Role of fractional and coronary flow reserve in clinical decision making in intermediate coronary lesions

Impact of core laboratory assessment on treatment decisions and clinical outcomes using combined fractional flow reserve and coronary flow reserve measurements - DEFINE-FLOW core laboratory sub-study

OBJECTIVE

The role of combined FFR/CFR measurements in decision-making on coronary revascularization remains unclear. DEFINE-FLOW prospectively assessed the relationship of FFR/CFR agreement with 2-year major adverse cardiac event (MACE) and target vessel failure (TVF) rates, and uniquely included core-laboratory analysis of all pressure and flow tracings. We aimed to document the impact of core-laboratory analysis on lesion classification, and the relationship between core-laboratory fractional flow reserve (FFR) and coronary flow reserve (CFR) values with clinical outcomes and angina burden during follow-up.

METHODS

In 398 vessels (348 patients) considered for intervention, ≥1 coronary pressure/flow tracing was approved by the core-laboratory. Revascularization was performed only when both FFR(≤0.80) and CFR(<2.0) were abnormal, all others were treated medically.

RESULTS

MACE was lowest for concordant normal FFR/CFR, but was not significantly different compared with either discordant group (low FFR/normal CFR: HR:1.63; 95%CI:0.61-4.40; P = 0.33; normal FFR/low CFR: HR:1.81; 95%CI:0.66-4.98; P = 0.25). Moreover, MACE did not differ between discordant groups treated medically and the concordant abnormal group undergoing revascularization (normal FFR/low CFR: HR:0.63; 95%CI:0.23-1.73;P = 0.37; normal FFR/low CFR: HR:0.70; 95%CI:0.22-2.21;P = 0.54). Similar findings applied to TVF.

CONCLUSIONS

Patients with concordantly normal FFR/CFR have very low 2-year MACE and TVF rates. Throughout follow-up, there were no differences in event rates between patients in whom revascularization was deferred due to preserved CFR despite reduced FFR, and those in whom PCI was performed due to concordantly low FFR and CFR. These findings question the need for routine revascularization in vessels showing low FFR but preserved CFR.

CLINICAL TRIAL REGISTRATION

http://ClinicalTrials.govNCT02328820.

Genotyping of interleukins-18 promoters and their correlation with coronary artery stenosis in Saudi population

BACKGROUND

Complex coronary atherosclerotic lesions often lead to coronary occlusion, clinically represented as a single-vessel disease (SVD) and multivessel disease (MVD). These occlusions could hinder the blood flow in coronary arteries that affects appropriate management of the CVD. The current study intended to genotype interleukin (IL)-18 promoter's hotspots (rs187238, rs1946518, and rs1946519) and their possible association with coronary artery stenosis.

MATERIAL AND METHODS

The IL-18 promoter genotyping was performed by the Sanger method along with the examination of biochemical parameters in 125 study subjects categorized into three groups, viz. controls, SVD and MVD.

RESULTS

The current study observed a significant association of diabetes, hypertension, and dyslipidemia between the studied group's viz. healthy controls, SVD, and MVD. Fasting blood sugar and glycosylated hemoglobin (HBA1C) were also significantly enhanced from 4.82 vs. 8.01 and 4.33 vs. 8.27, in SVD, and MVD respectively. Despite the visible differences in the pattern of genotypic and allelic expressions, the current study did not show any statistically significant correlation with IL-18 promoter polymorphism at its hotspots with controls, SVD, and MVD subjects. The only exception of the above results was the distribution of allelic frequency at the rs1946519 hotspot, where a significant change (P < 0.05) was observed.

CONCLUSION

This study is of additional value to our previous reports, revealing the pattern of genotypes and allelic frequency of IL-18 promoters in a small cohort of Saudi ethnicity. Further investigations on larger sample size are recommended to envisage the presence of functional mutations in the IL-18 gene that could establish or rule out the possible association of IL-18 polymorphism with SVD and MVD.

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.

Objective Identification of Intermediate Lesions Inducing Myocardial Ischemia Using Sequential Intracoronary Pressure and Flow Measurements

Background

Although ischemic heart disease has a complex and multilevel origin, the diagnostic approach is mainly focused on focal obstructive disease as assessed by pressure‐derived indexes. The prognostic relevance of coronary flow over coronary pressure has been suggested and implies that identification of relevant perfusion abnormalities by invasive physiology techniques is critical for the correct identification of patients who benefit from coronary revascularization. The purpose of this study was to evaluate the diagnostic potential of a sequential approach using pressure‐derived indexes instantaneous wave‐free ratio (iFR), fractional flow reserve (FFR), and coronary flow reserve (CFR) measurements to determine the number of intermediate lesions associated with flow abnormalities after initial pressure measurements.

Methods and Results

A total of 366 intermediate lesions were assessed with simultaneous intracoronary pressure and flow velocity measurements. Contemporary clinical iFR, FFR, and CFR cut points for myocardial ischemia were applied. A total of 118 (32%) lesions were FFR+ and 136 (37%) lesions were iFR+. Subsequent CFR assessment resulted for FFR in a total of 91 (25%) FFR+/CFR+ and for iFR a total of 111 (30%) iFR+/CFR+ lesions. An iFR, FFR, and invasive flow velocity assessment approach would have yielded 20% of lesions (74 of 366) as ischemic.

Conclusions

Ultimately, 20% of intermediate lesions are associated with flow abnormalities after applying a pressure and flow velocity sequential approach. If iFR is borderline, FFR has limited additional value, in contrast with CFR. These results emphasize the use of coronary physiology in assessing stenosis severity but may also further question the contemporary reputation of a pressure‐based approach as a gold standard for the detection of myocardial ischemia in ischemic heart disease.

Time course of coronary flow capacity impairment in ST-segment elevation myocardial infarction

BACKGROUND

Microvascular dysfunction in the setting of ST-elevated myocardial infarction (STEMI) plays an important role in long-term poor clinical outcome. Coronary flow reserve (CFR) is a well-established physiological parameter to interrogate the coronary microcirculation. Together with hyperaemic average peak flow velocity, CFR constitutes the coronary flow capacity (CFC), a validated risk stratification tool in ischaemic heart disease with significant prognostic value. This mechanistic study aims to elucidate the time course of the microcirculation as reflected by alterations in microcirculatory physiological parameters in the acute phase and during follow-up in STEMI patients.

METHODS

We assessed CFR and CFC in the culprit and non-culprit vessel in consecutive STEMI patients at baseline (n = 98) and after one-week (n = 64) and six-month follow-up (n = 65).

RESULTS

A significant trend for culprit CFC in infarct size as determined by peak troponin T (p = 0.004), time to reperfusion (p = 0.038), the incidence of final Thrombolysis In Myocardial Infarction 3 flow (p = 0.019) and systolic retrograde flow (p = 0.043) was observed. Non-culprit CFC linear contrast analysis revealed a significant trend in C-reactive protein (p = 0.027), peak troponin T (p < 0.001) and heart rate (p = 0.049). CFC improved both in the culprit and the non-culprit vessel at one-week (both p < 0.001) and six-month follow-up (p = 0.0013 and p < 0.001) compared with baseline.

CONCLUSION

This study demonstrates the importance of microcirculatory disturbances in the setting of STEMI, which is relevant for the interpretation of intracoronary diagnostic techniques which are influenced by both culprit and non-culprit vascular territories. Assessment of non-culprit vessel CFC in the setting of STEMI might improve risk stratification of these patients following coronary reperfusion of the culprit vessel.

Stress Echocardiography in the Era of Fractional Flow Reserve

Purpose of Review

It is the aim of this review to demonstrate the relevance of stress echocardiography in the era of fractional flow reserve by establishing the current use of stress echocardiography and fractional flow reserve, underlining their physiological basis and through this demonstrating the clear differences in their application.

Recent Findings

The importance of the microcirculation is only now being understood, no more so than in the fact that abnormalities in the microcirculation, determined by abnormal coronary flow reserve, predict adverse mortality regardless of the normality of the epicardial coronary lesions. Stress echocardiography therefore gives a fuller picture of the overall cardiovascular risk to our patients in its ability to interrogate the epicardial vessels down to the microcirculation, with a number of techniques available to measure coronary flow reserve such as myocardial perfusion stress echocardiography and transthoracic Doppler stress echocardiography of epicardial coronary vessels. Fractional flow reserve can then add further information by determining whether a coronary artery lesion is responsible for myocardial ischaemia.

Summary

In an era of fractional flow reserve affording the resolution of myocardial ischaemia down to the specific lesion, it can be tempting to think that other generally non-invasive techniques no longer have a role in the investigation and management of coronary artery disease. This, however, betrays a lack of understanding of the scope and complexity of coronary artery disease from epicardial vessels down to the microvasculature, the physiological basis of the tests available and therefore what, in fact, is actually being measured. For some, fractional flow reserve is held as a gold standard by which to compare other techniques such as stress echocardiography as correct or incorrect. However, these tests do not measure the same thing, and therefore, they cannot be directly compared. Stress echocardiography gives a fuller picture through its ability to account for the coronary flow reserve, considering the epicardial vessels down to the microvasculature. Fractional flow reserve is far more specific, looking at the effect of the lesion being interrogated. Furthermore, where fractional flow reserve is normal, we now know that knowledge of the coronary flow reserve is critical as it is this that allows us to predict the overall mortality risk of our patient. We therefore require a combination of the two techniques.

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.

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.

Coronary flow capacity: concept, promises, and challenges

The vasodilator capacity of the coronary circulation is an important diagnostic and prognostic characteristic, and its accurate assessment is therefore an important frontier. The coronary flow capacity (CFC) concept was introduced to overcome the limitations associated with the use of coronary flow reserve (CFR) for this purpose, which are related to the sensitivity of CFR to physiological alterations in systemic and coronary hemodynamics. CFC was developed from positron emission tomography, and was subsequently extrapolated to invasive coronary physiology. These studies suggest that CFC is a robust framework for the identification of clinically relevant coronary flow abnormalities, and improves identification of patients at risk for adverse events over the use of CFR alone. This Review will discuss the concept of CFC, its promises in the setting of ischaemic heart disease, and its challenges both in theoretical and practical terms.

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

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

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.

Coronary wave intensity during the Valsalva manoeuvre in humans reflects altered intramural vessel compression responsible for extravascular resistance

Our aim was to investigate the effect of altered cardiac-coronary interaction during the Valsalva manoeuvre (VM) on coronary wave intensity and the response of coronary microvascular resistance. In 13 patients, left ventricular (P(LV)) and aortic pressure were measured during catheterization, together with intracoronary pressure and blood flow velocity (U) via a dual-sensor guide wire advanced into an angiographically normal coronary artery. Signals were analysed for the following phases of VM: baseline (B1), onset of strain (S1), sustained strain (S2), onset of release (R1), maximal response during recovery (R2), and baseline after VM. The immediate effects of VM were most evident from diastolic P(LV) (LVDP), which increased from 11.0 ± 2.3 to 36.4 ± 2.7 mmHg between B1 and S1 and fell from 28.3 ± 3.4 to 8.3 ± 1.9 mmHg between S2 and R1. Wave intensities and rate pressure product (RPP) were only minimally affected at these transient phases, but coronary wave energies decreased by about 50% and RPP by 38% from S1 to S2, together with a 30% depression of LVdP/dt. All signals were restored to baseline values during the recovery. U did not vary significantly throughout the VM. Despite the depressed cardiac performance during VM strain, microvascular resistance, calculated with LVDP as backpressure, decreased by 31% from B1 to S2, whereas an increase via metabolically induced vasoconstriction was expected. Since coronary U remained essentially constant despite the marked reduction in oxygen consumption, microvascular vasoconstriction must have been compensated by a decrease in the contraction-mediated impediment on coronary blood flow, as confirmed by the reduced coronary wave energies.

Coronary pressure-flow relations as basis for the understanding of coronary physiology

Recent technological advancements in the area of intracoronary physiology, as well as non-invasive contrast perfusion imaging, allow to make clinical decisions with respect to percutaneous coronary interventions and to identify microcirculatory coronary pathophysiology. The basic characteristics of coronary hemodynamics, as described by pressure-flow relations in the normal and diseased heart, need to be understood for a proper interpretation of these physiological measurements. Especially the hyperemic coronary pressure-flow relation, as well as the influence of cardiac function on it, bears great clinical significance. The interaction of a coronary stenosis with the coronary pressure-flow relation can be understood from the stenosis pressure drop-flow velocity relationship. Based on these relationships the clinically applied concepts of coronary flow velocity reserve, fractional flow reserve, stenosis resistance and microvascular resistance are discussed. Attention is further paid to the heterogeneous nature of myocardial perfusion, the vulnerability of the subendocardium and the role of collateral flow on hyperemic coronary pressure-flow relations. This article is part of a Special Issue entitled "Coronary Blood Flow".