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Guidelines on diabetes, pre-diabetes, and cardiovascular diseases: executive summary,
The Task Force on Diabetes and Cardiovascular Diseases of the European Society of Cardiology (ESC) and of the European Association for the Study of Diabetes (EASD)
Authors/Task Force Members,
gorzata Bartnik
Sweden
Germany
Poland
Belgium
UK
The Netherlands
Italy
Sweden
Finland
Sweden
Italy
Sweden
Finland
Iceland
Other Contributors,
Belgium
Italy
Sweden
Finland
ESC Committee for Practice Guidelines (CPG),
Italy
France
Poland
UK
France
The Netherlands
Norway
Greece
France
Italy
Portugal
Germany
Spain
Spain
Document Reviewers,
The Netherlands
France
France
Germany
Italy
Denmark
Germany
Spain
Ireland
Portugal
Germany
Finland
Israel
Austria
Italy
UK
* Corresponding author. Lars Rydén, Department of Cardiology, Karolinska University Hospital Solna, SE-171 76 Stockholm, Sweden. Tel: +49 89 3068 2523; Fax: +49 89 3068 3906. Eberhard Standl, Department of Endocrinology, Munich Schwabing Hospital, D-80804 Munich, Germany. Tel: +49 89 3068 2523; Fax: +49 89 3068 3906. E-mail address: lars.ryden{at}ki.se; eberhard.standl{at}lrz.uni_muenchen.de
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Preamble |
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Top
Preamble
IntroductionGuidelines and Expert Consensus documents aim to present management and recommendations based on all of the relevant evidence on a particular subject in order to help physicians to select the best possible management strategies for the individual patient, suffering from a specific condition, taking into account not only the impact on outcome, but also the risk benefit ratio of a particular diagnostic or therapeutic procedure. The ESC recommendations for guidelines production can be found on the ESC website
. In brief, the ESC appoints experts in the field to carry out a comprehensive and critical evaluation of the use of diagnostic and therapeutic procedures and to assess the risk–benefit ratio of the therapies recommended for management and/or prevention of a given condition. The strength of evidence for or against particular procedures or treatments is weighed according to predefined scales for grading recommendations and levels of evidence, as outlined below. Once the document has been finalized and approved by all the experts involved in the Task Force, it is submitted to outside specialists for review. If necessary, the document is revised once more to be finally approved by the Committee for Practice Guidelines and selected members of the Board of the ESC.
The ESC Committee for Practice Guidelines (CPG) supervises and coordinates the preparation of new Guidelines and Expert Consensus Documents produced by Task Forces, expert groups, or consensus panels. The chosen experts in these writing panels are asked to provide disclosure statements of all relationships they may have, which might be perceived as real or potential conflicts of interest. These disclosure forms are kept on file at the European Heart House, headquarters of the ESC. The Committee is also responsible for the endorsement of these Guidelines and Expert Consensus Documents or statements.
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Introduction |
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Diabetes and cardiovascular diseases (CVD) often appear as two sides of a coin: diabetes mellitus (DM) has been rated as an equivalent of coronary heart disease, and conversely, many patients with established coronary heart disease suffer from diabetes or its pre-states. Thus, it is high time that diabetologists and cardiologists join their forces to improve the quality management in diagnosis and care for the millions of patients who have both cardiovascular and metabolic diseases in common. The cardio-diabetological approach not only is of utmost importance for the sake of those patients, but also instrumental for further progress in the fields of cardiology and diabetology and prevention.
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The ESC and the EASD accepted this challenge and have developed joint, evidence-based guidelines for diabetes and CVD. Experts from both sides were asked to form a Task Force. The core approach of the group is depicted in Figure 1. An algorithm was developed to help discover CVD in patients with diabetes, and vice versa, the metabolic diseases in patients with coronary heart disease, setting the basis for appropriate joint therapy.
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This executive summary, an abridged version of the full document, is intended for the practising physician. It focuses on the background and the most relevant references behind the given recommendations. More detailed information to be found in the full text document. The numbering of references is the same in the executive summary as in this document. Figures and tables are, however, numbered in numerical order in the executive summary and do therefore not necessarily have the same numbers in the full-text document. The latter also contains a detailed chapter on the pathophysiological connections between glucose abnormalities and CVD and much more information on the economical aspects on diabetes and CVD. The full text guidelines will be available from the ESC/EASD web pages (www.escardio.org and www.easd.org).
It is a privilege for the co-chairmen having been able to work with the best reputed experts in the field and to give these guidelines now to the community of cardiologists and diabetologists. We wish to thank all members of the task force, who so generously shared their knowledge, as well as the referees for their tremendous input. Special thanks go to Professor Carl Erik Mogensen for his advice on the diabetic renal disease and microalbuminuria sections. We would also like to thank the ESC and the EASD for making these guidelines possible. Finally, we want to express our appreciation of the guideline team at the Heart House, especially Veronica Dean, for extremely helpful support.
Stockholm and Munich September 2006
Professor Lars Rydén, Past-President ESC
Professor Eberhard Standl, Vice President EASD
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Definition, classification, and screening of diabetes and pre-diabetic glucose abnormalities |
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aClass of recommendation.
bLevel of evidence.
DM is a metabolic disorder of multiple aetiology characterized by chronic hyperglycaemia with disturbances of carbohydrate, fat, and protein metabolism resulting from defects of insulin secretion, insulin action, or a combination of both.1 Type 1 diabetes is due to a virtually complete lack of endogenous pancreatic insulin production, whereas in type 2 diabetes, the rising blood glucose results from a combination of genetic predisposition, unhealthy diet, physical inactivity, and increasing weight with a central distribution resulting in complex pathophysiological processes. DM is associated with the development of specific long-term organ damage due to microvascular disease (diabetes complications). Patients with diabetes are also at a particularly high risk for cardiovascular, cerebrovascular, and peripheral artery disease.
Definition and classification of diabetes
Criteria for glucometabolic disturbances as established by the World Health Organization (WHO)4,5 and the American Diabetes Association (ADA)6,7 are outlined in Table 1.
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Classification of diabetes (Table 2) includes aetiological types and different clinical stages of hyperglycaemia.8 Four main aetiological categories have been identified as diabetes type 1, type 2, other specific types, and gestational diabetes, as detailed in the WHO document.4
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Type 1 diabetes. It is characterized by deficiency of insulin due to destructive lesions of pancreatic ß-cells, typically occurs in young subjects, but may occur at any age.9 People who have antibodies to pancreatic ß-cells, such as glutamic acid decarboxylase antibodies, are likely to develop either typical acute onset or slow-progressive insulin-dependent diabetes.10,11
Type 2 diabetes. It is caused by a combination of decreased insulin secretion and decreased insulin sensitivity. Early stages of type 2 diabetes is characterized by insulin resistance causing excessive post-prandial hyperglycaemia. This is followed by a deteriorating first-phase insulin response to increased blood glucose concentrations.12 Type 2 diabetes, comprising over 90% of adults with diabetes, typically develops after middle age. The patients are often obese and physically inactive.
Gestational Diabetes. This constitutes any glucose perturbation that develops during pregnancy and disappears after delivery. Approximately 70% of females with gestational diabetes will develop diabetes over time.13
The currently valid clinical classification criteria, issued by the WHO4 and ADA,7 are currently under review by the WHO. Updated criteria will be introduced soon. The WHO recommendations for glucometabolic classification are based on measuring both fasting and 2 h post-load glucose concentrations and recommend that a standardized 75 g OGTT should be performed in the absence of overt hyperglycaemia.4 The cutpoints for diabetes on fasting and 2 h post-load glucose values were primarily determined by the values where the prevalence of diabetic retinopathy, which is a specific complication of hyperglycaemia, starts to increase. Even though macrovascular diseases are major causes of death in patients with type 2 diabetes and IGT, macrovascular disease has not been considered in the classification. The National Diabetes Data Group2 and the WHO3 coined the term IGT, an intermediate category between normal glucose tolerance and diabetes. The ADA6 and the WHO Consultation4 proposed some changes to the diagnostic criteria for diabetes and introduced a new category called impaired fasting glucose/glycaemia (IFG). The ADA recently decreased the lower cutoff point for IFG from 6.1 to 5.6 mmol/L,7 but this has been criticized and has not yet been adopted by the WHO expert group, which recommends keeping the previous cutpoints as shown in the WHO consultation report in 1999. These criteria were reviewed by a new WHO expert group in 2005.
In order to standardize glucose determinations, plasma has been recommended as the primary specimen. Many equipment uses either whole blood or venous or capillary blood. Cutoff points for these vehicles have been given15 as outlined in Table 3.
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Glucometabolic categorization based on FPG may differ from that based on a 2 h post-load glucose. Having a normal FPG requires the ability to maintain an adequate basal insulin secretion and an appropriate hepatic insulin sensitivity to control hepatic glucose output. During an OGTT, the normal response to the absorption of the glucose load is both to suppress hepatic glucose output and to enhance hepatic and skeletal muscle glucose uptake. To keep a post-load glucose level within the normal range requires appropriate dynamics of the ß-cell secretory response, amount, and timing, in combination with adequate hepatic and muscular insulin sensitivity.1,16,17
Glycated haemoglobin
Glycated haemoglobin (HbA1c), a useful measure of the efficacy of glucose-lowering treatment, is an integrated summary of circadian blood glucose during the preceding 6–8 weeks, equivalent to the lifespan of erythrocytes.18 HbA1c has never been recommended as a diagnostic test for diabetes. HbA1c is insensitive in the low range. A normal HbA1c cannot exclude the presence of diabetes or IGT.
Markers of glucometabolic perturbations
A difficulty in the diagnosis of diabetes is the lack of an identified, unique biological marker that would separate people with IFG, IGT, or diabetes from people with normal glucose metabolism. The use of diabetic retinopathy has been discussed. The limitation is that this condition usually becomes evident only after several years of hyperglycaemic exposure.1,5–10 Thus far, total mortality and CVD have not been considered for defining those glucose categories that carry a significant risk. Nevertheless, the vast majority of people with diabetes die from CVD, and asymptomatic glucometabolic perturbations more than double mortality and the risk for myocardial infarction (MI) and stroke. Since the majority of type 2 diabetic patients develop CVD, which is a more severe and costly complication of diabetes than retinopathy, CVD should be considered when defining cutpoints for glucose.
Comparisons between FPG and 2 h post-load glucose
The DECODE study has shown that any mortality risk in people with elevated FPG is related to a concomitant elevated 2 h post-load glucose.15,19,20 Thus, the current cutoff point for diabetes based on a 2 h post-load glucose level of 
11.1 mmol/L may be too high. It has been noted that, although an FPG level 7.0 mmol/L and a 2 h post-load glucose level of 11.1 mmol/L sometimes identify the same individuals, often they may not coincide. In the DECODE study21 recruiting patients with diabetes by either criterion alone or their combination, only 28% met both, 40% met the fasting, and 31% the 2 h post-load glucose criterion only. Among those who met the 2 h post-load glucose criterion, 52% did not meet the fasting criterion, and 59% of those who met the fasting criterion did not meet the 2 h post-load glucose criterion.
Screening for undiagnosed diabetes
Recent estimates suggest that 195 million people throughout the world have diabetes. This number will increase to 330, maybe even to 500 million, by 2030.23,24 Up to 50% of all patients with type 2 diabetes are undiagnosed21,22,34 since they remain asymptomatic for many years. Detecting these patients is important for public health and everyday clinical practice. Mass screening for asymptomatic diabetes has not been recommended pending evidence that the prognosis of such patients will improve by early detection and treatment.25,26 Indirect evidence suggests that screening might be beneficial, improving possibilities for the prevention of cardiovascular complications. In addition, people with IGT might benefit from lifestyle or pharmacological intervention to reduce or delay the progression to diabetes.27
Detection of people at high risk for diabetes
Typically, persons at high risk for developing diabetes and those with asymptomatic diabetes are unaware of their high-risk status. Although much attention has been directed at detecting undiagnosed type 2 diabetes, only recently attention has turned to those with lesser degrees of glucometabolic abnormalities, which tend to share the same risk factors with type 2 diabetes. Three general approaches for early detection exist: (i) measuring blood glucose to explicitly determine prevalent impaired glucose homeostasis (IGH), a strategy that will detect undiagnosed diabetes as well; (ii) using demographic and clinical characteristics and previous laboratory tests to determine the likelihood of future incident diabetes, a strategy that leaves current glycaemic state ambiguous; (iii) collecting questionnaire-based information on factors that provide information about the presence and extent of a number of aetiological factors for type 2 diabetes, a strategy that also leaves the current glycaemic state ambiguous. The two latter approaches can serve as primary and cost-efficient screening tools, identifying a subgroup of the population in whom glycaemic testing may be targeted with a particular yield. The second option is particularly suited for certain groups, including those with pre-existing CVD and women who have had gestational diabetes, whereas the third option is better suited for the general population (Figure 3). Glycaemic testing is necessary as a secondary step in all three approaches to accurately define IGH, since the initial screening step is not diagnostic.
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There will be a trade-off between sensitivity and specificity among the strategies. False labelling may be a problem in the first approach only, since the two other deal with elevated risk factors that are less sensitive to misclassification, and by their own right already should lead to lifestyle advice.25 Including more glycaemic tests will contribute more explicit information on the glycaemic status, whereas fewer tests result in more uncertainty. If a strategy does not incorporate an OGTT at any stage, individual glucose tolerance cannot be determined. Fasting glucose and HbA1c will not reveal information about glucose excursions after meals or a glucose load.
It is necessary to separate three different scenarios: (i) general population; (ii) subjects with assumed metabolic abnormalities, including those who are obese, hypertensive, or who have a family history of diabetes; and (iii) patients with prevalent CVD. When patients with prevalent CVD have glucometabolic abnormalities, in most cases, it is the 2 h post-load glucose value which is elevated, whereas fasting glucose is often normal.30 Thus, the measurement of fasting glucose alone should be avoided in such patients. Since patients with CVD by definition can be considered at high risk, there is no need to carry out a separate diabetes risk assessment, but an OGTT should be carried out in them. In the general population, the appropriate strategy is to start with risk assessment as the primary screening tool combined with subsequent glucose testing of individuals identified to be at a high risk.31 This tool predicts the 10 year risk of type 2 diabetes with 85% accuracy, and in addition, it detects current asymptomatic diabetes and abnormal glucose tolerance.32,33
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Epidemiology of diabetes, IGH, and cardiovascular risk |
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aClass of recommendation.
bLevel of evidence.
Prevalence of disease categories and age
Plasma glucose age and gender
The mean 2 h plasma glucose concentration rises with age in European populations, particularly after the age of 50. Women have significantly higher mean 2 h plasma glucose concentrations than men, in particular, after the age of 70 years, probably due to survival disadvantage in men compared with women. Mean fasting plasma glucose (FPG) concentration increases only slightly with age. It is higher in men than in women during the age period 30–69 years and becomes higher in women after 70 years.
Prevalence of diabetes and IGH
The age-specific prevalence of diabetes rises with age up to the seventh to eighth decades in both men and women (Figure 4).31 The prevalence is less than 10% in subjects below the age of 60 and 10–20% between 60 and 69 years; 15–20% in the oldest age groups have previously known diabetes, and a similar proportion have screen-detected asymptomatic diabetes. This suggests that the lifetime risk of diabetes in European people is 30–40%.
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The prevalence of IGT increases linearly with age, but the prevalence of impaired fasting glycaemia does not. In middle-aged people, the prevalence of IGH is
15%, whereas in the elderly, 35–40% of European people have IGH. The prevalence of diabetes and IGT defined by isolated post-load hyperglycaemia is higher in women than in men, but the prevalence of diabetes and IFG diagnosed by isolated fasting hyperglycaemia is higher in men than in women.14
Diabetes and coronary artery disease
The most common cause of death in European adults with diabetes is coronary artery disease (CAD). Several studies have demonstrated they have a risk that is two to three times higher than that among people without diabetes.39 There are wide differences in the prevalence of CAD in patients with type 140 or 2 diabetes and also between different populations. In the EURODIAB IDDM Complication Study, involving 3250 type 1 diabetic patients from 16 European countries, the prevalence of CVD was 9% in men and 10% in women,43 increasing with age, from 6% in the age group of 15–29 years to 25% in the age group of 45–59 years, and with the duration of diabetes. In type 1 diabetic patients, the risk of CAD increases dramatically with the onset of diabetic nephropathy. Up to 29% of patients with childhood-onset type 1 diabetes and nephropathy will, after 20 years with diabetes, have CAD compared with only 2–3% in similar patients without nephropathy.44
Several studies compared the magnitude of risk for CAD associated with the history of type 2 diabetes or the presence of previous CAD. In 51 735 Finnish men and women, aged 25–74 years, who were followed for an average of 17 years, and comprising 9201 deaths, the combined hazard ratios for coronary mortality, adjusted for other risk factors,49 among men with diabetes only, with MI only, and with both diseases, were 2.1, 4.0, and 6.4, respectively, compared with men without either disease. The corresponding hazards ratios for women were 4.9, 2.5, and 9.4. Hazards ratios for total mortality were 1.8, 2.3, and 3.7 in men and 3.2, 1.7, and 4.4 in women. Diabetic men and women had comparable mortality rates, whereas coronary mortality among men was markedly higher. Thus, a history of diabetes and MI markedly increased CVD and all-cause mortality. The relative effect of diabetes was larger in women, whereas the relative effect of the history of MI was more substantial among men. The increased risk of CAD in subjects with diabetes was only partly explained by concomitant risk factors including hypertension, obesity, dyslipidaemia, and smoking. Thus, the diabetic state or hyperglycaemia itself and its consequences are very important for the increased risk for CAD and related mortality. Further support to the important relation between diabetes and MI was obtained from the Interheart study.160 Diabetes increased the risk by more than two times in men and women, independent of ethnicity.
IGH and CAD
Cardiovascular risk and post-prandial hyperglycaemia
The major disagreement in the classification of glucose homeostasis between the criteria issued by the WHO and ADA focuses on whether diabetes should be diagnosed by means of a fasting or a 2 h post-load plasma glucose. Hence it is clinically important to know how these two entities relate to mortality and the risk for CVD. In the Japanese Funagata Diabetes Study, survival analysis concluded that IGT, but not IFG, was a risk factor for CVD.63 In a recent Finnish study, IGT at baseline was an independent risk predictor of incident CVD and premature all-cause and cardiovascular mortality, a finding not confounded by the development of clinically diagnosed diabetes during follow-up.29 The Chicago Heart Study of approximately 12 000 men without a history of diabetes showed that white men with asymptomatic hyperglycaemia [1 h glucose 11.1 mmol/L (200 mg/dL)] had an increased risk of CVD mortality compared with men with a low post-load glucose <8.9 mmol/L (160 mg/dL).58 Several studies assessed the association of CVD with fasting and 2 h post-load plasma glucose. On the basis of longitudinal studies in Mauritius, Shaw et al.62 reported that people with isolated post-challenge hyperglycaemia doubled their CVD mortality compared with non-diabetic persons, whereas there was no significant increase in mortality related to isolated fasting hyperglycaemia [FPG7.0 mmol/L (126 mg/dL) and 2 h post-load plasma glucose <11.1 mmol/L (200 mg/dL)]. The most convincing evidence for a relation between abnormal glucose tolerance and an increased CAD risk has been provided by the DECODE study, jointly analysing data from more than 10 prospective European cohort studies including more than 22 000 subjects.68,69 Death rates from all causes, CVD, and CAD were higher in diabetic subjects diagnosed by 2 h post-load plasma glucose than in those not meeting this criterion. Significantly increased mortality was also observed in subjects with IGT, whereas there was no difference in mortality between subjects with impaired and normal fasting glucose. Multivariate analyses showed that high 2 h post-load plasma glucose predicted mortality from all causes, CVD, and CAD, after adjustment for other major cardiovascular risk factors, but high fasting glucose alone did not. High 2 h post-load plasma glucose was a predictor for death, independent of FPG, whereas increased mortality in people with elevated FPG largely related to the simultaneous elevation of the 2 h post-load glucose. The largest absolute number of excess CVD mortality was observed in subjects with IGT, especially those with normal FPG. The relation between 2 h post-load plasma glucose and mortality was linear, but such a relation was not seen with FPG.
Glycaemic control and cardiovascular risk
Although several prospective studies have unequivocally confirmed that post-load hyperglycaemia increases CVD morbidity and mortality, it still remains to be demonstrated that lowering a high 2 h post-load plasma glucose will reduce this risk. Studies are underway but thus far data are scarce. A secondary endpoint analysis of the STOP-NIDDM (Study TO Prevent Non-Insulin-Dependent Diabetes Mellitus) revealed statistically significant reductions in CVD event rates in IGT subjects receiving acarbose compared with placebo.70 Since acarbose specifically reduces post-prandial glucose excursions, this is the first demonstration that lowering post-prandial glucose may lead to a reduction in CVD events. It should, however, be noted that the power in this analysis is low due a very small number of events.
The largest trial in type 2 diabetic patients so far, the United Kingdom Prospective Diabetes Study (UKPDS),71 was not powered to test the hypothesis that lowering blood glucose by intensive treatment can reduce the risk of MI, although there was a 16% (marginally significant) reduction in intensively treated patients compared with conventionally treated patients. In this study, post-load glucose excursions were not measured, and over the 10 years of follow-up, the difference in the HbA1c concentrations between the intensive and conventional groups was only 0.9% (7.0 vs. 7.9%). Moreover, the drugs used for intensive treatment, sulphonylureas, long-acting insulin, and metformin, mainly influence FPG, but not post-prandial glucose excursions. The German Diabetes Intervention Study, recruiting newly diagnosed type 2 diabetic patients, is so far the only intervention study that has demonstrated that controlling post-prandial hyperglycaemia (blood glucose measured 1 h after breakfast) had a greater impact on CVD and all-cause mortality than controlling fasting blood glucose.72 During the 11 year follow-up, poor control of fasting glycaemia did not significantly increase the risk of MI or mortality, whereas poor vs. good control of post-prandial glucose was associated with a significantly higher mortality. Additional support is obtained from a meta-analysis of seven long-term studies using acarbose in type 2 diabetic patients. The risk for MI was significantly lower in patients receiving acarbose compared with those on placebo.73
Gender difference in CAD related to diabetes
In the middle-aged general population, men have a two to five times higher risk for CAD than women.74,75 The Framingham Study was the first to underline that women with diabetes seem to lose their relative protection against CAD compared with men.76 The reason for the higher relative risk of CAD in diabetic women than diabetic men is still unclear. A meta-analysis of 37 prospective cohort studies, including 447 064 diabetic patients estimated the diabetes associated, gender-related risk of fatal CAD.81 CAD mortality was higher in patients with diabetes than in those without (5.4 vs. 1.6%). The overall relative risk among people with and without diabetes was significantly greater among women with diabetes 3.50 (95% CI 2.70–4.53) than among men with diabetes 2.06 (1.81–2.34).
Glucose homeostasis and cerebrovascular disease
Diabetes and stroke
Cerebrovascular disease is a predominant long-term cause of morbidity and mortality in patients with both type 1 and type 2 diabetes. Since the first observations, presented by the Framingham investigators, several large population-based studies have verified an increased frequency of stroke in the diabetic population.85,88 Diabetes was the strongest single risk factor for stroke (relative risk for men 3.4 and for women 4.9) in a prospective study from Finland with a follow-up of 15 years.82 DM may also cause microatheromas in small vessels, leading to lacunar stroke, one of most common subtypes of ischaemic stroke. Stroke patients with diabetes, or with hyperglycaemia in the acute stage of stroke, have a higher mortality, worse neurological outcome, and more severe disability than those without.82,90–101
There is much less information concerning the risk of stroke in type 1 than type 2 diabetes. The World Health Organization Multinational Study of Vascular Disease in Diabetes indicated increased cerebrovascular mortality in type 1 diabetic patients, however, with considerable variations among countries.103 The data from the nationwide cohort of more than 5000 Finnish childhood-onset type 1 diabetic patients showed that, by the age of 50 years (i.e. after 20–40 years with diabetes), the risk for an acute stroke was equal to that of an acute coronary event without any gender-related difference.44 Presence of diabetic nephropathy was the strongest predictor of stroke, causing a 10-fold increase of risk.
IGT and stroke
Considerably less is known about the frequency of asymptomatic diabetes and IGT in patients with stroke. In a recent Austrian study104 involving 238 patients, 20% had previously known diabetes, 16% newly diagnosed diabetes, 23% IGT, but only 0.8% had IFG. Thus, as few as 20% had a normal glucose homeostasis. Another 20% of the patients had hyperglycaemic values, which could not be fully classified owing to missing data in the OGTT. In an Italian study, 106 patients were recruited with acute ischaemic stroke and without any history of diabetes, 81 patients (84%) had abnormal glucose metabolism at discharge (39% IGT and 27% newly detected diabetes) and 62 (66%) after three months.105
Prevention of CVD in people with IGH
Although overall trends in CVD mortality have shown a significant downward trend in developed countries during the last decades, it has been suggested that the decline has been smaller or not existent at all in diabetic subjects.106 A more recent study reports on a 50% reduction in the rate of incident CVD events among adults with diabetes. The absolute risk of CVD was, however, two-fold greater than among persons without diabetes.161 More data are needed to judge this issue in European populations.
An imminent issue is to prove that prevention and control of post-prandial hyperglycaemia will cause a reduction in mortality, CVD, and other late complications of type 2 diabetes. There is also a need to reconsider the thresholds used to diagnose hyperglycaemia.20 The majority of premature deaths related to IGH occur in people with IGT,15,19 obviating the need for increased attention to people with a high 2 h post-load plasma glucose. A first step would be to detect such people through systematic screening of high-risk groups (see chapter on definition, classification, and screening of diabetes and pre-diabetic glucose abnormalities). The best way to prevent the negative health consequences of hyperglycaemia may be to prevent the development of type 2 diabetes. Controlled clinical outcome trials among asymptomatic subjects with hyperglycaemia are underway, but results will only be available after some years. Meanwhile, the only way to make clinical treatment decisions in such subjects is to make inferences from the observational epidemiological data and pathophysiological studies.
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Identification of subjects at high risk for CVD or diabetes |
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aClass of recommendation.
bLevel of evidence.
Metabolic syndrome
In 1988, Reaven118 described a syndrome on the basis of the clustering of the following abnormalities: resistance to insulin-stimulated glucose uptake, hyperinsulinemia, hyperglycaemia, increased very low density lipoprotein triglycerides, decreased high-density lipoprotein (HDL) cholesterol, and high blood pressure. Subsequently, this syndrome became referred to as the ‘metabolic syndrome’.120 More recently, several new components have been proposed as belonging to the syndrome, including markers of inflammation, microalbuminuria, hyperuricaemia, and fibrinolytic and coagulation abnormalities.121
Definitions
Currently, there are at least five definitions of the metabolic syndrome proposed by the WHO in 1998122 (revised in 19994); the European Group for Study of Insulin Resistance (EGIR) in 1999124,125; the National Cholesterol Education Programme (NCEP) Adult Treatment Expert Panel III in 2001126,127; the American Association of Clinical Endocrinologists (AACE) in 2003128,129; and the International Diabetes Federation (IDF) Consensus Panel.130 The WHO and EGIR definitions were primarily proposed for research purposes and the NCEP and AACE definitions for clinical use. The 2005 IDF definition aims at worldwide clinical practice. Tables listing the various definitions are presented in the chapter on pathophysiology in the full-text version of these guidelines (www.escardio.org).
Studies on the relationship between the presence of metabolic syndrome and the risk of mortality and morbidity are still scarce, particularly the comparison of risk by different definitions of the syndrome. Several studies in Europe revealed that the presence of the metabolic syndrome increased CVD and all-cause mortality,131–134 but a couple of reports from the USA have shown inconsistent evidence. On the basis of the data of 2431 US adults aged 30–75 years participating in the second National Health and Nutrition Examination Survey (NHANES II), it was found that the metabolic syndrome was associated with a moderately increased risk of mortality from CVD but not significantly associated with mortality from all-causes, coronary heart disease, or stroke.136 In the San Antonio Heart Study, after excluding subjects with diabetes, the corresponding relative risk for all-cause mortality decreased substantially from 1.45 (1.07–1.96) to 1.06 (0.71–1.58) for the NCEP definition and from 1.23 (0.90–1.66) to 0.81 (0.53–1.24) for a modified WHO syndrome.137 A recent study revealed that the NCEP metabolic syndrome is inferior to established predictive models for either type 2 diabetes or CVD.138 Lawlor et al.139 recently showed that point estimates of the effect for each definition of the syndrome were similar or even weaker than those for individual factors, suggesting there is little additional prognostic value in defining the individual factors as a syndrome for predicting CVD mortality. Although each definition of the metabolic syndrome includes several risk factors, they are defined dichotomously. Thus, such a prognostic formula cannot predict CVD as accurately as a risk model on the basis of continuous variables.
Risk charts
The first of risk chart, the Framingham risk score, has been available since 1967, comprising the major risk factors known by that time: gender, age, systolic blood pressure, total cholesterol, cigarette smoking, and diabetes. The most recent Framingham score added HDL-cholesterol and deleted left ventricular hypertrophy.140 The Framingham and other risk scores have been tested in different populations,141–149 and the conclusion from the comparative studies is that, although the absolute risk may differ from population to population, the proportionate risk ranking provided by these scores is consistent across populations. The definition of the NCEP metabolic syndrome and the Framingham cardiovascular risk score were compared for the prediction of cardiovascular events. Data from the population-based San Antonio Study138 showed that the Framingham risk score predicted CVD better than the metabolic syndrome. This is not surprising considering that the Framingham score, in contrast to the metabolic syndrome, was specifically developed to predict cardiovascular events and that it differs by including smoking as a risk factor.
More recently a European Heart Score, based on fatal events, has been generated from pooled data from more than 200 000 men and women,150 taking the overall CVD risk profile into account. Diabetes was not uniformly defined in these cohorts and, because of that, not taken into account in the risk chart. It is, however, stated that the presence of diabetes positions the person at a high risk level. Results from a number of cohort studies, particularly the large European DECODE study, do, however, indicate that either fasting or 2 h post-load plasma glucose is an independent risk factor for all-cause and cardiovascular morbidity and mortality even in people without diagnosed diabetes.15,19,20,69 The DECODE group developed a CVD risk score, which is presently the only one of its kind including IGT or IFG in the risk function determination.157
A population strategy for altering lifestyle and environmental factors, the underlying causes of the mass occurrence of CAD, has been considered since 1982 in a report of the WHO Expert Committee on Prevention of Coronary Heart Disease. This is in accordance with the notion that even small decreases in the risk factor pattern at a population level, through the large number of individuals involved, will affect the health of many people.158 Such an approach has proved successful in Finland.158 For public health purposes, there is a need to develop a CVD risk assessment tool on the basis of easily available information similar to the one developed to predict the development of type 2 diabetes in Finland.32 This Finnish Diabetes Risk Score (FINDRISC) predicts the 10 year risk for developing type 2 diabetes with 85% accuracy. It also detects asymptomatic diabetes and abnormal glucose tolerance with high reliability in other populations.32,111 In addition, FINDRISC predicts the incidence of MI and stroke.163 Such high-risk individuals identified by a simple scoring system can be a target for proper management, not only for diabetes prevention, but also for CVD prevention.
Preventing progression to diabetes
The development of type 2 diabetes is often preceded by a variety of altered metabolic states, including IGT, dyslipidaemia, and insulin resistance.170 Although not all patients with such metabolic abnormalities progress to diabetes, their risk of developing the disease is significantly enhanced. Carefully conducted clinical studies174–178 have demonstrated that effective lifestyle intervention strategies and drug treatments can prevent or at least delay the progression to type 2 diabetes in high-risk individuals.
In the Swedish Malmö study, increased physical exercise and weight loss prevented or delayed type 2 diabetes in subjects with IGT to less than half the risk in the control group, during 5 years of follow-up.174
In a Chinese study from Da Qing, 577 individuals with IGT were randomized into one of four groups: exercise only, diet only, diet plus exercise, and a control group.175 The cumulative incidence of type 2 diabetes during 6 years was significantly lower in the three intervention groups than in the control group (41% in the exercise group, 44% in the diet group, 46% in the diet plus exercise group, and 68% in the control group).
In the Finnish Diabetes Prevention Study, a 5% reduction in bodyweight, achieved through an intensive diet and exercise programme, was associated with a 58% reduction in the risk of developing type 2 diabetes (P<0.001) in overweight middle-aged men and women with IGT.176 The reduction in the risk of progression to diabetes was directly related to the magnitude of the changes in lifestyle; none of the patients who had achieved at least four of the intervention goals by 1 year developed type 2 diabetes during follow-up.108,179
The US Diabetes Prevention Programme, comparing active lifestyle modification or metformin to standard lifestyle advice combined with placebo, found that lifestyle modification reduced the incidence of type 2 diabetes by 58% in overweight American adults with IGT.109 The goal of the programme was to achieve 7% reduction in body weight and physical activity of moderate intensity for at least 150 min per week. The cumulative incidence of diabetes was 4.8, 7.8, and 11.0 cases per 100 person-years in the lifestyle, metformin, and control groups, respectively. This reduction in incidence equated to one case of diabetes prevented for every seven people with IGT treated for 3 years in the lifestyle intervention group, compared with 14 for the metformin group.
In the light of these impressive results, the ADA and the National Institutes of Diabetes, Digestive and Kidney Diseases (NIDDK) recommend that people over 45 years with BMI25 kg/m2 should be screened for evidence of high blood glucose. Those with evidence of a pre-diabetic state should be given appropriate counselling on the importance of weight loss through a programme of dietary modification and exercise.180 In addition, since patients with the metabolic syndrome have an increased risk of CVD and mortality,131,132,136 lifestyle interventions in obese patients and those with evidence of obesity or hyperglycaemia are likely to be beneficial in terms of overall health and life expectancy. The numbers needed to treat (NNT) to prevent one case of type 2 diabetes with lifestyle intervention in people with IGT is dramatically low (Table 4).
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In the recently reported Indian Diabetes Prevention Programme (IDPP), lifestyle and metformin showed similar capability to reduce the incidence of diabetes, but a combination of these two treatment possibilities did not improve the outcome.
The Diabetes REduction Assessment with ramipril and rosiglitazone Medication (DREAM)268,318 trial investigated prospectively whether these two pharmacological compounds may reduce the onset of diabetes, using a factorial design, in people with impaired glucose tolerance, impaired fasting glucose or both. The primary endpoint was the development of diabetes or death. After a median follow up time of three years, the incidence of this endpoint did not differ significantly between ramipril and placebo (18.1% vs. 19.5%; HR 0.91; 95% CI 0.81–1.03). Rosiglitazone reduced the endpoint significantly (n=F306; 11.6%) compared with placebo (n=686; 26.0%; HR 0.40; 0.35–0.46; P<0.0001). Thus the effect of rosiglitazone on the likelihood to develop diabetes in people with impaired glucose homeostasis was as could be expected considering its known glucose lowering property. Overall, total cardiovascular events did not differ significantly between the rosiglitazone and placebo groups. In the rosiglitazone group, however, body weight increased significantly (P<0.0001) and more heart failure cases (0.5 vs. 0.1%; P<0.01) were found. The DREAM trial was neither planned nor powered to evaluate cardiovascular outcomes, which would have demanded a longer trial period. Also, a longer follow-up is needed to see whether the glucometabolic effect of rosiglitazone on glucose only lasts as long as the treatment is continued, or if it is sustained. Thus, rosiglitazone cannot, until further evidence has been gained, be considered appropriate management to reduce the risk of CVD in people with impaired glucose homeostasis. The Indian Diabetes Prevention Programme shows that lifestyle modification and metformin prevent type 2 diabetes in Asian Indian subjects with IGT (IDPP-1).37
The recent data from the STOP-NIDDM trial have for the first time suggested that acute cardiovascular events in people with IGT may be prevented by treatment that reduces post-prandial glucose levels.70 Furthermore, data based on NHANES III have shown that control of low-density lipoprotein (LDL) cholesterol, HDL-cholesterol, and blood pressure to normal levels in patients with the metabolic syndrome (without diabetes and CAD) would result in preventing 51% of coronary events in men and 43% in women; control of these risk factors to optimal levels would result in preventing 81 and 82% of events, respectively.183
Prevention of CVD by physical activity
Studies assessing the association between physical activity and the risk of cardiovascular mortality among diabetic patients indicate that regular physical activity is associated with reduced CVD and total mortality.186–191 In the Aerobic Center Longitudinal Study, the low fitness group had a high relative risk for total mortality compared with the fit group.186 Other types of physical activity, such as occupational and daily commuting physical activities on foot or by bicycle, have also been found to be associated with reduced cardiovascular mortality among diabetic patients191; People physically active at their work had a 40% lower cardiovascular mortality compared with people with low physical activity at work. A high level of leisure-time physical activity was associated with a 33% drop in cardiovascular mortality, and moderate activity was linked to a 17% drop in cardiovascular mortality compared with the most sedentary group. Doing one, two, or three types of moderate or high occupational, commuting, and leisure-time physical activity reduced significantly total and CVD mortalities.190 Thus, the reduction in cardiovascular risk associated with physical activity may be comparable with that of pharmacological treatment prescribed to patients with type 2 diabetes. The ADA, the National Cholesterol Education Programme Expert Panel, and International Diabetes Federation (European Region) have recommended physical activity for the primary and secondary prevention of CVD complications among diabetic patients.127,193,194 The level of physical activity can be assessed using simple questionnaires or pedometers. The most important thing is that it is done and that health workers motivate diabetic patients to be physically active.
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Treatment to reduce cardiovascular risk |
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Lifestyle and comprehensive management
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6.5%c)aClass of recommendation.
bLevel of evidence.
cDiabetes Control and Complication Trial-standardized.
Long-term hyperglycaemia, i.e. DM—both type 1 and type 2, is strongly associated with specific microvascular complications of the retina and the kidneys and with abundant macrovascular disease of the heart, brain, and lower limbs as well as with neuropathy of the autonomic and peripheral nerve system.286–294 Macrovascular events are about 10 times more common than severe microvascular complications and already occur at excessive rates in patients with glucometabolic disturbances, even before the onset of overt type 2 diabetes.295–297 Hyperglycaemia is only one of a cluster of vascular risk factors, which is often referred to as the metabolic syndrome.118,131,135,300 Hence, treatment modalities have to be rather complex and strongly based on non-pharmacological therapy including lifestyle changes and self-monitoring and it requires structured patient education.301–305 This has to include a heavy emphasis on smoking cessation.
Prior to treatment randomization, patients enrolled into the UKPDS underwent 3 months of non-pharmacological treatment. Along with an average decrease of 5 kg body weight, HbA1c decreased 2% to an absolute value close to 7%.303 Hence, non-pharmacological therapy seems to be at least as effective as any glucose-lowering drug therapy, which yields a mean HbA1c-lowering effect of 1.0–1.5% in placebo-controlled randomized studies (Table 5).
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The specific recommendations include 30 min of physical activity at least five times a week, restriction of calorie intake to
1500 kcal per day, restriction of fat intake to 30–35% of total daily energy uptake (reservation of 10% for mono-unsaturated fatty acids, e.g. olive oil), avoidance of trans-fats, increased fibre uptake to 30 g per day, and the avoidance of liquid mono- and disaccharides.108,109,301,303,307,308 Risk stratification for concomitant associated hypertension, dyslipidaemia, and microalbuminuria is mandatory for comprehensive management of patients with diabetes.131,135,275,298–300 The recognition of the underlying insulin resistance with increased visceral adiposity is a key factor for an appropriate therapy, not only of hyperglycaemia, but also of hypertension and dyslipidaemia.269–300 Using this approach and applying multiple risk factor interventions to high-risk type 2 diabetic patients, as done in the Steno 2 study, are extremely compelling in terms of overall outcome.309 Targeting hyperglycaemia, hypertension, and dyslipidaemia, together with the administration of acetyl-salicylic acid to high-risk patients with established microalbuminuria, resulted in >50% reduction of major macrovascular events with an NNT of as low as 5 over an 8 year long period (P=0.008). This multiple risk factor intervention approach proved highly effective in less than 4 years in terms of microvascular outcomes, thereby confirming the results of UKPDS. Still, the ability to achieve pre-defined targets in Steno 2 was far from complete and strikingly variable. By far, the most difficult target to achieve was HbA1c (Figure 5).
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This notion was also apparent in the UKPDS,71,291 fostering the concept of glucose-lowering polypharmacy, like antihypertensive therapy. To reach targets is the crucial objective of comprehensive management. In this context and, in addition, every diabetic patient with some indication of vascular damage, be it macrovascular or microvascular, should be considered for antiplatelet drug therapy, especially acetyl-salicylic acid.309,310 Further details on target levels are outlined in Table 13. It should be noted that failure to reach the target HbA1c level should be avoided and that early escalation of glucose-lowering therapy is essential.
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