Long-term prognostic implications of CT angiography-derived fractional flow reserve: Results from the DISCOVER-FLOW study

BACKGROUND & OBJECTIVES

The long-term prognostic implications of CT angiography-derived fractional flow reserve (FFRCT) remains unclear. We aimed to explore the long-term outcomes of FFRCT in the first-in-human study of it.

MATERIALS & METHODS

A total of 156 vessels from 102 patients with stable coronary artery disease, who underwent coronary CT angiography (CCTA) and invasive FFR measurement, were followed. The primary endpoint was target vessel failure (TVF), including cardiovascular death, target vessel myocardial infarction, and target vessel revascularization. Outcome analysis with FFRCT was performed on a per-vessel basis using a marginal Cox proportional hazard model.

RESULTS

During median 9.9 years of follow-up, TVF occurred in 20 (12.8%) vessels. FFRCT ​≤0.80 discriminated TVF (hazard ratio [HR] 2.61, 95% confidence interval [CI] 1.06, 6.45). Among 94 vessels with deferral of percutaneous coronary intervention (PCI), TVF risk was inversely correlated with FFRCT ​(HR 0.62 per 0.1 increase, 95% CI 0.44, 0.86), with the cumulative incidence of TVF being 2.6%, 15.2%, and 28.6% for vessels with FFRCT ​>0.90, 0.81-0.90, and ≤0.80, respectively (p-for-trend 0.005). Predictive value for clinical outcomes of FFRCT was similar to that of invasive FFR (c-index 0.79 vs 0.71, P ​= ​0.28). The estimated TVF risk was higher in the deferral of PCI group than the PCI group for vessels with FFRCT ≤0.81.

CONCLUSION

FFRCT showed improved long-term risk stratification and displayed a risk continuum similar to invasive FFR.

CLINICAL TRIAL REGISTRATION

NCT01189331.

Preventive PCI or medical therapy alone for vulnerable atherosclerotic coronary plaque: Rationale and design of the randomized, controlled PREVENT trial

BACKGROUND

Acute coronary syndromes are commonly caused by the rupture of vulnerable plaque, which often appear angiographically not severe. Although pharmacologic management is considered standard therapy for stabilizing plaque vulnerability, the potential role of preventive local treatment for vulnerable plaque has not yet been determined. The PREVENT trial was designed to compare preventive percutaneous coronary intervention (PCI) plus optimal medical therapy (OMT) with OMT alone in patients with functionally nonsignificant high-risk vulnerable plaques.

METHODS

The PREVENT trial is a multinational, multicenter, prospective, open-label, active-treatment-controlled randomized trial. Eligible patients have at least 1 angiographically significant stenosis (diameter stenosis >50% by visual estimation) without functional significance (fractional flow reserve [FFR] >0.80). Target lesions are assessed by intracoronary imaging and must meet at least 2 imaging criteria for vulnerable plaque; (1) minimal lumen area <4.0 mm2; (2) plaque burden >70%; (3) maximal lipid core burden index in a 4 mm segment >315 by near infrared spectroscopy; and (4) thin cap fibroatheroma as determined by virtual histology or optical coherence tomography. Enrolled patients are randomly assigned in a 1:1 ratio to either preventive PCI with either bioabsorbable vascular scaffolds or metallic everolimus-eluting stents plus OMT or OMT alone. The primary endpoint is target-vessel failure, defined as the composite of death from cardiac causes, target-vessel myocardial infarction, ischemic-driven target-vessel revascularization, or hospitalization for unstable or progressive angina, at 2 years after randomization.

RESULTS

Enrollment of a total of 1,608 patients has been completed. Follow-up of the last enrolled patient will be completed in September 2023 and primary results are expected to be available in early 2024.

CONCLUSIONS

The PREVENT trial is the first large-scale, randomized trial to evaluate the effect of preventive PCI on non-flow-limiting vulnerable plaques containing multiple high-risk features that is appropriately powered for clinical outcomes. PREVENT will provide compelling evidence as to whether preventive PCI of vulnerable plaques plus OMT improves patient outcomes compared with OMT alone.

CLINICAL TRIAL REGISTRATION

URL: https://www.

CLINICALTRIALS

gov. Unique identifier: NCT02316886.

KEY POINTS

The PREVENT trial is the first, large-scale randomized clinical trial to evaluate the effect of preventive PCI on non-flow-limiting vulnerable plaque with high-risk features. It will provide compelling evidence to determine whether PCI of focal vulnerable plaques on top of OMT improves patient outcomes.

Intracoronary physiology-guided percutaneous coronary intervention in patients with diabetes

OBJECTIVE

The risk of vessel-oriented cardiac adverse events (VOCE) in patients with diabetes mellitus (DM) undergoing intracoronary physiology-guided coronary revascularization is poorly defined. The purpose of this work is to evaluate the risk of VOCE in patients with and without DM in whom percutaneous coronary intervention (PCI) was performed or deferred based on pressure-wire functional assessment.

METHODS

This is a retrospective analysis of a multicenter registry of patients evaluated with fractional flow reserve (FFR) and/or non-hyperaemic pressure ratio (NHPR). Primary endpoint was a composite of VOCE including cardiac death, vessel-related myocardial infarction (MI), and ischemia-driven target vessel revascularization (TVR).

RESULTS

A large cohort of 2828 patients with 3353 coronary lesions was analysed to assess the risk of VOCE at long-term follow-up (23 [14-36] months). Non-insulin-dependent-DM (NIDDM) was not associated with the primary endpoint in the overall cohort (adjusted Hazard Ratio [aHR] 1.18, 95% CI 0.87-1.59, P = 0.276) or in patients with coronary lesions treated with PCI (aHR = 1.30, 95% CI 0.78-2.16, P = 0.314). Conversely, insulin-dependent diabetes mellitus (IDDM) demonstrated an increased risk of VOCE in the overall cohort (aHR 1.76, 95% CI 1.07-2.91, P = 0.027), but not in coronary lesions undergoing PCI (aHR 1.26, 95% CI 0.50-3.16, P = 0.621). Importantly, in coronary lesions deferred after functional assessment IDDM (aHR 2.77, 95% CI 1.11-6.93, P = 0.029) but not NIDDM (aHR = 0.94, 95% CI 0.61-1.44, P = 0.776) was significantly associated with the risk of VOCE. IDDM caused a significant effect modification of FFR-based risk stratification (P for interaction < 0.001).

CONCLUSION

Overall, DM was not associated with an increased risk of VOCE in patients undergoing physiology-guided coronary revascularization. However, IDDM represents a phenotype at high risk of VOCE.

Impact of intensively lowered low-density lipoprotein cholesterol on deferred lesion prognosis

OBJECTIVES

The aim of this study was to investigate the impact of intensively lowered low-density lipoprotein cholesterol (LDL-C) level on the deferred lesion prognosis after revascularization deferral based on fractional flow reserve (FFR).

BACKGROUND

Lowering LDL-C is associated with lower cardiovascular event rate, but its benefit on the deferred lesion prognosis has not been well evaluated.

METHODS

This retrospective, single-center, observational study analyzed 192 deferred lesions with FFR value >0.80 in 192 patients with stable coronary artery disease. According to the first follow-up LDL-C level, they were assigned to the LOW group (<70 mg/dL) or the HIGH group (≥70 mg/dL). Deferred lesion failure (DLF) was defined as the composite of deferred lesion revascularization and deferred vessel myocardial infarction.

RESULTS

Of all participants, 61 and 131 patients were assigned to the LOW and the HIGH group, respectively. During the median follow-up of 2.8 years, DLF occurred in 1 and 14 patients in the LOW group and the HIGH group (1.6% and 10.7%, log-rank p = .043), respectively. The incidence of any unplanned revascularization was also significantly lower in the LOW group than in the HIGH group (3.3% vs. 14.5%, log-rank p = .032).

CONCLUSIONS

The incidence of DLF was significantly lower in the patients with LDL-C < 70 mg/dL than in those with LDL-C ≥ 70 mg/dL at the first follow-up after FFR-based deferral of revascularization.

Long-term outcome after deferred revascularization due to negative fractional flow reserve in intermediate coronary lesions

Objectives

The aim was to assess long‐term outcome after deferring intervention of coronary lesions with a fractional flow reserve (FFR) value of >0.80 in a real‐world patient population and then to identify factors associated with deferred target lesion failure (DTLF).

Background

Deferring coronary interventions of intermediate lesions based on FFR measurement is safe, irrespective of the extent of coronary artery disease. However, FFR values near the cut‐off of >0.80 may have less favorable outcome.

Methods

A retrospective analysis was performed in patients with deferred coronary intervention based on FFR value >0.80. The primary endpoint was DTLF, a composite of acute coronary syndrome (ACS) and any coronary revascularization, related to the initially deferred stenosis.

Results

A total of 600 patients, mean age of 66 ± 10 years, and 751 coronary lesions with negative FFR values (mean 0.88 ± 0.04) were included. The mean follow‐up was 27 ± 15 months. DTLF occurred in 44 patients (7.3%), revascularization in 42 (7%), and ACS without revascularization in 2 patients (0.3%). Patients with DTLF more often had diabetes mellitus, previous coronary artery bypass grafting, multivessel disease (MVD), and lower FFR at inclusion. Multivariable regression analysis showed that lower deferred FFR values [FFR 0.81–0.85: hazard ratio (HR) 2.79 (95% CI [confidence interval]; 1.46–5.32), p .002], MVD [HR 1.98 (95% CI; 1.05–3.75), p .036], distal lesions [HR 2.43 (95% CI; 1.29–4.57), p .006], and lesions located in a saphenous vein graft (SVG) [HR 6.35 (95% CI; 1.81–22.28), p .004] were independent predictors for DTLF.

Conclusions

The long‐term rate of DTLF of initially deferred coronary lesions was 7.3%. Independent predictors for DTLF are lower deferred FFR value, the presence of MVD, distal lesions, and lesions in SVG.

Deferred vs. performed revascularization for coronary stenosis with grey-zone fractional flow reserve values: data from the IRIS-FFR registry

Aims

The optimal fractional flow reserve (FFR) cut-off value for revascularization is debated. We evaluated the prognosis for deferred and performed revascularization in coronary stenosis with FFR values in the grey zone (0.75-0.80).

Methods and results

This study included 1334 native coronary stenosis with grey-zone FFR values in 1334 patients from the prospective multicentre Interventional Cardiology Research In-cooperation Society Fractional Flow Reserve registry. Revascularization was deferred for 683 patients (deferred group) and performed for 651 (performed group). The primary outcome, a composite of death, target-vessel myocardial infarction (MI), and target vessel revascularization (TVR) occurred in 55 (8.1%) patients in the deferred group and 55 (8.4%) in the performed group [adjusted hazard ratio (aHR) 1.05, 95% confidence interval (CI) 0.67-1.66; P = 0.79] during a median follow-up of 2.9 years (interquartile range 1.5-4.1 years). Overall mortality and spontaneous MI did not differ between the groups (mortality 2.5% vs. 2.0%; aHR 0.82, 95% CI 0.34-2.00; P = 0.66; spontaneous MI 0.7% vs. 0.5%; aHR 1.85, 95% CI 0.35-9.75; P = 0.47). Myocardial infarction was significantly higher in the performed group (0.7% vs. 3.2%; aHR 0.27, 95% CI 0.09-0.80; P = 0.02) mainly because of a higher risk of periprocedural MI. Target vessel revascularization was significantly higher in the deferred group (5.7% vs. 3.7%; aHR 2.17, 95% CI 1.17-4.02; P = 0.01).

Conclusion

For coronary stenosis with grey-zone FFR, revascularization was not associated with better clinical outcomes. The higher likelihood of periprocedural MI with revascularization was offset by the higher likelihood of TVR with deferral.

Trial registration

Clinicaltrials.gov identifier: NCT01366404.

Coronary lesion progression as assessed by fractional flow reserve (FFR) and angiography

AIMS

The aim of this study was to explore the evolution of coronary lesions which had repeated physiologic evaluation by FFR as an endpoint, describe the clinical significance of longitudinal FFR change (ΔFFR=FFRfollow-up-FFRbaseline) and its correlation with angiographic indices, and identify predictors of FFRfollow-up.

METHODS AND RESULTS

A retrospective, single-centre analysis of 414 stenoses (331 patients) with consecutive FFR measurements at least six months apart was performed (median time interval: 24 [17, 37] months). The change in percent diameter stenosis was 2% (-5%, 11%). FFR values at baseline and follow-up were 0.86 (0.82, 0.90) and 0.83 (0.79, 0.90), respectively (<0.0001). The median ΔFFR was -0.007 (-0.028, 0.010) per year. Worsening FFR (ΔFFR <-0.05) was observed in 105 (25%) stenoses, stable FFR (-0.05 ≤ΔFFR ≤0.05) in 276 (67%) and improving FFR (ΔFFR >0.05) in 33 (8%) stenoses. The number of haemodynamically significant stenoses (FFR ≤0.80) was higher at follow-up compared to baseline (33% versus 17%, p<0.0001); ΔFFR correlated weakly with delta diameter stenosis (Δ%DS, ρ=-0.111, p=0.024). In mixed effects repeated measures analysis, only lesion location had an independent correlation with FFR values after adjusting for multiple confounders. In ROC analysis, FFRbaseline values predicted future clinically significant values (c-statistic: 0.736 [95% CI: 0.682-0.783]).

CONCLUSIONS

FFR values decrease slowly over a two-year follow-up. FFRbaseline, but not angiographic indices, is a predictor of significant functional atherosclerosis progression, predicting which stenoses will require revascularisation.

Evaluation of intermediate coronary stenoses in acute coronary syndromes using pressure guidewire

Fractional flow reserve (FFR) is increasingly used to guide myocardial revascularisation. However, supporting evidence regarding its use originates from studies that have enrolled mainly patients with stable angina, while patients with acute coronary syndromes (ACS) have not been included. Notably, multifactorial microvascular dysfunction and an increased sympathetic tone in patients with ACS may lead to blunted response to adenosine and false-negative results of FFR due to submaximal hyperaemia. This may raise the possibility of deferring treatment of stenosis that instead would have needed dilatation, thus leaving a residual risk of preventable cardiac events. In this literature review, we aim at summarising laboratory and clinical investigations concerning the use of FFR in culprit and non-culprit lesions in ACS. Furthermore, we will report recent data on instantaneous wave-free ratio, an adenosine-free index of functional stenosis severity, in stable coronary artery disease and in patients with ACS.

Invasive FFR and Noninvasive CFR in the Evaluation of Ischemia: What Is the Future?

This review provides an integrative and forward-looking perspective on the gamut of coronary physiology for the diagnosis and management of atherosclerosis. Because clinical events serve as the ultimate gold standard, the future of all diagnostic tests, including invasive fractional flow reserve and noninvasive coronary flow reserve, depends on their ability to improve patient outcomes. Given the prominent role of acute coronary syndromes and invasive procedures in cardiology, we practically consider 2 broad categories of patients with coronary disease: acute and stable. For patients with acute coronary disease, coronary physiology may potentially refine treatment of the culprit lesion. For both patients with stable and acute nonculprit disease, reducing hard endpoints with revascularization potentially occurs at the severe end of the focal physiological spectrum, an area under-represented in existing trials. Nonepicardial disease and diffuse atherosclerosis remain underexplored aspects of coronary physiology for testing of novel treatments.

Fractional Flow Reserve and Cardiac Events in Coronary Artery Disease: Data From a Prospective IRIS-FFR Registry (Interventional Cardiology Research Incooperation Society Fractional Flow Reserve)

BACKGROUND

We evaluated the prognosis of deferred and revascularized coronary stenoses after fractional flow reserve (FFR) measurement to assess its revascularization threshold in clinical practice.

METHODS

The IRIS-FFR registry (Interventional Cardiology Research In-cooperation Society Fractional Flow Reserve) prospectively enrolled 5846 patients with ≥1coronary lesion with FFR measurement. Revascularization was deferred in 6468 lesions and performed in 2165 lesions after FFR assessment. The primary end point was major adverse cardiac events (cardiac death, myocardial infarction, and repeat revascularization) at a median follow-up of 1.9 years and analyzed on a per-lesion basis. A marginal Cox model accounted for correlated data in patients with multiple lesions, and a model to predict per-lesion outcomes was adjusted for confounding factors.

RESULTS

For deferred lesions, the risk of major adverse cardiac events demonstrated a significant, inverse relationship with FFR (adjusted hazard ratio, 1.06; 95% confidence interval, 1.05-1.08; P<0.001). However, this relationship was not observed in revascularized lesions (adjusted hazard ratio, 1.00; 95% confidence interval, 0.98-1.02; P=0.70). For lesions with FFR ≥0.76, the risk of major adverse cardiac events was not significantly different between deferred and revascularized lesions. Conversely, in lesions with FFR ≤0.75, the risk of major adverse cardiac events was significantly lower in revascularized lesions than in deferred lesions (for FFR 0.71-0.75, adjusted hazard ratio, 0.47; 95% confidence interval, 0.24-0.89; P=0.021; for FFR ≤0.70, adjusted hazard ratio 0.47; 95% confidence interval, 0.26-0.84; P=0.012).

CONCLUSIONS

This large, prospective registry showed that the FFR value was linearly associated with the risk of cardiac events in deferred lesions. In addition, revascularization for coronary artery stenosis with a low FFR (≤0.75) was associated with better outcomes than the deferral, whereas for a stenosis with a high FFR (≥0.76), medical treatment would be a reasonable and safe treatment strategy.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01366404.

Factors associated with deferred lesion failure following fractional flow reserve assessment in patients with diabetes mellitus

OBJECTIVE

To explore the predictors of deferred lesion failure (DLF) in patients with diabetes mellitus (DM) and lesions with a fractional flow reserve (FFR) >0.80 and to examine whether a predictive relationship between negative FFR values (>0.80-1.00) and DLF exists.

BACKGROUND

DM is associated with rapidly progressive atherosclerosis and predictors of DLF in FFR negative lesions in this high-risk group are unknown.

METHODS

All DM patients who underwent FFR-assessment between 1/01/2010 and 31/12/2013 were included, and followed until 1/7/2015. Patients carrying ≥1 FFR negative lesion(s) were assessed for DLF, and multivariate models used to identify independent factors associated with DLF.

RESULTS

A total of 205 patients with 252 FFR >0.80 lesions were identified. At a mean follow-up of 3.1 ± 1.4 years, DLF occurred in 29/205 (14.1%) patients, 31/252 (12.3%) lesions. Using marginal Cox regression multivariate analysis, insulin requiring DM [HR 2.24 (95%CI; 1.01-4.95), P = 0.046] and prior revascularization [HR 2.70 (95%CI 1.21-6.01), P = 0.015] were identified as being associated with a higher incidence of DLF. Absolute FFR values in FFR negative lesions in DM patients are not predictive of DLF (receiver operating characteristics curve analysis: area under the curve: 0.57 ± 0.06, 95%CI 0.46-0.69).

CONCLUSIONS

In DM patients with FFR negative lesions, insulin requiring DM and prior revascularization are predictors for DLF. In contrast to non-DM patients, no predictive relationship between absolute negative FFR values (ranging >0.80-1.00) and the risk of DLF exists in DM patients. © 2017 Wiley Periodicals, Inc.

Clinical Outcomes in Patients with Deferred Coronary Lesions according to Disease Severity Assessed by Fractional Flow Reserve

Data on the clinical outcomes in deferred coronary lesions according to functional severity have been limited. This study evaluated the clinical outcomes of deferred lesions according to fractional flow reserve (FFR) grade using Korean FFR registry data. Among 1,294 patients and 1,628 lesions in Korean FFR registry, 665 patients with 781 deferred lesions were included in this study. All participants were consecutively categorized into 4 groups according to FFR; group 1: ≥ 0.96 (n = 56), group 2: 0.86-0.95 (n = 330), group 3: 0.81-0.85 (n = 170), and group 4: ≤ 0.80 (n = 99). Primary endpoint was major adverse cardiac events (MACE), a composite of all-cause death, myocardial infarction, and target vessel revascularization. The median follow-up period was 2.1 years. During follow-up, the incidence of MACE in groups 1-4 was 1.8%, 7.6%, 8.8%, and 13.1%, respectively. Compared to group 1, the cumulative rate by Kaplan-Meier analysis of MACE was not different for groups 2 and 3. However, group 4 had higher cumulative rate of MACE compared to group 1 (log-rank P = 0.013). In the multivariate Cox hazard models, only FFR (hazard ratio [HR], 0.95; P = 0.005) was independently associated with MACE among all participants. In contrast, previous history of percutaneous coronary intervention (HR, 2.37; P = 0.023) and diagnosis of acute coronary syndrome (ACS) (HR, 2.35; P = 0.015), but not FFR, were independent predictors for MACE in subjects with non-ischemic (FFR ≥ 0.81) deferred coronary lesions. Compared to subjects with ischemic deferred lesions, clinical outcomes in subjects with non-ischemic deferred lesions according to functional severity are favorable. However, longer-term follow-up may be necessary.

Clinical outcomes of deferred revascularisation using fractional flow reserve in patients with and without diabetes mellitus

Objective

Deferred revascularisation based upon fractional flow reserve (FFR >0.80) is associated with a low incidence of target lesion failure (TLF). Whether deferred revascularisation is also as safe in diabetes mellitus (DM) patients is unknown.

Methods

All DM patients and the next consecutive Non-DM patients who underwent a FFR-assessment between 1/01/2010 and 31/12/2013 were included, and followed until 1/07/2015. Patients with lesions FFR >0.80 were analysed according to the presence vs. absence of DM, while patients who underwent index revascularisation in FFR-assessed or other lesions were excluded. The primary endpoint was the incidence of TLF; a composite of target lesion revascularisation (TLR) and target vessel myocardial infarction (TVMI).

Results

A total of 250 patients (122 DM, 128 non-DM) who underwent deferred revascularisation of all lesions (FFR >0.80) were compared. At a mean follow up of 39.8 ± 16.3 months, DM patients compared to non-DM had a higher TLF rate, 18.1 vs 7.5 %, logrank p ≤ 0.01, Cox regression-adjusted HR 3.65 (95 % CI 1.40–9.53, p < 0.01), which was largely driven by a higher incidence of TLR (17.2 vs. 7.5 %, HR 3.52, 95 % CI 1.34–9.30, p = 0.01), whilst a non-significant but numerically higher incidence of TVMI (6.1 vs. 2.0 %, HR 3.34, 95 % CI 0.64–17.30, p = 0.15) was observed.

Conclusions

This study, the largest to directly compare the clinical outcomes of FFR-guided deferred revascularisation in patients with and without DM, shows that DM patients are associated with a significantly higher TLF rate. Whether intravascular imaging, additional invasive haemodynamics or stringent risk factor modification may impact on this higher TLF rate remains unknown.

New Invasive Assessment Measures of Coronary Artery Disease Severity

Ischemic heart disease is the leading cause of mortality worldwide. The assessment and treatment of patients with ischemic heart disease have advanced greatly over the past decade. Particular attention has been given recently to the recognition of lesions that cause ischemia or that are prone to plaque rupture. New invasive measures of coronary artery disease have been developed, including fractional flow reserve, intravascular ultrasound, optical coherence tomography, and most recently, near-infrared spectroscopy. These technologies have helped to guide the assessment of hemodynamically significant lesions and have shown particular promise in guiding percutaneous coronary interventions. However, mortality and the rate of revascularization have shown mixed results to date. This review seeks to investigate the use and potential benefit of these technologies, with particular attention to clinical end points.

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.

Fundamentals in clinical coronary physiology: why coronary flow is more important than coronary pressure

Wide attention for the appropriateness of coronary stenting in stable ischaemic heart disease (IHD) has increased interest in coronary physiology to guide decision making. For many, coronary physiology equals the measurement of coronary pressure to calculate the fractional flow reserve (FFR). While accumulating evidence supports the contention that FFR-guided revascularization is superior to revascularization based on coronary angiography, it is frequently overlooked that FFR is a coronary pressure-derived estimate of coronary flow impairment. It is not the same as the direct measures of coronary flow from which it was derived, and which are critical determinants of myocardial ischaemia. This review describes why coronary flow is physiologically and clinically more important than coronary pressure, details the resulting limitations and clinical consequences of FFR-guided clinical decision making, describes the scientific consequences of using FFR as a gold standard reference test, and discusses the potential of coronary flow to improve risk stratification and decision making in IHD.

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.