discharge records in Minneapolis-St. Paul metropolitan area hospitals was abstracted in 1970,1980, and 1985. Results: The prevalence of diabetes among Ml ...
Trends in Prevalence of Diabetes Mellitus in Patients With Myocardial Infarction and Effect of Diabetes on Survival
). Michael Sprafka, PhD Gregory L. Burke, MD Aaron R. Folsom, MD Paul G. McGovern, PhD Lorraine P. Hahn, MPH
The Minnesota Heart Survey
Objective: The purpose of this study was to document trends in the prevalence of diabetes among men and women hospitalized for myocardial infarction (Ml) and to determine the effect of diabetes on in-hospital case fatality rates and long-term survival. Research Design and Methods: The Minnesota Heart Survey is a population-based surveillance system that has monitored trends in coronary heart disease morbidity since 1970. As part of this effort, a 50% random sample of acute Ml discharge records in Minneapolis-St. Paul metropolitan area hospitals was abstracted in 1970,1980, and 1985. Results: The prevalence of diabetes among Ml patients was compared over time, and the data indicated a significant increase between 1970 and 1985 in both men (8.2 vs. 16.8%, P < 0.001) and women (16.0 vs. 25.8%, P - 0.01). Diabetic individuals had an odds ratio of inhospital death after an Ml 1.5 times that of nondiabetic individuals (P < 0.01) after controlling for the effects of sex, age, and year of M l . Among discharged Ml survivors, the risk of death was 40% higher (P < 0.01) in diabetic individuals than nondiabetic individuals after 6 yr of follow-up. Compared with nondiabetic individuals, diabetic individuals appeared more likely to have cardiac (pump) failure with acute M l . Conclusions: Our findings suggest that the risk of coronary heart disease morbidity and mortality attributable to diabetes may be increasing over time. Therefore, clinicians need to take extra care in the management of Mis in diabetic individuals, and public health efforts to reduce diabetes prevalence are warranted. Diabetes Care 14:537-43,1991
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any studies have reported that diabetes mellitus is associated with increased coronary heart disease morbidity and mortality. Compared with the general population, diabetic individuals have a twofold increase in coronary heart
DIABETES CARE, VOL. 14, NO. 7, JULY 1991
disease mortality (1-3), and it is estimated that coronary heart disease accounts for —30-50% of all diabetic deaths after 40 yr of age (4,5). The prevalence of diabetes is increased in patients suffering a myocardial infarction (Ml; 6,7), and both the short- and long-term prognosis after an Ml is poorer among diabetic individuals (8-15). In addition, there is evidence that diabetic women have a poorer prognosis than diabetic men after an Ml (11). Whether elevated coronary heart disease risk and poorer survival among diabetic individuals is attributable to the diabetic state or an unfavorable coronary heart disease risk-factor profile is unclear. Autopsies have shown capillary changes in the diabetic heart absent in nondiabetic individuals (16-18). Other studies have reported that diabetic individuals have more hypertension (19-21), higher triglyceride levels (22-24), and lower high-density lipoprotein cholesterol (21) than nondiabetic individuals. Few population-based data are available describing time trends of Ml prevalence and concomitant diabetes. The Minnesota Heart Survey, a population-based surveillance system measuring trends in coronary heart disease mortality, morbidity, and risk factors, collected acute coronary heart disease discharge data in 1970, 1980, and 1985 from Minneapolis-St. Paul metropolitan area hospitals. The purpose of this report was to document trends in the prevalence of diabetes among
From the Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis, Minnesota. Address correspondence and reprint requests to J. Michael Sprafka, PhD, Division of Epidemiology, School of Public Health, University of Minnesota, 1-210 Moos Tower, 515 Delaware Street, SE, Minneapolis, MN 55455. Received for publication 24 September 1990 and accepted in revised form 29 January 1991.
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men and women hospitalized for Ml and to determine the effect of diabetes on in-hospital case fatality rates and long-term survival.
RESEARCH DESIGN AND METHODS Cardiovascular disease morbidity and its trends over time have been assessed through ongoing surveillance of hospital discharges for acute Ml in the seven-county Minneapolis-St. Paul metropolitan area. Lists of all coronary heart disease discharges were obtained from 35 of 36 area hospitals in 1970 and from all 31 hospitals in 1980 and 1985. A 50% random sample of acute coronary heart disease discharges was selected from these lists in all survey years. Nurse abstractors reviewed the selected medical records and used a standardized protocol to obtain detailed patient information including presenting symptoms (e.g., 1st blood pressure, 1st pulse pressure, rales, 3rd heart sound), past medical history, cardiac enzyme levels, 12-lead electrocardiograms (ECG), medical procedures, and autopsy results. Physician-diagnosed diabetes, as indicated in the discharge diagnoses of the medical record, was used for the definition of diabetes. G.L.B. reviewed all charts to determine the absence or presence of congestive heart failure and abnormal X rays. All Ml diagnoses were validated using ECG (Minnesota Code), chest pain, cardiac enzyme (aspartate aminotransferase and lactate dehydrogenase), and autopsy data. Five percent of the records were reabstracted by a different nurse abstractor, and the results indicated a >95% concordance for the variables used to define Ml. To ensure consistent diagnostic criteria throughout all survey years, creatine kinase and creatine kinase myocardial bound, unavailable in 1970, were not used as diagnostic criteria. Patients were classified according to whether Ml was definite, possible, or absent with four major criteria to categorize these events: /) the presence or absence of acute chest pain, 2) peak levels of cardiac enzymes, 3) ECG changes compatible with an acute Ml, and 4) the presence of an acute Ml by necropsy (a recent Ml documented within 8 wk of death). Enzyme levels for each potential Ml were classified as 7) abnormal: peak level two times the upper
limits of normal (ULN) as reported by each individual hospital, 2) equivocal: peak level greater than or equal once and less than twice ULN, 3) normal: no enzyme levels exceeded ULN, and 4) missing: no enzymes available. ECG tracings for each potential Ml were classified as 7) evolving: new significant Q waves that persisted in greater than or equal to one tracing, 2) diagnostic: significant Q waves (indeterminant age) noted on initial ECG, 3) equivocal: ST-T wave changes or minor Q waves, and 4) other: normal and uncodable ECGs. Table 1 shows the format used to place patients into categories, and only definite Mi's were used in this analysis. All patients were systematically followed to determine vital status with the National Death Index for events after 1979 and MINNDEX, a single state (i.e., Minnesota) death certificate search system, for deaths occurring before 1979. The MINNDEX system has been validated against the National Death Index and was found to agree on the survival status of 98% of the people tested (26). Estimates of diabetes prevalence and hospital case fatality rates (death during hospitalization) were age adjusted by the direct method to the 1980 MinneapolisSt. Paul Ml population. The Mantel-Haenszel x2-testfor trend was used to estimate the significance of case fatality-rate differences, adjusted for age, between diabetic and nondiabetic Ml patients at each time period (27). Logistic regression was used to determine the impact of diabetes on hospital case fatality, controlling for the effects of age, sex, and year of Ml. In addition, 6-yr post-MI survival for patients discharged alive was calculated for the 1980 survey population by sex and diabetes status, and the Cox proportional hazards model was used to estimate the relative risk of death in diabetic individuals compared with nondiabetic individuals controlling for the effect of age, sex, and year of Ml (i.e., 1970 vs. 1980).
RESULTS The age-adjusted prevalence of diabetes reported in hospitalized patients with definite Ml increased significantly between 1970 and 1985 in both men (P < 0.001)
TABLE 1 Format used to place patients into myocardial infarction (Ml) categories Chest pain absent
Chest pain present ECG classification (Minnesota code)
Abnormal enzymes
Evolving diagnostic Diagnostic Equivocal Other
Definite Definite Definite Definite
Ml Ml Ml Ml
Equivocal enzymes Definite Possible Possible Possible
Ml Ml Ml Ml
Missing enzymes Definite Possible Possible Possible
Ml Ml Ml Ml
Normal enzymes Definite Ml No Ml No Ml No Ml
Abnormal enzymes Definite Definite Possible Possible
Ml Ml Ml Ml
Equivocal enzymes
Missing enzymes
Normal enzymes
Definite Ml Possible Ml Possible Ml No Ml
Definite Ml No Ml No Ml No Ml
Definite Ml No Ml No Ml No Ml
ECG, electrocardiogram. If an autopsy was available and showed an acute Ml within 8 wk of death, the patient was designated as a definite Ml. Categories described in METHODS.
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J.M. SPRAFKA AND ASSOCIATES
TABLE 2 Prevalence per 100 of diabetes among patients hospitalized with definite myocardial infarction by age, sex, and year in the Minnesota Heart Survey Women
Men Age (yr)
1970
1980
1985
1970
1980
1985
30-39 40-49 50-59 60-69 70-74 Total*
0.0 (17) 4.0(101) 6.9 (174) 8.5 (189) 12.2 (82) 8.2
20.8 (24) 3.0 (99) 10.2 (206) 17.6(222) 15.9(82) 13.6
27.8(18) 4.5 (89) 9.7 (206) 20.7(241) 24.5 (106) 16.8
40.0 (5) 15.4(13) 12.5 (48) 19.2 (104) 12.7(63) 16.0
0.0 (2) 10.0(10) 18.0(50) 23.7 (97) 25.4(71) 20.5
25.0 (4) 23.8(21) 27.8.(54) 23.5 (119) 28.6 (63) 25.8
Number of myocardial infarctions are in parentheses. *Age adjusted to the 1980 myocardial infarction population.
and women (P = 0.01; Table 2). In general, the prevalence of diabetes was higher in older than younger age groups and tended to increase over time in each age group. Between 1970 and 1985, in-hospital fatality rates of Ml patients declined significantly in women with comorbid diabetes (38.8 vs. 16.2, P = 0.004) but not in men (21.4 vs. 18.0, P = 0.7; Table 3). In contrast, nondiabetic Ml patient in-hospital fatality rates declined significantly in both men (21.6 vs. 10.1, P < 0.001) and women (25.7 vs. 16.6, P = 0.01). Ml case fatality was significantly higher in diabetic than nondiabetic men in 1985 (18.0 vs. 10.1, P < 0.01) and in diabetic versus nondiabetic women in 1970 (38.8 vs. 25.7, P = 0.04). However, no significant differences between diabetic and nondiabetic Ml case fatality rates were found for the other periods of observation. Multiple logistic regression indicated that the odds of in-hospital death was 1.5 times greater for diabetic individuals after Ml compared with nondiabetic individuals controlling for the effects of sex, age, and year of Ml (Table 4). Women had greater odds of in-hospital death than men (P = 0.004), and the odds increased with increasing age. Significant improvements in mortality occurred in 1980 and 1985 relative to 1970. No second- or third-order interaction terms were significant. Six-year follow-up data from 1970 and 1980 were
used to evaluate the long-term survival differences between diabetic and nondiabetic Ml patients discharged alive (Table 5). The risk of death among Ml survivors was 40% higher among those with diabetes after controlling for the effect of sex, age, and year of Ml. The risk of death increased with increasing age; however, sex and year of Ml did not contribute to excess risk of death after discharge. No second- or third-order interaction terms were significant, and the proportional hazards assumption was supported for all variables in the model. The proportion of Ml patients discharged alive who were still alive at 6-year follow-up was calculated for the 1980 survey population by sex and diabetes status (Fig. 1). Most of the excess risk appeared to occur during the first year after the Ml. However, the BreslowDay test for heterogeneity, grouping events by year, indicated that the excess risk of death experienced by individuals with diabetes did not change significantly with increasing time after Ml for men (P = 0.8) or women (P = 0.03), supporting the results from the proportional hazards model. Measures of severity of Ml at presentation to hospital are shown by diabetes status and year in Table 6. Diabetic individuals had more evidence of cardiac pump failure with Ml than nondiabetic individuals. The percentage of diabetic individuals with third heart sounds, abnormal X rays, and digitalis was significantly higher
TABLE 3 In-hospital myocardial infarction case fatality rate by sex, year, and diabetes status in the Minnesota Heart Survey Women
Men Nondiabetic
Diabetic Year 1970 1980 1985
Rate/100 42 81 105
21.4 17.6 18.0
Diabetic
Rate/100 521 552
555
21.6 13.7 10.1*
Nondiabetic
Rate/100 38 51 67
38.8 36.6 16.2
Rate/100 195 179
194
25.7* 16.6 16.6
n, total number of myocardial infarctions. Age-adjusted to the 1980 Minneapolis-St. Paul myocardial infarction population. *P < 0.05 vs. diabetic patients of the same sex.
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TABLE 4 Multiple logistic modeling of the effect of diabetes on inhospital mortality after myocardial infarction in the Minnesota Heart Survey
100 90"
Variable
p (mean ± SE)
OR
95% Cl
P
Diabetes Sex Age (yr) 50-59 60-69 70-74 Year 1980 1985
0.37 ± 0.14 0.34 ± 0.12
1.5 1.4
1.1-1.9 1.1-1.8
0.009 0.004
0.33 ± 0.22 0.98 ± 0.21 1.41 ± 0.22
1.4 2.7 4.1
0.9-2.2 1.8-4.0 2.7-6.3
0.10
