Fractional Flow Reserve Assessment Research Articles

The influence of side branch stenosis on fractional flow reserve assessment of the main branch in a swine model.

The aim of this study was to explore the effect of one stenosis in a daughter artery on the fractional flow reserve (FFR) of another stenosis parallels in side branch. The impact of one stenosis on the FFR of another parallel stenosis has not been evaluated. The proximal segments of the left anterior descending (LAD) and left circumflex (LCX) arteries were exposed and encircled with a Teflon pledget complex in seven swine (55-70 kg). Five degrees of stenosis (to approximate angiographic diameter stenoses of 0%, 25%, 50%, 75%, and 100%) were made by tightening the pledgets. FFR was evaluated simultaneously in the LAD and the LCX with two pressure wires in each coronary artery. A mixed-effects linear model was used to evaluate the association between the FFR values. A total of 115 paired FFR values were obtained. The FFR of the LAD and LCX were not significantly associated with each other (F = 0.237 and P = 0.627 for the LCX FFR to predict the LAD FFR; F = 0.541 and P = 0.463 for the LAD FFR to predict the LCX FFR). The individual FFR values of each parallel stenosis in the LAD and the LCX were not significantly influenced by each other. This relationship was independent of the mean aortic pressure and heart rate. © 2016 Wiley Periodicals, Inc.

The Multi-center Evaluation of the Accuracy of the Contrast MEdium INduced Pd/Pa RaTiO in Predicting FFR (MEMENTO-FFR) Study.

Adenosine administration is needed for the achievement of maximal hyperaemia fractional flow reserve (FFR) assessment. The objective was to test the accuracy of Pd/Pa ratio registered during submaximal hyperaemia induced by non-ionic contrast medium (contrast FFR [cFFR]) in predicting FFR and comparing it to the performance of resting Pd/Pa in a collaborative registry of 926 patients enrolled in 10 hospitals from four European countries (Italy, Spain, France and Portugal). Resting Pd/Pa, cFFR and FFR were measured in 1,026 coronary stenoses functionally evaluated using commercially available pressure wires. cFFR was obtained after intracoronary injection of contrast medium, while FFR was measured after administration of adenosine. Resting Pd/Pa and cFFR were significantly higher than FFR (0.93±0.05 vs. 0.87±0.08 vs. 0.84±0.08, p<0.001). A strong correlation and a close agreement at Bland-Altman analysis between cFFR and FFR were observed (r=0.90, p<0.001 and 95% CI of disagreement: from -0.042 to 0.11). ROC curve analysis showed an excellent accuracy (89%) of the cFFR cut-off of ≤0.85 in predicting an FFR value ≤0.80 (AUC 0.95 [95% CI: 0.94-0.96]), significantly better than that observed using resting Pd/Pa (AUC: 0.90, 95% CI: 0.88-0.91; p<0.001). A cFFR/FFR hybrid approach showed a significantly lower number of lesions requiring adenosine than a resting Pd/Pa/FFR hybrid approach (22% vs. 44%, p<0.0001). cFFR is accurate in predicting the functional significance of coronary stenosis. This could allow limiting the use of adenosine to obtain FFR to a minority of stenoses with considerable savings of time and costs.

Comparison of Fractional Flow Reserve Assessment With Demand Stress Myocardial Contrast Echocardiography in Angiographically Intermediate Coronary Stenoses

Real-time myocardial contrast echocardiography (RTMCE) directly measures capillary flow (CBF), which in turn is a major regulator of coronary flow and resistance during demand or hyperemic stress. Although fractional flow reserve (FFR) was developed to assess the physiological relevance of an epicardial stenosis, it assumes maximal microvascular vasodilation and minimal resistance during vasodilator stress. Therefore, we sought to determine the relationship between CBF assessed with RTMCE during stress echocardiography and FFR in intermediate coronary lesions. Sixty-seven vessels with 50% to 80% diameter stenoses by quantitative coronary angiography in 58 consecutive patients were examined with FFR and RTMCE (mean age, 60±13 years). RTMCE was performed using an incremental dobutamine (n=32) or exercise (n=26) stress protocol, and myocardial perfusion was assessed using a continuous infusion of ultrasound contrast. The presence or absence of inducible perfusion defects and wall motion abnormalities were correlated with FFR. Mean percent diameter stenosis was 60±9%. Eighteen stenoses (27%) had an FFR ≤ 0.8. Although 17 of the 18 stenoses that were FFR+ had abnormal CBF during RTMCE, 28 of the 49 stenoses (57%) that were FFR had abnormal CBF, and 24 (49%) had abnormal wall motion in the corresponding coronary artery territory during stress echocardiography. In a significant percentage of intermediate stenoses with normal FFR values, CBF during demand stress is reduced, resulting in myocardial ischemia.

Effect of Fractional Flow Reserve (≤0.90 vs >0.90) on Long-Term Outcome (>10 Years) in Patients With Nonsignificant Coronary Arterial Narrowings

We assessed the long-term (>10years) clinical course of patients with documented coronary lesions deemed nonsignificant according to fractional flow reserve (FFR) assessment and investigated whether the initial FFR value impacted on prognosis. From January 2000 to October 2003, all patients submitted to coronary angiography with FFR measurement were included in a single-center, prospective registry. Patients with an FFR value >0.80 were treated medically without revascularization. Major adverse cardiac events (MACE) (death, acute coronary syndrome (ACS), or coronary revascularization) were compared according to initial FFR value (absolute value and by category, ≤0.90 vs >0.90). Analyses were performed using a multivariable Cox model and propensity score matching. Among 257 patients (332 lesions) treated medically initially, 131 (51%, 143 lesions) had FFR ≤0.90 and 126 (49%, 189 lesions) >0.90. During follow-up (median duration, 11.6years), 82 (31.9%) had a MACE, 38 (14.8%) died, 17 (6.6%) had ACS, 93 (36.2%) had repeat coronary angiography, and 27 (10.5%) had revascularization. There was no clinical, biologic or angiographic difference between patients with initial FFR value ≤0.90 versus >0.90. Adjusted Cox model showed no difference in relative risk of MACE, death, ACS, or revascularization. Coronary angiographies were numerically more frequent in patients with FFR ≤0.90, versus FFR >0.90. These findings were confirmed by propensity score-matched comparison. In patients with coronary narrowings left unrevascularized based on FFR, an FFR value between 0.80 and 0.90 has no impact on long-term outcome compared with those with FFR >0.90. In conclusion, patients with high FFR values should not be considered as having a lower risk of coronary event.

Impact of Routine Fractional Flow Reserve Evaluation During Coronary Angiography on Management Strategy and Clinical Outcome: One-Year Results of the POST-IT.

Penetration of fractional flow reserve (FFR) in clinical practice varies extensively, and the applicability of results from randomized trials is understudied. We describe the extent to which the information gained from routine FFR affects patient management strategy and clinical outcome. Nonselected patients undergoing coronary angiography, in which at least 1 lesion was interrogated by FFR, were prospectively enrolled in a multicenter registry. FFR-driven change in management strategy (medical therapy, revascularization, or additional stress imaging) was assessed per-lesion and per-patient, and the agreement between final and initial strategies was recorded. Cardiovascular death, myocardial infarction, or unplanned revascularization (MACE) at 1 year was recorded. A total of 1293 lesions were evaluated in 918 patients (mean FFR, 0.81±0.1). Management plan changed in 406 patients (44.2%) and 584 lesions (45.2%). One-year MACE was 6.9%; patients in whom all lesions were deferred had a lower MACE rate (5.3%) than those with at least 1 lesion revascularized (7.3%) or left untreated despite FFR≤0.80 (13.6%; log-rank P=0.014). At the lesion level, deferral of those with an FFR≤0.80 was associated with a 3.1-fold increase in the hazard of cardiovascular death/myocardial infarction/target lesion revascularization (P=0.012). Independent predictors of target lesion revascularization in the deferred lesions were proximal location of the lesion, B2/C type and FFR. Routine FFR assessment of coronary lesions safely changes management strategy in almost half of the cases. Also, it accurately identifies patients and lesions with a low likelihood of events, in which revascularization can be safely deferred, as opposed to those at high risk when ischemic lesions are left untreated, thus confirming results from randomized trials. URL: http://www.clinicaltrials.gov. Unique identifier: NCT01835808.

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

BackgroundFFR 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). MethodsPatients 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. ResultsIn 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). ConclusionAmong 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.

A machine-learning approach for computation of fractional flow reserve from coronary computed tomography.

Fractional flow reserve (FFR) is a functional index quantifying the severity of coronary artery lesions and is clinically obtained using an invasive, catheter-based measurement. Recently, physics-based models have shown great promise in being able to noninvasively estimate FFR from patient-specific anatomical information, e.g., obtained from computed tomography scans of the heart and the coronary arteries. However, these models have high computational demand, limiting their clinical adoption. In this paper, we present a machine-learning-based model for predicting FFR as an alternative to physics-based approaches. The model is trained on a large database of synthetically generated coronary anatomies, where the target values are computed using the physics-based model. The trained model predicts FFR at each point along the centerline of the coronary tree, and its performance was assessed by comparing the predictions against physics-based computations and against invasively measured FFR for 87 patients and 125 lesions in total. Correlation between machine-learning and physics-based predictions was excellent (0.9994, P < 0.001), and no systematic bias was found in Bland-Altman analysis: mean difference was -0.00081 ± 0.0039. Invasive FFR ≤ 0.80 was found in 38 lesions out of 125 and was predicted by the machine-learning algorithm with a sensitivity of 81.6%, a specificity of 83.9%, and an accuracy of 83.2%. The correlation was 0.729 (P < 0.001). Compared with the physics-based computation, average execution time was reduced by more than 80 times, leading to near real-time assessment of FFR. Average execution time went down from 196.3 ± 78.5 s for the CFD model to ∼2.4 ± 0.44 s for the machine-learning model on a workstation with 3.4-GHz Intel i7 8-core processor.

The influence of artery wall curvature on the anatomical assessment of stenosis severity derived from fractional flow reserve: a computational fluid dynamics study

This study aims to investigate the influence of artery wall curvature on the anatomical assessment of stenosis severity and to identify a region of misinterpretation in the assessment of per cent area stenosis (AS) for functionally significant stenosis using fractional flow reserve (FFR) as standard. Five artery models of different per cent AS severity (70, 75, 80, 85 and 90%) were considered. For each per cent AS severity, the angle of curvature of the arterial wall varied from straight to an increasingly curved model (0°, 30°, 60°, 90° and 120°). Computational fluid dynamics was performed under transient physiologic hyperemic flow conditions to investigate the influence of artery wall curvature on the pressure drop and the FFR. The findings in this study may be useful in in vitro anatomical assessment of functionally significant stenosis. The FFR decreased with increasing stenosis severity for a given curvature of the artery wall. Moreover, a significant decrease in FFR was found between straight and curved models discussed for a given severity condition. These findings indicate that the curvature effect was included in the FFR assessment in contrast to minimum lumen area (MLA) or per cent AS assessment. The MLA or per cent AS assessment may lead to underestimation of stenosis severity. From this numerical study, an uncertainty region could be evaluated using the clinical FFR cutoff value of 0.8. This value was observed at 81.98 and 79.10% AS for arteries with curvature angles of 0° and 120° respectively. In conclusion, the curvature of the artery should not be neglected in in vitro anatomical assessment.

PD/PA VARIATION PREVALENCE AND 2-HOUR REPEATABILITY DURING FRACTIONAL FLOW RESERVE ASSESSMENT

Variation of coronary/aortic (Pd/Pa) pressure during adenosine infusion has been recently emphasized. We aimed to assess Pd/Pa variation prevalence and repeatability during fractional flow reserve (FFR) assessment. We retrospectively analyzed data from 76 patients subjected to FFR assessment twice

CT myocardial perfusion and coronary CT angiography: Influence of coronary calcium on a stress–rest protocol

BackgroundHigh amounts of coronary artery calcium limit image quality and diagnostic accuracy of multidetector computed tomography (MDCT) angiography (CTA) regarding the assessment of obstructive coronary artery disease (CAD). CT myocardial perfusion imaging may represent an opportunity to overcome this limitation. ObjectiveTo explore the additive value of CT myocardial perfusion to CTA depending on the patient's calcium score and in comparison to the reference standard of invasive coronary angiography plus fractional flow reserve (FFR) measurement. MethodsSymptomatic patients with intermediate pretest probability of CAD were prospectively recruited and underwent both cardiac MDCT (64-slice scanner, retrospectively-gated stress–rest protocol) and invasive coronary angiography including FFR assessment. We defined hemodynamically significant CAD by the presence of occlusive or subocclusive (99%) stenosis, >50% stenosis in left main or FFR≤0.80. Stress CT myocardial perfusion imaging was performed in all patients in addition to CTA. The additive value of CT myocardial perfusion to rule in or rule out the presence of hemodynamically relevant stenosis on a per-patient basis was assessed and analyzed relative to the patient's calcium score. Results95 patients were included in the analysis (62 ± 8.2 years, 68%males). Hemodynamically significant CAD was present in 42 patients. Sixty-four patients had a fully evaluable CTA examination. Per-patient, CTA alone had a sensitivity, specificity and AUC of 100%, 59% and 0.79 respectively (77% patients correctly classified). Adding CT myocardial perfusion to evaluate uninterpretable vessel territories in CTA in 66 patients with a calcium score>100 yielded a sensitivity of 88%, a specificity of 74% and an AUC of 0.81 (81% patients correctly classified), and in 52 patients with a calcium score>400 sensitivity was 91%, specificity 70%, and AUC 0.80 (82% patients correctly classified, p = 0.733 versus using perfusion imaging in all patients). ConclusionsFrom a pragmatic standpoint, limiting the use of CT perfusion to individuals with a calcium score above 400 might be a feasible strategy to optimize the diagnostic accuracy of CT imaging for diagnosis of obstructive CAD.

Efficacy of combined administration of intracoronary papaverine plus intravenous adenosine 5′-triphosphate in assessment of fractional flow reserve

BackgroundInducing maximal coronary hyperemia is important to measure fractional flow reserve (FFR) accurately. Intravenous adenosine and adenosine 5′-triphosphate (ATP) have been used to achieve maximal hyperemia. However, they may not induce maximal hyperemia in all patients. The present study evaluated the combined effect of intracoronary papaverine and intravenous ATP on FFR measurements. MethodsFFR measurements with administration of intracoronary papaverine (12mg in the left coronary artery and 8mg in the right coronary artery), intravenous ATP (140μg/kg/min), and combined administration of intracoronary papaverine and intravenous ATP were performed in 51 patients with 57 intermediate lesions. ResultsThe mean FFR after intravenous ATP was higher compared to intracoronary papaverine and intravenous ATP plus intracoronary papaverine (0.76±0.13 vs. 0.75±0.13 vs. 0.75±0.13, p=0.01). FFR-positive lesions (FFR ≤0.80) were observed more frequently with intravenous ATP plus intracoronary papaverine compared to intravenous ATP (64.9% vs. 47.4%, p=0.02). Of 32 and 25 FFR-negative lesions with intravenous ATP and intracoronary papaverine, 11 (34%) and 7 (28%) had positive FFR after administration of intravenous ATP plus intracoronary papaverine. No ventricular tachycardia or ventricular fibrillation was observed after administration of intracoronary papaverine. ConclusionsMaximal hyperemia may not be induced with intravenous ATP in all lesions. When sufficient hyperemia is doubtful during intravenous infusion of ATP, additional intracoronary administration of papaverine may be a possible option.

0090: Comparison between non-invasive coronary flow reserve, instantaneous wave-free ratio, and fractional flow reserve, to assess the functional significance of LAD stenosis of intermediate severity

Assessment of the functional significance of left anterior descending coronary artery (LAD) stenosis of intermediate severity (IS) is challenging. A direct comparison of fractional flow reserve (FFR), instantaneous wave-free ratio (IFR), and non-invasive coronary flow reserve (CFR) has never been performed. Our objective was to test the usefulness of noninvasive CFR by comparison to invasive FFR and IFR in patients with LAD stenosis of angiographic IS and stable coronary artery disease. 58 stable consecutive patients (mean age, 68±10 years; with angiographic proximal or mid LAD stenosis of IS (40-70% diameter stenosis on quantitative coronary angiography), no previous anterior myocardial infarction, were prospectively studied. They underwent iFR which was calculated as a trans-lesion pressure ratio during a specific period of baseline diastole, FFR with intracoronary bolus adenosine (150μg), and CFR using intravenous adenosine (140μg/kg/min over 2min) in the distal part of the LAD, the same day. CFR was defined as hyperemic peak diastolic LAD flow velocity divided by baseline flow velocity, and FFR was defined as distal pressure divided by mean aortic pressure during maximal hyperemia. The mean values of iFR, FFR, and CFR were 0.88±0.07, 0.81±0.08, and 2.4±0.6 respectively. A significant correlation was found between CFR and FFR (r=0.72, curvilinear relationship), FFR and IFR (r=0.63, linear relationship), and between CFR and IFR (r=0.44) (all, p<0.01). Using a ROC curve analysis, the best cut-off to detect a significant lesion based on FFR assessment (FFR <0.8, n=16) was iFR ≤0.86 with a sensitivity (Se) of 75%, specificity (Sp) of 81%, AUC 0.8±0.05; and CFR ≤2 with a Se of 82%, Sp of 85%, AUC 0.9±0.03, (all, p<0.001). Based on these cut-offs, discordant results between CFR and FFR were observed in 9 cases (accuracy 84%), between CFR and iFR in 14 cases (accuracy 76%), and between iFR and FFR in 11 cases (accuracy 81%). In stable patients with LAD stenosis of IS, non-invasive CFR is a useful tool to detect a significant lesion based on FFR. Furthermore, CFR is better correlated to FFR than to iFR, and its accuracy seems as good as iFR in this setting.

Fractional Flow Reserve Assessment of Coronary Artery Stenosis.

Objective proof of focal lesions is mandatory, and the best invasive method of physiological testing is fractional flow r eserve (FFR). The increased trans-stenotic gradient is measured via the guiding catheter and pressure transducer on a 0.014" coronary wire at maximal hyperaemia induced by adenosine. Patients with a FFR of less than 0.8 should undergo myocardial revascularisation by percutaneous coronary intervention or coronary artery bypass graft, particularly if the proximal and middle segments of the main coronary arteries and large side-branches are affected; there is no prognostic revascularisation benefit in patients with moderate stenoses and FFR greater than 0.80. FFR assessment of coronary lesions is superior to other invasive morphological studies, such as intracoronary ultrasound or optical coherence tomography. Its use in non-culprit vessels in acute coronary syndromes is currently under scrutiny. Recent advances in computed tomographic technique allow non-invasive assessment of FFR, but clinical validation has yet to be obtained.

Fractional Flow Reserve Assessment of a Significant Coronary Stenosis Masked by a Downstream Serial Lesion.

Fractional flow reserve (FFR) has been recognized as an effective tool to determine functional significance in intermediate coronary lesions and FFR-guided percutaneous coronary intervention (PCI) improves clinical outcomes. However, hemodynamic interaction between serial stenoses within one coronary artery complicates the assessment of functional severity of each individual lesion. We present a case in which FFR measurement by intracoronary bolus injection of adenosine helps to make appropriate revascularization decision in serial stenoses when the procedures are performed systemically and properly.

CT-based myocardial ischemia evaluation: quantitative angiography, transluminal attenuation gradient, myocardial perfusion, and CT-derived fractional flow reserve.

The detection of hemodynamically significant stenosis is important because ischemia-guided revascularization improves overall patient outcomes. Fractional flow reserve (FFR), which is measured during invasive coronary angiography, is regarded as the gold standard for determining hemodynamically significant coronary stenosis. Although coronary computed tomography angiography (CCTA) has been widely used to exclude significant coronary artery disease in patients with low to intermediate pretest probability, anatomic assessment by CCTA using diameter stenosis ≥50% does not correlate well with the functional assessment of FFR. To overcome the weaknesses of conventional CCTA, such as its low specificity and positive predictive value, especially in patients with a small-diameter artery, poor image quality, or high calcium score, more sophisticated CCTA analysis methods have been developed to detect hemodynamically significant coronary stenosis. Studies that use the quantification of coronary plaque, transluminal attenuation gradient (TAG), CT myocardial perfusion (CTP), and CT-derived FFR have been conducted to validate their diagnostic performances, though each method has its pros and cons. This review provides details on the quantification of coronary plaque, TAG, CTP, and CT-derived FFR, including a definition of each, how to gather and interpret data, and the strengths and limitations of each. Further, we provide an overview of recent clinical studies.

Fractional Flow Reserve Assessment of a Coronary Artery Fistula

&lt;p&gt;Petit J., Assadi R., and Hilliard A. Fractional Flow Reserve Assessment of a Coronary Artery Fistula. International Cardiovascular Forum Journal. 2015;4:64-65 DOI: 10.17987/icfj.v4i0.123&lt;/p&gt;

Association between fractional flow reserve and coronary plaque characteristics assessed by optical coherence tomography

BackgroundThe assessment of fractional flow reserve (FFR) in coronary lesions determines the strategy of percutaneous coronary intervention. However, the association between FFR and characteristics of the underlying coronary plaque has not been sufficiently investigated. MethodsA total of 110 coronary lesions in 106 patients were evaluated using both FFR and optical coherence tomography (OCT). Coronary plaques were classified into fibrous, fibrocalcific, or fibroatheroma according to OCT evaluation at the site of minimal lumen area. Plaque microstructures such as cap thickness, macrophage accumulation, intimal vasculature, or cholesterol crystals were also evaluated. ResultsLesions with FFR≤0.8 showed a higher frequency of fibroatheroma, macrophage accumulation, and cholesterol crystals when compared to those with FFR>0.8. The angle of lipid was wider in lesions with FFR≤0.8 (145.1±63.0° vs. 120.7±48.9°, p=0.047), and the longitudinal length was longer in those with FFR≤0.8 (4.2±2.8mm vs. 2.5±2.9mm, p=0.007). However, multiple linear regression analysis revealed that the morphological characteristics of plaques assessed by OCT were not independently associated with FFR. Minimal lumen area [coefficient, 0.035; 95% confidence interval (CI), 0.022–0.048; p<0.001] and area stenosis (coefficient, −0.003; 95% CI, −0.005 to −0.001; p=0.001) assessed by OCT significantly correlated with FFR. ConclusionThe morphological characteristics of coronary plaque derived from OCT are not directly related to FFR.

Abstract 10860: Association Between Fractional Flow Reserve and Coronary Plaque Characteristics Assessed by Optical Coherence Tomography

Introduction: The assessment of fractional flow reserve (FFR) in coronary lesions determines the strategy of percutaneous coronary intervention. However, the association between FFR and characteristics of underlying coronary plaque has not been sufficiently investigated. Methods: A total of 110 coronary lesions in 106 patients were evaluated using both FFR and optical coherence tomography (OCT). Coronary plaque was classified into fibrous, fibrocalcific, or fibroatheroma according to OCT evaluation at the site of minimal lumen area. Plaque microstructures such as cap thickness, macrophage accumulation, intimal vasculature, or cholesterol crystal were also evaluated. Results: Compared to lesions with FFR &gt;0.8, those with FFR ≤0.8 showed a higher frequency of fibroatheroma, macrophage accumulation, and cholesterol crystal. However, multiple linear regression analysis revealed that any morphological characteristics of plaques assessed by OCT were not independently associated with FFR. Minimal lumen area (coefficient, 0.036; 95% confidence interval [CI], 0.022-0.049; p&lt;0.001) and area stenosis (coefficient, - 0.003; 95% CI, -0.005--0.001; p&lt;0.001) assessed by OCT significantly correlated with FFR. Thin-cap fibroatheroma was identified in 12 (10.9%) of all 110 lesions. There were no significant differences of minimal lumen area, area stenosis, or FFR between lesions with and without thin-cap fibroatheroma. Conclusions: Morphological characteristics of coronary plaque are not directly related to FFR. Conversely, the extent of functional or anatomical stenosis cannot identify the lesion with thin-cap fibroatheroma.

Abstract 19177: Loss of Coronary Perfusion Efficiency in Microvascular Disease

Introduction: Coronary Microvascular Disease (MVD) is associated with an unfavorable prognosis, even in the absence of significant epicardial disease. The pathophysiological basis of increased cardiac events is unclear. The aim of this study was to characterize the forces that govern myocardial perfusion at rest and during stress. Methods: Patients with chest pain syndromes requiring Fractional Flow Reserve (FFR) assessment were screened and those with a FFR&gt;0.80 were included. MVD was defined by coronary flow reserve (CFR) &lt; 2.0. Controls were those with CFR&gt;2.0. Simultaneous intracoronary pressure (P d ) and flow velocity (U) recordings were made at rest and hyperemia. Microvascular Resistance (MR)= P d /U. Wave intensity = dP d /dt x dU/dt and wave separation analysis was used to identify the waves that accelerate and decelerate flow. The proportional contribution of accelerating waves was assessed as an index of coronary perfusion efficiency. Results: 39 consecutive patients were enrolled, 21 had MVD and 18 comprised controls. The groups were matched for atherosclerotic risk factors, rate-pressure-product and P d . Coronary flow velocity in MVD patients was higher at rest (21.5±6.4 vs. 14.1±4.5cms -1 , p &lt; 0.001) but lower during hyperemia (28.3±13.0 vs. 45.1±13.1cms -1 , p &lt; 0.001) compared to controls. While resting MR was lower in MVD (501±162 vs. 755±262 mmHg.cm -1 .s, p = 0.001), hyperemic MR was significantly lower in controls. At rest the magnitude of the accelerating waves was higher in the MVD group than controls. The percentage contribution of accelerating waves increased with hyperemia in controls but decreased in MVD patients (figure). Conclusion: MVD manifests as resting microvascular dilation as well as diminished response to stress. While the normal heart has improved efficiency during hyperemia, in MVD efficiency decreases and as a result, flow augmentation is attenuated. These processes render the myocardium more susceptible to ischemia.

Combining Baseline Distal-to-Aortic Pressure Ratio and Fractional Flow Reserve in the Assessment of CoronaryStenosis Severity.

This study sought to understand the physiological basis of baseline distal-to-aortic pressure ratio (Pd/Pa) and fractional flow reserve (FFR) agreement and discordance, using coronary flow reserve (CFR), stenosis resistance, and microcirculatory resistance measurements, and form there, to investigate the potential value of combining Pd/Pa with FFR in the diagnostic rationale. Pd/Pa is always available before FFR assessment, and emerging data supports the notion that baseline indices can determine the ischemic potential of coronary stenosis in selected subsets. A total of 467 stenosed vessels from 363 patients were investigated with pressure and flow sensors during baseline and hyperemia: 168 vessels (135 patients) with thermodilution-derived flow, and 299 vessels (228 patients) with Doppler-derived flow. Pd/Pa correlated more strongly with CFR than FFR (ρ difference= 0.129; p for ρ comparison<0.001). Although Pd/Pa and FFR were closely correlated (ρ= 0.798; 95% confidence interval: 0.767 to 0.828), categorical discordance was observed in 19.3% of total vessels. Such discordance was associated with the patients' clinical profile and was characterized by contrastive changes in stenosis resistance, microcirculatory resistance, and the underlying CFR. Notably, all stenosis with Pd/Pa≤0.83 (n= 74, 15.8%) progressed to FFR≤0.80, and although no Pd/Pa cutoff was able to exclude the development of FFR≤0.80 in the high end of values, only 15 (10.1%) vessels with Pd/Pa≥0.96 (n=149,31.9%) developed FFR≤0.80, from which none had definite ischemia, as defined by CFR≤1.74. Combining baseline Pd/Pa with FFR seems to provide a more comprehensive physiological examination of stenosed coronary arteries and a closer pressure-based appraisal of the flow reserve of the downstream myocardialbed.