Epicardial fat from echocardiography: a new method for visceral adipose tissue prediction

Perivascular Fat: Innocent Bystander or Active Player in Vascular Disease?

Although nearly all arteries are surrounded by perivascular fat, its role in vascular function and disease is clearly understudied. At least one type of perivascular fat, epicardial adipose tissue, appears to be related to both weight and age and tends to express proatherogenic/proinflammatory products in subjects with cardiovascular disease. Perivascular fat may evolve from primordial cells in the adventitia or from circulating precursors migrating through the arterial wall. Once deposited periarterially, adipose tissue may release locally a large number of products, which potentially interact with the arterial wall. Additionally, the authors propose that perivascular fat, per se, may attract circulating monocytes through the release of chemokines such as monocyte chemoattractant protein-1. Some of the macrophages traversing the arterial wall en route to the perivascular fat may be redirected and eventually populate the arterial wall itself, thereby enhancing vascular inflammatory processes and accelerating atherosclerosis.

Pericardial fat mimicking pericardial effusion on two-dimensional echocardiography

A 78-year-old overweight woman with diabetes mellitus, bronchial asthma, and Sheehan's syndrome on chronic steroid therapy presented with mild short-lived hematemesis, significant hypotension disproportionate to the degree of bleeding and radiographic evidence of cardiomegaly. Endoscopy showed duodenal ulcer. During evaluation of the unexplained brief hypotension and cardiomegaly, 2D-echocardiogram demonstrated anterior and posterior echo-free spaces consistent with large pericardial effusion (PE). However, subsequent elective surgical pericardiotomy unexpectedly revealed large amounts of pericardial fat. Pericardial fat was also noted on magnetic resonance imaging of the chest. Our case illustrates a potential pitfall of 2D-echocardiography in the diagnosis of PE.

Myocardial triglyceride content and epicardial fat mass in human obesity: relationship to left ventricular function and serum free fatty acid levels

CONTEXT AND OBJECTIVE

Ectopic fat accumulation within and around the myocardial wall has been implicated in the pathogenesis of heart disease in obesity. We evaluated myocardial and epicardial fat, left ventricular (LV) function, and metabolic risk factors in nine (five lean, four moderately obese) men.

METHODS

Myocardial fat percent was quantified in the septum by proton magnetic resonance spectroscopy. Reproducibility was assessed by triplicate systolic and diastolic measurements. LV parameters and epicardial fat were determined by magnetic resonance imaging. Waist-to-hip ratio and liver enzymes (alanine transaminase) were used as surrogate markers of visceral and liver fat contents.

RESULTS

Myocardial fat (2.1 +/- 0.5 vs. 0.8 +/- 0.1, P = 0.03) and epicardial fat (120 +/- 33 vs. 55 +/- 12 g, P = 0.08) were higher in obese than lean subjects. Individuals with above-median alanine transaminase values had a 4-fold elevation in myocardial fat. The coefficient of variation of repeated myocardial fat percent determinations was 17 +/- 3 and 23 +/- 3% in systole and diastole, respectively. Myocardial fat was correlated with free fatty acid (FFA) levels (r = 0.76; P = 0.017), epicardial fat (r = 0.69; P = 0.042), and waist-to-hip ratio (r = 0.70; P = 0.035), and it showed a tendency to associate positively with LV work. Epicardial fat was associated with peripheral vascular resistance (positively) and the cardiac index (negatively). FFA levels were significantly correlated with LV mass (r = 0.72; P = 0.030) and forward work (r = 0.74; P = 0.023).

CONCLUSIONS/INTERPRETATION

The accumulation of triglyceride in and around the myocardium of moderately obese individuals is significant, and it is related to FFA exposure, generalized ectopic fat excess, and peripheral vascular resistance. These changes precede LV overload and hypertrophy.

Different "weight" of cardiac and general adiposity in predicting left ventricle morphology

Excess adiposity has been widely related to cardiac morphological changes. Nevertheless, the mechanistic link between increased adiposity and left ventricular (LV) morphology is controversial and not completely understood. In this context, several authors have recently debated the different "weight" of BMI as an index of general adiposity vs. the importance of the epicardial fat depot as a marker of local visceral adiposity in obesity-related LV changes. Studies in uncomplicated obesity suggest that the role of BMI in predicting LV abnormalities remains rather doubtful. In contrast, several lines of evidence suggest that cardiac adiposity could play an important part in the development of cardiac modifications. Epicardial fat as an index of cardiac adiposity could have a functional and mechanical role in obesity-related LV abnormalities. Epicardial fat is clinically correlated with LV mass, atrial dimensions, and diastolic function, but a causal effect of epicardial adipose tissue on cardiac chamber modifications remains to be demonstrated. Nevertheless, the close anatomical and functional relationship of epicardial adipose tissue to the adjacent myocardium should readily allow local, paracrine interactions between these tissues.

Validity of a new automated software program for visceral adipose tissue estimation

INTRODUCTION

Given the considerable time and research cost of analyzing biomedical images to quantify adipose tissue volumes, automated image analysis methods are highly desirable. Hippo Fat is a new software program designed to automatically quantify adipose tissue areas from magnetic resonance images without user inputs. Hippo Fat has yet to be independently validated against commonly used image analysis software programs.

OBJECTIVE

Our aim was to compare estimates of VAT (visceral adipose tissue) and SAT (subcutaneous adipose tissue) using the new Hippo Fat software against those from a widely used, validated, computer-assisted manual method (slice-O-matic version 4.2, Tomovision, Montreal, CA, USA) to assess its potential utility for large-scale studies.

METHODS

A Siemens Magnetom Vision 1.5-T whole-body scanner and a T1-weighted fast-spin echo pulse sequence were used to collect multiple, contiguous axial images of the abdomen from a sample of 40 healthy adults (20 men) aged 18-77 years of age, with mean body mass index of 29 kg/m(2) (range=19-43 kg/m(2)).

RESULTS

Hippo Fat provided estimates of VAT and SAT that were highly correlated with estimates using slice-O-matic (R (2)>0.9). Average VAT was 9.4% lower and average SAT was 3.7% higher using Hippo Fat compared to slice-O-matic; the overestimation of SAT tended to be greater among individuals with greater adiposity. Individual-level differences for VAT were also substantial; Hippo Fattrade mark gave estimates of VAT ranging from 1184 cm(3) less to 566 cm(3) more than estimates for the same person using slice-O-matic.

CONCLUSION

Hippo Fat provides a rapid method of quantifying total VAT, although the method does not provide estimates that are interchangeable with slice-O-matic at either the group (mean) or individual level.

Relationship of epicardial adipose tissue with atrial dimensions and diastolic function in morbidly obese subjects

Obesity is associated with atrial dilation and diastolic dysfunction although the causative mechanisms are not completely understood. In this study we showed for the first time that increase in epicardial fat thickness is significantly correlated with atria enlargement and impairment in diastolic filling in morbidly obese subjects.

Subepicardial adipose tissue and the presence and severity of coronary artery disease

BACKGROUND

Mechanistic studies suggest that paracrine effects of subepicardial adipose tissue may promote coronary atherosclerosis, but this has not been confirmed in clinical studies.

METHODS AND RESULTS

Of 180 consecutive patients who underwent echocardiography and coronary angiography within 1 week (mean 2.5+/-2.0 days), 139 (80 men, 68+/-13 years) were studied. Subepicardial adipose tissue on the free wall of right ventricle was measured at end-diastole from parasternal long- and short-axis views of three cardiac cycles. Angiograms were analyzed for the presence, extent and severity of coronary artery disease (CAD), using a 27-segment classification. The number of segments with at least 20% (CAGE > or = 20) and 50% (CAGE > or = 50) stenosis was recorded. Age showed a significant correlation with subepicardial adipose tissue thickness measured from parasternal long- (r=0.25, p=0.003) and short-axis view (r=0.23, p=0.01). No significant correlation was found between subepicardial adipose tissue thickness and any angiographic or other clinical variables (p>0.05). Neither the proportion of patients with significant or any CAD nor the severity score, CAGE > or = 20, and CAGE > or = 50 among each of four quartiles was significantly associated with subepicardial adipose tissue thickness.

CONCLUSIONS

In this selected population, the amount of subepicardial adipose tissue thickness was not associated with the severity of CAD. Whether subepicardial adipose tissue has any atherosclerotic effect remains to be proven.

Epicardial adipose tissue: anatomic, biomolecular and clinical relationships with the heart

A growing amount of evidence suggests that regional fat distribution plays an important part in the development of an unfavorable metabolic and cardiovascular risk profile. Epicardial fat is a metabolically active organ that generates various bioactive molecules, which might significantly affect cardiac function. This small, visceral fat depot is now recognized as a rich source of free fatty acids and a number of bioactive molecules, such as adiponectin, resistin and inflammatory cytokines, which could affect the coronary artery response. The observed increases in concentrations of inflammatory factors in patients who have undergone coronary artery bypass grafting remain to be confirmed in healthy individuals. Furthermore, epicardial adipose mass might reflect intra-abdominal visceral fat. Therefore, we propose that echocardiographic assessment of this tissue could serve as a reliable marker of visceral adiposity. Epicardial adipose tissue is also clinically related to left ventricular mass and other features of the metabolic syndrome, such as concentrations of LDL cholesterol, fasting insulin and adiponectin, and arterial blood pressure. Echocardiographic assessment of epicardial fat could be a simple and practical tool for cardiovascular risk stratification in clinical practice and research. In this paper, we briefly review the rapidly emerging evidence pointing to a specific role of epicardial adipose tissue both as a cardiac risk marker and as a potentially active player in the development of cardiac pathology.

Mapping epicardial fat with multi-detector computed tomography to facilitate percutaneous transepicardial arrhythmia ablation

A sizable portion of ventricular tachycardia circuits are epicardial, especially in patients with non-ischemic cardiomyopathy, e.g. Chagas disease. Thus there is a growing interest among the electrophysiologists in transepicardial mapping and myocardial ablation for treatment of arrhythmias. However, increased epicardial fat can be a significant hindrance in procedural success as it can mimic infarct during mapping and can also decrease the effectiveness of ablation. Quantitative knowledge of epicardial fat pre-procedure can potentially significantly facilitate the conduct and outcomes of these procedures. In this study we assessed the epicardial fat distribution and thickness in vivo in 59 patients who underwent multi-detector computed tomography (MDCT) for coronary artery assessment using a 16-slice scanner. Multiplanar reconstructions were obtained in the ventricular short axis at the basal, mid ventricular, and near the apex level, and in a four-chamber view. In the short axis slices, we measured epicardial fat diameter in nine segments, and in the four-chamber view, it was measured in five segments. In grooved segments the maximum fat thickness was recorded, while in non-grooved segments thickness at three equally spaced points were averaged. The results were as follows starting clockwise: superior inter-ventricular (IV) groove (all measurements are in mm, in basal, mid ventricular, and apical levels, respectively) (11.2, 8.6, 7.3), left ventricular (LV) superior lateral wall (1.0, 1.5, 1.7), LV inferior lateral wall (1.3, 2.2, 3.5), inferior IV groove (9.2, 6.5, 6.1), right ventricular (RV) diaphragmatic wall (1.4, 0.2, 1.0), acute margin (9.2, 7.3, 7.8), RV anterior free wall inferior (6.8, 4.0, 4.7), RV anterior free wall superior (6.5, 3.2, 3.1), RV superior wall (5.6, 2.7, 4.0), We measured the following four-chamber segments: LV apex (2.8 mm), left atrio-ventricular (AV) groove (12.7), right AV groove (14.8), RV apex (4.8), and anterior IV groove (7.7). The mean epicardial fat thickness for all cases was 5.3 mm (S.D. 1.6). The mean total epicardial fat for patients over 65 was 22% greater than younger patients, with a 36% increase along the RV anterior free wall, 57% along the RV diaphragmatic wall and 38% along the LV lateral wall. Women averaged 17% more total epicardial fat. In conclusion, this study was designed to provide an epicardial fat map for physicians performing percutaneous epicardial mapping and interventions. While the acute margin and RV anterior free wall tend to have high epicardial fat, and the LV lateral wall and RV diaphragmatic wall tend to have little to no fat, there is significant variation between patients. MDCT is a reliable modality for visualizing epicardial fat, and should be considered prior to undergoing procedures that are affected by epicardial fat content, especially in elderly and female populations.

Relation between epicardial adipose tissue and left ventricular mass

Visceral adiposity is a cardiovascular risk factor of growing interest. This study sought to evaluate the hypothesis of a relation between epicardial adipose tissue, the visceral adipose tissue deposited around the heart, and left ventricular morphology in healthy subjects with a wide range of adiposity. We found for the first time that an increase in epicardial fat is significantly related to an increase in left ventricular mass.

Echocardiographic epicardial adipose tissue is related to anthropometric and clinical parameters of metabolic syndrome: a new indicator of cardiovascular risk

Metabolic syndrome is related to multiple cardiovascular risk factors. Visceral adipose tissue (VAT) plays a key role in metabolic syndrome. Easy detection of VAT could be an important tool to increase knowledge of metabolic syndrome. The objective of this study was to study the relationship of echocardiographic epicardial adipose tissue to anthropometric and clinical parameters of metabolic syndrome. We selected 72 consecutive subjects, 46.5 +/- 17.4 yr of age, with a body mass index between 22 and 47 kg/m(2). Each subject underwent transthoracic echocardiogram to measure epicardial fat thickness on right ventricle and magnetic resonance imaging to calculate visceral adipose tissue. Anthropometric, metabolic, and cardiac parameters were also evaluated. Echocardiographic epicardial adipose tissue showed a very good correlation with magnetic resonance imaging abdominal VAT and epicardial fat measurement (Bland-Altman plot and linear regression). Multiple regression analysis showed that waist circumference (r(2) = 0.428; P = 0.01), diastolic blood pressure (r(2) = 0. 387; P = 0.02), and fasting insulin (r(2) = 0.387; P = 0.03) were the strongest independent variables correlated with epicardial adipose tissue. Echocardiographic epicardial adipose tissue could be applied as an easy and reliable imaging indicator of VAT and cardiovascular risk.