CT Attenuation of Pericoronary Adipose Tissue in Normal Versus Atherosclerotic Coronary Segments as Defined by Intravascular Ultrasound

Perivascular adipose tissue as a source of therapeutic targets and clinical biomarkers

Obesity is a modifiable cardiovascular risk factor, but adipose tissue (AT) depots in humans are anatomically, histologically, and functionally heterogeneous. For example, visceral AT is a pro-atherogenic secretory AT depot, while subcutaneous AT represents a more classical energy storage depot. Perivascular adipose tissue (PVAT) regulates vascular biology via paracrine cross-talk signals. In this position paper, the state-of-the-art knowledge of various AT depots is reviewed providing a consensus definition of PVAT around the coronary arteries, as the AT surrounding the artery up to a distance from its outer wall equal to the luminal diameter of the artery. Special focus is given to the interactions between PVAT and the vascular wall that render PVAT a potential therapeutic target in cardiovascular diseases. This Clinical Consensus Statement also discusses the role of PVAT as a clinically relevant source of diagnostic and prognostic biomarkers of vascular function, which may guide precision medicine in atherosclerosis, hypertension, heart failure, and other cardiovascular diseases. In this article, its role as a 'biosensor' of vascular inflammation is highlighted with description of recent imaging technologies that visualize PVAT in clinical practice, allowing non-invasive quantification of coronary inflammation and the related residual cardiovascular inflammatory risk, guiding deployment of therapeutic interventions. Finally, the current and future clinical applicability of artificial intelligence and machine learning technologies is reviewed that integrate PVAT information into prognostic models to provide clinically meaningful information in primary and secondary prevention.

Pericoronary adipose tissue differences among plaque types: a retrospective assessment

PURPOSE

To assess differences in pericoronary adipose tissue (PCAT) in patients with different plaque types by using several quantitative parameters of PCAT and investigate the relationship between PCAT and different plaque types.

MATERIALS AND METHODS

We retrospectively recruited 488 patients diagnosed with stable coronary artery disease (CAD) via coronary computed tomographic angiography, including 279 with calcified plaques (CP), 153 with non-calcified plaques (NCP), and 56 with mixed plaques (MP). Volume, fat attenuation index (FAI), and 10^th percentile, 90^th percentile, median, and minimum Hounsfield unit (HU) values of PCAT surrounding plaques were quantified. Clinical features and quantitative PCAT parameters were compared between different plaque types.

RESULTS

No intergroup differences were observed for age, sex, body mass index, risk factors, and plaque location. Length and PCAT volume in the NCP group were lower than those of the CP and MP groups (P < 0.001), whereas there were no significant differences between the CP and MP groups (P > 0.05). Patients with NCP and MP had a higher FAI and 10^th percentile, 90^th percentile, median, and minimum HU values of PCAT than CP (P < 0.001); however these values were not significantly different between the NCP and MP groups (P > 0.05).

CONCLUSION

The quantitative parameters of PCAT, as a biosensor for CAD, vary among the different plaque types.

Relationship between epicardial adipose tissue attenuation and coronary artery disease in type 2 diabetes mellitus patients

BACKGROUND AND AIMS

High epicardial adipose tissue (EAT) attenuation is a key characteristic of adipose tissue dysfunction and associated with coronary artery disease (CAD). As little is known about the modulation of EAT attenuation by metabolic disorders, we investigated the association between EAT attenuation and CAD risk factors, CAD presence and CAD severity in type 2 diabetes mellitus (T2DM) patients.

METHODS

We included 276 inpatients with T2DM and 305 control patients with normal glucose metabolism (NGM), who underwent cardiac computed tomography angiography (CCTA) and coronary artery calcium (CAC) scoring. EAT attenuation and volume were evaluated by contrast-enhanced CCTA image analysis. Furthermore, segment stenosis scores (SSSs) of the left main coronary artery (LMCA), left anterior descending artery (LAD), left circumflex artery (LCX), right coronary artery (RCA), diagonal/intermediate branch (D/I) and obtuse marginal branch (OM) were calculated to assess CAD severity.

RESULTS

T2DM patients showed higher significant CAC scores, coronary plaque prevalence, total SSSs and LMCA-SSSs, LAD-SSSs, LCX-SSSs, RCA-SSSs and D/I-SSSs compared with NGM controls. In contrast to NGM controls, EAT volume was significantly increased in T2DM patients, whereas EAT attenuation was similar. In T2DM patients, EAT attenuation was associated with discrete CAD risk factors, the presence of coronary and triple-vessel plaques, as well as LAD-SSSs, LCX-SSSs, RCA-SSSs and total SSSs. In addition, EAT attenuation was only associated with the total SSS of calcified plaques, but not with noncalcified plaques.

CONCLUSION

In T2DM patients, high EAT attenuation is associated with the presence and severity of CAD in general and with coronary stenosis caused by calcified plaques in particular.

Pericoronary Adipose Tissue as a Marker of Cardiovascular Risk: JACC Review Topic of the Week

Vascular inflammation is a key driver in atherosclerotic progression and plaque rupture. Recent evidence has shown that coronary computed tomography provides a noninvasive method of quantifying coronary inflammation by mapping changes in pericoronary adipose tissue (PCAT) radiodensity, which are associated with cardiovascular diseases. However, there are significant knowledge gaps in the performance and measurement of PCAT that complicate its interpretation. In this review the authors aim to summarize the role of PCAT in cardiac imaging and explore the clinical implications and applicability as a novel biomarker of cardiovascular risk, as well as to discuss its limitations and potential pitfalls.

Association Between Perivascular Adipose Tissue Density and Atherosclerosis in the Descending Thoracic Aorta

Radiodensity measured by computed tomography (CT) in Hounsfield Units (HU) is emerging as a clinical tool for detecting perivascular adipose tissue (PVAT) inflammation. In the present study, we hypothesized that PVAT radiodensity might predict the risk of descending thoracic aorta atherosclerosis. A total of 73 subjects who underwent CT angiography to investigate aortic disease were retrospectively analyzed. PVAT radiodensity, aortic complex plaque (ACP), mean plaque-burden score (MPBS), and plaque density were measured, and the association between them was analyzed. Perivascular adipose tissue radiodensity (HU) in patients with different aortic plaques grades (grade 1, 2, 3, and 4) were -93.71 ± 2.50, -93.63 ± 3.93, -90.24 ± 4.49, and -89.90 ± 5.18, respectively, and the difference was significant (P = .010). In the regression analysis, PVAT radiodensity was an independent predictor of ACP, with an OR of 1.263. In the linear analysis, PVAT radiodensity was an independent predictor of MPBS, with a β-coefficient of .073. In the univariate analysis, only the PVAT radiodensity was significantly associated with plaque density, with a β-coefficient of -1.666. In conclusion, PVAT density was independently related to descending thoracic aorta atherosclerosis.

Pre-diabetes is associated with attenuation rather than volume of epicardial adipose tissue on computed tomography

The volume of epicardial adipose tissue (EATV) is increased in type-2 diabetes (T2D), while its attenuation (EATA) appears to be decreased. Similar patterns have been suggested in pre-diabetes, but data is scarce. In both pre-diabetes and T2D, any independent role of EATV and EATA in disease development remains to be proven, a task complicated by their substantial co-variation with other anthropometrics, e.g. BMI, waist circumference, and abdominal visceral adipose tissue (VAT). EATV and EATA was quantified in computed tomography (CT) images in a population study (n = 1948) using an automatic technique. Data was available on BMI, waist circumference, abdominal visceral adipose tissue (VAT) area, insulin resistance (IR) and glucose tolerance, the latter ranging from normal (NGT), over pre-diabetes (impaired fasting glucose [IFG, n = 414] impaired glucose tolerance [IGT, n = 321] and their combination [CGI, n = 128]), to T2D. EATV was increased in pre-diabetes, T2D and IR in univariable analyses and when adjusting for BMI, however not when adjusting for waist or VAT. EATA was reduced in pre-diabetes, T2D and IR in univariable analyses and when adjusting for BMI and waist, however not when adjusting for VAT. Adjustment for other co-variates had little influence on the results. In conclusion, EATV is increased and EATA reduced in pre-diabetes, T2D and IR, however, significant co-variation with other anthropometrics, especially VAT, obscures their function in disease development. The current results do not exclude a pathophysiological role of epicardial fat, but future studies need to adjust for anthropometrics, or focus on the microenvironment within the pericardial sac.

Pericoronary fat attenuation index-a new imaging biomarker and its diagnostic and prognostic utility: a systematic review and meta-analysis

Pericoronary fat attenuation index (FAI) on coronary computed tomography angiography imaging has been proposed as a novel marker of coronary vascular inflammation with prognostic value for major cardiovascular events. To date, there is no systematic review of the published literature and no meta-analysed data of previously published results. We performed a systematic review and meta-analysis according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. We systematically explored published literature in MEDLINE (PubMed) before 20 January 2022 for studies assessing FAI in both diagnostic and prognostic clinical settings in patients with or without cardiovascular disease. The primary outcome was the mean difference in FAI attenuation between stable and unstable coronary plaques. The secondary outcome was the hazard ratio (HR) of high FAI values for future cardiovascular events. We calculated I2 to test heterogeneity. We used random-effects modelling for the meta-analyses to assess the primary and secondary outcomes. This study is registered with PROSPERO (CRD42021229491). In total, 20 studies referred in a total of 7797 patients were included in this systematic review, while nine studies were used for the meta-analysis. FAI was significantly higher in unstable compared with stable plaques with a mean difference of 4.50 Hounsfield units [95% confidence interval (CI): 1.10-7.89, I2 = 88%] among 902 patients. Higher pericoronary FAI values offered incremental prognostic value for major adverse cardiovascular events (MACEs) in studies with prospective follow-up (HR = 3.29, 95% CI: 1.88-5.76, I2 = 75%) among 6335 patients. Pericoronary FAI seems to be a promising imaging biomarker that can be used for the detection of coronary inflammation, possibly to discriminate between stable and unstable plaques, and inform on the prognosis for future MACE. Further validation of these findings and exploration of the cost-effectiveness of the method before implementation in clinical practice are needed.

Cardiovascular risk stratification by coronary computed tomography angiography imaging: current state-of-the-art

Current cardiovascular risk stratification by use of clinical risk score systems or plasma biomarkers is good but less than satisfactory in identifying patients at residual risk for coronary events. Recent clinical evidence puts now further emphasis on the role of coronary anatomy assessment by coronary computed tomography angiography (CCTA) for the management of patients with stable ischaemic heart disease. Available computed tomography (CT) technology allows the quantification of plaque burden, identification of high-risk plaques, or the functional assessment of coronary lesions for ischaemia detection and revascularization for refractory angina symptoms. The current CT armamentum is also further enhanced by perivascular Fat Attenuation Index (FAI), a non-invasive metric of coronary inflammation, which allows for the first time the direct quantification of the residual vascular inflammatory burden. Machine learning and radiomic features' extraction and spectral CT for tissue characterization are also expected to maximize the diagnostic and prognostic yield of CCTA. The combination of anatomical, functional, and biological information on coronary circulation by CCTA offers a unique toolkit for the risk stratification of patients, and patient selection for targeted aggressive prevention strategies. We hereby provide a review of the current state-of-the art in the field and discuss how integrating the full capacities of CCTA into clinical care pathways opens new opportunities for the tailored management of coronary artery disease.

Impact of H-Type Hypertension on Pericarotid Adipose Tissue and Plaque Characteristics Based on Computed Tomography (CT) Angiography: A Propensity Score Matching Study

BACKGROUND We analyzed the correlation among the inflammatory changes in pericarotid adipose tissue (PCAT), plaque characteristics, and H-type hypertension on CT angiography (CTA) and explored the utility of CTA in the prevention and treatment of carotid atherosclerosis. MATERIAL AND METHODS A total of 135 patients who underwent head and neck CTA to investigate carotid artery atherosclerosis were retrospectively analyzed. The plaque characteristic parameters (plaque burden and remodeling index), PCAT attenuation value, and net enhancement value around the carotid artery, where the plaques were located, were recorded, and confounding factors were matched by propensity score analysis. A paired t test was used to compare the differences in fat tissue inflammatory changes and plaque characteristic parameters between the 2 groups, and logistic regression analysis was used to evaluate the relationship between plaque characteristics and the attenuation values and net enhancement values of PCAT. The correlation coefficient was calculated between type H hypertension and plaque risk grade. RESULTS The results of the experiment indicate that PCAT attenuation values and net enhancement values gradually increased as the degree of hypertension increased. Compared with those of patients in the normal Hcy group, these values increased more clearly in patients with high Hcy (HHcy) (r=0.641, P<0.001, r=0.581, P<0.001), although, regardless of whether the Hcy value increased, there were significant differences between the groups. However, this effect was more pronounced in patients with H-type hypertension. Logistic regression analysis of risk factors for carotid atherosclerotic plaque suggests that Hcy (OR=1.391, 95% CI 1.146-1.689, P=0.001), PCAT attenuation values (OR=1.212, 95% CI 1.074-1.367, P=0.002), and net enhancement values (OR=1.201, 95% CI 1.042-1.383, P=0.011) were independent risk factors for plaque vulnerability. CONCLUSIONS Our results suggest that H-type hypertension is significantly associated with PCAT attenuation and net enhancement and that PCAT net enhancement values are useful in predicting plaque risk as attenuation.

Association of Pericoronary Adipose Tissue Quality Determined by Dual-Layer Spectral Detector CT With Severity of Coronary Artery Disease: A Preliminary Study

Background: Pericoronary adipose tissue (PCAT) is considered as a source of inflammatory mediators, leading to the development of coronary atherosclerosis. The study aimed to investigate the correlation between PCAT quality derived from dual-layer spectral detector CT (SDCT) and the severity of coronary artery disease (CAD), and whether PCAT parameters were independently associated with the presence of CAD.

Materials and Methods: A total of 403 patients with symptoms of chest pain who underwent SDCT were included. PCAT quality including fat attenuation index (FAI) measured from conventional polychromatic CT images (FAI_120kvp) and spectral virtual mono-energetic images at 40 keV (FAI_40keV), slope of spectral HU curve (λ_HU), and effective atomic number (Eff-Z) were measured around the lesions representing the maximal degree of vascular stenosis in each patient. Meanwhile, overall epicardial adipose tissue (EAT) attenuation was acquired in the conventional polychromatic energy imaging.

Results: FAI_40keV, λ_HU, Eff-Z, and FAI_120kvp increased along with the degree of CAD in general and were superior to the overall EAT attenuation for detecting the presence of CAD. Multivariate logistic regression analysis indicated that FAI_40keV was the most powerful independent indicator (odds ratio 1.058, 95% CI 1.044–1.073; p < 0.001) of CAD among these parameters. Using an optimal cut-off (−131.8 HU), FAI_40keV showed higher diagnostic accuracy of 80.6% compared with the other parameters.

Conclusions: These preliminary findings suggest that FAI_40keV on SDCT may be an appealing surrogate maker to allow monitoring of PCAT changes in the development of CAD.

Imaging residual inflammatory cardiovascular risk

Targeting residual cardiovascular risk in primary and secondary prevention, would allow deployment of novel therapeutic agents, facilitating precision medicine. For example, lowering vascular inflammation is a promising strategy to reduce the residual inflammatory cardiovascular risk in patients already receiving optimal medical therapy, but prescribing novel anti-inflammatory treatments will be problematic due to the lack of specific companion diagnostic tests, to guide their targeted use in clinical practice. Currently available tests for the detection of coronary inflammation are either non-specific for the cardiovascular system (e.g. plasma biomarkers) or expensive and not readily available (e.g. hybrid positron emission tomography imaging). Recent technological advancements in coronary computed tomography angiography (CCTA) allow non-invasive detection of high-risk plaque features (positive remodelling, spotty calcification, low attenuation plaque, and napkin-ring sign) and help identify the vulnerable patient, but they provide only indirectly information about coronary inflammation. Perivascular fat attenuation index (FAI), a novel method for assessing coronary inflammation by analysing routine CCTA, captures changes in the perivascular adipose tissue composition driven by inflammatory signals coming from the inflamed coronary artery, by analysing the three-dimensional gradients of perivascular attenuation, followed by adjustments for technical, anatomical, and biological factors. By detecting vascular inflammation, perivascular FAI enhances cardiovascular risk discrimination which could aid more cost-effective deployment of novel therapeutic agents. In this article, we present the existing non-invasive modalities for the detection of coronary inflammation and provide a practical guide for their use in clinical practice.

The Emerging Role of CT-Based Imaging in Adipose Tissue and Coronary Inflammation

A large body of evidence arising from recent randomized clinical trials demonstrate the association of vascular inflammatory mediators with coronary artery disease (CAD). Vascular inflammation localized in the coronary arteries leads to an increased risk of CAD-related events, and produces unique biological alterations to local cardiac adipose tissue depots. Coronary computed tomography angiography (CTA) provides a means of mapping inflammatory changes to both epicardial adipose tissue (EAT) and pericoronary adipose tissue (PCAT) as independent markers of coronary risk. Radiodensity or attenuation of PCAT on coronary CTA, notably, provides indirect quantification of coronary inflammation and is emerging as a promising non-invasive imaging implement. An increasing number of observational studies have shown robust associations between PCAT attenuation and major coronary events, including acute coronary syndrome, and 'vulnerable' atherosclerotic plaque phenotypes that are associated with an increased risk of the said events. This review outlines the biological characteristics of both EAT and PCAT and provides an overview of the current literature on PCAT attenuation as a surrogate marker of coronary inflammation.

Pericoronary Adipose Tissue Attenuation Is Associated with High-Risk Plaque and Subsequent Acute Coronary Syndrome in Patients with Stable Coronary Artery Disease

BACKGROUND

High-risk plaques (HRP) detected on coronary computed tomography angiography (CTA) confer an increased risk of acute coronary syndrome (ACS). Pericoronary adipose tissue attenuation (PCAT) is a novel biomarker of coronary inflammation. This study aimed to evaluate the association of PCAT with HRP and subsequent ACS development in patients with stable coronary artery disease (CAD).

METHODS

Patients with stable CAD who underwent coronary CTA from 2011 to 2016 and had available outcome data were included. We studied 41 patients with HRP propensity matched to 41 controls without HRP (60 ± 10 years, 67% males). PCAT was assessed using semi-automated software on a per-patient basis in the proximal right coronary artery (PCATRCA) and a per-lesion basis (PCATLesion) around HRP in cases and the highest-grade stenosis lesions in controls.

RESULTS

PCATRCA and PCATLesion were higher in HRP patients than controls (PCATRCA: -80.7 ± 6.50 HU vs. -84.2 ± 8.09 HU, p = 0.03; PCATLesion: -79.6 ± 7.86 HU vs. -84.2 ± 10.3 HU, p = 0.04), and were also higher in men (PCATRCA: -80.5 ± 7.03 HU vs. -86.1 ± 7.08 HU, p < 0.001; PCATLesion: -79.6 ± 9.06 HU vs. -85.2 ± 7.96 HU, p = 0.02). Median time to ACS was 1.9 years, within a median follow-up of 5.3 years. PCATRCA alone was higher in HRP patients who subsequently presented with ACS (-76.8 ± 5.69 HU vs. -82.0 ± 6.32 HU, p = 0.03). In time-dependent analysis, ACS was associated with HRP and PCATRCA.

CONCLUSIONS

PCAT attenuation is increased in stable CAD patients with HRP and is associated with subsequent ACS development. Further investigation is required to determine the clinical implications of these findings.

Imaging of the Pericoronary Adipose Tissue (PCAT) Using Cardiac Computed Tomography: Modern Clinical Implications

Modern coronary computed tomography angiography (CTA) is the gold standard to visualize the epicardial adipose tissue (EAT) and pericoronary adipose tissue (PCAT). The EAT is a metabolic active fat depot enclosed by the visceral pericardium and surrounds the coronary arteries. In disease states with increased EAT volume and dysfunctional adipocytes, EAT secretes an increased amount of adipocytokines and the resulting imbalance of proinflammatory and anti-inflammatory mediators potentially causes atherogenic effects on the coronary vessel wall in a paracrine way ("outside-to-inside" signaling). These EAT-induced atherogenic effects are reported to increase the risk for the development of coronary artery disease, myocardial ischemia, high-risk plaque features, and future major adverse cardiac events. Coronary inflammation plays a key role in the development and progression of coronary artery disease; however, its noninvasive detection remains challenging. In future, this clinical dilemma might be changed by the CTA-derived analysis of the PCAT. On the basis of the concept of an "inside-to-outside" signaling between the inflamed coronary vessel wall and the surrounding PCAT recent evidence demonstrates that PCAT computed tomography attenuation especially around the right coronary artery derived from routine CTA is a promising imaging biomarker and "sensor" to noninvasively detect coronary inflammation. This review summarizes the biological and technical principles of CTA-derived PCAT analysis and highlights its clinical implications to improve modern cardiovascular prevention strategies.

Reciprocal communication of pericoronary adipose tissue and coronary atherogenesis

OBJECTIVE

Pericoronary adipose tissue (PCAT) has been linked to underlying coronary artery disease (CAD) and proposed to modulate adjacent atherosclerotic plaque formation over pro-inflammatory pathways. In vitro and ex vivo studies support the bilateral communication of adipose tissue and vessel wall. We quantified PCAT and its dynamics in a low coronary risk cohort with a semi-automated software in serial coronary computed tomography angiography (CTA).

METHODS

We retrospectively included patients from a tertiary care hospital who underwent serial coronary CTA with a low cardiovascular risk profile. All examinations were evaluated in a standardized approach: epicardial adipose tissue (EAT) volume and attenuation was quantified in total, in the atrioventricular (RCA, LCX) or interventricular (LAD) sulcus and within a 5 mm radius for each coronary artery (PCAT). Coronary plaques were quantified using a semi-automated software and compared for progression, stability or regression.

RESULTS

Of 120 patients (27% females), 59.2% showed atherosclerotic plaques. After 36 months mean follow-up, 22 (18.3%) showed plaque regression, 39 (32.5%) were stable and 49 (40.8%) were progressive. Total EAT volume decreased by -15.6 ± 37.2 mm³ in the regressive group, increased by 2.7 ± 30.6 mm³ in the stable group and by 24.3 ± 37.1 mm³ in the progressive group (p = 0.003). Per-vessel analysis showed a significant decrease of PCAT attenuation in patients with CAD regression (-3.8 ± 7.6HU) compared to the stable (1.2 ± 9.1HU) and progressive group (3.5 ± 8.2HU, p < 0.0001). Mean sulcus EAT attenuation did not show a significant change (p = 0.135).

CONCLUSION

Epicardial adipose tissue volume is mutually changing with the progression or regression of coronary artery disease. Perivascular but not epicardial attenuation levels correlate to adjacent plaque and support a direct bilateral influence.

High levels of eicosapentaenoic acid are associated with lower pericoronary adipose tissue attenuation as measured by coronary CTA

BACKGROUND AND AIMS

Higher pericoronary adipose tissue (PCAT) attenuation, a novel marker of inflammation in coronary CT angiography (CTA), has been shown to indicate increased cardiac mortality. Supplementation of eicosapentaenoic acid (EPA) has been shown to decrease cardiovascular death. Whether blood levels of n-3 fatty acids are associated with differences in PCAT attenuation is unknown.

METHODS

This is a cross-sectional analysis including 64 symptomatic patients who underwent coronary CTA. PCAT attenuation was measured in Hounsfield Units (HU) around the proximal 40 mm of the right coronary artery using semi-automated software. Erythrocyte membrane fatty acid composition was analyzed using gas chromatography. Individual fatty acids were expressed as a percentage of total identified fatty acids.

RESULTS

The patient cohort was divided into two groups using the median PCAT attenuation of -78.1 HU (each n = 32). No differences were seen in age, sex, BMI or traditional cardiovascular risk factors (CVRF) between groups (all p > 0.05). In univariable analysis, significantly higher values of EPA (1.00% [0.78; 1.26] vs. 0.78% [0.63; 0.99]; p = 0.02) were seen in patients with lower PCAT attenuation. All other fatty acids showed no differences (all p > 0.05). Moreover, a significant negative correlation was seen between PCAT attenuation and EPA (CC: 0.38; p = 0.002). In multivariable analysis, an inverse association of EPA with PCAT attenuation existed (ß = -0.31, p = 0.017), independent of age, gender, BMI and number of CVRF (all p > 0.1).

CONCLUSIONS

High levels of EPA are associated with lower PCAT attenuation on coronary CTA. This may indicate a different composition of pericoronary adipose tissue, potentially caused by a lower degree of coronary inflammation.

An Update on [18F]Fluoride PET Imaging for Atherosclerotic Disease

Atherosclerosis is the leading cause of life-threatening morbidity and mortality, as the rupture of atherosclerotic plaques leads to critical atherothrombotic events such as myocardial infarction and ischemic stroke, which are the 2 most common causes of death worldwide. Vascular calcification is a complicated pathological process involved in atherosclerosis, and microcalcifications are presumed to increase the likelihood of plaque rupture. Despite many efforts to develop novel non-invasive diagnostic modalities, diagnostic techniques are still limited, especially before symptomatic presentation. From this point of view, vulnerable plaques are a direct target of atherosclerosis imaging. Anatomic imaging modalities have the limitation of only visualizing macroscopic structural changes, which occurs in later stages of disease, while molecular imaging modalities are able to detect microscopic processes and microcalcifications, which occur early in the disease process. Na[¹⁸F]-fluoride positron emission tomography/computed tomography could allow the early detection of plaque instability, which is deemed to be a primary goal in the prevention of cardiac or brain ischemic events, by quantifying the microcalcifications within vulnerable plaques and evaluating the atherosclerotic disease burden.

Determinants of Pericoronary Adipose Tissue Attenuation on Computed Tomography Angiography in Coronary Artery Disease

Background Recent studies have reported the association between pericoronary inflammation assessed by pericoronary adipose tissue attenuation (PCATA) on computed tomography angiography and worse outcomes in patients with coronary artery disease. We investigated the determinants predicting increased PCATA in patients with known or suspected coronary artery disease. Methods and Results A total of 540 patients who underwent computed tomography angiography and invasive coronary angiography were studied. Mean computed tomography attenuation values of PCAT (-190 to -30 Hounsfield units) (PCATA) were assessed at the proximal 40-mm segments of all 3 major coronary arteries by crude analysis. Univariable and multivariable analyses were performed to determine the predictors of increased PCATA surrounding the proximal right coronary artery. Mean right coronary artery-PCATA was -72.22±8.47 Hounsfield units and the average of 3-vessel PCATA was -70.24±6.60 Hounsfield units. Multivariable linear regression analysis revealed that the independent determinants of right coronary artery-PCATA were male (β coefficient=4.965, P<0.001), left ventricular mass index (β coefficient=0.040, P=0.025), and angiographically significant stenosis (diameter stenosis >50%) (β coefficient=2.418, P=0.008). Sex-related determinants were NT-proBNP level (N-terminal pro-B-type natriuretic peptide; β coefficient <0.001, P=0.026), Agatston score (β coefficient=-0.002, P=0.010), left ventricular mass index (β coefficient=0.041, P=0.028), and significant stenosis (β coefficient=4.006, P<0.001) in male patients and left ventricular ejection fraction (β coefficient=-0.217, P=0.010) and significant stenosis (β coefficient=3.835, P=0.023) in female patients. Conclusions Right coronary artery-PCATA was associated with multiple clinical characteristics, established risk factors, and the presence of significant stenosis. Our results suggest that clinically significant factors such as sex, left ventricular hypertrophy, ejection fraction, calcification, and epicardial stenosis should be taken into account in the assessment of pericoronary inflammation using computed tomography angiography.

Perivascular Fat Density and Contrast Plaque Enhancement: Does a Correlation Exist?

BACKGROUND AND PURPOSE

Inflammatory changes in the fat tissue surrounding the coronary arteries have been associated with coronary artery disease and high-risk vulnerable plaques. Our aim was to investigate possible correlations between the presence and degree of perivascular fat density and a marker of vulnerable carotid plaque, namely contrast plaque enhancement on CTA.

MATERIALS AND METHODS

One-hundred patients (76 men, 24 women; mean age, 69 years) who underwent CT angiography for investigation of carotid artery stenosis were retrospectively analyzed. Contrast plaque enhancement and perivascular fat density were measured in 100 carotid arteries, and values were stratified according to symptomatic (ipsilateral-to-cerebrovascular symptoms)/asymptomatic status (carotid artery with the most severe degree of stenosis). Correlation coefficients (Pearson ρ product moment) were calculated between the contrast plaque enhancement and perivascular fat density. The differences among the correlation ρ values were calculated using the Fisher r-to-z transformation. Mann-Whitney analysis was also calculated to test differences between the groups.

RESULTS

There was a statistically significant positive correlation between contrast plaque enhancement and perivascular fat density (ρ value = 0.6582, P value = .001). The correlation was stronger for symptomatic rather than asymptomatic patients (ρ value = 0.7052, P value = .001 versus ρ value = 0.4092, P value = .001).

CONCLUSIONS

There was a positive association between perivascular fat density and contrast plaque enhancement on CTA. This correlation was stronger for symptomatic rather than asymptomatic patients. Our results suggest that perivascular fat density could be used as an indirect marker of plaque instability.

Relation between quantity and quality of peri-coronary epicardial adipose tissue and its underlying hemodynamically significant coronary stenosis

BACKGROUND

We aimed to investigate the association of lesion-specific epicardial adipose tissue (EAT) volume and density with the presence of myocardial ischemia.

METHODS

We enrolled 45 patients (55 lesions) with known or suspected coronary artery disease who underwent coronary computed tomography angiography (CTA) followed by invasive fractional flow reserve (FFR) assessment within 30 days. EAT volume (index) and density in patient-, vessel- and lesion-level were measured on CTA images. Lesion-specific ischemia was defined as a lesion with stenosis diameter > 90% or FFR ≤0.80. Multivariate analysis determined the independent association of EAT parameters with lesion-specific ischemia.

RESULTS

Mean age of the patients was 60 years, and 75% were male. Overall, 55.6% of patients had ischemic lesions and a mean FFR baseline value of 0.82 ± 0.10. Total EAT volume index was significantly higher in patients with functionally or anatomically significant stenosis. Specifically, peri-lesion EAT volume index, not the density, was positively correlated with lesion-specific ischemia independent of luminal stenosis and plaque characteristics (hazard ratio 1.56, 95% confidence interval 1.04-2.33, P = 0.032; per 0.1 ml/m² increase). Moreover, peri-lesion EAT volume was negatively correlated with lesion FFR values, whereas total EAT volume was positively correlated with fat accumulation and glucose metabolism. In addition, there was no association of EAT volume or density with myocardial ischemia in vessel-level analysis.

CONCLUSIONS

Lesion-specific EAT volume index, but not density, seems positively and independently associated with myocardial ischemia, while its incremental diagnostic value of lesion-specific ischemia should be further investigated.

Effects of epicardial adipose tissue volume and density on cardiac structure and function in patients free of coronary artery disease

PURPOSE

To determine the association of epicardial adipose tissue (EAT) volume and density with cardiac geometry and function.

METHODS

We included 178 consecutive patients who performed coronary computed tomography angiography but were not diagnosed with coronary artery disease (CAD). The EAT volume, density, and following cardiac structure and function parameters were measured: left ventricular ejection fraction, left ventricular mass (LVM), left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), left ventricular stroke volume (LVSV), left ventricular end-diastolic diameter (LVEDD), interventricular septal thickness (IVST) and posterior wall thickness (PWT). All the parameters were standardized using the height^2.7.

RESULTS

A significant correlation was found between larger EAT volume and increased LVM, LVEDV, LVESV, LVSV, LVEDD, IVST and corresponding standardized indexes (P < 0.05 for all). Higher EAT density significantly correlated with increased LVM, LVEDV, LVESV, LVSV, LVEDD, IVST, PWT and corresponding standardized indexes (P < 0.05 for all). The largest cardiac structure and function parameters were observed in the population with above-median EAT volume and density.

CONCLUSION

Both large EAT volume and high EAT density were associated with cardiac structure and function in patients with no CAD. The EAT density may render complementary information to EAT volume regarding cardiac geometry changes.

Novel imaging biomarkers: epicardial adipose tissue evaluation

Epicardial adipose tissue (EAT) is a metabolically activated beige adipose tissue, non-homogeneously surrounding the myocardium. Physiologically, EAT regulates toxic fatty acids, protects the coronary arteries against mechanical strain, regulates proinflammatory cytokines, stimulates the production of nitric oxide, reduces oxidative stress, and works as a thermogenic source against hypothermia. Conversely, EAT has pathologic paracrine interactions with the surrounded vessels, and might favour the onset of atrial fibrillation. In addition, initial atherosclerotic lesions can promote inflammation and trigger the EAT production of cytokines increasing vascular inflammation, which, in turn, may help the development of collateral vessels but also of self-stimulating, dysregulated inflammatory process, increasing coronary artery disease severity. Variations in EAT were also linked to metabolic syndrome. Echocardiography first estimated EAT measuring its thickness on the free wall of the right ventricle but does not allow accurate volumetric EAT estimates. Cardiac CT (CCT) and cardiac MR (CMR) allow for three-dimensional EAT estimates, the former showing higher spatial resolution and reproducibility but being limited by radiation exposure and long segmentation times, the latter being radiation-free but limited by lower spatial resolution and reproducibility, higher cost, and difficulties for obese patients. EAT radiodensity at CCT could to be related to underlying metabolic processes. The correlation between EAT and response to certain pharmacological therapies has also been investigated, showing promising results. In the future, semi-automatic or fully automatic techniques, machine/deep-learning methods, if validated, will facilitate research for various EAT measures and may find a place in CCT/CMR reporting.

Perivascular Adipose Tissue and Coronary Atherosclerosis: from Biology to Imaging Phenotyping

PURPOSE OF REVIEW

Perivascular adipose tissue (PVAT) has a complex, bidirectional relationship with the vascular wall. In disease states, PVAT secretes pro-inflammatory adipocytokines which may contribute to atherosclerosis. Recent evidence demonstrates that pericoronary adipose tissue (PCAT) may also function as a sensor of coronary inflammation. This review details PVAT biology and its clinical translation to current imaging phenotyping.

RECENT FINDINGS

PCAT attenuation derived from routine coronary computed tomography (CT) angiography is a novel noninvasive imaging biomarker of coronary inflammation. Pro-inflammatory cytokines released from the arterial wall diffuse directly into the surrounding PCAT and inhibit adipocyte lipid accumulation in a paracrine manner. This can be detected as an increased PCAT CT attenuation, a metric which associates with high-risk plaque features and independently predicts cardiac mortality. There is also evidence that PCAT attenuation relates to coronary plaque progression and is modified by systemic anti-inflammatory therapies. Due to its proximity to the coronary arteries, PCAT has emerged as an important fat depot in cardiovascular research. PCAT CT attenuation has the potential to improve cardiovascular risk stratification, and future clinical studies should examine its role in guiding targeted medical therapy.

Cardiac Computed Tomography

Unstable coronary plaques that are prone to erosion and rupture are the major cause of acute coronary syndromes. Our expanding understanding of the biological mechanisms of coronary atherosclerosis and rapid technological advances in the field of medical imaging has established cardiac computed tomography as a first-line diagnostic test in the assessment of suspected coronary artery disease, and as a powerful method of detecting the vulnerable plaque and patient. Cardiac computed tomography can provide a noninvasive, yet comprehensive, qualitative and quantitative assessment of coronary plaque burden, detect distinct high-risk morphological plaque features, assess the hemodynamic significance of coronary lesions and quantify the coronary inflammatory burden by tracking the effects of arterial inflammation on the composition of the adjacent perivascular fat. Furthermore, advances in machine learning, computational fluid dynamic modeling, and the development of targeted contrast agents continue to expand the capabilities of cardiac computed tomography imaging. In our Review, we discuss the current role of cardiac computed tomography in the assessment of coronary atherosclerosis, highlighting its dual function as a clinical and research tool that provides a wealth of structural and functional information, with far-reaching diagnostic and prognostic implications.

Statins Reduce Epicardial Adipose Tissue Attenuation Independent of Lipid Lowering: A Potential Pleiotropic Effect

Background

High epicardial adipose tissue (EAT) attenuation (Hounsfield units [HUs]) on computed tomography is considered a marker of inflammation and is associated with an increased risk of cardiovascular events. Statins reduce the volume of EAT, but it is unknown whether they affect EAT HUs.

Methods and Results

We reviewed the chest computed tomographic scans of 420 postmenopausal women randomized to either 80 mg of atorvastatin or 40 mg of pravastatin daily and rescanned after 1 year to measure change in coronary artery calcium score. EAT HUs were measured near the proximal right coronary artery and remote from any area of coronary artery calcium. Computed tomographic images were also queried for subcutaneous adipose tissue (SubQ) attenuation (HUs) change over time. The mean patients’ age was 65±6 years. The baseline EAT HU value was higher than the SubQ HU value (−89.4±24.0 HU versus −123.3±30.4 HU; P<0.001). The EAT HU value decreased significantly in the entire cohort (−5.4±29.7 HU [−6% change]; P<0.001), but equally in the patients given atorvastatin and pravastatin (−6.35+31 HU and −4.55+28 HU; P=0.55). EAT HU change was not associated with change in total cholesterol, low‐density lipoprotein cholesterol, coronary artery calcium, and EAT volume (all P=not significant). Change in high‐density lipoprotein cholesterol was marginally associated with EAT HU change (P=0.07). Statin treatment did not induce a change in SubQ HUs.

Conclusions

Statins induced a decrease in EAT HUs over time, independent of intensity of low‐density lipoprotein cholesterol lowering. The positive effect on EAT and the neutral effect on SubQ suggest that statins induced a decrease in metabolic activity in EAT by reduction in cellularity, vascularity, or inflammation. The clinical significance of the observed change in EAT HUs remains to be demonstrated.

The role of perivascular adipose tissue in the development of cardiovascular diseases. The importance of diagnosis for assessing the risk stratification of cardiovascular diseases

Obesity is closely associated with metabolic and cardiovascular diseases, including dyslipidemia, coronary artery disease, hypertension, and heart failure. Adipose tissue (AT) is identified as a complex endocrine organ, with a wide range of regulatory functions at the cellular, tissue and systemic levels. Various terms, including paracardiac, epicardial and pericardial, are used to describe the fatty deposits surrounding the heart. Among all the fat depots, perivascular AT (PVAT) is of great biological significance for the cardiovascular system due to its anatomical proximity to the vessels. Recent studies have shown the presence of a complex, bidirectional paracrine and vasocardial signaling system between the vascular wall and PVAT. In the review, we will discuss the biological role of PVAT in both the physiological state and cardiovascular pathology, emphasizing its dual proatherogenic and antiatherogenic role. Let us consider PVAT as a target for various therapeutic agents in cardiovascular diseases. We will also analyze data on the role of non-invasive techniques as a diagnostic tool for assessing coronary artery inflammation.

State-of-the-art review article. Atherosclerosis affecting fat: What can we learn by imaging perivascular adipose tissue?

Perivascular adipose tissue (PVAT) surrounding the human coronary arteries, secretes a wide range of adipocytokines affecting the biology of the adjacent vascular wall in a paracrine way. However, we have recently found that PVAT also behaves as a sensor of signals coming from the vascular wall, to which it reacts by changing its morphology and secretory profile. Indeed, vascular inflammation, a key feature of vascular disease pathogenesis, leads to the release of inflammatory signals that disseminate into local fat, inducing local lipolysis and inhibiting adipogenesis. This ability of PVAT to sense inflammatory signals from the vascular wall, can be used as a "thermometer" of the vascular wall, allowing for non-invasive detection of coronary inflammation. Vascular inflammation induces a shift of PVAT's composition from lipid to aqueous phase, resulting into increased computed tomography (CT) attenuation around the inflamed artery, forming a gradient with increasing attenuation closer to the inflamed coronary artery wall. These spatial changes in PVAT's attenuation are easily detected around culprit lesions during acute coronary syndromes. A new biomarker designed to captured these spatial changes in PVAT's attenuation around the human coronary arteries, the Fat Attenuation Index (FAI), has additional predictive value in stable patients for cardiac mortality and non-fatal heart attacks, above the prediction provided by the current state of the art that includes risk factors, calcium score and presence of high risk plaque features. The use of perivascular FAI in clinical practice may change the way we interpret cardiovascular CT angiography, as it is applicable to any coronary CT angiogram, and it offers dynamic information about the inflammatory burden of the coronary arteries, providing potential guidance for preventive measures and invasive treatments.

Peri-Coronary Adipose Tissue Density Is Associated With 18F-Sodium Fluoride Coronary Uptake in Stable Patients With High-Risk Plaques

OBJECTIVES

This study aimed to assess the association between increased lesion peri-coronary adipose tissue (PCAT) density and coronary ¹⁸F-sodium fluoride (¹⁸F-NaF) uptake on positron emission tomography (PET) in stable patients with high-risk coronary plaques (HRPs) shown on coronary computed tomography angiography (CTA).

BACKGROUND

Coronary ¹⁸F-NaF uptake reflects the rate of calcification of coronary atherosclerotic plaque. Increased PCAT density is associated with vascular inflammation. Currently, the relationship between increased PCAT density and ¹⁸F-NaF uptake in stable patients with HRPs on coronary CTA has not been characterized.

METHODS

Patients who underwent coronary CTA were screened for HRP, which was defined by 3 concurrent plaque features: positive remodeling; low attenuation plaque (LAP) (<30 Hounsfield units [HU]) and spotty calcification; and obstructive coronary stenosis ≥50% (plaque volume >100 mm³). Patients with HRPs were recruited to undergo ¹⁸F-NaF PET/CT. In lesions with stenosis ≥25%, quantitative plaque analysis, mean PCAT density, maximal coronary motion-corrected ¹⁸F-NaF standard uptake values (SUVmax), and target-to-background ratios (TBR) were measured.

RESULTS

Forty-one patients (age 65 ± 6 years; 68% men) were recruited. Fifty-one lesions in 23 patients (56%) showed increased coronary ¹⁸F-NaF activity. Lesions with ¹⁸F-NaF uptake had higher surrounding PCAT density than those without ¹⁸F-NaF uptake (-73 HU; interquartile range -79 to -68 HU vs. -86 HU; interquartile range -94 to -80 HU; p < 0.001). ¹⁸F-NaF TBR and SUVmax were correlated with PCAT density (r = 0.63 and r = 0.68, respectively; all p < 0.001). On adjusted multiple regression analysis, increased lesion PCAT density and LAP volume were associated with ¹⁸F-NaF TBR (β = 0.25; 95% confidence interval: 0.17 to 0.34; p < 0.001 for PCAT, and β = 0.07; 95% confidence interval: 0.03 to 0.11; p = 0.002 for LAP).

CONCLUSIONS

In patients with HRP features on coronary CTA, increased density of PCAT was associated with focal ¹⁸F-NaF PET uptake. Simultaneous assessment of these imaging biomarkers by ¹⁸F-NaF PET and CTA might refine cardiovascular risk prediction in stable patients with HRP features.

Non-invasive detection of coronary inflammation using computed tomography and prediction of residual cardiovascular risk (the CRISP CT study): a post-hoc analysis of prospective outcome data

BACKGROUND

Coronary artery inflammation inhibits adipogenesis in adjacent perivascular fat. A novel imaging biomarker-the perivascular fat attenuation index (FAI)-captures coronary inflammation by mapping spatial changes of perivascular fat attenuation on coronary computed tomography angiography (CTA). However, the ability of the perivascular FAI to predict clinical outcomes is unknown.

METHODS

In the Cardiovascular RISk Prediction using Computed Tomography (CRISP-CT) study, we did a post-hoc analysis of outcome data gathered prospectively from two independent cohorts of consecutive patients undergoing coronary CTA in Erlangen, Germany (derivation cohort) and Cleveland, OH, USA (validation cohort). Perivascular fat attenuation mapping was done around the three major coronary arteries-the proximal right coronary artery, the left anterior descending artery, and the left circumflex artery. We assessed the prognostic value of perivascular fat attenuation mapping for all-cause and cardiac mortality in Cox regression models, adjusted for age, sex, cardiovascular risk factors, tube voltage, modified Duke coronary artery disease index, and number of coronary CTA-derived high-risk plaque features.

FINDINGS

Between 2005 and 2009, 1872 participants in the derivation cohort underwent coronary CTA (median age 62 years [range 17-89]). Between 2008 and 2016, 2040 patients in the validation cohort had coronary CTA (median age 53 years [range 19-87]). Median follow-up was 72 months (range 51-109) in the derivation cohort and 54 months (range 4-105) in the validation cohort. In both cohorts, high perivascular FAI values around the proximal right coronary artery and left anterior descending artery (but not around the left circumflex artery) were predictive of all-cause and cardiac mortality and correlated strongly with each other. Therefore, the perivascular FAI measured around the right coronary artery was used as a representative biomarker of global coronary inflammation (for prediction of cardiac mortality, hazard ratio [HR] 2·15, 95% CI 1·33-3·48; p=0·0017 in the derivation cohort, and 2·06, 1·50-2·83; p<0·0001 in the validation cohort). The optimum cutoff for the perivascular FAI, above which there is a steep increase in cardiac mortality, was ascertained as -70·1 Hounsfield units (HU) or higher in the derivation cohort (HR 9·04, 95% CI 3·35-24·40; p<0·0001 for cardiac mortality; 2·55, 1·65-3·92; p<0·0001 for all-cause mortality). This cutoff was confirmed in the validation cohort (HR 5·62, 95% CI 2·90-10·88; p<0·0001 for cardiac mortality; 3·69, 2·26-6·02; p<0·0001 for all-cause mortality). Perivascular FAI improved risk discrimination in both cohorts, leading to significant reclassification for all-cause and cardiac mortality.

INTERPRETATION

The perivascular FAI enhances cardiac risk prediction and restratification over and above current state-of-the-art assessment in coronary CTA by providing a quantitative measure of coronary inflammation. High perivascular FAI values (cutoff ≥-70·1 HU) are an indicator of increased cardiac mortality and, therefore, could guide early targeted primary prevention and intensive secondary prevention in patients.

FUNDING

British Heart Foundation, and the National Institute of Health Research Oxford Biomedical Research Centre.

Associations of cardiovascular fat radiodensity and vascular calcification in midlife women: The SWAN cardiovascular fat ancillary study

BACKGROUND AND AIMS

Fat radiodensity, measured via CT Hounsfield units (HU), is a potential marker of fat quality. We sought to determine the cross-sectional associations of total heart fat (TAT) and aortic perivascular fat (PVAT) radiodensity with cardiovascular risk factors, coronary artery calcification (CAC), and aortic calcification (AC) in midlife women.

METHODS

Fat radiodensity, CAC, and AC were quantified using CT scans. A total of 528 women (mean age: 50.9 ± 2.9 years; 37% Black) were included in analyses.

RESULTS

Women in the lowest TAT radiodensity tertile were more likely to have adverse cardiovascular risk factors. Independent of cardiovascular risk factors, women in the middle and high TAT radiodensity tertiles were less likely to have CAC (OR (95% CI): 0.32 (0.18, 0.59); 0.43 (0.24, 0.78), respectively) compared with women in the lowest TAT radiodensity tertile. Although adjusting for BMI attenuated the overall association, women in the middle TAT radiodensity tertile remained at significantly lower odds of CAC when compared to the low radiodensity tertile, 0.47 (0.24, 0.93), p=0.03. No significant associations were found for PVAT radiodensity and calcification measures in multivariable analysis.

CONCLUSIONS

Lower TAT radiodensity was associated with a less favorable cardiometabolic profile. Women with mid-range TAT radiodensity values had a lower odds of CAC presence, independent of CVD risk factors and BMI. More research is necessary to understand radiodensity as a surrogate marker of fat quality in midlife women.

Perivascular adipose tissue and coronary atherosclerosis

Adipose tissue (AT) is no longer viewed as a passive, energy-storing depot, and a growing body of evidence supports the concept that both quantitative and qualitative aspects of AT are critical in determining an individual's cardiometabolic risk profile. Among all AT sites, perivascular AT (PVAT) has emerged as a depot with a distinctive biological significance in cardiovascular disease given its close anatomical proximity to the vasculature. Recent studies have suggested the presence of complex, bidirectional paracrine and vasocrine signalling pathways between the vascular wall and its PVAT, with far-reaching implications in cardiovascular diagnostics and therapeutics. In this review, we first discuss the biological role of PVAT in both cardiovascular health and disease, highlighting its dual pro-atherogenic and anti-atherogenic roles, as well as potential therapeutic targets in cardiovascular disease. We then review current evidence and promising new modalities on the non-invasive imaging of epicardial AT and PVAT. Specifically, we present how our expanding knowledge on the bidirectional interplay between the vascular wall and its PVAT can be translated into novel clinical diagnostics tools to assess coronary inflammation. To this end, we present the example of a new CT-based method that tracks spatial changes in PVAT phenotype to extract information about the inflammatory status of the adjacent vasculature, highlighting the numerous diagnostic and therapeutic opportunities that arise from our increased understanding of PVAT biology.