Insulin treatment, endogenous insulin concentration, and ECG abnormalities in diabetic Pima Indians. Cross-sectional and prospective analyses

The prevalence and incidence of CHD, defined by ECG abnormalities according to the Tecumseh criteria for Minnesota Codes, were determined in Pima Indians greater than or equal to 25 yr of age. In a cross-sectional analysis, the age-sex-adjusted prevalence (+/- SE) of ECG abnormalities was higher in 1454 NIDDM patients (6.86 +/- 0.65%) than in 1696 nondiabetic subjects (3.23 +/- 0.63%; prevalence rate ratio = 2.12; 95% CI 1.39-3.25). In a prospective analysis, the age-sex-adjusted incidence (+/- SE) of ECG abnormalities was higher in 824 NIDDM patients (12.77 +/- 1.67) than in 935 nondiabetic subjects (5.93 +/- 1.43 cases/1000 person-yr; incidence rate ratio = 2.15; 95% CI 1.26-3.69). The prevalence of ECG abnormalities in insulin-treated NIDDM patients was significantly higher than in NIDDM patients not treated with insulin (age-sex-adjusted OR = 2.83; 95% CI 1.84-4.33); and this association persisted when adjusted for other factors such as sBP, BMI, duration of diabetes, serum cholesterol concentration, and oral hypoglycemic agents (OR = 2.12; 95% CI 1.34-3.37). In the prospective analysis, the incidence of ECG abnormalities in NIDDM patients treated with insulin was higher than in those NIDDM patients not treated with insulin, but, when controlled for age, sex, duration of diabetes, and oral hypoglycemic agents in a proportional-hazards model, the relationship with insulin treatment was not statistically significant (incidence rate ratio = 1.36; 95% CI 0.80-2.31). This suggests that insulin treatment may be a marker of more severe diabetes, and that factors associated with clinical indications for insulin treatment, rather than insulin treatment per se, are related causally to CHD. On the other hand, endogenous fasting and 2-h postload serum insulin concentrations were not associated with ECG abnormalities among 761 NIDDM patients not treated with insulin nor among 1226 nondiabetic subjects. Furthermore, in the prospective study, neither endogenous fasting nor 2-h postload serum insulin was associated with the subsequent development of ECG abnormalities in NIDDM patients or nondiabetic subjects.

Low incidence of fatal coronary heart disease in Pima Indians despite high prevalence of non-insulin-dependent diabetes

The incidence of fatal coronary heart disease (CHD) was determined in a population of Pima Indians from the Gila River Indian Community in Arizona. Between 1975 and 1984, 394 deaths occurred among 4,828 subjects aged 5 years or older, and 199 of these occurred in the 1,093 persons with non-insulin-dependent diabetes. Only 28 deaths were attributed to CHD; all occurred among the 689 diabetic persons 45 years of age or older. No CHD deaths occurred among the 419 nondiabetic subjects 45 years of age or older. The rate of fatal CHD among the diabetic subjects was higher in men than in women and increased with advancing age and duration of diabetes. A higher incidence of fatal CHD was associated with proteinuria, renal insufficiency, medial arterial calcification, diabetic retinopathy, insulin therapy, and an abnormal electrocardiogram. In Pima Indians aged 50-79 years, the incidence of fatal CHD was less than half that found in the Framingham population after controlling for age, sex, and diabetes (incidence rate ratio, 0.4; 95% confidence interval, 0.2-0.7). Factors protecting Pima Indians from fatal CHD may include racial heritage, low serum concentrations of total and low density lipoprotein cholesterol, and rarity of heavy smoking. Among the diabetic subjects, mortality from diabetic renal disease, which shows many of the same risk factors, may selectively compete and remove those at risk for fatal CHD. This would not, however, explain the lack of fatal CHD among the nondiabetic subjects. Fatal CHD shares many of the risk factors associated with the specific microvascular complications of diabetes, and diabetes and its associated attributes are the major predictors of fatal CHD in this population.

Coronary heart disease in the Pima Indians. Electrocardiographic findings and postmortem evidence of myocardial infarction in a population with a high prevalence of diabetes mellitus

The frequency of electrocardiographic evidence of coronary heart disease (CHD) and the rate of autopsy-proved myocardial infarction were determined in the Pima, a tribe of American Indians with a high prevalence of diabetes mellitus. The electrocardiograms of 701 Pimas, aged 40 years and over (85 per cent of the adult reservation population, 45 per cent of whom had diabetes) were read according to the Minnesota Code, and 120 postmortem examinations were reviewed for evidence of myocardial infarction. The frequency of CHD as evidenced by major Q-wave changes in the Pima (1.6/100) was about one-half that found in Tecumseh, Michigan (p less than 0.10). The relatively low rate of myocardial infarction at autopsy (15 per cent of males and 8 per cent of females aged 40 years and over) was consistent with the low prevalence of Q-wave changes. The subjects with diabetes had a higher rate of CHD than nondiabetics, both electrocardiographically and at postmortem examination, although the differences were not statistically significant. The low prevalence of CHD in the living Pima and the low rate of infarction at autopsy indicate that this tribe has a low frequency of CHD despite the extraordinarily high prevalence of diabetes mellitus.