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Cardiovascular System and Diabetes in Children
- Magdi H El Habbal (11 June 2000)
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Absolute risk, multiple risk factors, and diabetes care: how to make wise decisions?
- K M Venkat Narayan, A Fagot-Campagna, E Gregg, J Saaddine, R Valdez, M Engelau (27 June 2000)
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REDUCING VASCULAR DISEASE IN DIABETES
- Tahseen Chowdhury (11 July 2000)
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Magdi H El Habbal, Consultant Paediatrician Southend General Hospital
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In the issue of the Journal 9.6.2000, Byrne and Wild 1 outlined the need for more evidence based approach to managing risk factors in type 2 diabetes. However, in many section of their editorial the statements were more generalized which imply application for type 1 diabetes. In the same issue, Jones et al.2 showed the high prevalence of eating disorders in adolescent females with type 1 diabetes. Thus, the readers of that issue are left with a message that in children prevention of cardiovascular risk factors are mainly related to controlling diet and blood pressure. We examined 18 children with insulin dependent diabetes (median age 11.3 years; range 7.6-15.0 years) were age and sex matched with 17 non- diabetic controls, (schoolmates, median age 10 years; range 7.2-14.2 years). We measured blood pressure, evaluated left ventricular functions by using 2-dimensional echocardiography and determined myocardial re- polarization (QT interval and dispersions) from standard 12-lead electrocardiogram. The blood pressures were similar in patients and control. The diabetic children had normal left ventricular function but there was a difference in the rate of change of myocardial circumferential fiber shortening being higher in the diabetics than the control. The medians of QTc intervals were 413 msec (range 383-443 msec) in the diabetics vs 388 msec (range 359-417 msec) in control, p=0.017. The medians of QT dispersion were 44 msec (range 15-73 msec) in the diabetics vs 22 msec (range 8- 36 msec) in control, p = 0.011. The changes in dispersions were related to the duration of diabetes (r = 0.76). The mean of haemoglobin A1c was 8%. The children were not over weight and had no eating disorder. It appears that cardiovascular changes in type 1 diabetes occur early and are related to the duration of the disease which require attention in childhood. This distinction needs to be made clear in future reports. |
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K M Venkat Narayan, Chief, Diabetes Epidemiology Section Centers for Disease Control and Prevention, A Fagot-Campagna, E Gregg, J Saaddine, R Valdez, M Engelau
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Byrne and Wild1 make two important - but often ignored - points about the use of evidence-based interventions to reduce risk of cardiovascular disease (CVD) among people with diabetes. We agree with both these points and wish to elaborate on their importance. First, thresholds for treatment decisions should be based on the absolute risk (for example, 2-3% risk per year as recommended by European and British guidelines1) . All too often the relative risk, a measure popularized by epidemiological studies and clinical trials aimed at understanding causal association, is the only measure published and considered when developing treatment decisions. The relative measure may often mislead those making clinical and public health policy decisions because two interventions with the same relative risk reduction can have large differences in their absolute risk reduction (and thus different numbers needed to treat [NNT]) because of differences in baseline incidence of the outcome. For example, in the Systolic Hypertension in Elderly Program (SHEP) trial,2 the relative risk reduction for all CVD and for strokes was 0.30 for each, but one CVD event was avoidable for every 19 people treated while one stroke was prevented for every 570 people. Thus, for both clinical and public health policy, it is really the absolute benefit that matters. Medical and epidemiological journals therefore should popularize the presentation of absolute risk and NNT. Second, prevention of CVD among people with diabetes should focus on multiple rather than single risk factors. As the United Kingdom Prospective Diabetes Study (UKPDS) showed, blood pressure control may result in equal – if not greater – benefits than glycemic.3,4 Furthermore, as Bryne and Wild1 point out, several other strategies are available for CVD risk reduction among people with diabetes – notably, lipid control, aspirin, and ACE therapy. Invariably, perfect control of all the risk factors for CVD will remain a daunting task. The major challenge, therefore, will be determining the optimal mixture of CVD interventions that will achieve the greatest benefit from existing resources. Additionally, the absolute benefit of interventions for a specific outcome (e.g., mortality, morbidity, quality of life) and their relative cost-effectiveness should be considered. These well may vary by population sub-groups (e.g., by age, sex, ethnicity), individual patient preferences, and the clinical policies of local physicians. However, emphasis on quantitative methods such as optimization models may help make the trade-off more explicit and allow more informed clinical and public health decision-making. Health care resources will always be scarce. Thus, we must continually attempt to get the best value out of our expenditures and be careful not to allow the perfect to become the enemy of the good. REFERENCES 1. Byrne CD, Wild SH. Diabetes Care needs evidence based interventions to reduce risk of vascular disease. BMJ 2000;320:1554-1555. 2. The UK Prospective Diabetes Study (UKPDS) Group. Intensive blood- glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complication in-patients with type 2 diabetes (UKPDS 33). Lancet 1998;352:837-53. 3. The UK Prospective Diabetes Study (UKPDS) Group. Tight blood pressure control and risk of macrovascular and microvascular complications in type 2 diabetes (UKPDS 38). Br Med J 1998;317:703-13. 4. SHEP Cooperative Research Group. Prevention of stroke by antihypertensive drug treatment in older persons with isolated systolic hypertension. Final results of the Systolic Hypertension in the Elderly Program (SHEP). JAMA 1991;265:3255-64. |
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Tahseen Chowdhury
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Editor - Byrne and Wild's editorial raises several issues that we wish to discuss1. Blood pressure lowering has a major impact on mortality in diabetic patients. The Systolic Hypertension in the Elderly Program (SHEP),2 and Systolic Hypertension in Europe (Syst-Eur)3 suggest large reductions in mortality in treated diabetic subjects. The Hypertension Optimal Therapy (HOT) study cited by the authors, also demonstrated a marked benefit in diabetic subjects. The lowest risk achieved in the diabetic cohort was at 139.7/81.1mmHg, and taken with the achieved blood pressure in the UKPDS tight control group (144/82), suggest a target blood pressure of 140/80 and not the 130/80 suggested by Byrne and Wild. 140/80 is the target suggested by the British Hypertension Society Guidelines in diabetic subjects4. The authors also suggest that decisions on therapy should be based on calculated vascular risk >3%. This calculation can be done using the Joint British Societies Guidelines charts5, which are generally used to make decisions on lipid lowering therapy rather than anti-hypertensive therapy. We would like to highlight some drawbacks with their routine use. The instructions for the chart state that "the chart should not be used to estimate risk after treatment of hyperlipidaemia or blood pressure has been initiated." Thus in the large number of diabetic patients already on blood pressure lowering therapy, these charts should not be used to determine prescribing lipid lowering therapy. Although most clinicians take a pragmatic approach, this highlights a potentially serious drawback of coronary risk calculators using the Framingham equation. The instructions also state that "decision on drug therapy should be based on repeat risk factor assessment over a period of time". This is impractical in busy diabetic clinics where many patients may only be seen annually, and multiple measurements would only delay therapy. The charts are also limited by the fact that the Framingham Equation is not validated in non-white ethnic groups. If, as suggested, patients with diabetes and another risk factor have as high a risk of myocardial infarction as a non-diabetic who has had a previous infarct, should we be intervening at a similar level in diabetic patients as we are in post-MI non-diabetic patients? Many doctors find the use of the coronary risk prediction charts cumbersome, and would prefer the use of absolute values in diabetic patients. Indeed, the Joint British Societies Guidelines suggest that whilst strong evidence is not yet available for primary prevention in diabetic patients, extrapolating from primary and secondary prevention studies, it is reasonable to treat a cholesterol/HDL ratio above 5.5 in diabetic patients with one additional risk factor. Diabetes care involves intervention into multiple risk factors, including lifestyle, glycaemia, blood pressure and lipids. All clinicians using calculation of cardiovascular risk for decision making in diabetic subjects should be aware of the potential limitations of such calculations. Tahseen Chowdhury
Daniel Darko
David Hopkins
Jennifer Shields
1. Byrne CD, Wild SH. Diabetes care needs evidence based interventions to reduce vascular disease. BMJ 2000; 320: 1554-1555 (10 June) 2. Curb JD, Pressel SL, Cutler JA, Savage PJ, Applegate WB, Black H, et al. Effect of diuretic based antihypertensive treatment on cardiovascular disease risk in older diabetic patients with isolated systolic hypertension. JAMA 1996; 276: 1886-1892. 3. Tuomilehto J, Rastenyte D, Birkenhager WM, Thijs L, Antikainen R, Bulpitt CJ, et al. Effects of calcium channel blockade in older patients with diabetes and systolic hypertension. N Engl J Med 1999; 340: 677-684. 4. Ramsay LE, Williams B, Dennis Johnston G, MacGregor GA, Poston L, Potter JF, et al. British Hypertension Society guidelines for hypertension management 1999: summary. BMJ 1999;319:630-635. 5. Wood D, Durrington P, Poulter N, McInnes G, Rees A, Wray R. Joint British recommendations on prevention of coronary heart disease in clinical practice. Heart 1998; 80 (Suppl 2): S1-S29. |
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