The Impact of Downstream Coronary Stenosis on Fractional Flow Reserve Assessment of Intermediate Left Main Coronary Artery Disease: Human Validation

ObjectivesThe aim of this study was to determine the impact of downstream coronary stenosis in the left anterior descending coronary artery (LAD) or left circumflex coronary artery (LCx) on the assessment of fractional flow reserve (FFR) across an intermediate left main coronary artery (LMCA) stenosis in humans with the pressure wire positioned in the nondiseased downstream vessel.BackgroundAccurate assessment of intermediate LMCA disease is critical for guiding decisions regarding revascularization. In theory, FFR across an intermediate LMCA stenosis will be affected by downstream disease, even if the pressure wire is positioned in the nondiseased downstream vessel.MethodsAfter percutaneous coronary intervention of the LAD, LCx, or both, an intermediate LMCA stenosis was created with a deflated balloon catheter. FFR was measured in the LAD and LCx coronary arteries before and after creation of downstream stenosis by inflating an angioplasty balloon within the newly placed stent. The true FFR (FFR_true) of the LMCA, measured in the nondiseased downstream vessel in the absence of stenosis in the other vessel, was compared with the apparent FFR (FFR_app) measured in the presence of stenosis.ResultsIn 25 patients, 91 pairs of measurements were made, 71 with LAD stenosis and 20 with LCx stenosis. FFR_true of the LMCA was significantly lower than FFR_app (0.81 ± 0.08 vs. 0.83 ± 0.08, p < 0.001), although the numerical difference was small. This difference correlated with the severity of the downstream disease (r = 0.35, p < 0.001). In all cases in which FFR_app was >0.85, FFR_true was >0.80.ConclusionsIn most cases, downstream disease does not have a clinically significant impact on the assessment of FFR across an intermediate LMCA stenosis with the pressure wire positioned in the nondiseased vessel.     

Diagnostic Accuracy of Myocardial Magnetic Resonance Perfusion to Diagnose Ischemic Stenosis With Fractional Flow Reserve as Reference: Systematic Review and Meta-Analysis

ObjectivesThis paper systematically analyzed the performance of magnetic resonance (MR) perfusion to diagnose coronary artery disease (CAD) with fractional flow reserve (FFR) as the reference standard.BackgroundMyocardial MR perfusion has passed the stage of a research technique and has demonstrated the ability to detect functional or ischemic stenosis of coronary arteries. However, the evidence is limited to single-center studies and small sample sizes.MethodsWe searched PubMed and Embase databases for all published studies that evaluated the accuracy of MR perfusion to diagnose CAD versus FFR. We used an exact binomial rendition of the bivariate mixed-effects regression model with test type as a random-effects covariate to synthesize the available data. Based on Bayes’ theorem, the post-test probability was calculated to guide MR perfusion’s clinical utility.ResultsWe identified 14 studies evaluating 1,073 arteries and 650 patients. The pooled sensitivity and specificity were 0.90 (95% confidence interval [CI]: 0.86 to 0.93) and 0.87 (95% CI: 0.82 to 0.90) at the patient level and 0.89 (95% CI: 0.83 to 0.92) and 0.86 (95% CI: 0.77 to 0.92) at the artery and territory levels, respectively. The area under the summary receiver-operating characteristic at the patient level was 0.95 (95% CI: 0.92 to 0.96) and 0.93 (95% CI: 0.91 to 0.95) at the artery and territory levels, respectively. MR perfusion could increase the post-test probability of CAD >80% in patients with a pre-test probability of >37% and can decrease post-test probability of CAD <20% with a pre-test probability of <72%.ConclusionsWith FFR as the reference standard, the diagnostic ability of MR perfusion to detect ischemic CAD is high.     

Intravascular Ultrasound-Derived Minimal Lumen Area Criteria for Functionally Significant Left Main Coronary Artery Stenosis

ObjectivesThis study sought to evaluate the intravascular ultrasound (IVUS) minimal lumen area (MLA) for functionally significant left main coronary artery (LMCA) stenosis using fractional flow reserve (FFR) as the standard.BackgroundThe evaluation of significant LMCA stenosis remains challenging.MethodsWe identified 112 patients with isolated ostial and shaft intermediate LMCA stenosis (angiographic diameter stenosis of 30% to 80%) who underwent IVUS and FFR measurement.ResultsThe FFR was ≤0.80 in 66 LMCA lesions (59%); these exhibited smaller reference vessels, smaller minimal lumen diameter, greater diameter of stenosis, longer lesion length, smaller MLA, larger plaque burden, and more frequent plaque rupture. The independent factors of an FFR of ≤0.80 were plaque rupture (odds ratio [OR]: 4.47; 95% Confidence Interval (CI): 1.35 to 14.8; p = 0.014); body mass index (OR: 1.19; 95% CI: 1.00 to 1.41; p = 0.05), age (OR: 0.95; 95% CI: 0.90 to 1.00; p = 0.031), and IVUS MLA (OR: 0.37; 95% CI: 0.25 to 0.56; p < 0.001). The optimal IVUS MLA cutoff value for an FFR of ≤0.80 was 4.5 mm² (77% sensitivity, 82% specificity, 84% positive predictive value, 75% negative predictive value, area under the curve: 0.83, 95% CI: 0.76 to 0.96; p < 0.001) overall and 4.1 to 4.5 mm² in various subgroups. Adjustment for the body surface area, body mass index, and left ventricular mass did not improve the diagnostic accuracy of the IVUS MLA.ConclusionsIn patients with isolated ostial and shaft intermediate LMCA stenosis, an IVUS-derived MLA of ≤4.5 mm² is a useful index of an FFR of ≤0.80.     

“Virtual” (Computed) Fractional Flow Reserve: Current Challenges and Limitations

Fractional flow reserve (FFR) is the “gold standard” for assessing the physiological significance of coronary artery disease during invasive coronary angiography. FFR-guided percutaneous coronary intervention improves patient outcomes and reduces stent insertion and cost; yet, due to several practical and operator related factors, it is used in <10% of percutaneous coronary intervention procedures. Virtual fractional flow reserve (vFFR) is computed using coronary imaging and computational fluid dynamics modeling. vFFR has emerged as an attractive alternative to invasive FFR by delivering physiological assessment without the factors that limit the invasive technique. vFFR may offer further diagnostic and planning benefits, including virtual pullback and virtual stenting facilities. However, there are key challenges that need to be overcome before vFFR can be translated into routine clinical practice. These span a spectrum of scientific, logistic, commercial, and political areas. The method used to generate 3-dimensional geometric arterial models (segmentation) and selection of appropriate, patient-specific boundary conditions represent the primary scientific limitations. Many conflicting priorities and design features must be carefully considered for vFFR models to be sufficiently accurate, fast, and intuitive for physicians to use. Consistency is needed in how accuracy is defined and reported. Furthermore, appropriate regulatory and industry standards need to be in place, and cohesive approaches to intellectual property management, reimbursement, and clinician training are required. Assuming successful development continues in these key areas, vFFR is likely to become a desirable tool in the functional assessment of coronary artery disease.     

Prevalence of Coronary Microvascular Dysfunction Among Patients With Chest Pain and Nonobstructive Coronary Artery Disease

ObjectivesThis study assessed the prevalence of coronary microvascular abnormalities in patients presenting with chest pain and nonobstructive coronary artery disease (CAD).BackgroundCoronary microvascular abnormalities mediate ischemia and can lead to an increased risk of cardiovascular events.MethodsUsing an intracoronary Doppler guidewire, endothelial-dependent microvascular function was examined by evaluating changes in coronary blood flow in response to acetylcholine, whereas endothelial-independent microvascular function was examined by evaluating changes in coronary flow velocity reserve in response to intracoronary adenosine. Patients were divided into 4 groups depending on whether they had a normal (+) or abnormal (−) coronary blood flow (CBF) in response to acetylcholine (Ach) and a normal (+) or abnormal (−) coronary flow velocity reserve (CFR) in response to adenosine (Adn): CBFAch+, CFRAdn+ (n = 520); CBFAch−, CFRAdn+ (n = 478); CBFAch+, CFRAdn− (n = 173); and CBFAch−, CFRAdn− (n = 268).ResultsTwo-thirds of all patients had some sort of microvascular dysfunction. Women were more prevalent in each group (56% to 82%). Diabetes was uncommon in all groups (7% to 12%), whereas hypertension and hyperlipidemia were relatively more prevalent in each group, although rates for most conventional cardiovascular risk factors did not differ significantly between groups. There were no significant differences in the findings of noninvasive functional testing between groups. In a multivariable analysis, age was the only variable that independently predicted abnormal microvascular function.ConclusionsPatients with chest pain and nonobstructive CAD have a high prevalence of coronary microvascular abnormalities. These abnormalities correlate poorly with conventional cardiovascular risk factors and are dissociated from the findings of noninvasive functional testing.     

Association of Epicardial Adipose Tissue With Progression of Coronary Artery Calcification Is More Pronounced in the Early Phase of Atherosclerosis: Results From the Heinz Nixdorf Recall Study

ObjectivesThis study sought to determine whether epicardial adipose tissue (EAT) volume predicts the progression of coronary artery calcification (CAC) score in the general population.BackgroundEAT predicts coronary events and is suggested to influence the development of atherosclerosis.MethodsWe included 3,367 subjects (mean age 59 ± 8 years; 47% male) from the population-based Heinz Nixdorf Recall study without known coronary artery disease at baseline. CAC was quantified from noncontrast cardiac electron beam computed tomography at baseline and after 5 years. EAT was defined as fat volume inside the pericardial sac and was quantified from axial computed tomography images. Association of EAT volume with CAC progression (log[CAC(follow-up) + 1] − log[CAC(baseline) + 1]) was depicted as percent progression of CAC + 1 per SD of EAT.ResultsSubjects with progression of CAC above the median had higher EAT volume than subjects with less CAC change (101.1 ± 47.1 ml vs. 84.4 ± 43.4 ml; p < 0.0001). In regression analysis, 6.3% (95% confidence interval [CI]: 2.3% to 10.4%; p = 0.0019) of progression of CAC + 1 was attributable to 1 SD of EAT, which persisted after adjustment for risk factors (6.1% [95% CI: 1.2% to 11.2%]; p = 0.014). For subjects with a CAC score of >0 to ≤100, progression of CAC + 1 by 20% (95% CI: 11% to 31%; p < 0.0001) was attributable to 1 SD of EAT. Effect sizes decreased with CAC at baseline, with no relevant link for subjects with a CAC score ≥400 (0.2% [95% CI: −3.5% to 4.2%]; p = 0.9). Likewise, subjects age <55 years at baseline showed the strongest association of EAT with CAC progression (20.6% [95% CI: 9.7% to 32.5%]; p < 0.0001). Interestingly, the effect of EAT on CAC progression was more pronounced in subjects with low body mass index (BMI), and decreased with degree of adiposity (BMI ≤25 kg/m²: 19.8% [95% CI: 9.2% to 31.4%]; p = 0.0001, BMI >40 kg/m²: 0.8% [95% CI: −26.7% to 38.9%]; p = 0.96).ConclusionsEAT is associated with the progression of CAC, especially in young subjects and subjects with low CAC score, suggesting that EAT may promote early atherosclerosis development.     

The 24-Month Prognosis of Patients With Positive or Intermediate Results in the Intracoronary Ergonovine Provocation Test

ObjectivesThis study was an observational, multicenter registry to determine clinical characteristics and 24-month prognosis of patients who underwent intracoronary ergonovine provocation tests.BackgroundThe clinical characteristics and prognosis of patients who underwent the ergonovine provocation for vasospastic angina were not fully elucidated.MethodsA total of 2,129 patients in the VA-KOREA (Vasospastic Angina in Korea) registry were classified into positive (n = 454), intermediate (n = 982), and negative (n = 693) groups by intracoronary ergonovine provocation tests. The 24-month incidences of cardiac death, new-onset arrhythmia, and acute coronary syndrome were determined (mean 26.7 ± 8.8 months).ResultsThe number of smokers, frequency of angina before angiography, high-sensitivity C-reactive protein, and triglyceride were higher in the positive group than in other groups. The clinical characteristics of the intermediate and the negative groups were very similar. In the positive group, the incidences of diffuse, focal, and mixed spasm were 65.9%, 23.6%, and 10.6%. Coronary spasm was more frequently provoked on atherosclerotic segments. The 24-month incidences of cardiac death, arrhythmia, and acute coronary syndrome were low (0.9%, 1.6%, and 1.9%, respectively) in the positive group, and there was no cardiac death in the intermediate group (p = 0.02). In the positive group, frequent angina, current smoking, and multivessel spasm were independent predictors for adverse events.ConclusionsThe 24-month prognosis of the positive group in the intracoronary ergonovine provocation test was relatively worse than that of the intermediate group. More intensive clinical attention should be paid to vasospastic angina patients with high-risk factors including frequent angina before angiography, current smoking, and multivessel spasm.     

Quantification of Myocardial Blood Flow in Absolute Terms Using 82Rb PET Imaging: The RUBY-10 Study

ObjectivesThe purpose of this study was to compare myocardial blood flow (MBF) and myocardial flow reserve (MFR) estimates from rubidium-82 positron emission tomography (⁸²Rb PET) data using 10 software packages (SPs) based on 8 tracer kinetic models.BackgroundIt is unknown how MBF and MFR values from existing SPs agree for ⁸²Rb PET.MethodsRest and stress ⁸²Rb PET scans of 48 patients with suspected or known coronary artery disease were analyzed in 10 centers. Each center used 1 of 10 SPs to analyze global and regional MBF using the different kinetic models implemented. Values were considered to agree if they simultaneously had an intraclass correlation coefficient >0.75 and a difference <20% of the median across all programs.ResultsThe most common model evaluated was the Ottawa Heart Institute 1-tissue compartment model (OHI-1-TCM). MBF values from 7 of 8 SPs implementing this model agreed best. Values from 2 other models (alternative 1-TCM and Axially distributed) also agreed well, with occasional differences. The MBF results from other models (e.g., 2-TCM and retention) were less in agreement with values from OHI-1-TCM.ConclusionsSPs using the most common kinetic model—OHI-1-TCM—provided consistent results in measuring global and regional MBF values, suggesting that they may be used interchangeably to process data acquired with a common imaging protocol.     

Fractional Flow Reserve in the Transradial Era: Will Hand Vein Adenosine Infusion Suffice?: A Comparative Study of the Extent,Rapidity, and Stability of Hyperemia From Hand and Femoral Venous Routes of Adenosine Administration

ObjectivesThe aim of this study was to assess adenosine infusion via a cannula in the back of the hand compared with central venous access to achieve peak hyperemia during fractional flow reserve (FFR).BackgroundAdenosine is often used to induce maximal hyperemia when measuring FFR. The gold standard is continuous infusion via a large central vein; however, the increasing use of the transradial route for angiography makes it desirable to have an alternative route for adenosine. Peripheral venous access is frequently obtained in the hand, but concern exists as to whether adenosine delivery from this site can achieve adequate vasodilation for accurate FFR measurement. Our aim was to address this.MethodsSubjects were selected from patients presenting for coronary angiography/intervention who required a pressure-wire study. Subjects received intravenous adenosine infusion sequentially via 2 routes: first, via a 20-gauge hand cannula, and then, after a washout period, via a 5- or 6-F femoral venous sheath. Adenosine was administered at 140 μg/kg/min from each site. Data interpretation was blinded. Minimal FFR achieved with intravenous adenosine from each infusion site was recorded as was the time to peak hyperemia.ResultsPaired (hand and femoral adenosine) recordings taken from 84 vessels in 61 patients were suitable for blinded analysis. The mean FFR measured using adenosine administered via hand and femoral routes was 0.85 with an SD of 0.08 (intraclass correlation = 0.986). Time to peak hyperemia was longer on average with hand-administered adenosine compared with femoral adenosine administration (63 s vs. 43 s; mean difference, 22 s with a 95% confidence interval: 18 s to 27 s; p < 0.0001). Formal comparison of FFR stability using Mann-Whitney analysis (2 tailed) gives p = 0.43, indicating no significant evidence of a difference in stability between the 2 routes.ConclusionsHand vein adenosine infusion produced FFR values very similar to those obtained using central femoral vein adenosine administration, with no systematic bias toward higher or lower reading from 1 site. This has important practical implications for radial access cases involving pressure-wire studies.     

Repeatability of Fractional Flow Reserve Despite Variations in Systemic and Coronary Hemodynamics

ObjectivesThis study classified and quantified the variation in fractional flow reserve (FFR) due to fluctuations in systemic and coronary hemodynamics during intravenous adenosine infusion.BackgroundAlthough FFR has become a key invasive tool to guide treatment, questions remain regarding its repeatability and stability during intravenous adenosine infusion because of systemic effects that can alter driving pressure and heart rate.MethodsWe reanalyzed data from the VERIFY (VERification of Instantaneous Wave-Free Ratio and Fractional Flow Reserve for the Assessment of Coronary Artery Stenosis Severity in EverydaY Practice) study, which enrolled consecutive patients who were infused with intravenous adenosine at 140 μg/kg/min and measured FFR twice. Raw phasic pressure tracings from the aorta (Pa) and distal coronary artery (Pd) were transformed into moving averages of Pd/Pa. Visual analysis grouped Pd/Pa curves into patterns of similar response. Quantitative analysis of the Pd/Pa curves identified the “smart minimum” FFR using a novel algorithm, which was compared with human core laboratory analysis.ResultsA total of 190 complete pairs came from 206 patients after exclusions. Visual analysis revealed 3 Pd/Pa patterns: “classic” (sigmoid) in 57%, “humped” (sigmoid with superimposed bumps of varying height) in 39%, and “unusual” (no pattern) in 4%. The Pd/Pa pattern repeated itself in 67% of patient pairs. Despite variability of Pd/Pa during the hyperemic period, the “smart minimum” FFR demonstrated excellent repeatability (bias −0.001, SD 0.018, paired p = 0.93, r² = 98.2%, coefficient of variation = 2.5%). Our algorithm produced FFR values not significantly different from human core laboratory analysis (paired p = 0.43 vs. VERIFY; p = 0.34 vs. RESOLVE).ConclusionsIntravenous adenosine produced 3 general patterns of Pd/Pa response, with associated variability in aortic and coronary pressure and heart rate during the hyperemic period. Nevertheless, FFR – when chosen appropriately – proved to be a highly reproducible value. Therefore, operators can confidently select the “smart minimum” FFR for patient care. Our results suggest that this selection process can be automated, yet comparable to human core laboratory analysis.     

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

ObjectivesThis 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.BackgroundCoronary 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.MethodsWe 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 (T_mn) (an inverse correlate to absolute flow) at rest and hyperemia.ResultsAll 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 T_mn in women (p = 0.005), suggesting increased resting coronary flow, whereas hyperemic T_mn was identical (p = 0.79). In multivariable analysis, female sex was an independent predictor of lower CFR and shorter resting T_mn.ConclusionsDespite 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.