rd [70-94 years] age tertiles, respectively, p<0.001) and showed significant correlation with age (r=-0.14, 95% CI: -0.21 to -0.06, p<0.001). The proportion of patients with FFR ≤0.80+iFR >0.89 discordance doubled in the first age tercile (14.1% vs 7.1% vs 7.0%, p=0.005).

CONCLUSIONS

The hyperaemic response of the microcirculation to adenosine administration is age dependent. FFR values increase with patient age, while iFR values remain constant across the age spectrum. These findings contribute to explaining differences observed in functional stenosis classification with hyperaemic and non-hyperaemic coronary indices.

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.

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.

Exploring diastolic pressure ratio to fractional flow reserve discordance and a hypothesis on tailoring diastolic pressure ratio cut-off values to improve diagnostic accuracy in the mid- and distal-LAD

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This study assessed diastolic pressure ratio to FFR discordance.

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12.7% of LAD lesions in this study had discordant result.

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2.4% of non-LAD lesions had discordant results.

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This represents a statistically significant difference in discordance rate.

Previous studies have identified a higher rate of discordance between non-hyperaemic pressure ratios and FFR in the LAD when compared to the other two coronary arteries. We hypothesised that in keeping with recently published data, we would identify a higher discordance rate between diastolic pressure ratio (DPR) and FFR in the LAD compared to the RCA or LCx. In our study, 12.7% of LAD lesions had discordant results compared with 2.4% of non-LAD lesions. This represents a statistically significant increased rate of discordance in LAD lesions compared to non-LAD lesions (p = 0.04986). Note was made of a tendency for non-proximal LAD lesions to be associated with false-positive DPR results in the borderline range (0.88 and 0.89). In a speculative, hypothesis generating post-hoc analysis, we found an improved diagnostic accuracy of DPR when the cut-off value for a positive DPR in the non-proximal LAD was changed to ≤0.87. It is fathomable that improvements in the diagnostic accuracy of DPR for FFR may be improved by tailoring DPR cut-offs to the location of the lesion assessed.

Anatomical-functional discordance between quantitative coronary angiography and diastolic pressure ratio during wave-free period

OBJECTIVES

This study sought to determine the predictors of anatomical-functional discordance between quantitative coronary angiography (QCA) derived diameter stenosis (QCA-DS) and diastolic pressure ratio during wave-free period (dPR_WFP ).

BACKGROUND

The discrepancy between angiographical stenosis and physiological significance is frequently experienced in clinical practice. Although the anatomical-functional discordance between angiography and fractional flow reserve (FFR) has been intensively investigated, that of resting index including dPR_WFP remains to be elucidated.

METHODS

In a total of 647 angiographically intermediate lesions with QCA-DS between 30 and 70% in 502 patients, predictors of having QCA-DS >50% and dPR_WFP > 0.89 (QCA-dPR_WFP mismatch), and those of having QCA-DS ≤50% and dPR_WFP ≤ 0.89 (QCA-dPR_WFP reverse mismatch) were determined. FFR ≤0.80 was defined as positive FFR and the predictors of QCA-FFR discordance were determined as well.

RESULTS

QCA-dPR_WFP mismatch and reverse mismatch were observed in 27.5 and 17.6% of cases, respectively. The predictors of mismatch were non-left anterior descending artery (LAD) lesion, large minimal lumen diameter, low baseline heart rate, and high coronary flow reserve (CFR), while those of reverse mismatch were LAD lesion, non-culprit lesion of acute coronary syndrome, long lesion length, low left ventricular ejection fraction, and low CFR and index of microcirculatory resistance. Age, sex, and the culprit vessel of prior myocardial infarction were not significant determinants of QCA-dPR_WFP discordance unlike QCA-FFR discordance derived from the same cohort.

CONCLUSIONS

Anatomical-functional discordance between angiography and dPR_WFP was not uncommon. Predictors differed between QCA-dPR_WFP discordance and QCA-FFR discordance.

Preprocedural β-Blockers in the Functional Assessment of Intermediate Coronary Lesions by Instantaneous Wave-Free Ratio

AIM

Instantaneous wave-free ratio (iFR) has emerged as the strategy of choice for the assessment of intermediate coronary lesions. The impact of preprocedural β-blockers therapy on the iFR was the aim of this study.

METHODS

We included patients undergoing functional assessment of intermediate (40%-70%) coronary lesions in 2 centers. The iFR measurement was performed by pressure-recording guidewire and calculated at the core laboratory using the manufacturers' dedicated software. Minimal luminal diameter, reference diameter, percent diameter stenosis, and length of the lesion were measured. Positive iFR was considered for values <0.90.

RESULTS

We included 197 patients undergoing functional evaluation of 223 coronary lesions. Patients on β-blockers (69%) had more frequently hypertension (P = .05); previous myocardial infarction (P = .01); therapy with clopidogrel (P = .02), statins, and aspirin; and acute coronary syndrome at presentation (P < .001, respectively). Mean iFR values were slightly higher in patients on β-blockers (0.94 ± 0.06 vs 0.92 ± 0.06, P = .11). The rate of positive iFR was significantly lower with β-blockers (14.9% vs 27.5%, P = .04). On multivariate analysis, β-blockers use was a predictor of the significance of coronary stenoses (odds ratio [OR] = 0.48; 95% CI = 0.23-0.98; P = .05) together with lesion length (OR = 1.04; 95% CI = 1.01-1.07; P = .007).

CONCLUSION

Among patients undergoing iFR, preprocedural β-blockers are associated with higher absolute values and a lower rate of positive iFR.

Effect of Elevated Left Ventricular End Diastolic Pressure on Instantaneous Wave-Free Ratio and Fractional Flow Reserve Discordance

Background

Instantaneous wave-free ratio (iFR)-guided physiological assessment has been shown to be non-inferior to fractional flow reserve (FFR)-guided assessment for deciding best treatment strategy for angiographically intermediate stenosis. The diagnostic accuracy of iFR compared to FFR reported in various studies is around 80%. Many factors can lead to iFR/FFR discordance, though underlying physiological mechanism of discordance and its associated factors have not been fully evaluated. The effect of left ventricle end diastolic pressure (LVEDP) on iFR/FFR discordance is unknown and needs further evaluation.

Methods

We performed a single center, non-randomized, both retrospective and prospective study. A total of 65 patients with intermediate coronary stenosis undergoing physiological assessment were included in the study. Patients were assigned to two groups (normal LVEDP and high LVEDP group) based on LVEDP cutoff of 15 mm Hg. iFR and FFR were measured for each patient and iFR/FFR results were compared between the two groups.

Results

A significantly large number of patients in elevated LVEDP group had iFR/FFR discordance compared to normal LVEDP group (42.8% vs. 6.7%, P = 0.001). More patients with acute coronary syndrome (ACS) had discordance compared to stale coronary artery disease (CAD) patients (53% vs. 15%, P = 0.003).

Conclusions

Elevated LVEDP can affect iFR and FFR measurements and can lead to discordance. Further studies are required to determine effect of elevated LVEDP on iFR/FFR discordance and whether such discordance is clinically relevant. “Normal range” iFR results should be cautiously interpreted in patients with elevated LVEDP, especially those with ACS.

Physiology-Based Revascularization of Left Main Coronary Artery Disease

It is of critical importance to correctly assess the significance of a left main lesion. Underestimation of significance beholds the risk of inappropriate deferral of revascularization, whereas overestimation may trigger major but unnecessary interventions. This article addresses the invasive physiological assessment of left main disease and its role in deciding upon revascularization. It mainly focuses on the available evidence for fractional flow reserve and instantaneous wave-free ratio, their interpretation, and limitations. We also discuss alternative invasive physiological indices and imaging, as well as the link between physiology, ischemia, and prognosis.

Impact of aging on the effects of intracoronary adenosine, peak hyperemia and its duration during fractional flow reserve assessment

INTRODUCTION

Functional assessment of coronary stenoses is crucial for determining the correct therapeutic strategy. Age-related modifications in cardiovascular function could alter the functional significance of an intermediate coronary lesion. Therefore, the aim of the present study was to investigate the impact of age on fractional flow reserve (FFR) measurements in patients with intermediate coronary artery disease.

METHODS

We included patients undergoing coronary angiography at our Division of Cardiology from June 2008 to February 2019 for elective indication or recent acute coronary syndrome and receiving FFR assessment for an intermediate coronary stenosis (angiographic 40-70% stenoses). FFR measurement was performed by pressure-recording guidewire (Prime Wire; Volcano Imaging System Philips Healthcare, San Diego, California, USA), after induction of hyperemia with intracoronary boluses of adenosine (from 60 to 720 μg, with dose doubling at each step).

RESULTS

We included in our study 276 patients, undergoing FFR evaluation on 314 lesions, that were divided according to age (< or ≥70 years). Elderly patients displayed a higher cardiovascular risk profile and received more often specific therapy. We found significantly higher FFR values and lower Delta FFR and time to recovery in patients with age ≥70 years old even with high-dose adenosine. Elderly patients showed a trend in lower percentage of positive FFRs, especially with high-dose (P = 0.09). Overall, any FFR ≤ 0.80 was observed in 33.5% of younger patients and 21.1% of patients ≥70 years (P = 0.02). Results were confirmed after correction for baseline differences [adjusted odds ratio (95% confidence interval) = 0.60 (0.33-1.09), P = 0.08].

CONCLUSION

This is one of the first studies investigating the impact of age on the measurement of FFR with high-dose adenosine. Patients with age >70 years old with intermediate CAD are more likely to have higher FFR values and lower duration of hyperemia after adenosine boluses, as compared with younger patients.

Contrast FFR plus intracoronary injection of nitro-glycerine accurately predicts FFR for coronary stenosis functional assessment

BACKGROUND

Fractional flow reserve (FFR) is the "gold standard" for assessing the physiological significance of coronary disease. In the last decade, several alternative adenosine-free indexes have been proposed in order to facilitate the dissemination of the functional evaluation of coronary stenosis. Our aim was to investigate whether radiographic contrast plus intracoronary nitroglycerin (cFFR-NTG) can predict functional assessment of coronary stenosis offering superior diagnostic agreement with FFR compared to non-hyperemic indexes and contrast mediated FFR (cFFR).

METHODS

Three hundred twenty-nine lesions evaluated with pressure wire in 266 patients were prospectively included in this multicenter study.

RESULTS

The ROC curves for cFFR-NTG using an FFR≤0.80 showed a higher accuracy in predicting FFR (AUC=0.97) than resting Pd/Pa (AUC=0.90, P<0.01) and cFFR (AUC=0.93.5, P<0.01). A significant (P<0.01) strong correlation was found between FFR and the four analyzed indexes: Pd/Pa (r=0.78); iFR/RFR (r=0.73); cFFR(r=0.89) and cFFR-NTG (r=0.93). cFFR-NTG showed the closest agreement at Bland-Altman analysis. The cFFR-NTG cut off value >0.84 showed the highest negative predictive value (88%), specificity (91%), sensitivity (94%) and accuracy (92%) of the studied indexes.

CONCLUSIONS

Submaximal hyperemic adenosine-free indexes are an efficient alternative to adenosine for the physiological assessment of epicardial coronary disease. The most accurate index in predicting the functional significance of coronary stenosis using FFR as reference was cFFR-NTG.

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.

Diagnostic Performance and Pressure Stability of a Novel Myocardial Ischemic Diagnostic Index - The Intracoronary-Electrocardiogram-Triggered Distal Pressure/Aortic Pressure Ratio

Background: We hypothesized that the intracoronary-electrocardiogram (IC-ECG)-based pressure index would be more stable and precise than the instantaneous flow reserve (iFR). We investigated the usefulness of the IC-ECG-based pressure index for diagnosing myocardial ischemia. Methods and Results: Thirty-seven consecutive patients with coronary stenosis requiring physiological assessment were enrolled in the study. iFR was measured at rest and under hyperemia in 51 and 40 lesions, respectively. The IC-ECG-triggered distal pressure (Pd)/aortic pressure (Pa) ratio (ICE-T) was defined as the mean Pd/Pa ratio in the period corresponding to the isoelectric line. The ICE-T was significantly lower than the iFR both at rest and during hyperemia (P<0.00001 for both). Fluctuations in the ICE-T pressure parameters (Pd/Pa, Pa, and Pd) were significantly smaller than those of iFR both at rest and during hyperemia. The diagnostic accuracy of predicting a fractional flow reserve (FFR) ≤0.80 of the ICE-T at rest was significantly higher than that of iFR (P=0.008). Receiver operating characteristic curve analyses showed that the ICE-T predicts FFR ≤0.80 more accurately than the iFR (area under curve 0.897 vs. 0.810 for ICE-T and iFR, respectively). Conclusions: We identified the period in the IC-ECG in which resting Pd/Pa was low and constant. The IC-ECG-based algorithm may improve the accuracy of diagnosing myocardial ischemia, without increasing invasiveness, compared with pressure-dependent indices.

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.

Impact of Age on the Functional Evaluation of Intermediate Coronary Stenoses With Instantaneous Wave-Free Ratio and Fractional Flow Reserve

The optimal strategy for assessing the ischemic significance of intermediate coronary stenoses with adenosine-induced fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) is still debated. Few studies have previously assessed the impact of age on FFR and iFR, which was the aim of our study. Patients undergoing FFR and iFR evaluation for intermediate (40%-70%) coronary lesions were included and divided according to age. Fractional flow reserve was performed by intracoronary boluses of adenosine (60-1440 μg). Instantaneous wave-free ratio was automatically calculated. Among 148 patients undergoing FFR measurement of 166 lesions, 45.3% were ≥70 years. Elderly patients had higher minimal lumen diameter (P = .03). We also observed a linear relationship between iFR and FFR independently of age. Fractional flow reserve values were higher in the elderly patients, whereas iFR was not related to age. A total of 33 lesions had a positive iFR with no difference for age (17.3% vs 22%, P = .56), while FFR <0.80 was more infrequent in the elderly patients (17.1% vs 34.8%, P = .02). In intermediate coronary stenoses, iFR and FFR correlation is unaffected by age. Fractional flow reserve is higher in the elderly patients, whereas iFR is less affected by age. Future large-scale studies are needed to define whether iFR should be the preferred choice in elderly patients.

Objective Identification of Intermediate Lesions Inducing Myocardial Ischemia Using Sequential Intracoronary Pressure and Flow Measurements

Background

Although ischemic heart disease has a complex and multilevel origin, the diagnostic approach is mainly focused on focal obstructive disease as assessed by pressure‐derived indexes. The prognostic relevance of coronary flow over coronary pressure has been suggested and implies that identification of relevant perfusion abnormalities by invasive physiology techniques is critical for the correct identification of patients who benefit from coronary revascularization. The purpose of this study was to evaluate the diagnostic potential of a sequential approach using pressure‐derived indexes instantaneous wave‐free ratio (iFR), fractional flow reserve (FFR), and coronary flow reserve (CFR) measurements to determine the number of intermediate lesions associated with flow abnormalities after initial pressure measurements.

Methods and Results

A total of 366 intermediate lesions were assessed with simultaneous intracoronary pressure and flow velocity measurements. Contemporary clinical iFR, FFR, and CFR cut points for myocardial ischemia were applied. A total of 118 (32%) lesions were FFR+ and 136 (37%) lesions were iFR+. Subsequent CFR assessment resulted for FFR in a total of 91 (25%) FFR+/CFR+ and for iFR a total of 111 (30%) iFR+/CFR+ lesions. An iFR, FFR, and invasive flow velocity assessment approach would have yielded 20% of lesions (74 of 366) as ischemic.

Conclusions

Ultimately, 20% of intermediate lesions are associated with flow abnormalities after applying a pressure and flow velocity sequential approach. If iFR is borderline, FFR has limited additional value, in contrast with CFR. These results emphasize the use of coronary physiology in assessing stenosis severity but may also further question the contemporary reputation of a pressure‐based approach as a gold standard for the detection of myocardial ischemia in ischemic heart disease.

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.

Physiological Assessment of Coronary Lesions in 2020

PURPOSE OF REVIEW

Physiological assessment of coronary artery disease (CAD) is an essential component of the interventional cardiology toolbox. However, despite long-term data demonstrating improved outcomes, physiology-guided percutaneous coronary intervention (PCI) remains underutilized in current practice. This review outlines the indications and technical aspects involved in evaluating coronary stenosis physiology, focusing on the latest developments in the field.

RECENT FINDINGS

Beyond fractional flow reserve (FFR), non-hyperemic pressure ratios (NHPR) that assess coronary physiology at rest without hyperemia now abound. Additional advances in other alternative FFR approaches, including non-invasive coronary CT (FFR_CT), invasive angiography (FFR_angio), and optical coherence tomography (FFR_OCT), are being realized. Artificial intelligence algorithms and robust tools that enable detailed pre-procedure "virtual" intervention are also emerging. The benefits of coronary physiological assessment to determine lesion functional significance are well established. In addition to stable CAD, coronary physiology can be especially helpful in clinical scenarios such as left main and multivessel CAD, serial lesions, non-infarct-related arteries in acute coronary syndromes, and residual ischemia post-PCI. Today, coronary physiological assessment remains an indispensable tool in the catheterization laboratory, with an exciting technological future that will further refine clinical practice and improve patient care.

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

Background

The instantaneous wave-free ratio (iFR) is an invasive coronary physiological index that is not inferior to fractional flow reserve- (FFR-) guided revascularization. The indexes of iFR and FFR are similar and closely correlated, but there are a few key differences. Previous studies suggested that patient characteristics and lesion severity could induce discordance between iFR and FFR. This study aimed to clarify the hemodynamics and lesion characteristics that influence discordance between iFR and FFR.

Methods

In this retrospective study, we enrolled 225 patients (304 lesions) who underwent clinically indicated invasive coronary angiography and both iFR and FFR examinations between 2012 and 2017. We included only patients who underwent right heart catheterization and had blood pressure and heart rates recorded immediately prior to iFR and FFR.

Results

Discordance (iFR ≤0.89 and FFR >0.8 or iFR >0.89 and FFR ≤0.8) was observed in 80 lesions (26.3%). The heart rate, rate-pressure product, and cardiac index tended to be higher in the iFR ≤0.89 group than in the iFR >0.89 group. These trends were not seen between the FFR ≤0.8 group and FFR >0.8 group. A multivariate analysis showed that independent predictors of iFR ≤0.89 and FFR >0.8 discordance were female sex and higher rate-pressure product. iFR >0.89 and FFR ≤0.8 discordance was rare in hemodialysis patients.

Conclusion

Even if iFR is functionally significant in intermediate stenosis, additional FFR evaluations should be considered for women, especially those with a high rate-pressure product, to avoid unnecessary percutaneous coronary intervention. If iFR is not functionally significant with intermediate stenosis in hemodialysis patients, then further FFR evaluations are unnecessary.