Hybrid iFR-FFR decision-making strategy: implications for enhancing universal adoption of physiology-guided coronary revascularisation

Hybrid Instantaneous Wave-Free Ratio-Fractional Flow Reserve versus Fractional Flow Reserve in the Real World

BACKGROUND

The instantaneous wave-free ratio (iFR) is a novel method to assess the ischemic potential of coronary artery stenoses. Clinical trial data have shown that iFR has acceptable diagnostic agreement with fractional flow reserve (FFR), the reference standard for the functional assessment of coronary stenoses. This study compares iFR measurements with FFR measurements in a real world, single-center setting.

METHODS AND RESULTS

Instantaneous wave-free ratio and FFR were measured in 50 coronary artery lesions in 42 patients, with FFR ≤ 0.8 classified as functionally significant. An iFR-only technique, using a treatment cut-off value, iFR ≤ 0.89, provided a classification agreement of 84% with FFR ≤ 0.80. Use of a hybrid iFR-FFR technique, incorporating FFR measurement for lesions within the iFR gray zone of 0.86-0.93, would improve classification agreement with FFR to 94%, with diagnosis achieved without the need for hyperemia in 57% patients.

CONCLUSION

This study in a real-world setting demonstrated good classification agreement between iFR and FFR. Use of a hybrid iFR-FFR technique would achieve high diagnostic accuracy while minimizing adenosine use, compared with routine FFR.

Rationale and design of the SYNTAX II trial evaluating the short to long-term outcomes of state-of-the-art percutaneous coronary revascularisation in patients with de novo three-vessel disease

AIMS

The applicability of the results of the SYNTAX trial comparing percutaneous coronary intervention (PCI) using first-generation drug-eluting stents (DES) with coronary artery bypass graft (CABG) surgery for the treatment of patients with complex coronary artery disease (CAD) has been challenged by recent major technical and procedural developments in coronary revascularisation. Functional assessment of coronary lesions has contributed to marked improvements in both safety and efficacy of DES implantation. In addition, the recent development of the SYNTAX score II, a clinical tool based on anatomical and clinical factors, allows individualised objective decision making regarding the optimal revascularisation modality in patients with complex CAD. The ongoing SYNTAX II trial is currently evaluating the effectiveness of the clinical and technological advances in the treatment of patients with complex (de novo three-vessel) CAD.

METHODS AND RESULTS

The SYNTAX II trial is a multicentre, all-comers, open-label, single-arm trial aiming to recruit 450 patients with de novo three-vessel CAD in approximately 25 European interventional cardiology centres. All patients will be selected and treated following the SYNTAX II strategy, which includes: a) establishing the appropriateness of revascularisation utilising the SYNTAX score II as a clinical tool to allow objective decision making by the Heart Team, b) ischaemia-driven revascularisation based on functional intracoronary assessment, c) implantation of the new-generation everolimus-eluting platinum chromium coronary stent with thin struts and abluminal bioabsorbable polymer coating to promote rapid vessel healing, d) intravascular ultrasound-guided DES implantation, and e) treatment at centres with expertise in CTO recanalisation. The primary endpoint is a composite of the major adverse cardiac and cerebral events (MACCE) rate at one-year follow-up compared to the historical PCI arm of the SYNTAX trial. An exploratory endpoint will be MACCE at five-year follow-up compared to the historical surgical arm of the SYNTAX trial.

CONCLUSIONS

The SYNTAX II trial will provide valuable information on outcomes of state-of-the-art PCI for the contemporary management of complex (de novo three-vessel) CAD. SYNTAX II will be of critical value in the design of future trials in this arena.

Basal stenosis resistance index derived from simultaneous pressure and flow velocity measurements

AIMS

Vasodilator-free basal stenosis resistance (BSR) equals fractional flow reserve (FFR) accuracy for ischaemia-inducing stenoses. Nonetheless, basal haemodynamic variability may impair BSR accuracy compared with hyperaemic stenosis resistance (HSR). We evaluated the influence of basal haemodynamic variability, as encountered in practice, on BSR accuracy versus HSR when derived from simultaneous pressure and flow velocity measurements, and determined its diagnostic performance for HSR-defined significant stenoses.

METHODS AND RESULTS

Simultaneous coronary pressure and flow velocity were obtained in 131 stenoses. The impact of basal haemodynamic conditions on BSR was evaluated by means of their relationship with the relative difference between BSR and HSR. Diagnostic performance of BSR, FFR, iFR, and resting Pd/Pa was assessed by comparing the area under the curve (AUC), using HSR as reference standard. The relative difference between BSR and HSR was not associated with basal heart rate, aortic pressure or rate pressure product. Among all stenoses, as well as within the 0.6-0.9 FFR range, BSR AUC was significantly greater than resting Pd/Pa and iFR AUC; all other AUCs were equivalent.

CONCLUSIONS

With simultaneous pressure and flow velocity measurements, basal conditions do not systematically limit BSR accuracy compared with HSR. Consequently, diagnostic performance of BSR is equivalent to FFR, and closely approximates HSR.

Fractional flow reserve: a clinical perspective

Fractional flow reserve (FFR) is a reference invasive diagnostic test to assess the physiological significance of an epicardial coronary artery stenosis. FFR-guided percutaneous coronary intervention in stable coronary artery disease has been assessed in three seminal clinical trials and the indications for FFR assessment are expanding into other clinical scenarios. In this article we review the theoretical, experimental and clinical basis for FFR measurement. We place FFR measurement in the context of the comprehensive invasive assessment of coronary physiology in patients presenting with known or suspected angina pectoris in daily clinical practice, and review the recent developments in FFR assessment.

[The diagnostic value of measuring the momentary blood flow reserve versus non-invasive methods to detect myocardial ischemia in assessing the functional significance of borderline coronary artery stenoses]

AIM

To estimate the diagnostic value of measuring the momentary blood flow reserve (MBFR) versus the surrogate non-invasive standard (SNS) for myocardial ischemia verification (MIV) (a combination of stress echocardiography and single-photon emission computed tomography).

SUBJECTS AND METHODS

The investigation enrolled 50 patients with stable angina in the presence of chronic coronary heart disease (CHD) or suspected CHD, in whom coronary angiography (CA) revealed borderline coronary stenoses (50-70% lumen diameters). The examination algorithm had two options. In one option, when included in the study, patients had already CA results not older than 1 month, and MBFR was measured 4-7 days after non-invasive stress tests. In the other option, MBFR in the area of borderline coronary artery stenosis was measured simultaneously with CA; and the noninvasive stress tests were carried out in the following week. A total of 74 coronary stenoses were examined.

RESULTS

SNS for MIV was positive in 14 (28%) patients. When comparing with the non-invasive methods of myocardial ischemia verification, the area under the ROC curve for MBFR was 0.961±0.019 (95% confidence interval, 0.888-0.992). The optimal cut-point was 0.92, which is corresponded by a sensitivity of 100% and a specificity of 84%.

CONCLUSION

When compared with SNS for MIV, the method for measuring MBFR has a high diagnostic accuracy.

Use of the Instantaneous Wave-free Ratio or Fractional Flow Reserve in PCI

BACKGROUND

Coronary revascularization guided by fractional flow reserve (FFR) is associated with better patient outcomes after the procedure than revascularization guided by angiography alone. It is unknown whether the instantaneous wave-free ratio (iFR), an alternative measure that does not require the administration of adenosine, will offer benefits similar to those of FFR.

METHODS

We randomly assigned 2492 patients with coronary artery disease, in a 1:1 ratio, to undergo either iFR-guided or FFR-guided coronary revascularization. The primary end point was the 1-year risk of major adverse cardiac events, which were a composite of death from any cause, nonfatal myocardial infarction, or unplanned revascularization. The trial was designed to show the noninferiority of iFR to FFR, with a margin of 3.4 percentage points for the difference in risk.

RESULTS

At 1 year, the primary end point had occurred in 78 of 1148 patients (6.8%) in the iFR group and in 83 of 1182 patients (7.0%) in the FFR group (difference in risk, -0.2 percentage points; 95% confidence interval [CI], -2.3 to 1.8; P<0.001 for noninferiority; hazard ratio, 0.95; 95% CI, 0.68 to 1.33; P=0.78). The risk of each component of the primary end point and of death from cardiovascular or noncardiovascular causes did not differ significantly between the groups. The number of patients who had adverse procedural symptoms and clinical signs was significantly lower in the iFR group than in the FFR group (39 patients [3.1%] vs. 385 patients [30.8%], P<0.001), and the median procedural time was significantly shorter (40.5 minutes vs. 45.0 minutes, P=0.001).

CONCLUSIONS

Coronary revascularization guided by iFR was noninferior to revascularization guided by FFR with respect to the risk of major adverse cardiac events at 1 year. The rate of adverse procedural signs and symptoms was lower and the procedural time was shorter with iFR than with FFR. (Funded by Philips Volcano; DEFINE-FLAIR ClinicalTrials.gov number, NCT02053038 .).

Physiome approach for the analysis of vascular flow reserve in the heart and brain

This work reviews the key aspects of coronary and neurovascular flow reserves with an emphasis on physiomic modeling characteristics by the use of a variety of numerical approaches. First, we explain the definition of fractional flow reserve (FFR) in coronary artery and introduce its clinical significance. Then, computational researches for obtaining FFR are reviewed, and their clinical outcomes are compared. In the case of cerebrovascular reserve (CVR), in spite of substantial progress in the simulation of cerebral hemodynamics, only a few computational studies exist. Thus, we discuss the limitations of CVR simulation study and suggest the challenging issue to overcome these. Also, the future direction of physiomic researches for the flow reserves in coronary arteries and cerebral arteries is described. Also, we introduce a machine learning algorithm trained by the existing physiomic simulation data of flow reserve and suggest a prospective research direction related to this.

Instantaneous wave-free ratio derived from coronary computed tomography angiography in evaluation of ischemia-causing coronary stenosis: Feasibility and initial clinical research

The instantaneous wave-free ratio (iFR) closely related to fractional flow reserve (FFR) is a adenosine-independent physiologic index of coronary stenosis severity. We sought to evaluate whether iFR derived from coronary computed tomographic angiography (iFRCT) can be used as a novel noninvasive method for diagnosis of ischemia-causing coronary stenosis.We retrospectively enrolled 33 patients (47 lesions) with coronary artery disease (CAD) and examined with coronary computed tomographic angiography (CTA), invasive coronary angiography (ICA), and FFR. Patient-specific anatomical model of the coronary artery was built by original resting end-diastolic CTA images. Based on the model and computational fluid dynamics, individual boundary conditions were set to calculate iFRCT as the mean pressure distal to the stenosis divided by the mean aortic pressure during the diastolic wave-free period of rest state. Ischemia was assessed by an FFR of up to 0.8, while anatomically obstructive CAD was defined by a stenosis of at least 50% by ICA. The correlation between iFRCT and FFR was evaluated. The receiver operating characteristic (ROC) curve was used to select the cut-off value of iFRCT for diagnosis of ischemia-causing stenosis. The diagnostic performances of iFRCT, coronary CTA, and iFRCT plus CTA for ischemia-causing stenosis were compared with ROC curve and Delong method.On a per-vessel basis, iFRCT and FFR had linear correlation (r = 0.75, p < 0.01). ROC analysis identified an optimal iFRCT cut-off value of 0.82 for categorization based on an FFR cut-off value 0.8, and the diagnostic accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of iFRCT were 78.72%,70.59%, 83.33%,70.59%, and 83.33%, respectively. Compared with obstructive CAD diagnosed by coronary CTA (AUC = 0.60), iFRCT yielded diagnostic improvement over stenosis assessment with AUC increasing from 0.6 by CTA to 0.87 (P < 0.01) and 0.90 (P < 0.01) when iFRCT plus CTA.In conclusion, iFRCT is a promising index improving diagnostic performance over coronary CTA for detection of ischemia-causing coronary stenosis.

Prognostic Determinants of Coronary Atherosclerosis in Stable Ischemic Heart Disease

Risk stratification in patients with stable ischemic heart disease is essential to guide treatment decisions. In this regard, whether coronary anatomy, physiology, or plaque morphology is the best determinant of prognosis (and driver an effective therapeutic risk reduction) remains one of the greatest ongoing debates in cardiology. In the present report, we review the evidence for each of these characteristics and explore potential algorithms that may enable a practical diagnostic and therapeutic strategy for the management of patients with stable ischemic heart disease.

[Fractional flow reserve and instantaneous wave-free ratio for the physiological assessment of coronary artery stenosis in the catheterization laboratory: Practical tips]

In recent years, a large body of evidence has revealed the limitations of angiographic evaluation in determining the physiological significance of coronary stenosis, particularly when these are intermediate lesions. Percutaneous coronary interventions (PCI) guided by physiological assessment using fractional flow reserve (FFR) have been shown to reduce cardiovascular events when compared to angiography alone. Recently, another coronary physiologic parameter has been introduced: the "instantaneous wave-free ratio" (iFR). In this review, we will discuss the FFR, the iFR, and their use in the functional assessment of coronary stenosis in the cardiac catheterization laboratory. This review will cover theoretical aspects for non-interventional cardiologists, as well as practice points and common pitfalls related to coronary physiological assessment for interventional cardiologists.

Physiological assessment of coronary lesion severity: fractional flow reserve versus nonhyperaemic indices

Coronary angiography alone cannot accurately identify the haemodynamic impact of a coronary artery stenosis. Current international guidelines for myocardial revascularization recommend that inducible ischaemia should be demonstrated before the consideration of percutaneous coronary intervention. Invasive physiological assessment of coronary stenosis severity has increasingly been utilized for this purpose and use of the best validated technique, fractional flow reserve (FFR), has been shown to improve clinical outcomes in patients with stable and unstable coronary artery disease. This has led to the use of FFR being recommended in international revascularization guidelines, despite which, clinical uptake has been limited. One potential reason for slow adoption has been the requirement for maximal hyperaemia at the time of FFR measurement, usually achieved by the administration of pharmacological vasodilators such as adenosine. In some healthcare systems, adenosine is expensive and, in addition, its use can be associated with significant, albeit transient, adverse effects that patients (and some operators) find uncomfortable. Consequently, several methods of nonhyperaemic lesion assessment and their potential role in decision making have been reported. In this review we will review and discuss the current evidence for hyperaemic and nonhyperaemic methods of lesion assessment. We will also look at hybrid strategies that utilize both hyperaemic and nonhyperaemic methods as a means of potentially maintaining diagnostic accuracy while minimizing the requirement for adenosine administration and discuss whether or not they represent viable clinical alternatives.

Prospective Assessment of the Diagnostic Accuracy of Instantaneous Wave-Free Ratio to Assess Coronary Stenosis Relevance: Results of ADVISE II International, Multicenter Study (ADenosine Vasodilator Independent Stenosis Evaluation II)

OBJECTIVES

The purpose of this study was to assess the diagnostic accuracy of the instantaneous wave-free ratio (iFR) to characterize, outside of a pre-specified range of values, stenosis severity, as defined by fractional flow reserve (FFR) ≤0.80, in a prospective, independent, controlled, core laboratory-based environment.

BACKGROUND

Studies with methodological heterogeneity have reported some discrepancies in the classification agreement between iFR and FFR. The ADVISE II (ADenosine Vasodilator Independent Stenosis Evaluation II) study was designed to overcome limitations of previous iFR versus FFR comparisons.

METHODS

A total of 919 intermediate coronary stenoses were investigated during baseline and hyperemia. From these, 690 pressure recordings (n = 598 patients) met core laboratory physiology criteria and are included in this report.

RESULTS

The pre-specified iFR cut-off of 0.89 was optimal for the study and correctly classified 82.5% of the stenoses, with a sensitivity of 73.0% and specificity of 87.8% (C statistic: 0.90 [95% confidence interval (CI): 0.88 to 0.92, p < 0.001]). The proportion of stenoses properly classified by iFR outside of the pre-specified treatment (≤0.85) and deferral (≥0.94) values was 91.6% (95% CI: 88.8% to 93.9%). When combined with FFR use within these cut-offs, the percent of stenoses properly classified by such a pre-specified hybrid iFR-FFR approach was 94.2% (95% CI: 92.2% to 95.8%). The hybrid iFR-FFR approach obviated vasodilators from 65.1% (95% CI: 61.1% to 68.9%) of patients and 69.1% (95% CI: 65.5% to 72.6%) of stenoses.

CONCLUSIONS

The ADVISE II study supports, on the basis rigorous methodology, the diagnostic value of iFR in establishing the functional significance of coronary stenoses, and highlights its complementariness with FFR when used in a hybrid iFR-FFR approach. (ADenosine Vasodilator Independent Stenosis Evaluation II-ADVISE II; NCT01740895).

Fractional flow reserve-guided management in stable coronary disease and acute myocardial infarction: recent developments

Coronary artery disease (CAD) is a leading global cause of morbidity and mortality, and improvements in the diagnosis and treatment of CAD can reduce the health and economic burden of this condition. Fractional flow reserve (FFR) is an evidence-based diagnostic test of the physiological significance of a coronary artery stenosis. Fractional flow reserve is a pressure-derived index of the maximal achievable myocardial blood flow in the presence of an epicardial coronary stenosis as a ratio to maximum achievable flow if that artery were normal. When compared with standard angiography-guided management, FFR disclosure is impactful on the decision for revascularization and clinical outcomes. In this article, we review recent developments with FFR in patients with stable CAD and recent myocardial infarction. Specifically, we review novel developments in our understanding of CAD pathophysiology, diagnostic applications, prognostic studies, clinical trials, and clinical guidelines.

Coronary physiology assessment in the catheterization laboratory

Physicians cannot rely solely on the angiographic appearance of epicardial coronary artery stenosis when evaluating patients with myocardial ischemia. Instead, sound knowledge of coronary vascular physiology and of the methods currently available for its characterization can improve the diagnostic and prognostic accuracy of invasive assessment of the coronary circulation, and help improve clinical decision-making. In this article we summarize the current methods available for a thorough assessment of coronary physiology.

Comparison of instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR)--first real world experience

BACKGROUND

The instantaneous wave-free ratio (iFR) is a new adenosine-independent index of coronary stenosis severity. Most published data have been based on off-line analyses of pressure recordings in a core laboratory. We prospectively compared real-time iFR and fractional flow reserve (FFR) measurements.

METHODS AND RESULTS

iFR and FFR were measured in 151 coronary stenoses in 108 patients. Repeated iFR measurements were technically simple, showed excellent agreement [rs=0.99; p<0.0001], and the mean difference between consecutive iFR values was 0.0035 (limits of agreement: -0.019, 0.026). Mean iFR showed a significant correlation with FFR [rs=0.81; p<0.0001]. Receiver-operating characteristic analysis identified an optimal iFR cut-off value of 0.896 for categorization based on an FFR cut-off value 0.8. We compared two different iFR-based diagnostic strategies (iFR-only and hybrid iFR-FFR) with standard FFR: The iFR-only strategy showed good classification agreement (83.4%) with standard FFR. Use of the hybrid iFR-FFR strategy, assessing lesions in an iFR-gray zone of 0.86-0.93 by FFR, improved classification accuracy to 94.7%, and diagnosis would have been established in 61% of patients without adenosine-induced hyperemia. Notably, both iFR and FFR values were significantly higher in the posterior coronary vessels.

CONCLUSIONS

Real-time iFR measurements are easily performed, have excellent diagnostic performance and confirm available off-line core laboratory data. The excellent agreement between repeated iFR measurements demonstrates the reliability of single measurements. Combining iFR with FFR in a hybrid strategy enhances diagnostic accuracy, exposing fewer patients to adenosine. Overall, iFR is a promising method, but still requires prospective clinical endpoint trial evaluation.

Wave intensity analysis in the human coronary circulation in health and disease

Coronary artery hemodynamics are very different to that of the systemic arteries; unlike the systemic circulation, in the coronary circulation pressure is generated from both the proximal and distal end of the artery – due to the effect of contraction and relaxation of the myocardium on the microvasculature. As a result, the systemic artery hemodynamic model cannot be used to explain the pressure-flow relationship in the coronaries. Wave intensity analysis is an investigative tool that is able to distinguish simultaneous proximal and distal influences on coronary blood flow and is therefore uniquely suitable for the study of coronary haemodynamics. This review discusses the concept behind waveintensity analysis and evaluates how it has been used to characterise and provide new insights on coronary haemodynamics in health and disease.

Advances in coronary physiology

Pressure-wire technology, most typically fractional flow reserve (FFR), has provided interventional cardiologists with a means of determining the physiological importance of a stenosis during angiography. There has been renewed interest in coronary physiology in the light of guideline recognition, ongoing clinical research and new technologies changing the paradigm of how assessment is performed in the catheter laboratory. We reflect on FFR, with regards the potential effects of changing hemodynamics on FFR and the latest evidence with regards to outcomes. We also review the instantaneous wave-free ratio (iFR), a new pressure-only index, measured at rest, that is under active evaluation in several international randomized controlled trials. We review the accumulated evidence and discuss the important physiological concepts between pressure and flow that underlie the approach to using resting indices. Finally we investigate future developments, including physiological mapping with iFR-Pullback and the potential to predict the hemodynamic effect of stenting.

Pre-angioplasty instantaneous wave-free ratio pullback provides virtual intervention and predicts hemodynamic outcome for serial lesions and diffuse coronary artery disease

OBJECTIVES

The aim of this study was to perform hemodynamic mapping of the entire vessel using motorized pullback of a pressure guidewire with continuous instantaneous wave-free ratio (iFR) measurement.

BACKGROUND

Serial stenoses or diffuse vessel narrowing hamper pressure wire-guided management of coronary stenoses. Characterization of functional relevance of individual stenoses or narrowed segments constitutes an unmet need in ischemia-driven percutaneous revascularization.

METHODS

The study was performed in 32 coronary arteries with tandem and/or diffusely diseased vessels. An automated iFR physiological map, integrating pullback speed and physiological information, was built using dedicated software to calculate physiological stenosis severity, length, and intensity (ΔiFR/mm). This map was used to predict the best-case post-percutaneous coronary intervention (PCI) iFR (iFRexp) according to the stented location, and this was compared with the observed iFR post-PCI (iFRobs).

RESULTS

After successful PCI, the mean difference between iFRexp and iFRobs was small (mean difference: 0.016 ± 0.004) with a strong relationship between ΔiFRexp and ΔiFRobs (r = 0.97, p < 0.001). By identifying differing iFR intensities, it was possible to identify functional stenosis length and quantify the contribution of each individual stenosis or narrowed segment to overall vessel stenotic burden. Physiological lesion length was shorter than anatomic length (12.6 ± 1.5 vs. 23.3 ± 1.3, p < 0.001), and targeting regions with the highest iFR intensity predicted significant improvement post-PCI (r = 0.86, p < 0.001).

CONCLUSIONS

iFR measurements during continuous resting pressure wire pullback provide a physiological map of the entire coronary vessel. Before a PCI, the iFR pullback can predict the hemodynamic consequences of stenting specific stenoses and thereby may facilitate the intervention and stenting strategy.

Real-time use of instantaneous wave-free ratio: results of the ADVISE in-practice: an international, multicenter evaluation of instantaneous wave-free ratio in clinical practice

OBJECTIVES

To evaluate the first experience of real-time instantaneous wave-free ratio (iFR) measurement by clinicians.

BACKGROUND

The iFR is a new vasodilator-free index of coronary stenosis severity, calculated as a trans-lesion pressure ratio during a specific period of baseline diastole, when distal resistance is lowest and stable. Because all previous studies have calculated iFR offline, the feasibility of real-time iFR measurement has never been assessed.

METHODS

Three hundred ninety-two stenoses with angiographically intermediate stenoses were included in this multicenter international analysis. Instantaneous wave-free ratio and fractional flow reserve (FFR) were performed in real time on commercially available consoles. The classification agreement of coronary stenoses between iFR and FFR was calculated.

RESULTS

Instantaneous wave-free ratio and FFR maintain a close level of diagnostic agreement when both are measured by clinicians in real time (for a clinical 0.80 FFR cutoff: area under the receiver operating characteristic curve [ROC(AUC)] 0.87, classification match 80%, and optimal iFR cutoff 0.90; for a ischemic 0.75 FFR cutoff: iFR ROC(AUC) 0.90, classification match 88%, and optimal iFR cutoff 0.85; if the FFR 0.75-0.80 gray zone is accounted for: ROC(AUC) 0.93, classification match 92%). When iFR and FFR are evaluated together in a hybrid decision-making strategy, 61% of the population is spared from vasodilator while maintaining a 94% overall agreement with FFR lesion classification.

CONCLUSION

When measured in real time, iFR maintains the close relationship to FFR reported in offline studies. These findings confirm the feasibility and reliability of real-time iFR calculation by clinicians.

The instantaneous wave-free ratio (iFR) for evaluation of non-culprit lesions in patients with acute coronary syndrome and multivessel disease

BACKGROUND

Adenosine administration is currently required for evaluation of stenosis severity with fractional flow reserve (FFR). The instantaneous wave-free ratio (iFR) was recently introduced as an adenosine-free alternative in patients with stable CAD. The aim of the present study was to replicate the findings of previous iFR studies using an independent calculation algorithm and to evaluate the iFR for the assessment of non-culprit vessels in patients with acute coronary syndrome (ACS).

METHODS AND RESULTS

53 patients with ACS (65%) and at least one non-culprit intermediate lesion and 29 (35%) with stable CAD were included. A total of 123 stenoses were evaluated with both FFR and iFR. Classification match of iFR in ACS was not inferior to stable CAD (79.5% in ACS and 84.4% in CAD; p=0.497). Accordingly, no difference was observed in iFR/FFR correlation between ACS and stable CAD (r=0.66 in ACS vs. r=0.69 in CAD). Overall, a significant correlation was found between iFR and FFR (r=0.68; p<0.001) with a good diagnostic efficiency at ROC analysis (area under the curve: 0.87). In addition, neither the localization of the stenosis within the coronary tree (p=0.147) nor the time interval from the acute event (p=0.550) significantly influenced the concordance of iFR with FFR.

CONCLUSIONS

The iFR is a promising method for the assessment of non-culprit lesion severity in patients with acute coronary syndrome.

Assessment of coronary blood flow in the cardiac catheterization laboratory

Coronary blood flow is tightly autoregulated but is subject to epicardial and microvascular obstruction, primarily owing to coronary atherosclerosis. Because coronary flow limitation underlies ischemic heart disease, an understanding of coronary physiology is paramount. Measurement of coronary blood flow, once relegated to the research laboratory is now easily performed in the cardiac catheterization laboratory. In particular, the measurement of fractional flow reserve has been extensively studied and is an important adjunct to clinical decision making. Measurement of coronary flow informs clinicians of prognosis, guides revascularization therapy, and forms the basis of ongoing research in treatment of complex myocardial disease processes. Newer methods of assessing coronary flow measurements are undergoing validation for clinical use and should further enhance our ability to assess the importance of coronary flow in clinical disease.

Multicenter core laboratory comparison of the instantaneous wave-free ratio and resting Pd/Pa with fractional flow reserve: the RESOLVE study

OBJECTIVES

This study sought to examine the diagnostic accuracy of the instantaneous wave-free ratio (iFR) and resting distal coronary artery pressure/aortic pressure (Pd/Pa) with respect to hyperemic fractional flow reserve (FFR) in a core laboratory-based multicenter collaborative study.

BACKGROUND

FFR is an index of the severity of coronary stenosis that has been clinically validated in 3 prospective randomized trials. iFR and Pd/Pa are nonhyperemic pressure-derived indices of the severity of stenosis with discordant reports regarding their accuracy with respect to FFR.

METHODS

iFR, resting Pd/Pa, and FFR were measured in 1,768 patients from 15 clinical sites. An independent physiology core laboratory performed blinded off-line analysis of all raw data. The primary objectives were to determine specific iFR and Pd/Pa thresholds with ≥90% accuracy in predicting ischemic versus nonischemic FFR (on the basis of an FFR cut point of 0.80) and the proportion of patients falling beyond those thresholds.

RESULTS

Of 1,974 submitted lesions, 381 (19.3%) were excluded because of suboptimal acquisition, leaving 1,593 for final analysis. On receiver-operating characteristic analysis, the optimal iFR cut point for FFR ≤0.80 was 0.90 (C statistic: 0.81 [95% confidence interval: 0.79 to 0.83]; overall accuracy: 80.4%) and for Pd/Pa was 0.92 (C statistic: 0.82 [95% confidence interval: 0.80 to 0.84]; overall accuracy: 81.5%), with no significant difference between these resting measures. iFR and Pd/Pa had ≥90% accuracy to predict a positive or negative FFR in 64.9% (62.6% to 67.3%) and 48.3% (45.6% to 50.5%) of lesions, respectively.

CONCLUSIONS

This comprehensive core laboratory analysis comparing iFR and Pd/Pa with FFR demonstrated an overall accuracy of ~80% for both nonhyperemic indices, which can be improved to ≥90% in a subset of lesions. Clinical outcome studies are required to determine whether the use of iFR or Pd/Pa might obviate the need for hyperemia in selected patients.

Improvement in coronary haemodynamics after percutaneous coronary intervention: assessment using instantaneous wave-free ratio

Objective

To determine whether the instantaneous wave-free ratio (iFR) can detect improvement in stenosis significance after percutaneous coronary intervention (PCI) and compare this with fractional flow reserve (FFR) and whole cycle Pd/Pa.

Design

A prospective observational study was undertaken in elective patients scheduled for PCI with FFR ≤0.80. Intracoronary pressures were measured at rest and during adenosine-mediated vasodilatation, before and after PCI. iFR, Pd/Pa and FFR values were calculated using the validated fully automated algorithms.

Setting

Coronary catheter laboratories in two UK centres and one in the USA.

Patients

120 coronary stenoses in 112 patients were assessed. The mean age was 63±10 years, while 84% were male; 39% smokers; 33% with diabetes. Mean diameter stenosis was 68±16% by quantitative coronary angiography.

Results

Pre-PCI, mean FFR was 0.66±0.14, mean iFR was 0.75±0.21 and mean Pd/Pa 0.83±0.16. PCI increased all indices significantly (FFR 0.89±0.07, p<0.001; iFR 0.94±0.05, p<0.001; Pd/Pa 0.96±0.04, p<0.001). The change in iFR after intervention (0.20±0.21) was similar to ΔFFR 0.22±0.15 (p=0.25). ΔFFR and ΔiFR were significantly larger than resting ΔPd/Pa (0.13±0.16, both p<0.001). Similar incremental changes occurred in patients with a higher prevalence of risk factors for microcirculatory disease such as diabetes and hypertension.

Conclusions

iFR and FFR detect the changes in coronary haemodynamics elicited by PCI. FFR and iFR have a significantly larger dynamic range than resting Pd/Pa. iFR might be used to objectively document improvement in coronary haemodynamics following PCI in a similar manner to FFR.