Usefulness of 1H MR spectroscopy in the evaluation of myocardial metabolism in patients with dilated idiopathic cardiomyopathy: pilot study

Epicardial adipose tissue and cardiac lipotoxicity: A review

Epicardial adipose tissue (EAT) has morphological and physiological contiguity with the myocardium and coronary arteries, making it a visceral fat deposit with some unique properties. Under normal circumstances, EAT exhibits biochemical, mechanical, and thermogenic cardioprotective characteristics. Under clinical processes, epicardial fat can directly impact the heart and coronary arteries by secreting proinflammatory cytokines via vasocrine or paracrine mechanisms. It is still not apparent what factors affect this equilibrium. Returning epicardial fat to its physiological purpose may be possible by enhanced local vascularization, weight loss, and focused pharmacological therapies. This review centers on EAT's developing physiological and pathophysiological dimensions and its various and pioneering clinical utilities.

Cardiac 1H MR spectroscopy: development of the past five decades and future perspectives

Continued advances in laboratory medicine are required to realize the potential of individualized medicine to impact common cardiovascular diseases. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques have advanced over recent years and offer unique, powerful insights into cardiac anatomic and metabolic changes, respectively, occurring in both nascent and advanced heart disease. Although numerous MRI-based in vivo diagnostics are already used in routine clinical practice and more are anticipated, MRS has been less incorporated into routine clinical practice. Given the ability of ¹H MRS to identify and quantify specific molecules with high sensitivity and specificity, its potential utility should be successfully transition from "bench-to-bedside" is tantalizing. The present review will highlight the development of ¹H MRS techniques for cardiac applications, observations in seminal studies with ¹H MRS, and the prospects and challenges for widespread application in patients with cardiovascular disease.

The Role of Epicardial Adipose Tissue in Heart Disease

Recent studies focused on epicardial fat, formerly relatively neglected component of the heart, have elucidated some of its key roles. It possesses several properties that can distinguish it from other adipose tissue depots. Its unique anatomical location in the heart predisposes the epicardial fat to be an important player in the physiological and biochemical regulation of cardiac homeostasis. Obesity is associated with an increase in epicardial fat mass. Excess of cardiac fat can contribute to greater left ventricular mass and work, diastolic dysfunction and attenuated septal wall thickening. Imbalance in adipokines levels secreted in autocrine or paracrine fashion by epicardial fat can contribute to the activation of the key atherogenic pathways in the setting of metabolic syndrome. Epicardial fat has also been identified as an important source of pro-inflammatory mediators worsening endothelial dysfunction, eventually leading to coronary artery disease. Increased production of pro-inflammatory factors by epicardial fat can also contribute to systemic insulin resistance in patients undergoing cardiac surgery. Here we review the most important roles of epicardial fat with respect to heart disease in the context of other underlying pathologies such as obesity and type 2 diabetes mellitus.

MRS: a noninvasive window into cardiac metabolism

A well-functioning heart requires a constant supply of a balanced mixture of nutrients to be used for the production of adequate amounts of adenosine triphosphate, which is the main energy source for most cellular functions. Defects in cardiac energy metabolism are linked to several myocardial disorders. MRS can be used to study in vivo changes in cardiac metabolism noninvasively. MR techniques allow repeated measurements, so that disease progression and the response to treatment or to a lifestyle intervention can be monitored. It has also been shown that MRS can predict clinical heart failure and death. This article focuses on in vivo MRS to assess cardiac metabolism in humans and experimental animals, as experimental animals are often used to investigate the mechanisms underlying the development of metabolic diseases. Various MR techniques, such as cardiac (31) P-MRS, (1) H-MRS, hyperpolarized (13) C-MRS and Dixon MRI, are described. A short overview of current and emerging applications is given. Cardiac MRS is a promising technique for the investigation of the relationship between cardiac metabolism and cardiac disease. However, further optimization of scan time and signal-to-noise ratio is required before broad clinical application. In this respect, the ongoing development of advanced shimming algorithms, radiofrequency pulses, pulse sequences, (multichannel) detection coils, the use of hyperpolarized nuclei and scanning at higher magnetic field strengths offer future perspective for clinical applications of MRS.

Myocardial, perivascular, and epicardial fat

Myocardial fat content refers to the storage of triglyceride droplets within cardiomyocytes. In addition, the heart and arteries are surrounded by layers of adipose tissue, exerting vasocrine and paracrine control of the subtending tissues. The rapid development of the field of noninvasive imaging has made it possible to quantify ectopic fat masses and contents with an increasing degree of accuracy. Myocardial triglyceride stores are increased in obesity, impaired glucose tolerance, and type 2 diabetes. The role of intramyocardial triglyceride accumulation in the pathogenesis of left ventricular (LV) dysfunction remains unclear. Increased triglyceride content is associated with states of fatty acid overload to the heart, saturating the oxidative capacity. It may initially serve as a fatty acid sink to circumscribe the formation of toxic lipid species and subsequently foster cardiac damage. Epicardial and perivascular fat depots may exert a protective modulation of vascular function and energy partition in a healthy situation, but their expansion turns them into an adverse lipotoxic, prothrombotic, and proinflammatory organ. They are augmented in patients with metabolic disorders and coronary artery disease (CAD). However, the progressive association between the quantity of fat and disease severity in terms of extent of plaque calcification or noncalcified areas, markers of plaque vulnerability, and number of vessels involved is less confirmed. Functional or hybrid imaging may contribute to a better definition of disease severity and unveil the direct myocardial and vascular targets of adipose tissue action.

Metabolic toxicity of the heart: insights from molecular imaging

There is convincing evidence that alterations in myocardial substrate use play an important role in the normal and diseased heart. In this review, insights gained by using quantitative molecular imaging by positron emission tomography and magnetic resonance spectroscopy in the study of human myocardial metabolism will be discussed, and attention will be paid to the effects of nutrition, gender, aging, obesity, diabetes, cardiac hypertrophy, ischemia, and heart failure. The heart is an omnivore organ, relying on metabolic flexibility, which is compromised by the occurrence of defects in coronary flow reserve, insulin-mediated glucose disposal, and metabolic-mechanical coupling. Obesity, diabetes, and ischemic cardiomyopathy appear as states of high uptake and oxidation of fatty acids, that compromise the ability to utilize glucose under stimulated conditions, and lead to misuse of energy and oxygen, disturbing mechanical efficiency. Idiopathic heart failure is a complex disease frequently coexisting with diabetes, insulin resistance and hypertension, in which the end stage of metabolic toxicity manifests as severe mitochondrial disturbance, inability to utilize fatty acids, and ATP depletion. The current literature provides evidence that the primary events in the metabolic cascade outlined may originate in extra-cardiac organs, since fatty acid, glucose levels, and insulin action are mostly controlled by adipose tissue, skeletal muscle and liver, and that a broader vision of organ cross-talk may further our understanding of the primary and the adaptive events involved in metabolic heart toxicity.

Magnetic resonance imaging in myocardial ischemia

PURPOSE OF REVIEW

MRI is a novel strategy to assess myocardial ischemia. It provides information on myocardial perfusion, viability, and potentially the extent of coronary artery disease. This technology may replace many of the current noninvasive and, perhaps, invasive techniques in the diagnosis and management of patients with coronary artery disease. This review aims to cover the major advances in cardiac MRI related to both diagnosis and therapy of myocardial ischemia.

RECENT FINDINGS

Although improved image acquisition techniques have made it possible to obtain excellent image quality in most patients, powerful processing software has permitted the quantification of accurate and reproducible functional information regarding perfusion, wall motion, and viability. Stem cell delivery and gene therapy to the myocardium using cardiac MRI has been shown to be feasible. The use of 3-T systems for cardiac imaging and the imaging of atherosclerosis with MRI are currently being studied.

SUMMARY

MRI is a highly accurate method of characterizing both reversible and irreversible myocardial injury and of obtaining information on myocardial viability. It has the ability to prognostic patients by evaluating ejection fraction and contractility. Robust and uncomplicated methodologies for coronary MR angiography are almost on the horizon. Quantification of several parameters used to diagnose, prognosticate, and follow patients with ischemic heart disease should be much easier in the future. It may, with the recent advances in imaging such as 3-T systems, provide major noninvasive diagnostic capability. Cardiac MRI, with its improved imaging, and its ability to treat and monitor various forms of invasive and noninvasive therapy, may attain its potential as a "one-stop shop" in the near future.