Fractional flow reserve and instantaneous wave-free ratio in coronary artery bypass grafting: a meta-analysis and practice review

Objective

Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are invasive methods to assess the functional significance of intermediate severity coronary lesions. Both indexes have been extensively validated in clinical trials in guiding revascularisation in patients with stable ischaemic heart disease undergoing percutaneous coronary intervention (PCI) with improved clinical outcomes. However, the role of these tools in coronary artery bypass grafting (CABG) is less clear.

Methods

A meta-analysis of randomised trials and observational studies was carried out to help in determining the optimal strategy for assessing lesion severity and selecting graft targets in patients undergoing CABG. Electronic searches were carried out on Embase, MEDLINE, and Web of Science. A group of four authors independently screened and then assessed the retrieved records. Cochrane's Risk of Bias and Robins-I tools were used for bias assessment. A survey was conducted among surgeons and cardiologists to describe current attitudes towards the preoperative use of functional coronary investigations in practice.

Results

Clinical outcomes including mortality at 30 days, perioperative myocardial infarction, number of grafts, incidence of stroke, rate of further need for revascularisation, and patient-reported quality of life did not differ in CABG guided by functional testing from those guided by traditional angiography.The survey revealed that in half of the surgical and cardiology units functional assessment is performed in CABG patients; there is a general perception that functional testing has improved patient care and its use would clarify the role of moderate coronary lesions that often need multidisciplinary rediscussions; moderate stenosis are felt to be clinically relevant; and anatomical considerations need to be taken into account together with functional assessment.

Conclusions

At present, the evidence to support the routine use of functional testing in intermediate lesions for planning CABG is currently insufficient. The pooled data currently available do not show an increased risk in mortality, myocardial injury, and stroke in the FFR/iFR-guided group. Further trials with highly selected populations are needed to clarify the best strategy.

Systematic Review Registration

ClinicalTrials.gov, identifier (CRD42023414604).

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.

Comparison of Intravascular Imaging, Functional, or Angiographically Guided Coronary Intervention

BACKGROUND

In patients undergoing percutaneous coronary intervention (PCI), it remains unclear whether intravascular imaging guidance or functional guidance is the best strategy to optimize outcomes and if the results are different in patients with vs without acute coronary syndromes (ACS).

OBJECTIVES

The purpose of this study was to evaluate clinical outcomes with imaging-guided PCI or functionally guided PCI when compared with conventional angiography-guided PCI.

METHODS

We searched PUBMED and EMBASE for randomized controlled trials investigating outcomes with intravascular imaging-guided, functionally guided, or angiography-guided PCI. The primary outcome from this network meta-analysis was trial-defined major adverse cardiovascular event (MACE)-a composite of cardiovascular death, myocardial infarction (MI), and target lesion revascularization (TLR). PCI strategies were ranked (best to worst) using P scores.

RESULTS

Our search identified 32 eligible randomized controlled trials and included a total of 22,684 patients. Compared with angiography-guided PCI, intravascular imaging-guided PCI was associated with reduced risk of MACE (relative risk [RR]: 0.72; 95% CI: 0.62-0.82), cardiovascular death (RR: 0.56; 95% CI: 0.42-0.75), MI (RR: 0.81; 95% CI: 0.66-0.99), stent thrombosis (RR: 0.48; 95% CI: 0.31-0.73), and TLR (RR: 0.75; 95% CI: 0.57-0.99). Similarly, when compared with angiography-guided PCI, functionally guided PCI was associated with reduced risk of MACE and MI. Intravascular imaging-guided PCI ranked first for the outcomes of MACE, cardiovascular death, stent thrombosis, and TLR. The results were consistent in the ACS and non-ACS cohorts.

CONCLUSIONS

Angiography-guided PCI had consistently worse outcomes compared with intravascular imaging-guided and functionally guided PCI. Intravascular imaging-guided PCI was the best strategy to reduce the risk of cardiovascular events.

The Impact of Age on the Physiological Assessment of Borderline Coronary Stenoses

Background and Objectives: Coronary angiography is the gold standard for diagnosing coronary artery disease (CAD). In the case of borderline changes, patients require further diagnosis through ischemia assessment via one of the recommended methods of invasive evaluation. This study aimed to assess whether clinical factors influence the risk of a positive result in invasive myocardial ischemia assessment and if these potential factors change with the patient's age and the consistency of ischemia assessment. Materials and Methods: Data were collected retrospectively on all consecutive patients hospitalized in the University Hospital in Krakow between 2020 and 2021, on whom physiological assessments of coronary circulation were performed. Patients were divided into two groups: patients aged 60 or younger and patients older than 60. Results: Despite the older patients having more risk factors for CAD, their physiological assessment results of borderline lesions were similar to those of the younger patients. Positive fractional flow reserve (FFR) assessments were obtained from almost 50% of vessels. In the younger patients, cigarette use and type 2 diabetes mellitus increased the risk of a positive FFR result by 3.5 and 2.5 times, respectively. In the older patients, male gender and peripheral vascular disease significantly increased the risk of a positive FFR by 2.5 and 2 times, respectively. Conclusions: Clinical characteristics of patients undergoing physiological assessment of borderline coronary stenosis varied significantly by age. Refining the definition of borderline lesions to include age, gender, and other factors may improve the identification of patients who would benefit from physiological assessment and coronary revascularization.

Intravascular Imaging versus Physiological Assessment versus Biomechanics-Which Is a Better Guide for Coronary Revascularization

Today, coronary artery disease (CAD) continues to be a prominent cause of death worldwide. A reliable assessment of coronary stenosis represents a prerequisite for the appropriate management of CAD. Nevertheless, there are still major challenges pertaining to some limitations of current imaging and functional diagnostic modalities. The present review summarizes the current data on invasive functional and intracoronary imaging assessment using optical coherence tomography (OCT), and intravascular ultrasound (IVUS). Amongst the functional parameters-on top of fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR)-we point to novel angiography-based measures such as quantitative flow ratio (QFR), vessel fractional flow reserve (vFFR), angiography-derived fractional flow reserve (FFRangio), and computed tomography-derived flow fractional reserve (FFR-CT), as well as hybrid approaches focusing on optical flow ratio (OFR), computational fluid dynamics and attempts to quantify the forces exaggerated by blood on the coronary plaque and vessel wall.

Deferred Versus Performed Revascularization for Left Main Coronary Disease With Hemodynamic Significance

BACKGROUND

The majority of randomized controlled trials of revascularization decision-making excludes left main coronary artery disease (LMD). Therefore, contemporary clinical outcomes of patients with stable coronary artery disease and LMD with proven ischemia remain poorly understood. The aim of this study was to assess the long-term clinical outcomes of physiologically significant LMD according to the treatment strategies of revascularization versus revascularization deferral.

METHODS

In this international multicenter registry of stable LMD interrogated with the instantaneous wave-free ratio, patients with physiologically significant ischemia (instantaneous wave-free ratio ≤0.89) were analyzed according to the coronary revascularization (n=151) versus revascularization deferral (n=74). Propensity score matching was performed to adjust for baseline clinical characteristics. The primary end point was a composite of death, nonfatal myocardial infarction, and ischemia-driven target lesion revascularization of left main stem. The secondary end points were as follows: cardiac death or spontaneous LMD-related myocardial infarction; and ischemia-driven target lesion revascularization of left main stem.

RESULTS

At a median follow-up period of 2.8 years, the primary end point occurred in 11 patients (14.9%) in the revascularized group and 21 patients (28.4%) in the deferred group (hazard ratio, 0.42 [95% CI, 0.20-0.89]; P=0.023). For the secondary end points, cardiac death or LMD-related myocardial infarction occurred significantly less frequently in the revascularized group (0.0% versus 8.1%; P=0.004). The rate of ischemia-driven target lesion revascularization of left main stem was also significantly lower in the revascularized group (5.4% versus 17.6%; hazard ratio, 0.20 [95% CI, 0.056-0.70]; P=0.012).

CONCLUSIONS

In patients who underwent revascularization for stable coronary artery disease and physiologically significant LMD determined by instantaneous wave-free ratio, the long-term clinical outcomes were significantly improved as compared with those in whom revascularization was deferred.

Comparison of quantitative flow ratio with instantaneous wave-free ratio and resting full-cycle ratio during daily routine in the catheterization laboratory

BACKGROUND

Quantitative flow ratio (QFR) is a novel, software-based method to evaluate the physiology of coronary lesions. The aim of this study was to compare QFR with the established invasive measurements of coronary blood flow using instantaneous wave-free ratio (iFR) or resting full-cycle ratio (RFR) in daily cathlab routine.

METHODS

102 patients with stable coronary artery disease and a coronary stenosis of 40%-90% were simultaneously assessed with QFR and iFR or RFR. QFR-computation was performed by two certified experts using the appropriate software (QAngio XA 3D 3.2).

RESULTS

QFR showed a significant correlation (r = 0.75, p < 0.001) to iFR and RFR. The area under the receiver curve for all measurements was 0.93 (95% confidence interval, 0.87-0.98) for QFR compared to iFR or RFR. QFR based assessment required less time with a median of 501 s (IQR 421-659 s) compared to iFR or RFR which required a median of 734 s to obtain the result (IQR 512-967 s; p < 0.001). The median use of contrast medium was similar with 21 mL (IQR 16-30 mL) for the QFR-based and 22 mL (IQR 15-35 mL) for the iFR- or RFR-based diagnostic. QFR diagnostic required less radiation. The median dose area product for QFR was 307cGycm² (IQR 151-429 cGycm² ) compared to 599 cGycm² (IQR 345-1082 cGycm² ) for iFR or RFR, p < 0.001.

CONCLUSION

QFR measurements of coronary artery blood flow correlate with iFR or RFR measurements and are associated with shorter procedure times and reduced radiation dose.

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.

5-Year Outcomes of PCI Guided by Measurement of Instantaneous Wave-Free Ratio Versus Fractional Flow Reserve

BACKGROUND

Instantaneous wave-free ratio (iFR) is a coronary physiology index used to assess the severity of coronary artery stenosis to guide revascularization. iFR has previously demonstrated noninferior short-term outcome compared to fractional flow reserve (FFR), but data on longer-term outcome have been lacking.

OBJECTIVES

The purpose of this study was to investigate the prespecified 5-year follow-up of the primary composite outcome of all-cause mortality, myocardial infarction, and unplanned revascularization of the iFR-SWEDEHEART trial comparing iFR vs FFR in patients with chronic and acute coronary syndromes.

METHODS

iFR-SWEDEHEART was a multicenter, controlled, open-label, registry-based randomized clinical trial using the Swedish Coronary Angiography and Angioplasty Registry for enrollment. A total of 2,037 patients were randomized to undergo revascularization guided by iFR or FFR.

RESULTS

No patients were lost to follow-up. At 5 years, the rate of the primary composite endpoint was 21.5% in the iFR group and 19.9% in the FFR group (HR: 1.09; 95% CI: 0.90-1.33). The rates of all-cause death (9.4% vs 7.9%; HR: 1.20; 95% CI: 0.89-1.62), nonfatal myocardial infarction (5.7% vs 5.8%; HR: 1.00; 95% CI: 0.70-1.44), and unplanned revascularization (11.6% vs 11.3%; HR: 1.02; 95% CI: 0.79-1.32) were also not different between the 2 groups. The outcomes were consistent across prespecified subgroups.

CONCLUSIONS

In patients with chronic or acute coronary syndromes, an iFR-guided revascularization strategy was associated with no difference in the 5-year composite outcome of death, myocardial infarction, and unplanned revascularization compared with an FFR-guided revascularization strategy. (Evaluation of iFR vs FFR in Stable Angina or Acute Coronary Syndrome [iFR SWEDEHEART]; NCT02166736).

1-Year Outcomes of Blinded Physiological Assessment of Residual Ischemia After Successful PCI: DEFINE PCI Trial

OBJECTIVES

The aim of this study was to identify the post-percutaneous coronary intervention (PCI) target value of instantaneous wave-free ratio (iFR) that would best discriminate clinical events at 1 year in the DEFINE PCI (Physiologic Assessment of Coronary Stenosis Following PCI) study.

BACKGROUND

The impact of residual ischemia detected by iFR post-PCI on clinical and symptom-related outcomes is unknown.

METHODS

Blinded iFR pull back was performed after successful stent implantation in 500 patients. The primary endpoint was the rate of residual ischemia, defined as iFR ≤0.89, after operator-assessed angiographically successful PCI. Secondary endpoints included clinical events at 1 year and change in Seattle Angina Questionnaire angina frequency (SAQ-AF) score during follow-up.

RESULTS

As reported, 24.0% of patients had residual ischemia (iFR ≤0.89) after successful PCI, with 81.6% of cases attributable to angiographically inapparent focal lesions. Post-PCI iFR ≥0.95 (present in 182 cases [39%]) was associated with a significant reduction in the composite of cardiac death, spontaneous myocardial infarction, or clinically driven target vessel revascularization compared with post-PCI iFR <0.95 (1.8% vs 5.7%; P = 0.04). Baseline SAQ-AF score was 73.3 ± 22.8. For highly symptomatic patients (baseline SAQ-AF score ≤60), SAQ-AF score increased by ≥10 points more frequently in patients with versus without post-PCI iFR ≥0.95 (100.0% vs 88.5%; P = 0.01).

CONCLUSIONS

In DEFINE PCI, despite angiographically successful PCI, highly symptomatic patients at baseline without residual ischemia by post-PCI iFR had greater reductions in anginal symptoms at 1 year compared with patients with residual ischemia. Achieving post-PCI iFR ≥0.95 was also associated with improved 1-year event-free survival. (Physiologic Assessment of Coronary Stenosis Following PCI [DEFINE PCI]; NCT03084367).

Instantaneous wave-free ratio for guiding treatment of nonculprit lesions in patients with acute coronary syndrome: A retrospective study

BACKGROUND

The aim of this study was to analyze the feasibility of a physiological coronary evaluation with the instantaneous wave-free ratio (iFR) of nonculprit lesions in patients with acute coronary syndrome (ACS) successfully revascularized.

METHODS

A multicenter registry including patients of four high-volume PCI centers with ACS and underwent successful revascularization of the culprit vessel and had other nonculprit lesions that were physiologically evaluated with the iFR between January 2017 and December 2019. The primary endpoint was a composite of cardiac death, nonfatal myocardial infarction, probable or definitive stent thrombosis and new revascularization (MACEs).

RESULTS

A total of 356 patients with 472 nonculprit lesions were included. The mean age was 66 ± 11 years. The clinical presentation was ACS without persistent ST-segment elevation (NSTE-ACS) in 235 patients (66%) and ST-segment elevation myocardial infarction (STEMI) in 121 patients (34%). After a median follow-up period of 21 (14-30) months, the primary endpoint occurred in 32 patients (9%). There were no differences in outcomes regarding clinical presentation (NSTEMI vs. NSTE-ACS, 9.1 vs. 8.9%, p_adj  = 0.570) or iFR induced treatment strategy (patients with all lesions revascularized vs. patients with at least one lesion with an iFR > 0.89 deferred for revascularization, 10.5 vs. 8.4%, p_adj  = 0.476).

CONCLUSIONS

The use of the iFR to guide percutaneous coronary intervention decision making in nonculprit lesions seems to be feasible, with an acceptable percentage of MACEs at the mid-term follow-up. Patients with deferred revascularization of lesions without physiological significance and patients undergoing complete revascularization had a similar risk of MACEs.

Three Technologies That Will Guide Revascularization of Chronic Coronary Syndrome Patients into the 21st Century: A Review

Although medical therapy is the preferred first-line treatment for patients with chronic coronary syndrome (CCS), revascularization remains an important consideration. We present a review that identifies the three diagnostic technologies most important to guiding the decision to revascularize patients with CCS: (1) cardiac computed tomography, (2) intracoronary imaging, and (3) lesion-specific physiological guidance.

Invasive Coronary Physiology After Stent Implantation: Another Step Toward Precision Medicine

Intracoronary physiology is routinely used in setting the indication for percutaneous coronary intervention (PCI) but seldom in assessing procedural results. This attitude is increasingly challenged by accumulated evidence demonstrating the value of post-PCI functional assessment in predicting long-term patient outcomes. Besides fractional flow reserve, a number of new indexes recently incorporated to clinical practice, including nonhyperemic pressure and functional angiographic indexes, provide new opportunities for the physiological assessment of PCI results. Largely, the benefit of these tools is derived from longitudinal analysis of the treated vessel, which allows precise identification of the vessel segment accounting for a suboptimal functional result and enabling operators to perform accurate PCI optimization. In this document the authors review available evidence supporting why physiological assessment should be extended to immediate post-PCI with the aim of improving patient outcomes. A step-by-step guide on how available physiological tools can be used for such purpose is provided.

Correlation of Intravascular Ultrasound and Instantaneous Wave-Free Ratio in Patients With Intermediate Left Main Coronary Artery Disease

[Figure: see text].

Physiology-Based Revascularization: A New Approach to Plan and Optimize Percutaneous Coronary Intervention

Coronary physiological assessment using fractional flow reserve or nonhyperemic pressure ratios has become a standard of care for patients with coronary atherosclerotic disease. However, most evidence has focused on the pre-interventional use of physiological assessment to aid revascularization decision-making, whereas post-interventional physiological assessment has not been well established. Although evidence for supporting the role of post-interventional physiological assessment to optimize immediate revascularization results and long-term prognosis has been reported, a more thorough understanding of these data is crucial in incorporating post-interventional physiological assessment into daily practice. Recent scientific efforts have also focused on the potential role of pre-interventional fractional flow reserve or nonhyperemic pressure ratio pullback tracings to characterize patterns of coronary atherosclerotic disease to better predict post-interventional physiological outcomes, and thereby identify the appropriate revascularization target. Pre-interventional pullback tracings with dedicated post-processing methods can provide characterization of focal versus diffuse disease or major gradient versus minor gradient stenosis, which would result in different post-interventional physiological results. This review provides a comprehensive look at the current evidence regarding the evolving role of physiological assessment as a functional optimization tool for the entire process of revascularization, and not merely as a pre-interventional tool for revascularization decision-making.

Safety of coronary revascularization deferral based on fractional flow reserve and instantaneous wave-free ratio in patients with chronic kidney disease

Background

The safety of revascularization deferral according to pressure wire examination in patients with chronic kidney disease (CKD) has not been fully established.

Methods

From a retrospective cohort of 439 patients in whom revascularization was deferred after physiological assessment, we examined the incidence of patient-oriented composite endpoint (POCE: all-cause death, myocardial infarction [MI] and unplanned revascularization) in patients with CKD (estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73 m²) and without it.

Results

At 4 years of follow-up, the primary endpoint was met by 25.0% of patients with CKD and by 14.4% of patients without CKD (hazard ratio [HR] 1.56, 95% confidence interval [CI] 0.96–2.53, p = 0.071). The incidence of POCE was even higher in patients with an eGFR < 30 mL/min/1.73 m²: 43.8% (HR 3.10, 95% CI 1.08–8.92, p = 0.036). However, no differences were observed in the incidence of MI (4.2% vs. 4.4% in non-CKD), target vessel revascularization (5.8% vs. 5.9%), and target vessel MI (0.8% vs. 4.6%).

Conclusions

Patients with CKD in whom pressure-wire evaluation led to deferral of coronary revascularization develop more POCE in the long term, compared to patients with normal renal function. However, the increase in POCE in patients with CKD was seldom related to deferred vessels, thus suggesting an epiphenomenon of an intrinsically higher cardiovascular risk of CKD patients.

Fractional flow reserve, quantitative flow ratio, and instantaneous wave-free ratio: a comparison of the procedure-related dose of ionising radiation

Introduction

The development of interventional cardiology increases the number of invasive procedures which are inevitably associated with increased exposure to ionizing radiation and associated risks. A percutaneous coronary intervention (PCI) substantiated by evaluation of the coronary artery lesion’s functional significance is recommended by both European and American cardiologists. Nevertheless, the prevalence of physiology-guided PCIs does not exceed 10% all over the globe.

Aim

To identify the physiology evaluation method which is associated with the lowest exposure to ionising radiation.

Material and methods

Anonymised data of 421 patients with stable angina pectoris for whom elective coronary artery angiography followed by physiological assessment of intermediate coronary artery stenosis was performed were prospectively included in this study. Only diagnostic-procedure-related data of dose of ionizing radiation were analysed. Physiological assessment of coronary artery lesions was performed by fractional flow reserve (FFR), quantitative flow ratio (QFR), or instantaneous wave-free ratio (iFR).

Results

Compared to FFR as a reference, fluoroscopy time (FT) was almost half in QFR and almost double in iFR, p < 0.001. QFR was associated with more than 3 times shorter FT compared to iFR. The dose area product was 663.87 ±260.51 cGy/cm² (p = 0.03) lower in QFR compared to iFR.

Conclusions

QFR is associated with significantly reduced exposure to ionising radiation compared to both FFR and iFR. Therefore, wider QFR application in clinical practice could eliminate any additional exposure to ionising radiation and increase the prevalence of physiology-guided coronary artery revascularization.

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.

Coronary angiography-derived contrast fractional flow reserve

BACKGROUND

Based on coronary angiography and mean aortic pressure, a specially designed computational flow dynamics (CFD) method is proposed to determine contrast fractional flow reserve (cFFR) without using invasive pressure wire. This substudy assessed diagnostic performance of coronary angiography-derived cFFR in catheterization laboratory, based on a previous multicenter trial for online assessment of coronary angiography-derived FFR (caFFR).

METHODS

Patients with diagnosis of stable angina pectoris or unstable angina pectoris were enrolled in six centers. Wire-based FFR was measured in coronary arteries with 30-90% diameter stenosis. Offline angiography-derived cFFR was computed in blinded fashion against the wire-based FFR and caFFR at an independent core laboratory.

RESULTS

A total of 330 patients were enrolled to fulfill inclusion/exclusion criteria from June 26 to December 18, 2018. Offline angiography-derived cFFR and wire-based FFR results were compared in 328 interrogated vessels. The statistical analysis showed the highest diagnostic accuracy of 89.0 and 86.6% for angiography-derived cFFR with a cutoff value of 0.94 and 0.93 against the wire-based FFR with a cutoff value of 0.80 and 0.75, respectively. The corresponding sensitivity and specificity were 92.2 and 87.3% for the cutoff value of 0.94 and 80.0 and 88.4% for the cutoff value of 0.93, which are similar to those against the caFFR. The receiver-operating curve has area under the curve of 0.951 and 0.972 for the wire-based FFR with the cutoff value of 0.80 and 0.75, respectively.

CONCLUSIONS

Coronary angiography-derived cFFR showed higher accuracy, sensitivity, and specificity against wired-based FFR and caFFR. Hence, angiography-derived cFFR could enhance the hemodynamic assessment of coronary lesions.

Bridging the Gap in a Rare Cause of Angina

Myocardial bridging occurs when coronary arteries run intramurally. Episodes of tachycardia can cause a dynamic obstruction that extends into diastole, compromising coronary filling time, and subsequently leading to ischaemia. Myocardial ischaemia, acute coronary syndrome, coronary spasm, myocardial stunning, arrhythmia, takotsubo cardiomyopathy, and sudden cardiac death have all been reported with bridging. Atherosclerotic plaques develop proximally in the bridge due to low shear stress and high oscillatory wall-flow. Factors affecting atherosclerotic build-up include disrupted flow patterns (particularly flow recirculation, which exacerbates LDL internalisation), cell adhesion and monocyte adhesion to the endothelium. Endothelial health depends on arterial flow patterns, given that the vessel reacts differently to various flow types, as confirmed in 3D simulations. Medication is the first-line therapy, while surgical de-roofing and coronary bypass are reserved for severe stenosis. Distinguishing physiological arterial compression from pathological stenosis is essential. Deeper bridges correlating with recurrent angina with an instantaneous wave-free ratio ≤0.89 or fractional flow reserve ≤0.80 are treated.

Correlation between Preoperative Coronary Artery Stenosis Severity Measured by Instantaneous Wave-Free Ratio and Intraoperative Transit Time Flow Measurement of Attached Grafts

Background and Objectives: To assess the correlation between the degree of target coronary artery stenosis measured by instantaneous wave-free ratio (iFR) and the intraoperative transit time flow measurement (TTFM) of attached grafts as well as evaluate flow competition between the native coronary artery and the attached graft according to the severity of stenosis. Materials and Methods: In total, 89 grafts were subjected to intraoperative transit time flow measurement after coronary artery bypass grafting (CABG) in 25 patients with multivessel coronary artery disease (CAD). The iFR was evaluated for all coronary arteries with grafts. The coronary artery stenoses were divided into three groups based on the iFR value: iFR < 0.86 (group 1); iFR 0.86–0.90 (group 2); and iFR > 0.90 (group 3). Results: The mean graft flow (MGF) was 46.9 ± 18.4 mL/min for group 1, 45.3 ± 20.9 mL/min for group 2, and 31.3 ± 18.5 mL/min for group 3. A statistically significant difference was confirmed between groups 1 and 3 (p = 0.002) and between groups 2 and 3 (p = 0.025). The pulsatility index (PI) was 2.49 ± 1.20 for group 1, 2.66 ± 2.13 for group 2, and 4.70 ± 3.66 for group 3. A statistically significant difference was found between groups 1 and 3 (p = 0.006) and between groups 2 and 3 (p = 0.032). Backward flow was detected in 7.5% of grafts for group 1, in 16.6% of grafts for group 2, and in 16% of grafts for group 3. A statistically significant difference was found between groups 1 and 2 (p = 0.025) and between groups 1 and 3 (p = 0.029). Conclusions: The iFR is a useful tool for predicting the impact of competitive flow observed between a native artery and an attached graft. The effect of competitive flow significantly increases when the graft is attached to a vessel with mild coronary stenosis. In a coronary artery where the iFR was not hemodynamically significant, the MGF was lower, the PI was higher, and a larger proportion of grafts with backward flow (BF) was detected compared to when there was significant stenosis (iFR < 0.86).

Sex Differences in Instantaneous Wave-Free Ratio or Fractional Flow Reserve-Guided Revascularization Strategy

OBJECTIVES

This study sought to evaluate sex differences in procedural characteristics and clinical outcomes of instantaneous wave-free ratio (iFR)- and fractional flow reserve (FFR)-guided revascularization strategies.

BACKGROUND

An iFR-guided strategy has shown a lower revascularization rate than an FFR-guided strategy, without differences in clinical outcomes.

METHODS

This is a post hoc analysis of the DEFINE-FLAIR (Functional Lesion Assessment of Intermediate stenosis to guide Revascularization) study, in which 601 women and 1,891 men were randomized to iFR- or FFR-guided strategy. The primary endpoint was 1-year major adverse cardiac events (MACE), a composite of all-cause death, nonfatal myocardial infarction, or unplanned revascularization.

RESULTS

Among the entire population, women had a lower number of functionally significant lesions per patient (0.31 ± 0.51 vs. 0.43 ± 0.59; p < 0.001) and less frequently underwent revascularization than men (42.1% vs. 53.1%; p < 0.001). There was no difference in mean iFR value according to sex (0.91 ± 0.09 vs. 0.91 ± 0.10; p = 0.442). However, the mean FFR value was lower in men than in women (0.83 ± 0.09 vs. 0.85 ± 0.10; p = 0.001). In men, an FFR-guided strategy was associated with a higher rate of revascularization than an iFR-guided strategy (57.1% vs. 49.3%; p = 0.001), but this difference was not observed in women (41.4% vs. 42.6%; p = 0.757). There was no difference in MACE rates between iFR- and FFR-guided strategies in both women (5.4% vs. 5.6%, adjusted hazard ratio: 1.10; 95% confidence interval: 0.50 to 2.43; p = 0.805) and men (6.6% vs. 7.0%, adjusted hazard ratio: 0.98; 95% confidence interval: 0.66 to 1.46; p = 0.919).

CONCLUSIONS

An FFR-guided strategy was associated with a higher rate of revascularization than iFR-guided strategy in men, but not in women. However, iFR- and FFR-guided strategies showed comparable clinical outcomes, regardless of sex. (Functional Lesion Assessment of Intermediate Stenosis to guide Revascularization [DEFINE-FLAIR]; NCT02053038).

Long-Term Clinical Outcomes of Nonhyperemic Pressure Ratios: Resting Full-Cycle Ratio, Diastolic Pressure Ratio, and Instantaneous Wave-Free Ratio

Background

Nonhyperemic pressure ratios (NHPRs) such as instantaneous wave‐free ratio, resting full‐cycle ratio, or diastolic pressure ratio have emerged as invasive physiologic indices precluding the need for hyperemic agents. The current study sought to evaluate the long‐term prognostic implications of NHPRs compared with fractional flow reserve (FFR).

Methods and Results

NHPRs were calculated from resting pressure tracings by an independent core laboratory in 1024 vessels (435 patients). The association between NHPRs and the risk of 5‐year vessel‐oriented composite outcomes (VOCO, a composite of cardiac death, vessel‐related myocardial infarction, and ischemia‐driven revascularization) were analyzed among 864 deferred vessels. Lesions with positive NHPRs (instantaneous wave free ratio, resting full‐cycle ratio, and diastolic pressure ratio ≤0.89) or FFR (≤0.80) showed significantly higher risk of VOCO at 5 years than those with negative NHPRs or FFR, respectively. Discriminant ability for 5‐year VOCO was not different among NHPRs and FFR (C‐index: 0.623–0.641, P for comparison=0.215). In comparison of VOCO among the groups with deferred concordant negative (NHPRs−/FFR−), deferred discordant (NHPRs+/FFR− or NHPRs−/FFR+), and revascularized vessels, the cumulative incidence of VOCO were 7.5%, 14.4%, and 14.8% (log‐rank P<0.001), respectively. The deferred discordant group showed similar risk of VOCO with the revascularized vessel group (hazard ratio, 0.981; 95% CI 0.434–2.217, P=0.964).

Conclusions

Currently available invasive pressure‐derived indices showed similar prognostic implications for vessel‐related events at 5 years. Deferred lesions with discordant results between NHPRs and FFR did not show higher risk of vessel‐related events at 5 years than revascularized vessels.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifiers: NCT01621438, NCT01621438.

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.

Algorithmic Versus Expert Human Interpretation of Instantaneous Wave-Free Ratio Coronary Pressure-Wire Pull Back Data

Objectives

The aim of this study was to investigate whether algorithmic interpretation (AI) of instantaneous wave-free ratio (iFR) pressure-wire pull back data would be noninferior to expert human interpretation.

Background

Interpretation of iFR pressure-wire pull back data can be complex and is subjective.

Methods

Fifteen human experts interpreted 1,008 iFR pull back traces (691 unique, 317 duplicate). For each trace, experts determined the hemodynamic appropriateness for percutaneous coronary intervention (PCI) and, in such cases, the optimal physiological strategy for PCI. The heart team (HT) interpretation was determined by consensus of the individual expert opinions. The same 1,008 pull back traces were also interpreted algorithmically. The coprimary hypotheses of this study were that AI would be noninferior to the interpretation of the median expert human in determining: 1) the hemodynamic appropriateness for PCI; and 2) the physiological strategy for PCI.

Results

Regarding the hemodynamic appropriateness for PCI, the median expert human demonstrated 89.3% agreement with the HT in comparison with 89.4% for AI (p < 0.01 for noninferiority). Across the 372 cases judged as hemodynamically appropriate for PCI according to the HT, the median expert human demonstrated 88.8% agreement with the HT in comparison with 89.7% for AI (p < 0.0001 for noninferiority). On reproducibility testing, the HT opinion itself changed 1 in 10 times for both the appropriateness for PCI and the physiological PCI strategy. In contrast, AI showed no change.

Conclusions

AI of iFR pressure-wire pull back data was noninferior to expert human interpretation in determining both the hemodynamic appropriateness for PCI and the optimal physiological strategy for PCI.

Coronary Circulatory Indexes in Non-Infarct-Related Vascular Territories in a Porcine Acute Myocardial Infarction Model

OBJECTIVES

The aim of this study was to evaluate temporal changes in coronary hemodynamic and physiological indexes in the non-infarct-related artery (IRA), which might be affected by adjacent infarcted myocardium, using an experimental animal model of acute myocardial infarction.

BACKGROUND

There has been debate on the reliability of fractional flow reserve and resting pressure-derived indexes, including instantaneous wave-free ratio, in the non-IRA in patients with acute ST-segment elevation myocardial infarction.

METHODS

In Yorkshire swine, acute myocardial infarction was simulated with selective balloon occlusion at the left circumflex coronary artery as the IRA for 30 min. Non-IRA stenosis was created using bare-metal stent implantation in the left anterior descending coronary artery 4 weeks before the experiments. Serial changes in systemic hemodynamic status, coronary pressure, and Doppler-derived coronary flow velocity were measured in a nonoccluded left anterior descending coronary artery as the non-IRA from baseline, balloon occlusion of the left circumflex coronary artery, and 15 min after reperfusion of the left circumflex coronary artery.

RESULTS

Among the 6 experimental subjects, the median diameter stenosis of the non-IRA was 33.9% (interquartile range: 21.7% to 46.1%). During balloon occlusion of the IRA, there were transient significant changes in both resting and hyperemic aortic pressure, distal coronary pressure, averaged peak velocity, transstenotic pressure gradient, and microvascular resistance of the non-IRA (p < 0.020 for all). After reperfusion of the IRA, the resting averaged peak velocity (p = 0.002) and resting transstenotic pressure gradient (p = 0.004) were significantly increased and resting microvascular resistance (p = 0.004) was significantly decreased compared with their values in the baseline phase. However, the hyperemic averaged peak velocity (p = 0.479), hyperemic transstenotic pressure gradient (p = 0.778), and hyperemic microvascular resistance (p = 0.816) were not significantly different compared with those in the baseline phase. After reperfusion, fractional flow reserve in the non-IRA was not significantly different (0.94 ± 0.01 vs. 0.93 ± 0.01; p = 0.353), while coronary flow reserve (1.93 ± 0.07 vs. 1.36 ± 0.07; p = 0.025) and instantaneous wave-free ratio (0.97 ± 0.01 vs. 0.93 ± 0.01; p = 0.001) were significantly lower than baseline values.

CONCLUSIONS

In a porcine model of acute myocardial infarction, occlusion of the IRA induced significant changes in systemic hemodynamic status and coronary circulatory indexes of the non-IRA. However, after reperfusion of the IRA, fractional flow reserve did not change significantly, whereas coronary flow reserve and instantaneous wave-free ratio showed significant changes compared with baseline values.

Instantaneous Wave-Free Ratio (iFR) Correlates With Fractional Flow Reserve (FFR) Assessment of Coronary Artery Stenoses and Myocardial Bridges in Children

OBJECTIVES

Instantaneous wave-free ratio (iFR) has been proven to correlate with coronary flow reserve better than fractional flow reserve (FFR) and is non-inferior to FFR in guiding coronary revascularization in ischemic heart disease. There has been no study validating the utility of iFR in children.

METHODS

We performed a retrospective review of clinically indicated cases in which both FFR and iFR were obtained at Texas Children's Hospital from July, 2016 to March, 2019. FFR and iFR were obtained at baseline. Adenosine FFR (FFRa) was used for assessment of coronary artery (CA) stenoses and diastolic dobutamine FFR (dFFRd) for myocardial bridges (MBs). FFRa or dFFRd ≤0.8 and iFR ≤0.89 indicated significant flow impairment.

RESULTS

A total of 22 coronary arteries (9 CA stenoses and 13 MBs) were assessed in 20 patients with median age of 13 years (range, 4-21 years) and median weight of 60 kg (range, 19-110 kg). iFR correlated with FFRa (Spearman's rho, 0.87; P<.01) in CA stenoses and with dFFRd (Spearman's rho, 0.74; P<.01) in MBs and agreed with FFR in 20/22 cases (90.9%). In 1 patient with CA stenosis and 1 MB with normal FFR, iFR was positive and both patients underwent coronary revascularization.

CONCLUSIONS

iFR correlated with FFR in the assessment of CA stenoses in children. iFR does not require administration of pharmacological agents; thus, it may reduce procedural time, cost, and complications, and result in more widespread adoption of invasive assessment of CA lesions in young patients.

How to guide PCI?: A network meta-analysis

BACKGROUND

Traditional coronary angiography (CA) as a main technique has been used to determine the coronary artery anatomy and guide percutaneous coronary intervention (PCI). We mainly focused on whether the new techniques could improve the patients' mortality, major adverse cardiovascular events (MACEs), and myocardial infarction.

METHODS

For the network meta-analysis, we searched the trials of different PCI guidances from MEDLINE, Current Contents Connect, Google Scholar, EMBASE, Cochrane Library, PubMed, Science Direct, and Web of Science. The last search date was December 10, 2018.

RESULTS

The analyses of all results found that there was no significant difference in mortality among the groups. Randomized clinical trials (RCT) analysis showed that intravascular ultrasound (IVUS)-guided PCI was significantly superior to CA, fractional flow reserve, instantaneous wave-free ratio, optical coherence tomography. However, CA, fractional flow reserve, instantaneous wave-free ratio, and optical coherence tomography showed no difference in reducing mortality. The analyses of all results found that there was no significant difference in the incidence of MACEs among the groups. RCTs analysis showed that IVUS-guided PCI was significantly superior to CA, but there was no significant difference among the other groups. The analyses of all results or RCTs showed that there was no significant difference in myocardial infarction incidence among the groups.

CONCLUSION

IVUS-guided PCI is an effective method to decrease all-cause death MACEs.

Fractional Flow Reserve and Instantaneous Wave-Free Ratio for Nonculprit Stenosis in Patients With Acute Myocardial Infarction

OBJECTIVES

The aim of this study was to compare the changes of fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR) with severity of epicardial coronary stenosis between nonculprit vessel of acute myocardial infarction (AMI) and stable ischemic heart disease (SIHD).

BACKGROUND

There has been debate regarding the reliability of FFR or iFR for nonculprit stenosis in the acute stage of AMI.

METHODS

A total of 100 AMI patients underwent comprehensive physiologic assessment including FFR, iFR, coronary flow reserve (CFR), and index of microcirculatory resistance (IMR) for nonculprit vessel stenosis after primary percutaneous coronary intervention (PCI) for culprit vessel. The changes in FFR and iFR for diameter stenosis (%DS) of nonculprit vessel stenosis were compared with FFR and iFR measured in 203 patients with SIHD.

RESULTS

From 40% to 80% stenosis, FFR and iFR measured in nonculprit vessel of AMI patient showed significant decrease with worsening stenosis severity (all p values < 0.001). Nonculprit vessels of AMI patients showed lower CFR than SIHD; however, IMR was not different between the nonculprit vessel of AMI and SIHD patients. FFR and iFR were not significantly different between the nonculprit vessel of AMI and SIHD patients in all %DS groups from 40% to 80% (all p values > 0.05). In addition, percent difference of FFR and iFR according to the increase in %DS was also not significantly different between nonculprit vessel of AMI or SIHD. There was no significant interaction between clinical presentation and the changes of FFR and iFR for worsening %DS (interaction p value = 0.698 and 0.257, respectively).

CONCLUSIONS

Changes in FFR and iFR for the nonculprit stenosis of AMI patients were not significantly different from those in SIHD patients. These data support the use of invasive physiological parameters to guide treatment of nonculprit stenoses in the acute stage of successfully revascularized AMI.

Clinical Events After Deferral of LAD Revascularization Following Physiological Coronary Assessment

Background

Physicians are not always comfortable deferring treatment of a stenosis in the left anterior descending (LAD) artery because of the perception that there is a high risk of major adverse cardiac events (MACE). The authors describe, using the DEFINE-FLAIR (Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularisation) trial, MACE rates when LAD lesions are deferred, guided by physiological assessment using fractional flow reserve (FFR) or the instantaneous wave-free ratio (iFR).

Objectives

The purpose of this study was to establish the safety of deferring treatment in the LAD using FFR or iFR within the DEFINE-FLAIR trial.

Methods

MACE rates at 1 year were compared between groups (iFR and FFR) in patients whose physiological assessment led to LAD lesions being deferred. MACE was defined as a composite of cardiovascular death, myocardial infarction (MI), and unplanned revascularization at 1 year. Patients, and staff performing follow-up, were blinded to whether the decision was made with FFR or iFR. Outcomes were adjusted for age and sex.

Results

A total of 872 patients had lesions deferred in the LAD (421 guided by FFR, 451 guided by iFR). The event rate with iFR was significantly lower than with FFR (2.44% vs. 5.26%; adjusted HR: 0.46; 95% confidence interval [CI]: 0.22 to 0.95; p = 0.04). This was driven by significantly lower unplanned revascularization with iFR and numerically lower MI (unplanned revascularization: 2.22% iFR vs. 4.99% FFR; adjusted HR: 0.44; 95% CI: 0.21 to 0.93; p = 0.03; MI: 0.44% iFR vs. 2.14% FFR; adjusted HR: 0.23; 95% CI: 0.05 to 1.07; p = 0.06).

Conclusions

iFR-guided deferral appears to be safe for patients with LAD lesions. Patients in whom iFR-guided deferral was performed had statistically significantly lower event rates than those with FFR-guided deferral.

Physiologic Characteristics and Clinical Outcomes of Patients With Discordance Between FFR and iFR

OBJECTIVES

This study evaluated the physiologic characteristics of discordant lesions between instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR) and the prognosis at 5 years.

BACKGROUND

FFR or iFR have been standard methods for assessing the functional significance of coronary artery stenosis. However, limited data exist about the physiologic characteristics of discordant lesions and the prognostic implications resulting from these lesions.

METHODS

A total of 840 vessels from 596 patients were classified according to iFR and FFR; high iFR-high FFR (n = 580), low iFR-high FFR (n = 40), high iFR-low FFR (n = 69), and low iFR-low FFR (n = 128) groups, which were compared with a control group (n = 23). The differences in coronary circulatory indices including the coronary flow reserve (CFR), index of microcirculatory resistance (IMR), and resistance reserve ratio (RRR) (resting distal arterial pressure × mean transit time / hyperemic distal arterial pressure × hyperemic mean transit time), which reflect the vasodilatory capacity of coronary microcirculation, were compared. Patient-oriented composite outcomes (POCO) at 5 years including all-cause death, any myocardial infarction, and any revascularization were compared among patients with deferred lesions.

RESULTS

In the low iFR-high FFR group, CFR, RRR, and IMR measurements were similar to the low iFR-low FFR group: CFR 2.71 versus 2.43 (p = 0.144), RRR 3.36 versus 3.68 (p = 0.241), and IMR 18.51 versus 17.38 (p = 0.476). In the high iFR-low FFR group, the CFR, RRR, and IMR measurements were similar to the control group: CFR 2.95 versus 3.29 (p = 0.160), RRR 4.28 versus 4.00 (p = 0.414), and IMR 17.44 versus 17.06 (p = 0.818). Among the 4 groups, classified by iFR and FFR, CFR and RRR were all significantly different, except for IMR. However, there were no significant differences in the rates of POCO, regardless of discordance between the iFR and FFR. Only the low iFR-low FFR group had a higher POCO rate compared with the high iFR-high FFR group (adjusted hazard ratio: 2.46; 95% confidence interval: 1.17 to 5.16; p = 0.018).

CONCLUSIONS

Differences in coronary circulatory function were found, especially in the vasodilatory capacity between the low iFR-high FFR and high iFR-low FFR groups. FFR-iFR discordance was not related to an increased risk of POCO among patients with deferred lesions at 5 years. (Clinical, Physiological and Prognostic Implication of Microvascular Status;NCT02186093; Physiologic Assessment of Microvascular Function in Heart Transplant Patients; NCT02798731).

Fractional Flow Reserve/Instantaneous Wave-Free Ratio Discordance in Angiographically Intermediate Coronary Stenoses: An Analysis Using Doppler-Derived Coronary Flow Measurements

Objectives

The study sought to determine the coronary flow characteristics of angiographically intermediate stenoses classified as discordant by fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR).

Background

Discordance between FFR and iFR occurs in up to 20% of cases. No comparisons have been reported between the coronary flow characteristics of FFR/iFR discordant and angiographically unobstructed vessels.

Methods

Baseline and hyperemic coronary flow velocity and coronary flow reserve (CFR) were compared across 5 vessel groups: FFR+/iFR+ (108 vessels, n = 91), FFR–/iFR+ (28 vessels, n = 24), FFR+/iFR– (22 vessels, n = 22), FFR–/iFR– (208 vessels, n = 154), and an unobstructed vessel group (201 vessels, n = 153), in a post hoc analysis of the largest combined pressure and Doppler flow velocity registry (IDEAL [Iberian-Dutch-English] collaborators study).

Results

FFR disagreed with iFR in 14% (50 of 366). Baseline flow velocity was similar across all 5 vessel groups, including the unobstructed vessel group (p = 0.34 for variance). In FFR+/iFR– discordants, hyperemic flow velocity and CFR were similar to both FFR–/iFR– and unobstructed groups; 37.6 (interquartile range [IQR]: 26.1 to 50.4) cm/s vs. 40.0 [IQR: 29.7 to 52.3] cm/s and 42.2 [IQR: 33.8 to 53.2] cm/s and CFR 2.36 [IQR: 1.93 to 2.81] vs. 2.41 [IQR: 1.84 to 2.94] and 2.50 [IQR: 2.11 to 3.17], respectively (p > 0.05 for all). In FFR–/iFR+ discordants, hyperemic flow velocity, and CFR were similar to the FFR+/iFR+ group; 28.2 (IQR: 20.5 to 39.7) cm/s versus 23.5 (IQR: 16.4 to 34.9) cm/s and CFR 1.44 (IQR: 1.29 to 1.85) versus 1.39 (IQR: 1.06 to 1.88), respectively (p > 0.05 for all).

Conclusions

FFR/iFR disagreement was explained by differences in hyperemic coronary flow velocity. Furthermore, coronary stenoses classified as FFR+/iFR– demonstrated similar coronary flow characteristics to angiographically unobstructed vessels.

Technical aspects and limitations of fractional flow reserve measurement

BACKGROUND

The only indication for coronary revascularization is elimination of ischaemia. Invasive hemodynamic methods (fractional flow reserve - FFR and instantaneous wave-free ratio (iFR) are superior to coronary angiography in detection of lesions causing myocardial ischaemia. Current European guidelines for myocardial revascularization recommend using of FFR for detection of functional assessment of lesions severity in category IA and number of these procedures increases. However, routine usage of these methods requires knowledge of technical requirements and limitations.

AIM

The aim of the study is to summarise good clinical practice for FFR and iFR measurements with explanation of possible technical challenges, that are necessary for increasing of measurement accuracy.

CONCLUSIONS

Authors describe frequent technical mistakes and malpractice during invasive assessment of lesion severity in coronary arteries.

One-year clinical outcome of angiography, fractional flow reserve and instantaneous wave-free ratio guided percutaneous coronary intervention: A PRISMA-compliant meta-analysis

The present study aimed to compare the clinical outcome of patients with coronary artery disease (CAD) who underwent a revascularization using conventional coronary angiography or a physiologically guided revascularization with Fractional Flow Reserve (FFR). Furthermore, outcomes in FFR guided percutaneous coronary intervention (PCI) and instantaneous wave-free ratio (iFR) guided PCI were compared. The analysis was performed for reported outcomes at a 1-year follow-up. After searching PubMed, EMBASE, and Web of Science for suitable publications, a total of 15,880 subjects were included. Comparing angiography guided and FFR guided PCI showed no significant difference in major adverse cardiac events [odds ratio (OR), 0.78; 95% confidence interval (CI), 0.59-1.04; P=0.09; I²=73%], death from any cause (OR, 0.74; 95% CI, 0.46-1.18; P=0.20; I²=74%), myocardial infarction (OR, 0.93; 95% CI, 0.81-1.07; P=0.31; I²=0%) or unplanned revascularization (OR, 0.71; 95% CI, 0.41-1.23; P=0.22; I²=79%). In addition, no significant difference could be found between iFR and FFR guided PCI for major adverse cardiac events (OR, 0.97; 95% CI; 0.76-1.23; P=0.81; I²=0%), death from any cause (OR, 0.66; 95% CI, 0.40-1.11; P=0.12; I²=0%), myocardial infarction (OR, 0.83; 95% CI, 0.56-1.24; P=0.37) or unplanned revascularization (OR, 1.16; 95% CI, 0.85-1.58; P=0.34; I²=16%). Overall, there was a tendency towards better outcomes of FFR in all four clinical endpoints compared with angiography guiding of PCI, and furthermore iFR showed no significant inferiority when compared to FFR in said clinical endpoints. When conducting a network meta-analysis, the results confirmed a non-inferiority of iFR compared to angiography guided revascularization.

Coronary Hemodynamics in Patients With Severe Aortic Stenosis and Coronary Artery Disease Undergoing Transcatheter Aortic Valve Replacement: Implications for Clinical Indices of Coronary Stenosis Severity

OBJECTIVES

In this study, a systematic analysis was conducted of phasic intracoronary pressure and flow velocity in patients with severe aortic stenosis (AS) and coronary artery disease, undergoing transcatheter aortic valve replacement (TAVR), to determine how AS affects: 1) phasic coronary flow; 2) hyperemic coronary flow; and 3) the most common clinically used indices of coronary stenosis severity, instantaneous wave-free ratio and fractional flow reserve.

BACKGROUND

A significant proportion of patients with severe aortic stenosis (AS) have concomitant coronary artery disease. The effect of the valve on coronary pressure, flow, and the established invasive clinical indices of stenosis severity have not been studied.

METHODS

Twenty-eight patients (30 lesions, 50.0% men, mean age 82.1 ± 6.5 years) with severe AS and coronary artery disease were included. Intracoronary pressure and flow assessments were performed at rest and during hyperemia immediately before and after TAVR.

RESULTS

Flow during the wave-free period of diastole did not change post-TAVR (29.78 ± 14.9 cm/s vs. 30.81 ± 19.6 cm/s; p = 0.64). Whole-cycle hyperemic flow increased significantly post-TAVR (33.44 ± 13.4 cm/s pre-TAVR vs. 40.33 ± 17.4 cm/s post-TAVR; p = 0.006); this was secondary to significant increases in systolic hyperemic flow post-TAVR (27.67 ± 12.1 cm/s pre-TAVR vs. 34.15 ± 17.5 cm/s post-TAVR; p = 0.02). Instantaneous wave-free ratio values did not change post-TAVR (0.88 ± 0.09 pre-TAVR vs. 0.88 ± 0.09 post-TAVR; p = 0.73), whereas fractional flow reserve decreased significantly post-TAVR (0.87 ± 0.08 pre-TAVR vs. 0.85 ± 0.09 post-TAVR; p = 0.001).

CONCLUSIONS

Systolic and hyperemic coronary flow increased significantly post-TAVR; consequently, hyperemic indices that include systole underestimated coronary stenosis severity in patients with severe AS. Flow during the wave-free period of diastole did not change post-TAVR, suggesting that indices calculated during this period are not vulnerable to the confounding effect of the stenotic aortic valve.

Instantaneous Wave-Free Ratio for the Assessment of Intermediate Coronary Artery Stenosis in Patients With Severe Aortic Valve Stenosis: Comparison With Myocardial Perfusion Scintigraphy

OBJECTIVES

This study investigated the diagnostic performance of instantaneous wave-free ratio (iFR) in patients with aortic valve stenosis (AS).

BACKGROUND

The iFR was introduced as a new, nonpharmacologic stress index of coronary stenosis severity. However, the diagnostic performance of iFR has not been sufficiently explored in patients with severe AS.

METHODS

We analyzed 95 consecutive patients with AS (57 women) demonstrating intermediate coronary artery stenosis (116 vessels), and compared the iFR values with fractional flow reserve (FFR) values and with adenosine-stress myocardial perfusion imaging as indicators of myocardial ischemia.

RESULTS

The median value and interquartile range (first quartile [Q1], third quartile [Q3]) of the iFR was 0.86 (Q1 to Q3 range, 0.76 to 0.93), and that of the FFR was 0.84 (Q1 to Q3 range, 0.76 to 0.91). The iFR values correlated well with the FFR values (R = 0.854; p < 0.0001). A receiver operating characteristic analysis demonstrated an optimal cutoff of 0.82 for the iFR to indicate an FFR ≤0.75, with an area under the curve of 0.92. The optimal iFR cutoff value indicating myocardial ischemia on perfusion scintigraphy was 0.82 (area under the curve: 0.84).

CONCLUSIONS

In patients with severe AS, a good correlation exists between iFR and FFR. Both the iFR and FFR values exhibit good correlation with perfusion scintigraphy-identified myocardial ischemia. The iFR could be a safe diagnostic tool for patients with severe AS. (The Impact of FFR and iFR in Patients with Severe Aortic Stenosis; UMIN000024479).

Pooled diagnostic accuracy of resting distal to aortic coronary pressure referenced to fractional flow reserve: The importance of resting coronary physiology

INTRODUCTION

Both resting and hyperemic physiologic methods to guide coronary revascularization improve cardiovascular outcomes compared with angiographic guidance alone. Fractional flow reserve (FFR) remains underutilized due to concerns regarding hyperemia, prompting study of resting distal to aortic coronary pressure (Pd/Pa). Pd/Pa is a vasodilator-free resting index unlike FFR. While Pd/Pa is similar to another resting index, instantaneous wave-free ratio (iFR), it is a whole-cycle measurement not limited to the wave-free diastolic period. Pd/Pa is not validated clinically although multiple accuracy studies have been performed. Our meta-analysis examines the overall diagnostic accuracy of Pd/Pa referenced to FFR, the accepted invasive standard of ischemia.

METHODS

We searched PubMed, EMBASE, Central, ProQuest, and Web of Science databases for full text articles published through August 9, 2017 addressing the diagnostic accuracy of Pd/Pa referenced to FFR < 0.80. The following keywords were used: "distal coronary artery pressure" OR "Pd/Pa" AND "fractional flow reserve" OR "FFR."

RESULTS

In total, 14 studies comprising 7004 lesions were identified. Pooled diagnostic accuracy estimates of Pd/Pa versus FFR < 0.80 were: sensitivity, 0.77 (95% CI, 0.75-0.78); specificity, 0.82 (0.81-0.83); positive likelihood ratio, 4.7 (3.3-6.6); negative likelihood ratio, 0.29 (0.24-0.34); diagnostic odds ratio, 18.1 (14.4-22.6); area under the summary receiver-operating characteristic curve of 0.88; and diagnostic accuracy of 0.80 (0.76-0.83).

CONCLUSIONS

Pd/Pa shows adequate agreement with FFR as a resting index of coronary stenosis severity without the undesired effects and cost of hyperemic agents. Pd/Pa has the potential to guide coronary revascularization with easier application and availability compared with iFR and FFR.

"What is the impact of utilizing so-called best practices in percutaneous coronary intervention?": an interview with Atul Gupta

Atul Gupta, MD speaks to Adam Price-Evans, Managing Commissioning Editor of Future Cardiology. Atul Gupta is the Global Chief Medical Officer for the business group Image Guided Therapy at Philips, providing medical guidance to Philips' clinical vision and strategy. As a practicing interventional and diagnostic radiologist, he also serves as a key external clinical voice for Image Guided Therapy. His key responsibilities include supporting innovation and product development in cardiology, peripheral vascular, surgical, oncology interventions, clinical education, office-based labs, medical affairs and new business development and ventures. He went to medical school and completed his postgraduate training in diagnostic radiology and a fellowship in interventional radiology. He maintains a clinical practice, performing interventional and diagnostic radiology in both hospital and office-based lab settings.

[Comparison of Diagnostic Values of Instantaneous Wave-Free R atio and Fractional Flow R eserve With Noninvasive Methods for Evaluating Myocardial Ischemia in Assessment of the Functional Significance of Intermediate Coronary Stenoses in Patients With Chronic Ischemic Heart Disease]

OBJECTIVE

To compare the diagnostic accuracy of instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR) with noninvasive methods in assessment of the functional significance of moderate coronary stenoses in patients with chronic ischemic heart disease (IHD).

METHODS

We included in this study 50 patients with chronic or suspected IHD and moderate coronary stenoses (50-70%; 74 stenoses). Values of iFR and FFR were determined within 10 days after noninvasive stress tests (combination of stress-echo and SPECT). The values of iFR and FFR were compared with the results of noninvasive methods by ROC-analysis. Coronary artery stenosis was considered functionally important if at least one of noninvasive tests (stress-echo or SPECT) demonstrated positive result.

RESULTS

The results of noninvasive stress-tests were positive in 14 patients (28%). ROC area under the curve (AUC) for iFR - 0.961±0.019 (95%CI 0.888-0.992). The best cut-off point for iFR is 0.92 (sensitivity 100, specificity 84%). ROC AUC for FFR - 0.893±0.041 (95%CI 0.79-0.96). The best cut-off point for FFR is 0.81 (sensitivity 100% and specificity 69%). There was no significant difference between iFR and FFR ROC-curves (р=0.0845).

CONCLUSION

The values of iFR and FFR have equivalent agreement with the results of noninvasive tests commonly used to detect myocardial ischemia in patients with moderate coronary stenoses.

Diagnostic accuracy of instantaneous wave free-ratio in clinical practice

AIMS

To evaluate the correlation between iFR and FFR in real-world clinical practice.

METHODS AND RESULTS

Retrospective, single-centre study of 229 consecutive pressure-wire studies (n_p  = 158). Real-time iFR and FFR measurements were performed for angiographically borderline stenoses. Functionally significant stenoses were defined as iFR <0.86 or FFR ≤0.80. An iFR between 0.86 and 0.93 was considered within the grey zone (Hybrid approach). Median iFR and FFR (IQR) were 0.92 (0.87-0.95) and 0.83 (0.76-0.89), respectively. Pearson's correlation coefficient was 0.75 (P < 0.001). Bland-Altman plot showed a mean difference between iFR and FFR that remained consistent throughout the range of values. The optimal iFR cutoff was 0.91-sensitivity 80%, specificity 82% with ROC area under curve of 89%. Using the Hybrid iFR-FFR strategy, we demonstrated high accuracy of iFR results-sensitivity 95%, specificity 96%, PPV 95%, and NPV 96%. In addition, this method would have avoided adenosine in 56% of patients. Mean follow-up period was 17.2 (±3.4) months. All-cause mortality was 3.2% (n_p  = 5) and repeat intervention was required in six lesions (2.6%).

CONCLUSIONS

This study demonstrates that iFR is a valuable adjunct to FFR using the Hybrid iFR-FFR strategy in a real-world population. The use of adenosine may be avoided in about half the cases.