The prognostic value of combined intracoronary pressure and blood flow velocity measurements after deferral of percutaneous coronary intervention

Invasive assessment of coronary microvascular dysfunction and cardiovascular outcomes across the full spectrum of CHD: a meta-analysis

INTRODUCTION AND OBJECTIVES

Coronary microvascular dysfunction (CMD) is highly prevalent and is recognized as an important clinical entity in patients with coronary heart disease (CHD). Nevertheless, the association of CMD with adverse cardiovascular events in the spectrum of CHD has not been systemically quantified.

METHODS

We searched electronic databases for studies on patients with CHD in whom coronary microvascular function was measured invasively, and clinical events were recorded. The primary endpoint was major adverse cardiac events (MACE), and the secondary endpoint was all-cause death. Estimates of effect were calculated using a random-effects model from published risk ratios.

RESULTS

We included 27 studies with 11 404 patients. Patients with CMD assessed by invasive methods had a higher risk of MACE (RR, 2.18; 95%CI, 1.80-2.64; P<.01) and all-cause death (RR, 1.88; 95%CI, 1.55-2.27; P<.01) than those without CMD. There was no significant difference in the impact of CMD on MACE (interaction P value=.95) among different invasive measurement modalities. The magnitude of risk of CMD assessed by invasive measurements for MACE was greater in acute coronary syndrome patients (RR, 2.84, 95%CI, 2.26-3.57; P<.01) than in chronic coronary syndrome patients (RR, 1.77, 95%CI, 1.44-2.18; P<.01) (interaction P value<.01).

CONCLUSIONS

CMD based on invasive measurements was associated with a high incidence of MACE and all-cause death in patients with CHD. The magnitude of risk for cardiovascular events in CMD as assessed by invasive measurements was similar among different methods but varied among CHD populations.

Implementation of Microcirculation Examination in Clinical Practice-Insights from the Nationwide POL-MKW Registry

Background and Objectives: The assessment of coronary microcirculation may facilitate risk stratification and treatment adjustment. The aim of this study was to evaluate patients' clinical presentation and treatment following coronary microcirculation assessment, as well as factors associated with an abnormal coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) values. Materials and Results: This retrospective analysis included 223 patients gathered from the national registry of invasive coronary microvascular testing collected between 2018 and 2023. Results: The frequency of coronary microcirculatory assessments in Poland has steadily increased since 2018. Patients with impaired IMR (≥25) were less burdened with comorbidities. Patients with normal IMR underwent revascularisation attempts more frequently (11.9% vs. 29.8%, p = 0.003). After microcirculation testing, calcium channel blockers (CCBs) and angiotensin-converting enzyme inhibitors were added more often for patients with IMR and CFR abnormalities, respectively, as compared to control groups. Moreover, patients with coronary microvascular dysfunction (CMD, defined as CFR and/or IMR abnormality), regardless of treatment choice following microcirculation assessment, were provided with trimetazidine (23.2%) and dihydropyridine CCBs (26.4%) more frequently than those without CMD who were treated conservatively (6.8%) and by revascularisation (4.2% with p = 0.002 and 0% with p < 0.001, respectively). Multivariable analysis revealed no association between angina symptoms and IMR or CFR impairment. Conclusions: The frequency of coronary microcirculatory assessments in Poland has steadily increased. Angina symptoms were not associated with either IMR or CFR impairment. After microcirculation assessment, patients with impaired microcirculation, expressed as either low CFR, high IMR or both, received additional pharmacotherapy treatment more often.

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

BACKGROUND

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Particularities of coronary physiology in patients with atrial fibrillation: insights from combined pressure and flow indices measurements

Background

Symptoms suggestive of myocardial ischemia are frequently encountered in patients with atrial fibrillation (AF) even in the absence of obstructive coronary artery disease. Nevertheless, an in-depth characterisation of coronary physiology in patients with AF is currently lacking.

Objectives

We aim to provide an insight into the characteristics of coronary physiology in AF, by performing simultaneous invasive measurements of coronary flow- and pressure- indices in a real-life population of patients with AF and indication of coronary angiography.

Methods

This is a prospective open label study including patients with permanent or persistent AF and indication of coronary angiography showing intermediate coronary stenosis requiring routine physiological assessment (n = 18 vessels from 14 patients). We measured FFR (fractional flow reserve), and Doppler-derived coronary flow indices, including CFR (coronary flow reserve) and HMR (hyperaemic microvascular resistance).

Results

From the analysed vessels, 18/18 vessels (100%) presented a pathological CFR (<2.5), indicative of coronary microvascular dysfunction (CMD), and 3/18 (17%) demonstrated obstructive epicardial coronary disease (FFR ≤ 0.8). A large proportion of vessels (15/18; 83%) showed discordant FFR/CFR with preserved FFR and low CFR. 47% of the coronary arteries in patients with AF and non-obstructive epicardial coronary disease presented structural CMD (HMR ≥ 2.5 mmHg/cm/s), and were associated with high BMR and an impaired response to adenosine. Conversely, vessels from patients with AF and non-obstructive epicardial coronary disease with functional CMD (HMR < 2.5 mmHg/cm/s) showed higher bAPV. The permanent AF subpopulation presented increased values of HMR and BMR compared to persistent AF, while structural CMD was more often associated with persistent symptoms at 3 months, taking into account the limited sample size of our study.

Conclusion

Our findings highlight a systematically impaired CFR in patients with AF even in the absence of obstructive epicardial coronary disease, indicative of CMD. In addition, patients with AF presented more prevalent structural CMD (HMR ≥ 2.5 mmHg/cm/s), characterized by reduced hyperaemic responses to adenosine, possibly interfering with the FFR assessment.

Long-term outcomes of intermediate coronary stenosis in patients undergoing hemodialysis after deferred revascularization based on fractional flow reserve

OBJECTIVES

This study aimed to assess the long-term outcomes of patients undergoing hemodialysis (HD) after deferred revascularization based on fractional flow reserve (FFR).

BACKGROUND

FFR is a practical technique for assessing the functional severity of intermediate coronary stenosis. Prior research has revealed a satisfactory outcome in patients after the deferral of percutaneous coronary intervention for coronary lesions based on FFR measurement. However, little research has been conducted focusing on patients undergoing HD.

METHODS

The retrospective study comprised 225 consecutive patients with FFR assessment and deferred revascularization between January 2016 and December 2019. Based on a deferral cutoff FFR value of >0.80, we assessed the differences in all-cause death, major adverse cardiac events (MACEs), and target vessel failure (TVF) between the HD (n = 69) and non-HD groups (n = 156) during a mean ± standard deviation routine follow-up of 32.2 ± 13.4 months.

RESULTS

Although the HD group had significantly higher rates of diabetes mellitus than the non-HD group (53.6% vs. 37.2%, p = 0.021), there were no significant differences in sex, left ventricular ejection fraction, or other risk factors between the groups, nor with respect to stenosis diameter or mean FFR. The HD group had a significantly higher incidence of TVF than the non-HD group (34.8% vs. 14.1%, p < 0.001), as well as a significantly higher risk of all-cause death and MACEs.

CONCLUSIONS

The study revealed that deferred revascularization in coronary lesions with an FFR value of >0.80 in patients undergoing HD was associated with poor outcomes. Therefore, it is important to carefully monitor patients with intermediate coronary stenosis undergoing HD.

Functional significance of intermediate coronary stenosis in patients with single-vessel coronary artery disease: A comparison of dynamic SPECT coronary flow reserve with intracoronary pressure-derived fractional flow reserve (FFR)

BACKGROUND

The aim of this study was to investigate the correlation of coronary flow reserve (CFR) assessed by rest/stress myocardial perfusion imaging with dynamic single-photon emission computed tomography (SPECT) with intracoronary pressure-derived fractional flow reserve (FFR) in patients with single-vessel coronary artery disease (CAD).

METHODS

Patients with suspected or known stable CAD who were referred for invasive coronary angiography were prospectively enrolled. Both invasive FFR and SPECT were performed in subjects with single-vessel intermediate coronary stenosis. A cutoff value of < 0.8 was used to define abnormal FFR.

RESULTS

A total of 34 patients were enrolled. The mean age of the subjects was 62.1 ± 6.7 years, and 79.4% were male. SPECT-derived CFR showed a significantly moderate correlation with FFR (r = 0.505, P = .003). The diagnostic performance for the identification of abnormal FFR in terms of sensitivity, specificity, and accuracy was 88.9%, 83.3%, and 87.9%, respectively, for CFR, with an optimized cutoff value of 1.73.

CONCLUSION

In patients with single-vessel CAD, SPECT CFR was useful for the detection of functionally significant stenosis. Our data support the use of this technique as an optional method for hemodynamic assessment, especially when FFR results are in normal range.

Assessment and pathophysiology of microvascular disease: recent progress and clinical implications

The development of novel, non-invasive techniques and standardization of protocols to assess microvascular dysfunction have elucidated the key role of microvascular changes in the evolution of cardiovascular (CV) damage, and their capacity to predict an increased risk of adverse events. These technical advances parallel with the development of novel biological assays that enabled the ex vivo identification of pathways promoting microvascular dysfunction, providing novel potential treatment targets for preventing cerebral-CV disease. In this article, we provide an update of diagnostic testing strategies to detect and characterize microvascular dysfunction and suggestions on how to standardize and maximize the information obtained from each microvascular assay. We examine emerging data highlighting the significance of microvascular dysfunction in the development CV disease manifestations. Finally, we summarize the pathophysiology of microvascular dysfunction emphasizing the role of oxidative stress and its regulation by epigenetic mechanisms, which might represent potential targets for novel interventions beyond conventional approaches, representing a new frontier in CV disease reduction.

Physiologic Assessment of Coronary Stenosis: Current Status and Future Directions

PURPOSE OF REVIEW

Percutaneous coronary intervention (PCI) is a commonly used treatment option in coronary artery disease (CAD). Reduced major adverse cardiovascular events (MACE) in those randomized to PCI compared to optimal medical therapy have been demonstrated only if it is performed for physiologically significant coronary lesions. Despite data demonstrating improved outcomes primarily in stable CAD and then acute settings, physiology-guided PCI remains underutilized. This review summarizes the evidence and commonly used methods for physiologic assessment of coronary stenosis.

RECENT FINDINGS

Fractional flow reserve (FFR) is the gold standard for the analysis of lesion severity. Its use is limited by the need for adenosine, which adds time, complexity, and potential adverse effects. Non-hyperemic instantaneous wave-free ratio-guided revascularization and quantitative flow reserve ratio assessment both have shown safety and effectiveness with improved patient outcomes. Coronary physiological assessment solves the ambiguity of coronary angiography. Detecting physiologically significant stenoses is crucial to decide which lesion needs to be treated. Technological advances have led to the development of new assessment indices in addition to FFR.

Impact of clinical and haemodynamic factors on coronary flow reserve and invasive coronary flow capacity in non-obstructed coronary arteries: a patient-level pooled analysis of the DEBATE and ILIAS studies

AIMS

Coronary flow reserve (CFR) is a physiological index for the assessment of myocardial flow impairment due to focal or microcirculatory coronary artery disease (CAD). Coronary flow capacity (CFC) is another flow-based concept in diagnosing ischaemic heart disease, based on hyperaemic average peak velocity (hAPV) and CFR. We evaluated clinical and haemodynamic factors which potentially influence CFR and CFC in non-obstructed coronary arteries.

METHODS AND RESULTS

Intracoronary Doppler flow velocity measurements to obtain CFR and CFC were performed after inducing hyperaemia in 390 non-obstructed vessels of patients who were scheduled for elective percutaneous coronary intervention (PCI) of another vessel. Akaike's information criterion (AIC) revealed age, female gender, history of myocardial infarction, hypercholesterolaemia, diastolic blood pressure, oral nitrates and rate pressure product as independent predictors of CFR and CFC. After regression analysis, age and female gender were associated with lower CFR and age was associated with worse CFC in angiographically non-obstructed vessels.

CONCLUSIONS

Age and female gender are associated with lower CFR, and age with worse CFC in an angiographically non-obstructed coronary artery. CFC seems to be less sensitive to variations in clinical and haemodynamic parameters than CFR and is therefore a promising tool in contemporary clinical decision making in the cardiac catheterisation laboratory.

Contribution of Age-Related Microvascular Dysfunction to Abnormal Coronary: Hemodynamics in Patients With Ischemic Heart Disease

OBJECTIVES

This study sought to investigate the contribution of age-related microcirculatory dysfunction to abnormal coronary hemodynamics in patients with coronary atherosclerosis.

BACKGROUND

Impairment in myocardial blood supply in patients with coronary atherosclerosis can be accentuated due to age-related changes in microcirculatory function.

METHODS

Intracoronary pressure and flow were measured with the Doppler technique in 299 vessels (228 patients), and the thermodilution technique in 120 vessels (99 patients). In 172 patients, Doppler measurements were also performed in unobstructed vessels. Associations of coronary hemodynamics with aging were studied in both the stenosed and unobstructed arteries.

RESULTS

Aging was associated with a progressive increase in minimal microvascular resistance and a progressive decrease in hyperemic flow in both obstructed and nonobstructed coronary arteries. As such, coronary flow reserve decreased with advancing age. Epicardial stenosis severity assessed by resting Pd/Pa, basal stenosis resistance index, and hyperemic stenosis resistance index was equivalent across age groups. By contrast, fractional flow reserve increased with advancing age. Consequently, the adjusted risk of a fractional flow reserve/coronary flow reserve pattern reflective of concomitant focal epicardial and diffuse or microvascular disease (relative risk: 1.6; 95% confidence interval: 1.1 to 2.3; p = 0.017) increased with advancing age, whilst the adjusted risk of a fractional flow reserve/coronary flow reserve pattern reflective of non-flow-limiting stenosis with a healthy microcirculation decreased (relative risk: 0.7; 95% CI: 0.5 to 1.0; p = 0.022).

CONCLUSIONS

Aging is associated with progressive pan-myocardial impairment of coronary vasodilatory capacity due to an increase in minimal microvascular resistance. Concomitant aging-related impairment in microvascular function impacts the pathophysiology of ischemic heart disease in the individual patient and is not adequately identified by hyperemic coronary pressure measurements alone.

Invasive coronary physiology: a Dutch tradition

Invasive coronary physiology has been applied since the early days of percutaneous transluminal coronary angioplasty, and has become a rapidly emerging field of research. Many physiology indices have been developed, tested in clinical studies, and are now applied in daily clinical practice. Recent clinical practice guidelines further support the use of advanced invasive physiology methods to optimise the diagnosis and treatment of patients with acute and chronic coronary syndromes. This article provides a succinct review of the history of invasive coronary physiology, the basic concepts of currently available physiological parameters, and will particularly highlight the Dutch contribution to this field of invasive coronary physiology.

Long-term Patient Prognostication by Coronary Flow Reserve and Index of Microcirculatory Resistance: International Registry of Comprehensive Physiologic Assessment

BACKGROUND AND OBJECTIVES

Recent guideline recommends evaluation using of coronary flow reserve (CFR) and index of microcirculatory resistance (IMR) in patients with functionally insignificant stenosis. We evaluated clinical implications of CFR and IMR in patients with high fractional flow reserve (FFR) and deferred revascularization.

METHODS

A total of 867 patients (1,152 vessels) consigned to deferred revascularization who underwent comprehensive physiologic assessments were enrolled. Patients with high FFR (>0.80) were categorized by CFR (≤2) and IMR (≥23 U). Clinical outcome was assessed by patient-oriented composite outcome (POCO), a composite of any death, myocardial infarction (MI), and revascularization at 5 years.

RESULTS

Patients with low CFR (≤2) showed significantly greater risk of POCO than those with high CFR (>2) in both high-FFR (p=0.024) and low-FFR (p=0.034) groups. In patients with high FFR, those with low CFR and high IMR (overt microvascular disease) displayed the greatest risk of POCO overall (p=0.015), surpassing those with high CFR and low IMR (HR, 2.873; 95% CI, 1.476-5.594; p=0.002) and showing significantly greater risk of cardiac death or MI (HR, 5.662; 95% CI, 1.984-16.154; p=0.001). Overt microvascular disease was independently associated with POCO in the high-FFR population (HR, 2.282; 95% CI, 1.176-4.429; p=0.015).

CONCLUSION

Among patients with deferred revascularization, those with low CFR showed significantly greater risk of POCO than those with high CFR, regardless of FFR. In patients with high FFR, those with overt microvascular disease showed significantly greater risk of POCO and cardiac death or MI at 5-year, compared with the others.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03690713.

Prognostic Implications of Resistive Reserve Ratio in Patients With Coronary Artery Disease

Background

Resistive reserve ratio is a thermodilution‐based index which integrates both coronary flow and pressure. Resistive reserve ratio represents the vasodilatory capacity of interrogated vessels including both epicardial coronary artery and microvascular circulation. We evaluated the prognostic potential of resistive reserve ratio compared with pressure‐derived index (fractional flow reserve [FFR]) or flow‐derived index (coronary flow reserve [CFR]).

Methods and Results

A total of 1245 patients underwent coronary pressure and flow measurement using pressure‐temperature wire. Resistive reserve ratio was calculated by CFR adjusted using the ratio between resting and hyperemic distal coronary pressure ([resting mean transit time/hyperemic mean transit time]×[resting distal coronary pressure/hyperemic distal coronary pressure]). Clinical outcome was assessed by patient‐oriented composite outcome (POCO), a composite of any death, myocardial infarction, and revascularization at 5 years. At 5 years, the cumulative incidence of POCO was significantly different according to quartiles of resistive reserve ratio (9.9%, 11.3%, 17.2%, and 22.7% in quartiles 1 to 4, respectively, log rank P<0.001). Among patients with deferred revascularization, those with depressed resistive reserve ratio (<3.5) showed a significantly higher risk of POCO than those with preserved resistive reserve ratio (≥3.5) in patients with FFR>0.80 or patients with CFR>2.0. (FFR>0.80 group: 14.8% versus 6.0%; log rank P=0.001; CFR>2.0 group: 13.5% versus 7.1%; log rank P=0.045). Adding resistive reserve ratio into the model for 5‐year POCO showed significantly higher global Chi square value than FFR or CFR (P<0.001, respectively, for FFR and CFR). Resistive reserve ratio <3.5 was significantly associated with the risk of POCO at 5 years in multivariable model (adjusted hazard ratio 1.597, 95% CI, 1.098–2.271, P=0.014).

Conclusions

Resistive reserve ratio, which integrated both coronary flow and pressure, showed incremental prognostic implications in patients with coronary artery disease undergoing elective percutaneous coronary intervention guided by invasive physiologic evaluation.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT03690713.

Distal Evaluation of Functional performance with Intravascular sensors to assess the Narrowing Effect-combined pressure and Doppler FLOW velocity measurements (DEFINE-FLOW) trial: Rationale and trial design

BACKGROUND

It remains uncertain if invasive coronary physiology beyond fractional flow reserve (FFR) can refine lesion selection for revascularization or provide additional prognostic value. Coronary flow reserve (CFR) equals the ratio of hyperemic to baseline flow velocity and has a wealth of invasive and noninvasive data supporting its validity. Because of fundamental physiologic relationships, binary classification of FFR and CFR disagrees in approximately 30%-40% of cases. Optimal management of these discordant cases requires further study.

AIM

The aim of the study was to determine the prognostic value of combined FFR and CFR measurements to predict the 24-month rate of major adverse cardiac events. Secondary end points include repeatability of FFR and CFR, angina burden, and the percentage of successful FFR/CFR measurements which will not be excluded by the core laboratory.

METHODS

This prospective, nonblinded, nonrandomized, and multicenter study enrolled 455 subjects from 12 sites in Europe and Japan. Patients underwent physiologic lesion assessment using the 0.014" Philips Volcano ComboWire XT that provides simultaneous pressure and Doppler velocity sensors. Intermediate coronary lesions received only medical treatment unless both FFR (≤0.8) and CFR (<2.0) were below thresholds. The primary outcome is a 24-month composite of death from any cause, myocardial infarction, and revascularization.

CONCLUSION

The DEFINE-FLOW study will determine the prognostic value of invasive CFR assessment when measured simultaneously with FFR, with a special emphasis on discordant classifications. Our hypothesis is that lesions with an intact CFR ≥ 2.0 but reduced FFR ≤ 0.8 will have a 2-year outcome with medical treatment similar to lesions with FFR> 0.80 and CFR ≥ 2.0. Enrollment has been completed, and final follow-up will occur in November 2019.

Prognostic implications of resting distal coronary-to-aortic pressure ratio compared with fractional flow reserve: a 10-year follow-up study after deferral of revascularisation

Introduction

The distal coronary-to-aortic pressure ratio (P_d/P_a) is a non-hyperaemic physiological index to assess the functional severity of coronary stenoses. Studies comparing P_d/P_a with fractional flow reserve (FFR) show superior diagnostic efficiency for myocardial ischaemia. Nevertheless, a direct comparison regarding long-term clinical outcomes is still not available. The present observational study compared the prognostic value of P_d/P_a and FFR for major adverse cardiac events (MACE) during a 10-year follow-up period after deferral of revascularisation.

Methods

Between April 1997 and September 2006, we evaluated 154 coronary stenoses (154 patients) in which revascularisation was deferred with intracoronary pressure and flow measurements during the resting and hyperaemic state. Long-term follow-up (median: 11.8 years) was performed to document the occurrence of MACE, defined as a composite of cardiac death, myocardial infarction and target vessel revascularisation.

Results

The study population comprised angiographically intermediate coronary stenoses, with a mean diameter stenosis of 53 ± 8%, and intermediate physiological severity with a median FFR of 0.82 (Q1, Q3: 0.76, 0.88). The association of P_d/P_a with long-term MACE was similar to that of FFR [FFR-standardised hazard ratio (sHR): 0.77, 95% confidence interval (CI): 0.61–0.98; P_d/P_a-sHR: 0.80, 95% CI: 0.67–0.96]. In the presence of disagreement between P_d/P_a and FFR, normal P_d/P_a was generally associated with high coronary flow reserve (CFR) and a favourable clinical outcome, whereas abnormal P_d/P_a was generally associated with CFR around the ischaemic cut-point and an impaired clinical outcome, regardless of the accompanying FFR value.

Conclusion

The present study suggests that P_d/P_a provides at least equivalent prognostic value compared with FFR. When P_d/P_a disagreed with FFR, the baseline index conferred superior prognostic value in this study population.

Electronic supplementary material

The online version of this article (10.1007/s12471-020-01365-6) contains supplementary material, which is available to authorized users.

Relationship between FFR, CFR and coronary microvascular resistance - Practical implications for FFR-guided percutaneous coronary intervention

Objective

The aim was threefold: 1) expound the independent physiological parameters that drive FFR, 2) elucidate contradictory conclusions between fractional flow reserve (FFR) and coronary flow reserve (CFR), and 3) highlight the need of both FFR and CFR in clinical decision making. Simple explicit theoretical models were supported by coronary data analyzed retrospectively.

Methodology

FFR was expressed as a function of pressure loss coefficient, aortic pressure and hyperemic coronary microvascular resistance. The FFR-CFR relationship was also demonstrated mathematically and was shown to be exclusively dependent upon the coronary microvascular resistances. The equations were validated in a first series of 199 lesions whose pressures and distal velocities were monitored. A second dataset of 75 lesions with pre- and post-PCI measures of FFR and CFR was also analyzed to investigate the clinical impact of our hemodynamic reasoning.

Results

Hyperemic coronary microvascular resistance and pressure loss coefficient had comparable impacts (45% and 49%) on FFR. There was a good concordance (y = 0.96 x − 0.02, r² = 0.97) between measured CFR and CFR predicted by FFR and coronary resistances. In patients with CFR < 2 and CFR/FFR ≥ 2, post-PCI CFR was significantly >2 (p < 0.001), whereas it was not (p = 0.94) in patients with CFR < 2 and CFR/FFR < 2.

Conclusion

The FFR behavior and FFR-CFR relationship are predictable from basic hemodynamics. Conflicting conclusions between FFR and CFR are explained from coronary vascular resistances. As confirmed by our results, FFR and CFR are complementary; they could jointly contribute to better PCI guidance through the CFR-to-FFR ratio in patients with coronary artery disease.

Prognostic Value of Preserved Coronary Flow Velocity Reserve by Noninvasive Transthoracic Doppler Echocardiography in Patients With Angiographically Intermediate Left Main Stenosis

BACKGROUND

The potential of angiography to evaluate the hemodynamic severity of a left main coronary artery (LM) stenosis is limited. Noninvasive transthoracic Doppler echocardiographic coronary flow velocity reserve (CFVR) evaluation of intermediate coronary stenosis has demonstrated remarkably high negative prognostic value. The aim of this study was to assess clinical outcomes in patients with angiographically intermediate LM stenosis and preserved CFVR (>2.0) as evaluated by transthoracic Doppler echocardiographic CFVR.

METHODS

The initial study population included 102 patients with intermediate coronary stenosis of the LM referred for transthoracic Doppler echocardiographic CFVR assessment. Peak diastolic CFVR measurements were performed in the distal segment of the left anterior descending coronary artery after intravenous adenosine (140 μg/kg/min), and CFVR was calculated as the ratio between maximal hyperemic and baseline coronary flow velocity. Nineteen patients had impaired CFVR (≤2.0) and were excluded from further analysis, as well as two patients with poor acoustic windows. The final group consisted of 81 patients (mean age, 60 ± 9 years; 76 men) evaluated for adverse cardiac events including death, myocardial infarction, and revascularization.

RESULTS

Mean follow-up duration was 62 ± 26 months. Mean CFVR was 2.4 ± 0.4. Total event-free survival was 75 of 81 (92.6%), as six patients were referred for revascularization (five patients with coronary artery bypass grafting, one patient with percutaneous coronary intervention). There were no documented myocardial infarctions or cardiovascular deaths in the follow-up period.

CONCLUSIONS

In patients with angiographically intermediate and equivocal LM stenosis and preserved CFVR values of >2.0, revascularization can be safely deferred.

Assessing the Haemodynamic Impact of Coronary Artery Stenoses: Intracoronary Flow Versus Pressure Measurements

Fractional flow reserve (FFR)-guided percutaneous coronary intervention results in better long-term clinical outcomes compared with coronary angiography alone in intermediate stenoses in stable coronary artery disease (CAD). Coronary physiology measurements have emerged for clinical decision making in interventional cardiology, but the focus lies mainly on epicardial vessels rather than the impact of these stenoses on the myocardial microcirculation. The latter can be quantified by measuring the coronary flow reserve (CFR), a combined pressure and flow index with a strong ability to predict clinical outcomes in CAD. However, combined pressure-flow measurements show 30-40 % discordance despite similar diagnostic accuracy between FFR and CFR, which is explained by the effect of microvascular resistance on both indices. Both epicardial and microcirculatory involvement has been acknowledged in ischaemic heart disease, but clinical implementation remains difficult as it requires individual proficiency. The recent introduced pressure-only index instantaneous wave-free ratio, a resting adenosine-free stenosis assessment, led to a revival of interest in coronary physiology measurements. This review focuses on elaborating the coronary physiological parameters and potential of combined pressure-flow measurements in daily clinical practice.

Doppler Flow Velocity and Thermodilution to Assess Coronary Flow Reserve: A Head-to-Head Comparison With [15O]H2O PET

OBJECTIVES

This study sought to compare Doppler flow velocity reserve (CFR_Doppl) and thermodilution-derived coronary flow reserve (CFR_thermo) head-to-head with the gold standard for quantification of myocardial perfusion, [¹⁵O]H₂O positron emission tomography (PET).

BACKGROUND

Coronary flow reserve (CFR) is an important parameter for assessing coronary vascular function. To date, 2 techniques are available for invasive assessment of CFR: Doppler flow velocity and thermodilution. Although these techniques have been compared with each other, neither has been compared with [¹⁵O]H₂O PET perfusion imaging.

METHODS

CFR was assessed in 98 vessels of 40 consecutive stable patients with suspected coronary artery disease. Patients underwent [¹⁵O]H₂O PET, followed by invasive angiography in conjunction with simultaneous measurements of fractional flow reserve, CFR_Doppl, and CFR_thermo. Both normal and obstructed arteries were included.

RESULTS

The quality of Doppler flow velocity traces was significantly lower than that of thermodilution curves (p < 0.001). A moderate correlation was observed between CFR_Doppl and CFR_thermo (r = 0.59; p < 0.001). CFR_Doppl correlated well with PET-derived CFR (CFR_PET) (r = 0.82; p < 0.001). In contrast, the correlation between CFR_thermo and CFR_PET was only modest (r = 0.55; p < 0.001). This difference in correlation with CFR_PET was significant (t = 4.9; df = 95; p < 0.001). Bland-Altman analysis revealed a tendency of CFR_thermo to overestimate flow reserve at higher values.

CONCLUSIONS

Coronary flow reserve, determined using Doppler flow velocity, has superior agreement with [¹⁵O]H₂O PET in comparison with CFR_thermo.

Fractional Flow Reserve or Coronary Flow Reserve for the Assessment of Myocardial Perfusion : Implications of FFR as an Imperfect Reference Standard for Myocardial Ischemia

Purpose of Review

Accumulating evidence exists for the value of coronary physiology for clinical decision-making in ischemic heart disease (IHD). The most frequently used pressure-derived index to assess stenosis severity, the fractional flow reserve (FFR), has long been considered the gold standard for this purpose, despite the fact that the FFR assesses solely epicardial stenosis severity and aims to estimate coronary flow impairment in the coronary circulation. The coronary flow reserve (CFR) directly assesses coronary blood flow in the coronary circulation, including both the epicardial coronary artery and the coronary microvasculature, but is nowadays less established than FFR. It is now recognized that both tools may provide insight into the pathophysiological substrate of ischemic heart disease, and that particularly combined FFR and CFR measurements provide a comprehensive insight into the multilevel involvement of IHD. This review discusses the diagnostic and prognostic characteristics, as well as future implications of combined assessment of FFR and CFR pressure and flow measurements as parameters for inducible ischemia.

Recent Findings

FFR and CFR disagree in up to 40% of all cases, giving rise to fundamental questions regarding the role of FFR in contemporary ischemic heart disease management, and implying a renewed approach in clinical management of these patients using combined coronary pressure and flow measurement to allow appropriate identification of patients at risk for cardiovascular events.

Summary

This review emphasizes the value of comprehensive coronary physiology measurements in assessing the pathophysiological substrate of IHD, and the importance of acknowledging the broad spectrum of epicardial and microcirculatory involvement in IHD. Increasing interest and large clinical trials are expected to further strengthen the potential of advanced coronary physiology in interventional cardiology, consequently inducing reconsideration of current clinical guidelines.

Past, Present and Future of Coronary Physiology

It is well known that the apparent significant coronary stenosis on angiography sometimes does not cause significant ischemia, and vice versa. For this reason, decision-making based on coronary physiology is becoming more and more important. Fractional flow reserve (FFR), which has emerged as a useful tool to determine which lesions need revascularization in the catheterization laboratory, now has a class IA indication in the European Society of Cardiology guidelines. More recently, the instantaneous wave-free ratio, which is considered easier to use than FFR, has been graded as equivalent to FFR. This review discusses the concepts of FFR and instantaneous wave-free ratio, current evidence supporting their use, and future directions in coronary physiology.

Functional Approach for Coronary Artery Disease: Filling the Gap Between Evidence and Practice

The presence of myocardial ischemia is the most important prognostic factor in patients with coronary artery disease, and ischemia-directed revascularization has been a standard of care. Fractional flow reserve (FFR) is an invasive method used to detect the functionally significant epicardial coronary stenosis, and FFR-guided revascularization strategy has been proven to be superior to angiography-guided strategy. Recently, a hyperemia-free index, instantaneous wave free ratio (iFR), was developed and showed its non-inferiority for clinical outcomes compared with FFR-guided strategy. While evidence supporting the benefit of pressure wire assessment exists, there remain several unresolved issues, such as the mechanism of discordance between resting and hyperemic physiologic indices, clinical outcomes of patient/lesions with discordant results among the physiologic indices, role of physiologic indices beyond per-vessel decision tool, and the role of microvascular dysfunction in patient prognosis. The current article will review the recent studies performed to address these questions.

Invasive physiological indices to determine the functional significance of coronary stenosis

Physiological measurements are now commonly used to assess coronary lesions in the cardiac catheterisation laboratory, and this practice is evidence-based and supported by clinical guidelines. Fractional flow reserve is currently the gold standard method to determine whether coronary lesions are functionally significant, and is used to guide revascularization. There are however several other physiological measurements that have been proposed as alternatives to the fractional flow reserve. This review aims to comprehensively discuss physiological indices that can be used in the cardiac catheterisation laboratory to determine the functional significance of coronary lesions. We will focus on their advantages and disadvantages, and the current evidence supporting their use.

Discordance Between Fractional Flow Reserve and Coronary Flow Reserve: Insights From Intracoronary Imaging and Physiological Assessment

OBJECTIVES

The aim of this study was to investigate the epicardial and microvascular substrates associated with discordances between fractional flow reserve (FFR) and coronary flow reserve (CFR) values.

BACKGROUND

Discordances between FFR and CFR remain poorly characterized.

METHODS

FFR, hyperemic stenosis resistance (HSR), and intravascular ultrasound were performed as indexes of epicardial function and CFR and hyperemic microvascular resistance (HMR) as measures of microvascular function in 94 patients with moderate coronary stenosis. Maximal plaque burden (PB_max), HSR, and HMR were calculated in 4 quadrants based on values of FFR ≤0.80 and CFR ≤2.0 as follows: concordant normal (preserved FFR and CFR), concordant abnormal (low FFR and CFR), discordant low FFR and preserved CFR, and discordant preserved FFR and low CFR.

RESULTS

Sixty-four patients (68%) had concordant FFR and CFR findings, and 30 patients (32%) had discordant FFR and CFR. Compared with patients with preserved FFR and CFR, those with low FFR and CFR had higher PB_max (p = 0.003), higher HSR (p < 0.001), and similar HMR. Among patients with preserved FFR, those with reduced CFR had similar PB_max and HSR but a trend toward higher HMR (p = 0.058) compared with patients with preserved CFR. Among patients with reduced FFR, those with preserved CFR had lower PB_max (p = 0.004), a trend toward lower HSR (p = 0.065), and lower HMR (p = 0.03) compared with patients with reduced CFR. Furthermore, compared with patients with preserved FFR and low CFR, those with low FFR and preserved CFR had higher HSR (p = 0.022) but lower HMR (p = 0.003).

CONCLUSIONS

In patients with moderate coronary stenosis, preserved FFR and low CFR is associated with increased microvascular resistance, while low FFR and preserved CFR has modest epicardial stenosis and preserved microvascular function.

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.

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.

Targeting the dominant mechanism of coronary microvascular dysfunction with intracoronary physiology tests

The coronary microcirculation plays a key role in modulating blood supply to the myocardium. Several factors like myocardial oxygen demands, endothelial and neurogenic conditions determine its function. Although there is available evidence supporting microvascular dysfunction as an important cause of myocardial ischaemia, with both prognostic and symptomatic implications, its diagnosis and management in clinical practice is still relegated to a second plane. Both diagnostic and therapeutic approaches are hampered by the broadness of the concept of microvascular dysfunction, which fails addressing the plurality of mechanisms leading to dysfunction. Normal microcirculatory function requires both structural integrity of the microcirculatory vascular network and preserved signalling pathways ensuring adequate and brisk arteriolar resistance shifts in response to myocardial oxygen demands. Pathological mechanisms affecting these requirements include structural remodelling of microvessels, intraluminal plugging, extravascular compression or vasomotor dysregulation. Importantly, not every diagnostic technique provides evidence on which of these pathophysiological mechanisms is present or predominates in the microcirculation. In this paper we discuss the mechanisms of coronary microvascular dysfunction and the intracoronary tools currently available to detect it, as well as the potential role of each one to unmask the main underlying mechanism.

Clinical Outcomes of patients with coronary artery disease who underwent FFR evaluation of intermediate coronary lesionS- COFFRS study

Background

We undertook this study to validate the impact of FFR-guided coronary interventions among Indian patients, which is not readily available as of date. Our patients differ from their western counterparts, both in terms of risk profile (younger, more metabolic syndrome, lipid rich diet) as well as their coronary size.

Methods

We retrospectively evaluated 282 patients with intermediate stenosis in their coronary arteries, who underwent FFR to assess the functional severity of the lesion. There were 3 groups: Group 1–FFR > 0.8 and kept on medical follow-up; Group 2–FFR ≤ 0.8 and underwent revascularisation; and Group 3–FFR ≤ 0.8 and refused to undergo revascularization. 281(99.6%) patients had regular follow-up in our clinic.

Results

Median age-57 years (range = 28–78). Males = 230, 90 patients were in Group 1, 175 in group 2 (PCI in 144 & CABG in 31) and 17 in group 3. Median follow-up of patients was 17.9 months (2 to 56 months). Three patients(3.4%) in Group 1 had MACE (1 STEMI, 2 UA); 4 patients (2.3%) in Group 2 had Non-STE-ACS; 7 patients (41%) in Group 3 had MACE (3 deaths with acute LVF, 2 NSTEMI, 2 STEMI)

Conclusion

In our experience, MACE events were not higher in patients with FFR > 0.8 and kept under medical therapy and were similarly lower in patients with FFR ≤0.8 and underwent revascularisation (p = 0.73). Also MACE events were higher in patients with FFR ≤ 0.8 and did not undergo revascularisation compared to other two appropriately treated groups (p = 0.03). FFR based revascularization decision appears to be a safe strategy in Indian patients.

Effect of Sex Differences on Invasive Measures of Coronary Microvascular Dysfunction in Patients With Angina in the Absence of Obstructive Coronary Artery Disease

OBJECTIVES

This study investigated sex differences in coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR) in patients with angina in the absence of obstructive coronary artery disease.

BACKGROUND

Coronary microvascular dysfunction is associated with worse long-term outcomes, especially in women. Coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR) are 2 methods of assessing the coronary microcirculation.

METHODS

We prospectively enrolled 117 women and 40 men with angina in the absence of obstructive coronary artery disease. We performed CFR, IMR, fractional flow reserve, and quantitative coronary angiography in the left anterior descending artery. Coronary flow was assessed with a thermodilution method by obtaining mean transit time (Tmn) (an inverse correlate to absolute flow) at rest and hyperemia.

RESULTS

All patients had minimal atherosclerosis by quantitative coronary angiography (% diameter stenosis: 23.2 ± 12.3%), and epicardial disease was milder in women (fractional flow reserve: 0.88 ± 0.04 vs. 0.87 ± 0.04; p = 0.04). IMR was similar between the sexes (20.7 ± 9.8 vs. 19.1 ± 8.0; p = 0.45), but CFR was lower in women (3.8 ± 1.6 vs. 4.8 ± 1.9; p = 0.004). This was primarily due to a shorter resting Tmn in women (p = 0.005), suggesting increased resting coronary flow, whereas hyperemic Tmn was identical (p = 0.79). In multivariable analysis, female sex was an independent predictor of lower CFR and shorter resting Tmn.

CONCLUSIONS

Despite similar microvascular function in women and men by IMR, CFR is lower in women. This discrepancy appears to be due to differences in resting coronary flow between the sexes. The effect of sex differences should be considered in interpretation of physiological indexes using resting coronary flow.

Relation between fractional flow reserve value of coronary lesions with deferred revascularization and cardiovascular outcomes in non-diabetic and diabetic patients

BACKGROUND

FFR of deferred PCI lesions can predict future cardiovascular events. However, the prognostic utility of FFR remains unclear in diabetic patients in view of the potential impact of the diffuse nature of vascular disease process. We aimed to study the relation between fractional flow reserve (FFR) values and long-term outcomes of diabetic and non-diabetic patients with deferred percutaneous coronary intervention (PCI).

METHODS

Patients with FFR assessment and deferred PCI (n=630) were enrolled and stratified according to diabetes mellitus (DM) status and FFR values. Patients were followed over a median of 39months. Cox proportional hazard regression models were used to analyze the association between clinical endpoints and clinical factors such as DM and FFR.

RESULTS

In non-diabetics (n=450), higher FFR values were associated with less cardiovascular events (hazard ratio (HR) for death and myocardial infarction (MI) [95% confidence interval (CI)], 0.61[0.44 to 0.86] per 0.1 increase in FFR, p=0.007; HR for revascularization [95%CI], 0.66[0.49 to 0.9] per 0.1 increase in FFR, p=0.006). In diabetics (n=180), there was no difference in death and MI across the range of FFR values. Among those patients with an FFR >0.85, diabetics had a more than two-fold higher risk of death and MI than non-diabetics (HR [95% CI], 2.20 [1.19 to 4.01], p=0.015).

CONCLUSION

Among non-diabetic patients with deferred PCI, a higher FFR was associated with lower rates of death, MI and revascularization. On the contrary in diabetic patients with deferred revascularization, FFR was not able to differentiate the risk of cardiovascular events.

Fractional Flow Reserve: Does a Cut-off Value add Value?

Fractional flow reserve (FFR) has been shown to improve outcomes when used to guide percutaneous coronary intervention (PCI). There have been two proposed cut-off points for FFR. The first was derived by comparing FFR against a series of non-invasive tests, with a value of ≤0.75 shown to predict a positive ischaemia test. It was then shown in the DEFER study that a vessel FFR value of ≥0.75 was associated with safe deferral of PCI. During the validation phase, a 'grey zone' for FFR values of between 0.76 and 0.80 was demonstrated, where a positive non-invasive test may still occur, but sensitivity and specificity were sub-optimal. Clinical judgement was therefore advised for values in this range. The FAME studies then moved the FFR cut-off point to ≤0.80, with a view to predicting outcomes. The ≤0.80 cut-off point has been adopted into clinical practice guidelines, whereas the lower value of ≤0.75 is no longer widely used. Here, the authors discuss the data underpinning these cut-off values and the practical implications for their use when using FFR guidance in PCI.

Physiologic Assessment of Coronary Artery Disease: Focus on Fractional Flow Reserve

The presence of myocardial ischemia is the most important prognostic factor in patients with ischemic heart disease. Fractional flow reserve (FFR) is a gold standard invasive method used to detect the stenosis-specific myocardial ischemia. FFR-guided revascularization strategy is superior to angiography-guided strategy. The recently developed hyperemia-free index, instantaneous wave free ratio is being actively investigated. A non-invasive FFR derived from coronary CT angiography is now used in clinical practice. Due to rapid expansion of invasive and non-invasive physiologic assessment, comprehensive understanding of the role and potential pitfalls of each modality are required for its application. In this review, we focus on the basic and clinical aspects of physiologic assessment in ischemic heart disease.

Can Resting Indices Obviate the Need for Hyperemia and Promote the Routine Use of Physiologically Guided Revascularization?

This article assesses the data from contemporary human studies to address some of the common assumptions regarding hyperemic and baseline physiology in the context of the baseline pressure-derived index of instant wave-free ratio and the hyperemic index of fractional flow reserve. The article aims to determine if the available evidence supports the continued investigation, development, and use of baseline indices.

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.

Novel physiological insight into a lotus root appearance in stable coronary artery diseases; Report of two cases

So far physiological significance of multiple intraluminal channels separated by thin wall structures, so called "a lotus root appearance", in an angiographic insignificant lesion in patients with suspected angina pectoris has remained undetermined. Here we present two cases that showed a "reverse visual-functional mismatch" phenomenon of a lotus root appearance using the indexes of myocardial fractional flow reserve and/or coronary flow velocity reserve. Our findings may provide a novel physiological insight into a lotus root appearance as a high possibility of critical functional stenosis in those with stable coronary artery diseases.

Abnormal origins of the coronary arteries from the aortic root

Anomalous origin of a coronary artery from the aorta is a potentially serious anomaly that occurs in about 0.1-0.2% of the population. This percentage is small; however, it translates into about 4000 annual births with these anomalies. The clinical presentation of these anomalies is rare, and hence most are and will remain asymptomatic. The various anatomic anomalies are described, with anomalous origin of the left coronary artery that then passes between the aorta and pulmonary artery being the most serious of these anomalies. The pathophysiology resulting from these anomalies is described, as are methods for identifying those who require treatment; however, we still do not know the best methods of determining which patients need treatment.

Outcomes of coronary stenoses deferred revascularization for borderline versus nonborderline fractional flow reserve values

Current evidence supports deferral of revascularization for lesions with fractional flow reserve (FFR) values >0.80. The natural history after deferral of revascularization of lesions with borderline FFR values is unknown. This study evaluated the outcomes of patients after deferred revascularization of coronary stenoses based on a borderline FFR value. We retrospectively studied 720 patients with 881 intermediate-severity coronary stenoses who underwent FFR assessment from October 2002 to July 2010 and were deferred revascularization. Patients were divided into gray zone (0.75 to 0.80), borderline (0.81 to 0.85), and nonborderline (>0.85) FFR groups. Any subsequent percutaneous coronary intervention or coronary artery bypass grafting of a deferred stenosis during follow-up was classified as a deferred lesion intervention (DLI). Patient and/or lesion characteristics and clinical outcomes were compared between the FFR groups using univariate and propensity score-adjusted inverse probability of weighting Cox proportional hazards analyses. During a mean follow-up of 4.5 ± 2.1 years, 157 deferred lesions (18%) underwent DLI by percutaneous coronary intervention (n = 117) or coronary artery bypass grafting (n = 40). No statistically significant differences were observed in clinical outcomes between the gray zone and borderline FFR groups. Lesions with a borderline FFR were associated with a significantly higher risk of DLI compared with lesions with nonborderline FFR values (hazard ratio 1.63, 95% confidence interval 1.14 to 2.33, p = 0.007). Lesions deferred revascularization because of a borderline FFR (0.81 to 0.85) were associated with a higher risk of DLI compared with lesions with a nonborderline FFR (>0.85). Further study is needed to determine the optimal management of coronary stenoses with a borderline FFR value.

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.

Physiological basis and long-term clinical outcome of discordance between fractional flow reserve and coronary flow velocity reserve in coronary stenoses of intermediate severity

BACKGROUND

Discordance between fractional flow reserve (FFR) and coronary flow velocity reserve (CFVR) may reflect important coronary pathophysiology but usually remains unnoticed in clinical practice. We evaluated the physiological basis and clinical outcome associated with FFR/CFVR discordance.

METHODS AND RESULTS

We studied 157 intermediate coronary stenoses in 157 patients, evaluated by FFR and CFVR between April 1997 and September 2006 in which revascularization was deferred. Long-term follow-up was performed to document the occurrence of major adverse cardiac events: cardiac death, myocardial infarction, or target vessel revascularization. Discordance between FFR and CFVR occurred in 31% and 37% of stenoses at the 0.75, and 0.80 FFR cut-off value, respectively, and was characterized by microvascular resistances during basal and hyperemic conditions. Follow-up duration amounted to 11.7 years (Q1-Q3, 9.9-13.3 years). Compared with concordant normal results of FFR and CFVR, a normal FFR with an abnormal CFVR was associated with significantly increased major adverse cardiac events rate throughout 10 years of follow-up, regardless of the FFR cut-off applied. In contrast, an abnormal FFR with a normal CFVR was associated with equivalent clinical outcome compared with concordant normal results: ≤ 3 years when FFR <0.75 was depicted abnormal and throughout 10 years of follow-up when FFR ≤ 0.80 was depicted abnormal.

CONCLUSIONS

Discordance of CFVR with FFR originates from the involvement of the coronary microvasculature. Importantly, the risk for major adverse cardiac events associated with FFR/CFVR discordance is mainly attributable to stenoses where CFVR is abnormal. This emphasizes the requirement of intracoronary flow assessment in addition to coronary pressure for optimal risk stratification in stable coronary artery disease.

Increased hyperaemic coronary microvascular resistance adds to the presence of myocardial ischaemia

AIMS

It has been argued that hyperaemic microvascular resistance (HMR), defined as the ratio of mean distal coronary pressure to flow velocity, is overestimated in the presence of a coronary stenosis compared to actual microvascular resistance (MR), due to neglecting collateral flow. We aimed to test the hypothesis that HMR allows accurate identification of microvascular functional abnormalities by evaluating the association between high or low HMR and the presence of myocardial ischaemia on non-invasive stress testing.

METHODS AND RESULTS

Myocardial perfusion scintigraphy was performed in 228 patients, with 299 lesions to identify reversible myocardial ischaemia. Intracoronary distal pressure and flow velocity were assessed during adenosine-induced hyperaemia (20-40 µg, intracoronary) to determine hyperaemic stenosis resistance (HSR) and HMR. HMR >1.9 mmHg/cm/s was defined as high. The diagnostic odds ratio (OR) for myocardial ischaemia for lesions associated with high compared to low HMR was 2.6 (95% confidence interval [CI]: 1.5-4.4; p<0.001) overall, 3.3 (95% CI: 1.2-9.0; p=0.02) for lesions with HSR >0.8 mmHg/cm/s, and 1.3 (95% CI: 0.6-2.9; p=0.52) for lesions with HSR ≤0.8 mmHg/cm/s.

CONCLUSIONS

The increased risk of myocardial ischaemia in the presence of high HMR, uncorrected for collateral flow, demonstrates that HMR is reflective of an increase in actual MR, identifying pertinent pathophysiological alterations in the microvasculature.

Impact of hyperaemic microvascular resistance on fractional flow reserve measurements in patients with stable coronary artery disease: insights from combined stenosis and microvascular resistance assessment

BACKGROUND

Fractional flow reserve (FFR) aims to identify the extent of epicardial disease, but may be obscured by involvement of the coronary microvasculature. We documented the impact of hyperaemic stenosis resistance (HSR) and hyperaemic microvascular resistance (HMR) on FFR, and its relationship with myocardial ischaemia in patients with stable coronary artery disease.

METHODS AND RESULTS

We evaluated 255 coronary arteries with stenoses of intermediate severity by means of intracoronary pressure and flow measurements to determine FFR, HSR and HMR. Myocardial perfusion scintigraphy (MPS) was performed to identify inducible myocardial ischaemia. In 178 patients, HMR was additionally determined in a reference coronary artery. Target vessel HMR was stratified according to reference vessel HMR tertiles. The diagnostic OR for inducible ischaemia on MPS of a positive compared with a negative FFR was significantly higher only in the presence of a high HMR (at the 0.75 and 0.80 FFR cut-off). Among stenoses with a positive FFR, the prevalence of ischaemia was significantly higher when HMR was high despite equivalent FFR across the HMR groups. This was paralleled by a concomitant significant increase in HSR with increasing HMR across groups. The relation between FFR and HSR (r(2)=0.54, p<0.001) was modulated by the magnitude of HMR, and improved substantially after adjustment for HMR (adjusted-r(2)=0.73, p<0.001), where, for epicardial disease of equivalent severity, FFR increased with increasing HMR.

CONCLUSIONS

Identification of epicardial disease severity by FFR is partly obscured by the microvascular resistance, which illustrates the necessity of combined pressure and flow measurements in daily practice.