Advances in Cardiology最新文献

Both type I and type II diabetes are powerful and independent risk factors for coronary artery disease (CAD), stroke, and peripheral arterial disease. Atherosclerosis accounts for virtually 80% of all deaths among diabetic patients. Prolonged exposure to hyperglycemia is now recognized as a major factor in the pathogenesis of diabetic complications, including atherosclerosis. Hyperglycemia induces a large number of alterations at the cellular level of vascular tissue that potentially accelerates the atherosclerotic process. Animal and human studies have elucidated several major mechanisms that encompass most of the pathological alterations observed in the diabetic vasculture. These include: (1) Nonenzymatic glycosylation of proteins and lipids which can interfere with their normal function by disrupting molecular conformation, alter enzymatic activity, reduce degradative capacity, and interfere with receptor recognition. In addition, glycosylated proteins interact with a specific receptor present on all cells relevant to the atherosclerotic process, including monocyte-derived macrophages, endothelial cells, and smooth muscle cells. The interaction of glycosylated proteins with their receptor results in the induction of oxidative stress and proinflammatory responses. (2) Protein kinase C (PKC) activation with subsequent alteration in growth factor expression. (3) Shunting of excess intracellular glucose into the hexosamine pathway leads to O-linked glycosylation of various enzymes with perturbations in normal enzyme function. (4) Hyperglycemia increases oxidative stress through several pathways. A major mechanism appears to be the overproduction of the superoxide anion (O-2 ) by the mitochondrial electron transport chain. (5) Hyperglycemia promotes inflammation through the induction of cytokine secretion by several cell types including monocytes and adipocytes. Importantly, there appears to be a tight pathogenic link between hyperglycemia-induced oxidant stress and other hyperglycemia-dependent mechanisms of vascular damage described above, namely AGEs formation, PKC activation, and increased flux through the hexosamine pathway. For example, hyperglycemia-induced oxidative stress promotes both the formation of advanced glycosylation end products and PKC activation.

Arterial stiffness is an independent risk factor for premature cardiovascular morbidity and mortality that can be evaluated by noninvasive methods and can be reduced by good clinical management. The present chapter examines the association between arterial stiffness and cardiovascular risk factors including hypertension, metabolic syndrome, diabetes, advanced renal failure, hypercholesterolemia and obesity. The mechanisms responsible for the structural and functional modifications of the arterial wall are also described. We deal with parameters related to arterial compliance, focusing on two of them, pulse wave velocity and the augmentation index, useful in rapid assessment of arterial compliance by the bedside. Data that highlight the role of aortic pulse wave velocity and the augmentation index as independent factors in predicting fatal and nonfatal cardiovascular events in different populations are briefly presented. A number of lifestyle changes and traditional antihypertensive agents that improve arterial compliance are finally discussed. Novel therapies, such as statins, thiazolidindinediones, phosphodiesterase inhibitors and inhibitors or breakers of advanced glycation end product cross-links between colagen and elastin hold substantial promise.

Ischemic stroke and vascular cognitive impairment are leading causes of long-term disability and constitute a major public health burden and a significant economic burden to health systems. An increasing body of evidence demonstrates that disorders of glucose metabolism including diabetes, and the intermediate states of impaired fasting glucose and impaired glucose tolerance, as well as the cluster of risk factors known as the metabolic syndrome, are important risk factors for ischemic stroke. The associations with accelerated cognitive decline and dementia are also discussed. Underlying pathogenetic mechanisms are myriad but include insulin resistance, endothelial dysfunction, dyslipidemia, chronic inflammation, procoagulability, and impaired fibrinolysis. The high risk associated with diabetes and other disorders of glucose metabolism carries important implications for preventive strategies for cerebrovascular disease and vascular cognitive impairment that are currently under investigation.

Five types of oral antihyperglycemic drugs are currently approved for the treatment of diabetes: biguanides, sulfonylureas, meglitinides, glitazones and alpha-glucosidase inhibitors. We briefly review the cardiovascular effects of the most commonly used antidiabetic drugs in these groups in an attempt to improve knowledge and awareness regarding their influences and potential risks when treating patients with coronary artery disease (CAD). Regarding biguanides, gastrointestinal disturbances such as diarrhea are frequent, and the intestinal absorption of group B vitamins and folate is impaired during chronic therapy. This deficiency may lead to increased plasma homocysteine levels which, in turn, accelerate the progression of vascular disease due to adverse effects on platelets, clotting factors, and endothelium. The existence of a graded association between homocysteine levels and overall mortality in patients with CAD is well established. In addition, metformin may lead to lethal lactic acidosis, especially in patients with clinical conditions that predispose to this complication, such as heart failure or recent myocardial infarction. Sulfonylureas avoid ischemic preconditioning. During myocardial ischemia, they may prevent opening of the ATP-dependent potassium channels, impeding the necessary hyperpolarization that protects the cell by blocking calcium influx. Meglitinides may exert similar effects due to their analogous mechanism of action. During treatment with glitazones, edema has been reported in 5% of patients, and these drugs are contraindicated in diabetics with NYHA class III or IV cardiac status. The long-term effects of alpha-glucosidase inhibitors on morbidity and mortality rates and on diabetic micro- and macrovascular complications is still unknown. Combined sulfonylurea/metformin therapy reveals additive effects on mortality. Four points should be mentioned: (1) the five oral antidiabetic drug groups present proven or potential cardiac hazards; (2) these hazards are not mere 'side effects' but are deeply rooted in the drugs' mechanisms of action; (3) current data indicate that combined glibenclamide/metformin therapy seems to present a special risk and should be avoided in the long-term management of type 2 diabetics with proven CAD, and (4) Non-Insulin Antidiabetic Therapy in Diabetic Cardiac Patients 155 customized antihyperglycemic pharmacological approaches should be investigated for the optimal treatment of diabetic patients with heart disease. New possibilities are represented by incretin mimetic compounds, dipeptidyl peptidase (DPP)-4 inhibitors, inhaled insulin and eventually oral insulin.

The reported incidence of metabolic syndrome among patients with an acute coronary syndrome varies between 29 and 46%. The standard fasting cut-off levels for glucose and blood pressure cannot be applied on admission in patients with acute coronary syndrome and therefore modified criteria were used to define the metabolic syndrome. Patients with metabolic syndrome and acute coronary syndrome had increased incidence of heart failure, and worse long-term mortality compared to those without metabolic syndrome. However, they had less heart failure than those with known diabetes mellitus. Hyperglycemia as a risk factor for poor outcome is particularly significant in patients with metabolic syndrome. De novo identification of the metabolic syndrome on admission has the potential to improve risk stratification and management of patients with an acute coronary syndrome.