Coronary Vascular (DYS) Function and Invasive Physiology Assessment: Insights into Bolus and Continuous Thermodilution Methods.

A considerable number of patients with angina or myocardial ischemia have no significant coronary artery disease on invasive angiography. In recent years, several steps towards a better comprehension of the pathophysiology of these conditions, angina or ischemia with non-obstructive coronary arteries (ANOCA/INOCA), have been made. Nevertheless, several gaps in knowledge still remain. This review is intended to provide a comprehensive overview of ANOCA and INOCA, with a particular focus on pathophysiology, recent diagnostic innovations, gaps in knowledge and treatment modalities.

Serial stenosis assessment-can we rely on invasive coronary physiology.

Atherosclerosis is a widespread disease affecting coronary arteries. Diffuse atherosclerotic disease affects the whole vessel, posing difficulties in determining lesion significance by angiography. Research has confirmed that revascularization guided by invasive coronary physiology indices improves patients' prognosis and quality of life. Serial lesions can be a diagnostic challenge because the measurement of functional stenosis significance using invasive physiology is influenced by a complex interplay of factors. The use of fractional flow reserve (FFR) pullback provides a trans-stenotic pressure gradient (ΔP) for each of the lesions. The strategy of treating the lesion with greater ΔP first and then reevaluating another lesion has been advocated. Similarly, non-hyperemic indices can be used to assess the contribution of each stenosis and predict the effect of lesion treatment on physiology indices. Pullback pressure gradient (PPG) integrates physiological variables of coronary pressure along the epicardial vessel and characteristics of discrete and diffuse coronary stenoses into a quantitative index that can be used to guide revascularization. We proposed an algorithm that integrates FFR pullbacks and calculates PPG to determine individual lesion importance and to guide intervention. Computer modeling of the coronaries and the use of non-invasive FFR measurement together with mathematical algorithms for fluid dynamics can make predictions of lesion significance in serial stenoses easier and provide practical solutions for treatment. All these strategies need to be validated before widespread clinical use.

Reproducibility of bolus versus continuous thermodilution for assessment of coronary microvascular function in patients with ANOCA.

BACKGROUND: A bolus thermodilution-derived index of microcirculatory resistance (IMR) has emerged as the standard for assessing coronary microvascular dysfunction (CMD). Continuous thermodilution has recently been introduced as a tool to quantify absolute coronary flow and microvascular resistance directly. Microvascular resistance reserve (MRR) derived from continuous thermodilution has been proposed as a novel metric of microvascular function, which is independent of epicardial stenoses and myocardial mass. AIMS: We aimed to assess the reproducibility of bolus and continuous thermodilution in assessing coronary microvascular function. METHODS: Patients with angina and non-obstructive coronary artery disease (ANOCA) at angiography were prospectively enrolled. Bolus and continuous intracoronary thermodilution measurements were obtained in duplicate in the left anterior descending artery (LAD). Patients were randomly assigned in a 1:1 ratio to undergo either bolus thermodilution first or continuous thermodilution first. RESULTS: A total of 102 patients were enrolled. The mean fractional flow reserve (FFR) was 0.86±0.06. Coronary flow reserve (CFR) calculated with continuous thermodilution (CFRcont) was significantly lower than bolus thermodilution-derived CFR (CFRbolus; 2.63±0.65 vs 3.29±1.17; p<0.001). CFRcont showed a higher reproducibility than CFRbolus (variability: 12.7±10.4% continuous vs 31.26±24.85% bolus; p<0.001). MRR showed a higher reproducibility than IMR (variability 12.4±10.1% continuous vs 24.2±19.3% bolus; p<0.001). No correlation was found between MRR and IMR (r=0.1, 95% confidence interval: -0.09 to 0.29; p=0.305). CONCLUSIONS: In the assessment of coronary microvascular function, continuous thermodilution demonstrated significantly less variability on repeated measurements than bolus thermodilution.

Deferral of Coronary Revascularization in Patients With Reduced Ejection Fraction Based on Physiological Assessment: Impact on Long-Term Survival.

Background Deferring revascularization in patients with nonsignificant stenoses based on fractional flow reserve (FFR) is associated with favorable clinical outcomes up to 15 years. Whether this holds true in patients with reduced left ventricular ejection fraction is unclear. We aimed to investigate whether FFR provides adjunctive clinical benefit compared with coronary angiography in deferring revascularization of patients with intermediate coronary stenoses and reduced left ventricular ejection fraction. Methods and Results Consecutive patients with reduced left ventricular ejection fraction (≤50%) undergoing coronary angiography between 2002 and 2010 were screened. We included patients with at least 1 intermediate coronary stenosis (diameter stenosis ≥40%) in whom revascularization was deferred based either on angiography plus FFR (FFR guided) or angiography alone (angiography guided). The primary end point was the cumulative incidence of all-cause death at 10 years. The secondary end point (incidence of major adverse cardiovascular and cerebrovascular events) was a composite of all-cause death, myocardial infarction, any revascularization, and stroke. A total of 840 patients were included (206 in the FFR-guided group and 634 in the angiography-guided group). Median follow-up was 7 years (interquartile range, 3.22-11.08 years). After 1:1 propensity-score matching, baseline characteristics between the 2 groups were similar. All-cause death was significantly lower in the FFR-guided group compared with the angiography-guided group (94 [45.6%] versus 119 [57.8%]; hazard ratio [HR], 0.65 [95% CI, 0.49-0.85]; P<0.01). The rate of major adverse cardiovascular and cerebrovascular events was lower in the FFR-guided group (123 [59.7%] versus 139 [67.5%]; HR, 0.75 [95% CI, 0.59-0.95]; P=0.02). Conclusions In patients with reduced left ventricular ejection fraction, deferring revascularization of intermediate coronary stenoses based on FFR is associated with a lower incidence of death and major adverse cardiovascular and cerebrovascular events at 10 years.

Microvascular Dysfunction in Patients With Type II Diabetes Mellitus: Invasive Assessment of Absolute Coronary Blood Flow and Microvascular Resistance Reserve.

Background: Coronary microvascular dysfunction (CMD) is an early feature of diabetic cardiomyopathy, which usually precedes the onset of diastolic and systolic dysfunction. Continuous intracoronary thermodilution allows an accurate and reproducible assessment of absolute coronary blood flow and microvascular resistance thus allowing the evaluation of coronary flow reserve (CFR) and Microvascular Resistance Reserve (MRR), a novel index specific for microvascular function, which is independent from the myocardial mass. In the present study we compared absolute coronary flow and resistance, CFR and MRR assessed by continuous intracoronary thermodilution in diabetic vs. non-diabetic patients. Left atrial reservoir strain (LASr), an early marker of diastolic dysfunction was compared between the two groups. Methods: In this observational retrospective study, 108 patients with suspected angina and non-obstructive coronary artery disease (NOCAD) consecutively undergoing elective coronary angiography (CAG) from September 2018 to June 2021 were enrolled. The invasive functional assessment of microvascular function was performed in the left anterior descending artery (LAD) with intracoronary continuous thermodilution. Patients were classified according to the presence of DM. Absolute resting and hyperemic coronary blood flow (in mL/min) and resistance (in WU) were compared between the two cohorts. FFR was measured to assess coronary epicardial lesions, while CFR and MRR were calculated to assess microvascular function. LAS, assessed by speckle tracking echocardiography, was used to detect early myocardial structural changes potentially associated with microvascular dysfunction. Results: The median FFR value was 0.83 [0.79-0.87] without any significant difference between the two groups. Absolute resting and hyperemic flow in the left anterior descending coronary were similar between diabetic and non-diabetic patients. Similarly, resting and hyperemic resistances did not change significantly between the two groups. In the DM cohort the CFR and MRR were significantly lower compared to the control group (CFR = 2.38 ± 0.61 and 2.88 ± 0.82; MRR = 2.79 ± 0.87 and 3.48 ± 1.02 for diabetic and non-diabetic patients respectively, [p < 0.05 for both]). Likewise, diabetic patients had a significantly lower reservoir, contractile and conductive LAS (all p < 0.05). Conclusions: Compared with non-diabetic patients, CFR and MRR were lower in patients with DM and non-obstructive epicardial coronary arteries, while both resting and hyperemic coronary flow and resistance were similar. LASr was lower in diabetic patients, confirming the presence of a subclinical diastolic dysfunction associated to the microcirculatory impairment. Continuous intracoronary thermodilution-derived indexes provide a reliable and operator-independent assessment of coronary macro- and microvasculature and might potentially facilitate widespread clinical adoption of invasive physiologic assessment of suspected microvascular disease.

Microvascular Resistance Reserve for Assessment of Coronary Microvascular Function: JACC Technology Corner.

The need for a quantitative and operator-independent assessment of coronary microvascular function is increasingly recognized. We propose the theoretical framework of microvascular resistance reserve (MRR) as an index specific for the microvasculature, independent of autoregulation and myocardial mass, and based on operator-independent measurements of absolute values of coronary flow and pressure. In its general form, MRR equals coronary flow reserve (CFR) divided by fractional flow reserve (FFR) corrected for driving pressures. In 30 arteries, pressure, temperature, and flow velocity measurements were obtained simultaneously at baseline (BL), during infusion of saline at 10 mL/min (rest) and 20 mL/min (hyperemia). A strong correlation was found between continuous thermodilution-derived MRR and Doppler MRR (r = 0.88; 95% confidence interval: 0.72-0.93; P < 0.001). MRR was independent from the epicardial resistance, the lower the FFR value, the greater the difference between MRR and CFR. Therefore, MRR is proposed as a specific, quantitative, and operator-independent metric to quantify coronary microvascular dysfunction.

Simplified Assessment of the Index of Microvascular Resistance.

BACKGROUND: To validate a simplified invasive method for the calculation of the index of microvascular resistance (IMR). METHODS: This is a prospective, single-center study of patients with chronic coronary syndromes presenting with nonobstructive coronary artery disease. IMR was obtained using both intravenous (IV) adenosine and intracoronary (IC) papaverine. Each IMR measurement was obtained in duplicate. The primary objective was the agreement between IMR acquired using adenosine and papaverine. Secondary objectives include reproducibility of IMR and time required for the IMR measurement. RESULTS: One hundred and sixteen IMR measurements were performed in 29 patients. The mean age was 68.8 ± 7.24 years, and 27.6% was diabetics. IMR values were similar between papaverine and adenosine (17.7 ± 7.26 and 20.1 ± 8.6, p=0.25; Passing-Bablok coefficient A 0.58, 95% CI -2.42 to 3.53; coefficient B 0.90, 95% CI -0.74 to 1.07). The reproducibility of IMR was excellent with both adenosine and papaverine (ICC 0.78, 95% CI 0.63 to 0.88 and ICC 0.93, 95% CI 0.87 to 0.97). The time needed for microvascular assessment was significantly shortened by the use of IC papaverine (3.23 (2.84, 3.78) mins vs. 5.48 (4.94, 7.09) mins, p < 0.0001). CONCLUSION: IMR can be reliably measured using IC papaverine with similar results compared to intravenous infusion of adenosine with increased reproducibility and reduced procedural time. This approach simplifies the invasive assessment of the coronary microcirculation in the catheterization laboratory.

Mismatch between morphological and functional assessment of the length of coronary artery disease.

BACKGROUND: Morphological evaluation of coronary lesion length is a paramount step during invasive assessment of coronary artery disease. Likewise, the extent of epicardial pressure losses can be measured using longitudinal vessel interrogation with fractional flow reserve (FFR) pullbacks. We aimed to quantify the mismatch in lesion length between morphological (based on quantitative coronary angiography, QCA, and optical coherence tomography, OCT) and functional evaluations. METHODS: This is a prospective and multicenter study of patients evaluated by QCA, OCT and motorized fractional flow reserve pullbacks (mFFR). The difference in lesion length between the functional and anatomical evaluations was referred to as FAM. RESULTS: 117 patients (131 vessels) were included. Median lesion length derived from angiography was 16.05 mm [11.40-22.05], from OCT was 28.00 mm [16.63-38.00] and from mFFR 67.12 mm [25.38-91.37]. There was no correlation between QCA and mFFR lesion length (r = 0.124, 95% CI -0.168-0.396, p = 0.390). OCT lesion length did correlate with mFFR (r = 0.469, 95% CI 0.156-0.696, p = 0.004). FAM was strongly associated with the improvement in vessel conductance with percutaneous coronary intervention (PCI), higher mismatch was associated with lower post-PCI FFR. CONCLUSIONS: Lesion length assessment differs between morphological and functional evaluations. The morphological-functional mismatch in lesion length is frequent, and influences the results of PCI in terms of post-PCI FFR. Integration of the extent of pressure losses provides clinically relevant information that may be useful for clinical decision-making concerning revascularization strategy.

Reviewing imaging modalities for the assessment of plaque erosion.

Plaque rupture followed by intracoronary thrombus formation is recognized as the most common pathophysiological mechanism in acute coronary syndromes (ACS). The second most common underlying substrate for ACS is plaque erosion whose hallmark is thrombus formation without cap disruption. Invasive and non-invasive methods have emerged as a promising tool for evaluation of plaque features that either predict or detect plaque erosion. Optical coherence tomography (OCT), high-definition intravascular ultrasound (IVUS), near-infrared spectroscopy (NIRS), and near-infrared autofluorescence (NIRF) have been used to study plaque erosion. The detection of plaque erosion in the clinical setting, mainly facilitated by OCT, has shed light upon the complex pathophysiology underlying ACS not related to plaque rupture. Coronary computed tomography angiography (CCTA), which is to date the most commonly used non-invasive technique for coronary plaque evaluation, may also have a role in the evaluation of patients predisposed to erosion. Also, computational models enabling quantification of endothelial shear stress may pave the way to new research in coronary plaque pathophysiology. This review focuses on the recent imaging techniques for the evaluation of plaque erosion including invasive and non-invasive assessment.

Global Fractional Flow Reserve Value Predicts 5-Year Outcomes in Patients With Coronary Atherosclerosis But Without Ischemia.

Background Global fractional flow reserve (FFR) (ie, the sum of the FFR values in the 3 major coronary arteries) is a physiologic correlate of global atherosclerotic burden. The objective of the present study was to investigate the value of global FFR in predicting long-term clinical outcome of patients with stable coronary artery disease but no ischemia-inducing stenosis. Methods and Results We studied major adverse cardiovascular events (MACEs: all-cause death, myocardial infarction, and any revascularization) after 5 years in 1122 patients without significant stenosis (all FFR >0.80; n=275) or with at least 1 significant stenosis successfully treated by percutaneous coronary intervention (ie, post-percutaneous coronary intervention FFR >0.80; n=847). The patients were stratified into low, mid, or high tertiles of global FFR (≤2.80, 2.80-2.88, and ≥2.88). Patients in the lowest tertile of global FFR showed the highest 5-year MACE rate compared with those in the mid or high tertile of global FFR (27.5% versus 22.0% and 20.9%, respectively; log-rank P=0.040). The higher 5-year MACE rate was mainly driven by a higher rate of revascularization in the low global FFR group (16.4% versus 11.3% and 11.8%, respectively; log-rank P=0.038). In a multivariable model, an increase in global FFR of 0.1 unit was associated with a significant reduction in the rates of MACE (hazard ratio [HR], 0.988; 95% CI, 0.977-0.998; P=0.023), myocardial infarction (HR, 0.982; 95% CI, 0.966-0.998; P=0.032), and revascularization (HR, 0.985; 95% CI, 0.972-0.999; P=0.040). Conclusions Even in the absence of ischemia-producing stenoses, patients with a low global FFR, physiologic correlate of global atherosclerotic burden, present a higher risk of MACE at 5-year follow-up.

The Role of Quantitative Aortographic Assessment of Aortic Regurgitation by Videodensitometry in the Guidance of Transcatheter Aortic Valve Implantation.

BACKGROUND: Balloon post-dilatation (BPD) is often needed for optimizing transcatheter heart valve (THV) implantation, since paravalvular leak (PVL) after transcatheter aortic valve implantation is associated with poor outcome and mortality. Quantitative assessment of PVL severity before and after BPD is mandatory to properly assess PVL, thus improving implantation results and outcomes. OBJECTIVE: To investigate a quantitative angiographic assessment of aortic regurgitation (AR) by videodensitometry before and after BPD. METHODS: Videodensitometric-AR assessments (VD-AR) before and after BPD were analysed in 61 cases. RESULTS: VD-AR decreased significantly from 24.0[18.0-30.5]% to 12.0[5.5-19.0]% (p < 0.001, a two-tailed p < 0.05 defined the statistical significance). The relative delta of VD-AR after BPD ranged from -100% (improvement) to +40% (deterioration) and its median value was -46.2%. The frequency of improvement, no change, and deterioration were 70% (n = 43), 25% (n = 15) and 5% (n = 3), respectively. Significant AR (VD-AR > 17%) was observed in 47 patients (77%) before and in 19 patients (31%) after BPD. CONCLUSIONS: VD-AR after THV implantation provides a quantitative assessment of post-TAVI regurgitation and can help in the decision-making process on performing BPD and in determining its efficacy.

The Role of Quantitative Aortographic Assessment of Aortic Regurgitation by Videodensitometry in the Guidance of Transcatheter Aortic Valve Implantation / Papel da Avaliação Aortográfica Quantitativa da Regurgitação Aórtica por Videodensitometria na Orientação do Implante da Valva Aórtica Transcateter

Abstract Background: Balloon post-dilatation (BPD) is often needed for optimizing transcatheter heart valve (THV) implantation, since paravalvular leak (PVL) after transcatheter aortic valve implantation is associated with poor outcome and mortality. Quantitative assessment of PVL severity before and after BPD is mandatory to properly assess PVL, thus improving implantation results and outcomes. Objective: To investigate a quantitative angiographic assessment of aortic regurgitation (AR) by videodensitometry before and after BPD. Methods: Videodensitometric-AR assessments (VD-AR) before and after BPD were analysed in 61 cases. Results: VD-AR decreased significantly from 24.0[18.0-30.5]% to 12.0[5.5-19.0]% (p < 0.001, a two-tailed p < 0.05 defined the statistical significance). The relative delta of VD-AR after BPD ranged from -100% (improvement) to +40% (deterioration) and its median value was -46.2%. The frequency of improvement, no change, and deterioration were 70% (n = 43), 25% (n = 15) and 5% (n = 3), respectively. Significant AR (VD-AR > 17%) was observed in 47 patients (77%) before and in 19 patients (31%) after BPD. Conclusions: VD-AR after THV implantation provides a quantitative assessment of post-TAVI regurgitation and can help in the decision-making process on performing BPD and in determining its efficacy.

Resumo Fundamento: A pós-dilatação com balão (PDB) é normalmente necessária para otimização do implante da válvula cardíaca transcateter (THV), uma vez que o "escape" ou leak paravalvar (PVL) após implante de valva aórtica transcateter está associada com desfecho ruim e mortalidade. A avaliação quantitativa da gravidade do PVL antes e após a PDB é mandatória para se avaliar adequadamente o PVL e, assim, melhorar os resultados e os desfechos do implante. Objetivo: Investigar uma avalição angiográfica quantitativa da regurgitação aórtica (RA) por videodensitometria (VD-RA) antes e após a PDB. Métodos: Resultados da VD-RA antes e após a PDB foram analisados em 61 casos. Resultados Houve diminuição significativa da VD-RA de 24,0(18,0-30,5)% para 12,0(5,5-19,0)% (p < 0,001; p < 0,05 bilateral foi definido como significância estatística). O delta relativo de VD-RA após a PDB variou de -100% (melhora) a +40% (piora) e o valor mediano foi -46,2%. As frequências de melhora, ausência de mudança, e piora foram 70% (n = 43), 25% (n = 15) e 5% (n = 3), respectivamente. Observou-se RA significativo (VD-RA > 17%) em 47 pacientes (77%) antes e em 19 pacientes (31%) após a PDB. Conclusões: A VD-RA após o implante de THV possibilita a avaliação quantitativa da regurgitação pós-TAVI, e pode auxiliar na tomada de decisão quanto à realização ou não da PDB, bem como na avaliação de sua eficácia.

Outcomes After Coronary Stenting or Bypass Surgery for Men and Women With Unprotected Left Main Disease: The EXCEL Trial.

OBJECTIVES: The aim of the present study was to assess outcomes after coronary artery bypass grafting surgery (CABG) and percutaneous coronary intervention (PCI) according to sex in a large randomized trial of patients with unprotected left main disease. BACKGROUND: In the SYNTAX (Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery) trial, sex had a significant interaction effect with revascularization strategy, and women had an overall higher mortality when treated with PCI than CABG. METHODS: The EXCEL (Evaluation of XIENCE Versus Coronary Artery Bypass Surgery for Effectiveness of Left Main Revascularization) trial was a multinational randomized trial that compared PCI with everolimus-eluting stents and CABG in patients with unprotected left main disease. The primary endpoint was the composite of all-cause death, myocardial infarction, or stroke at 3 years. RESULTS: Of 1,905 patients randomized, 1,464 (76.9%) were men and 441 (23.1%) were women. Compared with men, women were older; had higher prevalence rates of hypertension, hyperlipidemia, and diabetes; and were less commonly smokers but had lower coronary anatomic burden and complexity (mean SYNTAX score 24.2 vs. 27.2, p < 0.001). By multivariate analysis, sex was not independently associated with either the primary endpoint (hazard ratio [HR]: 1.10; 95% confidence interval [CI]: 0.82 to 1.48; p = 0.53) or all-cause death (HR: 1.39; 95% CI: 0.92 to 2.10; p = 0.12) at 3 years. At 30 days, all-cause death, myocardial infarction, or stroke had occurred in 8.9% of woman treated with PCI, 6.2% of women treated with CABG, 3.6% of men treated with PCI, and 8.4% of men treated with CABG (p for interaction = 0.003). The 3-year rate of the composite primary endpoint was 19.7% in women treated with PCI, 14.6% in women treated with CABG, 13.8% in men treated with PCI, and 14.7% in men treated with CABG (p for interaction = 0.06). These differences were driven by higher periprocedural rates of myocardial infarction in women after PCI and in men after CABG. CONCLUSIONS: In patients with unprotected left main disease in the EXCEL trial, sex was not an independent predictor of adverse outcomes after revascularization. However, women undergoing PCI had a trend toward worse outcomes, a finding related to associated comorbidities and increased periprocedural complications. Further studies are required to determine the optimal revascularization modality in women with complex coronary artery disease.

Imaging assessment of bioresorbable vascular scaffolds.

Vascular reparative therapy has become a reality with bioresorbable scaffolds (BRSs). To assess acute and long-term performance of the device, multimodality imaging would be essential. Radiopacity of metal hinders the imaging assessment, whereas radiolucent polymeric scaffolds allow for a precise imaging assessment with either invasive or non-invasive modality at baseline and at follow-up, which is one of the advantages of polymeric BRSs. Recent large trials evaluating clinical results of the first-generation BRS technology raised concerns about the safety and efficacy of these devices, namely, scaffold thrombosis. Intensive research with multimodality imaging in the field is being conducted to have in-depth understanding of the issues, which will facilitate the improvement of implantation techniques and the development of the next-generation BRSs. The current review focuses on the clinical application of the imaging modalities to assess the short- and long-term performance of the Absorb BVS.

What does the future hold for novel intravascular imaging devices: a focus on morphological and physiological assessment of plaque.

INTRODUCTION: It is well recognized that a lesion that does not cause a hemodynamically significant stenosis can trigger a sudden cardiac event through plaque rupture. As a diagnostic tool, intravascular imaging was developed to circumvent limitations of coronary angiography; however, none of the intravascular imaging devices are individually able to provide complete assessment of the plaque morphology, geometry, physiology and biology. Therefore, over the past few years an effort was made to develop hybrid intravascular imaging catheters to provide more complete evaluation of coronary plaque pathobiology. Areas covered: This paper aims to give an overview of the recent developments on 1) single-modality intravascular imaging devices; 2) hybrid intravascular imaging devices and 3) the hemodynamic analysis in models reconstructed from the fusion of intravascular imaging and angiographic data. Expert commentary: Within five years, most of the hybrid imaging techniques which are now in pre-clinical phase will be utilized in the clinical arena, as NIRS-IVUS. Software for online blood simulation is likely to be developed that will enable ESS calculation while the patient is in the catheterization laboratory.

State of the art: pressure wire and coronary functional assessment.

The pressure wire has revolutionised cardiology by moving the focus of revascularisation from anatomy to physiology. This review provides a comprehensive viewpoint on the foundations of the field of intracoronary physiology, with emphasis on the development and clinical evidence of fractional flow reserve (FFR). Additionally, we critically appraise clinical decision making based on the evolving area of resting coronary physiology. The emerging role of coronary flow reserve and its complementariness with FFR is also discussed, and the importance of the invasive assessment of the coronary microcirculation in outlining prognosis is put into perspective. Overall, this review summarises the capacity of invasive coronary physiology indices to guide revascularisation and to discriminate patients at high risk of an adverse cardiovascular outcome.