This article or section possibly contains synthesis of material that does not verifiably mention or relate to the main topic.(March 2020) |
Diabetic cardiomyopathy | |
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Universal blue circle symbol for diabetes. [1] | |
Specialty | Cardiology |
Diabetic cardiomyopathy is a disorder of the heart muscle in people with diabetes. It can lead to inability of the heart to circulate blood through the body effectively, a state known as heart failure(HF), [2] with accumulation of fluid in the lungs (pulmonary edema) or legs (peripheral edema). Most heart failure in people with diabetes results from coronary artery disease, and diabetic cardiomyopathy is only said to exist if there is no coronary artery disease to explain the heart muscle disorder. [3]
One particularity of diabetic cardiomyopathy is the long latent phase, during which the disease progresses but is completely asymptomatic. In most cases, diabetic cardiomyopathy is detected with concomitant hypertension or coronary artery disease. One of the earliest signs is mild left ventricular diastolic dysfunction with little effect on ventricular filling. Also, the diabetic patient may show subtle signs of diabetic cardiomyopathy related to decreased left ventricular compliance or left ventricular hypertrophy or a combination of both. A prominent "a" wave can also be noted in the jugular venous pulse, and the cardiac apical impulse may be overactive or sustained throughout systole. After the development of systolic dysfunction, left ventricular dilation and symptomatic heart failure, the jugular venous pressure may become elevated, the apical impulse would be displaced downward and to the left. Systolic mitral murmur is not uncommon in these cases. These changes are accompanied by a variety of electrocardiographic changes that may be associated with diabetic cardiomyopathy in 60% of patients without structural heart disease, although usually not in the early asymptomatic phase. Later in the progression, a prolonged QT interval may be indicative of fibrosis. Given that diabetic cardiomyopathy's definition excludes concomitant atherosclerosis or hypertension, there are no changes in perfusion or in atrial natriuretic peptide levels up until the very late stages of the disease, [4] when the hypertrophy and fibrosis become very pronounced.
Defects in cellular processes such as autophagy and mitophagy are thought to contribute to the development of diabetic cardiomyopathy. [2] Diabetic cardiomyopathy is characterized functionally by ventricular dilation, enlargement of heart cells, prominent interstitial fibrosis and decreased or preserved systolic function [5] in the presence of a diastolic dysfunction. [6] [7] [8]
While it has been evident for a long time that the complications seen in diabetes are related to the hyperglycemia associated to it, several factors have been implicated in the pathogenesis of the disease. Etiologically, four main causes are responsible for the development of heart failure in diabetic cardiomyopathy: microangiopathy and related endothelial dysfunction, autonomic neuropathy, metabolic alterations that include abnormal glucose use and increased fatty acid oxidation, generation and accumulation of free radicals, and alterations in ion homeostasis, especially calcium transients.[ citation needed ] Additional effects include inflammation and upregulation of local angiotensin systems.
Diabetic cardiomyopathy may be associated with restrictive (HFpEF) and dilated phenotypes (HFrEF). HFpEF results predominantly from hyperinsulinemia, hyperglycemia, lipotoxicity, AGEs and microvascular rarefication. HFrEF is associated with autoimmunity, hyperglycemia, lipotoxicity, microvascular rarefication and AGE formation. [9]
Microangiopathy can be characterized as subendothelial and endothelial fibrosis in the coronary microvasculature of the heart. This endothelial dysfunction leads to impaired myocardial blood flow reserve as evidence by echocardiography. [10] About 50% of diabetics with diabetic cardiomyopathy show pathologic evidence for microangiopathy such as sub-endothelial and endothelial fibrosis, compared to only 21% of non-diabetic heart failure patients. [11] Over the years, several hypotheses were postulated to explain the endothelial dysfunction observed in diabetes. It was hypothesized that the extracellular hyperglycemia leads to an intracellular hyperglycemia in cells unable to regulate their glucose uptake, most predominantly, endothelial cells. Indeed, while hepatocytes and myocytes have mechanisms allowing them to internalize their glucose transporter, endothelial cells do not possess this ability. The consequences of increased intracellular glucose concentration are fourfold, all resulting from increasing concentration of glycolytic intermediates upstream of the rate-limiting glyceraldehyde-3-phosphate reaction which is inhibited by mechanisms activated by increased free radical formation, common in diabetes. [12] Four pathways, enumerated below all explain part of the diabetic complications. First, it has been widely reported since the 1960s that hyperglycemia causes an increase in the flux through aldose reductase and the polyol pathway. Increased activity of the detoxifying aldose reductase enzyme leads to a depletion of the essential cofactor NADH, thereby disrupting crucial cell processes. [13] Second, increasing fructose 6-phosphate, a glycolysis intermediate, will lead to increased flux through the hexosamine pathway. This produces N-acetyl glucosamine that can add on serine and threonine residues and alter signaling pathways as well as cause pathological induction of certain transcription factors. [12] Third, hyperglycemia causes an increase in diacylglycerol, which is also an activator of the Protein Kinase C (PKC) signaling pathway. Induction of PKC causes multiple deleterious effects, including but not limited to blood flow abnormalities, capillary occlusion and pro-inflammatory gene expression. [14] Finally, glucose, as well as other intermediates such as fructose and glyceraldehyde-3-phosphate, when present in high concentrations, promote the formation of advanced glycation endproducts (AGEs). These, in turn, can irreversibly cross link to proteins and cause intracellular aggregates that cannot be degraded by proteases and thereby, alter intracellular signalling. [15] Also, AGEs can be exported to the intercellular space where they can bind AGE receptors (RAGE). This AGE/RAGE interaction activates inflammatory pathways such as NF-κB, in the host cells in an autocrine fashion, or in macrophages in a paracrine fashion. Neutrophil activation can also lead to NAD(P)H oxidase production of free radicals further damaging the surrounding cells. [16] Finally, exported glycation products bind extracellular proteins and alter the matrix, cell-matrix interactions and promote fibrosis. [17] A major source of increased myocardial stiffness is crosslinking between AGEs and collagen. In fact, a hallmark of uncontrolled diabetes is glycated products in the serum and can be used as a marker for diabetic microangiopathy. [18]
While the heart can function without help from the nervous system, it is highly innervated with autonomic nerves, regulating the heart beat according to demand in a fast manner, prior to hormonal release. The autonomic innervations of the myocardium in diabetic cardiomyopathy are altered and contribute to myocardial dysfunction. Unlike the brain, the peripheral nervous system does not benefit from a barrier protecting it from the circulating levels of glucose. Just like endothelial cells, nerve cells cannot regulate their glucose uptake and suffer the same type of damages listed above. Therefore, the diabetic heart shows clear denervation as the pathology progresses. This denervation correlates with echocardiographic evidence of diastolic dysfunction and results in a decline of survival in patients with diabetes from 85% to 44%. Other causes of denervation are ischemia from microvascular disease and thus appear following the development of microangiopathy.[ citation needed ]
Diabetes is associated with increased inflammation, which is mediated by generation of abnormal fatty acids, AGEs and other mechanisms. [19] The resulting cytokine profile promotes hypertrophy and apoptosis of cardiomyocytes, abnormal calcium signaling, impaired myocardial contractility and myocardial fibrosis. [20] Additionally, it may lead to microvascular dysfunction, either directly or via endothelial damage, thereby promoting myocardial ischemia. [21]
Diagnostic approaches for diabetic cardiomyopathy include echocardiography, cardiac MRI investigations, Multi‐slice computed tomography (MsCT), and nuclear imaging. [22] Potential risks of the investigation (e.g. exposure to radiation) and diagnostic utility should be weighed for an optimised personalised procedure. [22]
At present, there is no effective specific treatment available for diabetic cardiomyopathy. [23] Treatment rationale centers around intense glycemic control through diet and preferential use of certain medications in diabetic patients at high risk for developing cardiovascular disease or heart failure. A rationale for therapeutic decision making in individuals with coexistent diabetes mellitus and HF is less clear because there is a possibility that additional factors beyond glycemia might contribute to the increased HF risk in diabetes mellitus. [24] Thiazolidinediones are not recommended in patients with NYHA Class III or IV heart failure secondary to fluid retention. [25]
As with most other heart diseases, ACE inhibitors can also be administered. An analysis of major clinical trials shows that diabetic patients with heart failure benefit from such a therapy to a similar degree as non-diabetics. [26] Similarly, beta blockers are also common in the treatment of heart failure concurrently with ACE inhibitors. [24]
Beta cells (β-cells) are specialized endocrine cells located within the pancreatic islets of Langerhans responsible for the production and release of insulin and amylin. Constituting ~50–70% of cells in human islets, beta cells play a vital role in maintaining blood glucose levels. Problems with beta cells can lead to disorders such as diabetes.
Hyperglycemia or hyperglycaemia is the situation in which blood glucose level is higher than in a healthy subject. A fasting healthy human shows blood glucose level up to 5.6 mmol/L (100 mg/dL). After a meal (postprandial) containing carbohydrates, healthy subjects show postpandrial euglycemic peaks of less than 140 mg/dL (7.8 mmol/L). Therefore, fasting hyperglycemia are values of blood glucose higher than 5.6 mmol/L (100 mg/dL) whereas postprandial hyperglycemia are values higher than 140 mg/dL (7.8 mmol/L). Postprandial hyperglycemic levels as high as 155 mg/dL (8.6 mmol/L) at 1-h are associated with T2DM-related complications, which worsen as the degree of hyperglycemia increases. Patients with diabetes are oriented to avoid exceeding the recommended postprandial threshold of 160 mg/dL (8.89 mmol/L) for optimal glycemic control. Values of blood glucose higher than 160 mg/dL are classified as ‘very high’ hyperglycemia, a condition in which an excessive amount of glucose (glucotoxicity) circulates in the blood plasma. These values are higher than the renal threshold of 180 mg/dL (10 mmol/L) up to which glucose reabsorption is preserved at physiological rates and insulin therapy is not necessary. Blood glucose values higher than the cutoff level of 200 mg/dL (11.1 mmol/L) are used to diagnose T2DM and strongly associated with metabolic disturbances, although symptoms may not start to become noticeable until even higher values such as 13.9–16.7 mmol/L (~250–300 mg/dL). A subject with a consistent fasting blood glucose range between ~5.6 and ~7 mmol/L is considered slightly hyperglycemic, and above 7 mmol/L is generally held to have diabetes. For diabetics, glucose levels that are considered to be too hyperglycemic can vary from person to person, mainly due to the person's renal threshold of glucose and overall glucose tolerance. On average, however, chronic levels above 10–12 mmol/L (180–216 mg/dL) can produce noticeable organ damage over time.
Microangiopathy is a disease of the microvessels, small blood vessels in the microcirculation. It can be contrasted to macroangiopathies such as atherosclerosis, where large and medium-sized arteries are primarily affected.
Microvascular angina (MVA), previously known as cardiac syndrome X, also known as coronary microvascular dysfunction(CMD) or microvascular coronary disease is a type of angina (chest pain) with signs associated with decreased blood flow to heart tissue but with normal coronary arteries.
Glycated hemoglobin is a form of hemoglobin (Hb) that is chemically linked to a sugar. 'Glycosylated haemoglobin' is a misnomer, as glycation and glycosylation are different processes, of which only the former is relevant in this case.
Advanced glycation end products (AGEs) are proteins or lipids that become glycated as a result of exposure to sugars. They are a bio-marker implicated in aging and the development, or worsening, of many degenerative diseases, such as diabetes, atherosclerosis, chronic kidney disease, and Alzheimer's disease.
Diabetic nephropathy, also known as diabetic kidney disease, is the chronic loss of kidney function occurring in those with diabetes mellitus. Diabetic nephropathy is the leading causes of chronic kidney disease (CKD) and end-stage renal disease (ESRD) globally. The triad of protein leaking into the urine, rising blood pressure with hypertension and then falling renal function is common to many forms of CKD. Protein loss in the urine due to damage of the glomeruli may become massive, and cause a low serum albumin with resulting generalized body swelling (edema) so called nephrotic syndrome. Likewise, the estimated glomerular filtration rate (eGFR) may progressively fall from a normal of over 90 ml/min/1.73m2 to less than 15, at which point the patient is said to have end-stage renal disease. It usually is slowly progressive over years.
Diabetic angiopathy is a form of angiopathy associated with diabetic complications. While not exclusive, the two most common forms are diabetic retinopathy and diabetic nephropathy, whose pathophysiologies are largely identical. Other forms of diabetic angiopathy include diabetic neuropathy and diabetic cardiomyopathy.
Tachycardia-induced cardiomyopathy (TIC) is a disease where prolonged tachycardia or arrhythmia causes an impairment of the myocardium, which can result in heart failure. People with TIC may have symptoms associated with heart failure and/or symptoms related to the tachycardia or arrhythmia. Though atrial fibrillation is the most common cause of TIC, several tachycardias and arrhythmias have been associated with the disease.
Fructosamines are compounds that result from glycation reactions between glucose and a primary amine, followed by isomerization via the Amadori rearrangement. Biologically, fructosamines are recognized by fructosamine-3-kinase, which may trigger the degradation of advanced glycation end-products. Fructosamine can also refer to the specific compound 1-amino-1-deoxy-D-fructose (isoglucosamine), first synthesized by Nobel laureate Hermann Emil Fischer in 1886.
RAGE, also called AGER, is a 35 kilodalton transmembrane receptor of the immunoglobulin super family which was first characterized in 1992 by Neeper et al. Its name comes from its ability to bind advanced glycation endproducts (AGE), which include chiefly glycoproteins, the glycans of which have been modified non-enzymatically through the Maillard reaction. In view of its inflammatory function in innate immunity and its ability to detect a class of ligands through a common structural motif, RAGE is often referred to as a pattern recognition receptor. RAGE also has at least one other agonistic ligand: high mobility group protein B1 (HMGB1). HMGB1 is an intracellular DNA-binding protein important in chromatin remodeling which can be released by necrotic cells passively, and by active secretion from macrophages, natural killer cells, and dendritic cells.
Alpha-glucosidase inhibitors (AGIs) are oral anti-diabetic drugs used for diabetes mellitus type 2 that work by preventing the digestion of carbohydrates. They are found in raw plants/herbs such as cinnamon and bacteria. Carbohydrates are normally converted into simple sugars (monosaccharides) by alpha-glucosidase enzymes present on cells lining the intestine, enabling monosaccharides to be absorbed through the intestine. Hence, alpha-glucosidase inhibitors reduce the impact of dietary carbohydrates on blood sugar.
Takotsubo cardiomyopathy or takotsubo syndrome (TTS), also known as stress cardiomyopathy, is a type of non-ischemic cardiomyopathy in which there is a sudden temporary weakening of the muscular portion of the heart. It usually appears after a significant stressor, either physical or emotional; when caused by the latter, the condition is sometimes called broken heart syndrome.
Amine oxidase, copper containing 3 (AOC3), also known as vascular adhesion protein (VAP-1) and HPAO is an enzyme that in humans is encoded by the AOC3 gene on chromosome 17. This protein is a member of the semicarbazide-sensitive amine oxidase family of enzymes and is associated with many vascular diseases.
The dawn phenomenon, sometimes called the dawn effect, is an observed increase in blood sugar (glucose) levels that takes place in the early-morning, often between 2 a.m. and 8 a.m. First described by Schmidt in 1981 as an increase of blood glucose or insulin demand occurring at dawn, this naturally occurring phenomenon is frequently seen among the general population and is clinically relevant for patients with diabetes as it can affect their medical management. In contrast to Chronic Somogyi rebound, the dawn phenomenon is not associated with nocturnal hypoglycemia.
Complications of diabetes are secondary diseases that are a result of elevated blood glucose levels that occur in diabetic patients. These complications can be divided into two types: acute and chronic. Acute complications are complications that develop rapidly and can be exemplified as diabetic ketoacidosis (DKA), hyperglycemic hyperosmolar state (HHS), lactic acidosis (LA), and hypoglycemia. Chronic complications develop over time and are generally classified in two categories: microvascular and macrovascular. Microvascular complications include neuropathy, nephropathy, and retinopathy; while cardiovascular disease, stroke, and peripheral vascular disease are included in the macrovascular complications.
In recent years it has become apparent that the environment and underlying mechanisms affect gene expression and the genome outside of the central dogma of biology. It has been found that many epigenetic mechanisms are involved in the regulation and expression of genes such as DNA methylation and chromatin remodeling. These epigenetic mechanisms are believed to be a contributing factor to pathological diseases such as type 2 diabetes. An understanding of the epigenome of diabetes patients may help to elucidate otherwise hidden causes of this disease.
Argpyrimidine is an organic compound with the chemical formula C11H18N4O3. It is an advanced glycation end-product formed from arginine and methylglyoxal through the Maillard reaction. Argpyrimidine has been studied for its food chemistry purposes and its potential involvement in aging diseases and diabetes mellitus.
Ischemic cardiomyopathy is a type of cardiomyopathy caused by a narrowing of the coronary arteries which supply blood to the heart. Typically, patients with ischemic cardiomyopathy have a history of acute myocardial infarction, however, it may occur in patients with coronary artery disease, but without a past history of acute myocardial infarction. This cardiomyopathy is one of the leading causes of sudden cardiac death. The adjective ischemic means characteristic of, or accompanied by, ischemia — local anemia due to mechanical obstruction of the blood supply.
Diabetes mellitus (DM) is a type of metabolic disease characterized by hyperglycemia. It is caused by either defected insulin secretion or damaged biological function, or both. The high-level blood glucose for a long time will lead to dysfunction of a variety of tissues.