Evaluating CMR

Exclusion of subjects with type 2 diabetes

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Patients with type 2 diabetes have a significantly greater risk of developing CHD compared to the general population (13-15). In this regard, it has been suggested that the risk of developing an acute myocardial infarction (MI) in diabetic patients without previous CHD may be equivalent to the risk of nondiabetic individuals who previously have had an MI (16). However, many CHD prediction models derived from the Framingham Heart Study (1), the PROCAM study (2), the SCORE project (3), and the Italian CUORE project (5) did not develop distinct risk charts for individuals with type 2 diabetes. These algorithms therefore tend to underestimate CHD risk in individuals with type 2 diabetes (17). This is a key point to keep in mind when using these charts to predict CHD risk in type 2 diabetic patients.

Moreover, in comparison with prediction models developed specifically for type 2 diabetic patients—such as the UKPDS risk engine—the Framingham risk score was not originally designed to be used in diabetics. Only 4% of the original cohort used to develop the equations had type 2 diabetes. Furthermore, the Framingham risk score used dichotomous variables for glycemia, such as the presence or absence of diabetes, instead of using an index of glycemic control. In addition, the Framingham Heart Study defined diabetes as casual blood glucose exceeding 8.3 mmol/l (150 mg/dl) at two clinic visits in the original cohort, or as fasting blood glucose exceeding 7.8 mmol/l (140 mg/dl) at the initial examination of Offspring Study participants. In contrast with current diabetes diagnostic criteria (7.0 mmol/l or 126.1 mg/dl), the Framingham Heart Study’s cutoff values may have meant diabetes was underreported in the cohort.

Reference

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1. Wilson PW, D'Agostino RB, Levy D, et al. Prediction of coronary heart disease using risk factor categories. Circulation 1998; 97: 1837-47.

2. Assmann G, Cullen P and Schulte H. Simple scoring scheme for calculating the risk of acute coronary events based on the 10-year follow-up of the prospective cardiovascular Munster (PROCAM) study. Circulation 2002; 105: 310-5.

3. Conroy RM, Pyorala K, Fitzgerald AP, et al. Estimation of ten-year risk of fatal cardiovascular disease in Europe: the SCORE project. Eur Heart J 2003; 24: 987-1003.

5. Ferrario M, Chiodini P, Chambless LE, et al. Prediction of coronary events in a low incidence population. Assessing accuracy of the CUORE Cohort Study prediction equation. Int J Epidemiol 2005; 34: 413-21.

13. Barrett-Connor EL, Cohn BA, Wingard DL, et al. Why is diabetes mellitus a stronger risk factor for fatal ischemic heart disease in women than in men? The Rancho Bernardo Study. JAMA 1991; 265: 627-31.

14. Koskinen P, Manttari M, Manninen V, et al. Coronary heart disease incidence in NIDDM patients in the Helsinki Heart Study. Diabetes Care 1992; 15: 820-5.

15. Manson JE, Colditz GA, Stampfer MJ, et al. A prospective study of maturity-onset diabetes mellitus and risk of coronary heart disease and stroke in women. Arch Intern Med 1991; 151: 1141-7.

16. Haffner SM, Lehto S, Ronnemaa T, et al. Mortality from coronary heart disease in subjects with type 2 diabetes and in nondiabetic subjects with and without prior myocardial infarction. N Engl J Med 1998; 339: 229-34.

17. McEwan P, Williams JE, Griffiths JD, et al. Evaluating the performance of the Framingham risk equations in a population with diabetes. Diabet Med 2004; 21: 318-23.

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