Few studies have examined associations between atherosclerotic risk factors and short-term mortality after first myocardial infarction (MI). Histories of 5 traditional atherosclerotic risk factors at presentation (diabetes, hypertension, smoking, dyslipidemia, and family history of premature heart disease) and hospital mortality were examined among 542,008 patients with first MIs in the National Registry of Myocardial Infarction (1994 to 2006). On initial MI presentation, history of hypertension (52.3%) was most common, followed by smoking (31.3%). The least common risk factor was diabetes (22.4%). Crude mortality was highest in patients with MI with diabetes (11.9%) and hypertension (9.8%) and lowest in those with smoking histories (5.4%) and dyslipidemia (4.6%). The inclusion of 5 atherosclerotic risk factors in a stepwise multivariate model contributed little toward predicting hospital mortality over age alone (C-statistic = 0.73 and 0.71, respectively). After extensive multivariate adjustments for clinical and sociodemographic factors, patients with MI with diabetes had higher odds of dying (odds ratio [OR] 1.23, 95% confidence interval [CI] 1.20 to 1.26) than those without diabetes and similarly for hypertension (OR 1.08, 95% CI 1.06 to 1.11). Conversely, family history (OR 0.71, 95% CI 0.69 to 0.73), dyslipidemia (OR 0.62, 95% CI 0.60 to 0.64), and smoking (OR 0.85, 95% CI 0.83 to 0.88) were associated with decreased mortality (C-statistic = 0.82 for the full model). In conclusion, in the setting of acute MI, histories of diabetes and hypertension are associated with higher hospital mortality, but the inclusion of atherosclerotic risk factors in models of hospital mortality does not improve predictive ability beyond other major clinical and sociodemographic characteristics.
The evidence is indisputable that 4 major traditional risk factors—smoking, hypertension, diabetes, and dyslipidemia—are predictive of coronary heart disease (CHD) occurrence, as initially reported from the Framingham study and subsequently validated by many other investigators. However, the relations between atherosclerotic risk factors and short-term prognosis after myocardial infarction (MI) are less well understood. We examined the relations between atherosclerotic risk factors and hospital mortality after first MI, one at a time and collectively for all the atherosclerotic risk factors combined. The main objective of this study was to use National Registry of Myocardial Infarction (NRMI) data to (1) describe the distributions of individual atherosclerotic risk factors and their associations among a cohort of patients with first MIs and (2) ascertain their relative contribution in predicting subsequent hospital mortality.
Methods
The NRMI is an industry-sponsored national registry of 2,160,671 patients admitted with confirmed MIs at 1,977 participating hospitals from 1994 to 2006. Institutional review board approval of data collection was obtained as required by the local hospitals. Given the potential complexity in studying patients with known cardiovascular disease, we first excluded patients with previous MIs, CHD, angina, heart failure, percutaneous coronary intervention, coronary artery bypass graft surgery, stroke, cerebrovascular disease, and peripheral vascular disease (n = 1,052,920). Next, any transfer patients (transfer in and transfer out) were excluded from the analysis because of the potential for incomplete reporting at initial hospital or subsequent outcome (n = 526,350). An additional 39,393 patients were excluded because of missing age, gender, weight, pulse, systolic blood pressure, and hospital characteristics. The diagnosis of MI was based on a clinical presentation consistent with MI and/or ≥1 of the following: (1) an elevated cardiac biomarker such as troponin and/or creatine kinase-MB; (2) electrocardiographic evidence of acute ST-segment elevation MI; (3) alternative enzymatic, scintigraphic, or autopsy evidence indicative of acute MI or necrosis; and (4) International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis code 410.X1. Case ascertainment and clinical data were previously validated by comparison to the Medicare-Cooperative Cardiovascular Project.
Five major atherosclerotic risk factors were recorded by review of the medical record during the index hospitalization period: smoking (current or former); history of diabetes, hypertension, or dyslipidemia; and family history of CHD, defined as an immediate relative diagnosed as having CHD before 60 years of age. These risk factors were identified before and during hospitalization, as documented in the medical record, and were based on patient or family self-report or previous records. Weight was available throughout the study period, but body mass index was available only in the NRMI for 2000 to 2006.
The descriptive results were stratified by the presence of 5 major atherosclerotic risk factors and further divided by gender and age. Multivariate logistic regression models were fit for successive blocks of covariates to assess the associations of atherosclerotic risk factors and hospital mortality. Variables in the mortality model were entered in a stepwise manner: (1) age, (2) atherosclerotic risk factors, (3) weight, (4) baseline and presenting characteristics ( Table 1 ) and hospital characteristics (such as facility type, MI volumes, census region, teaching, and rural location), calendar year. Two-tailed tests were used, and p values <0.05 were considered significant. All statistical analyses were done with SAS version 9.13, service pack 4 (SAS Institute Inc., Cary, North Carolina).
| Variable | Atherosclerotic Risk Factors at Presentation | ||||
|---|---|---|---|---|---|
| Smoking | Diabetes | Dyslipidemia | Hypertension | Family History of CHD | |
| (n = 169,674 [31.3%]) | (n = 121,630 [22.4%]) | (n = 151,849 [28.0%]) | (n = 283,215 [52.3%]) | (n = 151,595 [28.0%]) | |
| Age (years) | 57.7 ± 11.0 | 67.4 ± 12.5 | 63.3 ± 12.5 | 68.5 ± 13.3 | 60.7 ± 12.5 |
| Women | 31.7% | 46.9% | 39.1% | 47.8% | 35.8% |
| Race/ethnicity | |||||
| White | 82.7% | 76.7% | 84.8% | 81.1% | 86.8% |
| Black | 9.1% | 10.9% | 5.9% | 9.7% | 6.0% |
| Hispanic | 3.4% | 6.0% | 3.4% | 3.6% | 2.8% |
| Asian | 1.4% | 2.9% | 2.3% | 2.3% | 1.1% |
| Other | 3.4% | 3.6% | 3.6% | 3.2% | 3.3% |
| Smoking | 100.0% | 21.7% | 33.1% | 25.2% | 40.9% |
| Diabetes mellitus | 15.5% | 100.0% | 24.9% | 28.7% | 18.9% |
| Dyslipidemia | 29.6% | 31.1% | 100.0% | 32.4% | 36.1% |
| Hypertension | 42.1% | 66.9% | 60.5% | 100.0% | 48.4% |
| Family history of CHD | 36.5% | 23.6% | 36.1% | 25.9% | 100.0% |
| Body mass index (kg/m 2 ) ⁎ | 28.4 ± 6.2 | 30.2 ± 7.0 | 29.2 ± 6.1 | 28.8 ± 6.6 | 29.2 ± 6.2 |
| Underweight | 2.7% | 1.9% | 1.5% | 2.9% | 1.7% |
| Normal | 27.0% | 20.6% | 21.6% | 26.1% | 22.5% |
| 25–29.9 | 36.7% | 32.5% | 38.6% | 34.3% | 38.0% |
| 30–39.9 | 29.1% | 36.4% | 32.9% | 30.9% | 32.4% |
| ≥40 | 4.6% | 8.6% | 5.3% | 5.8% | 5.4% |
| ≥30 | 33.7% | 45.0% | 38.2% | 36.7% | 37.8% |
| Initial systolic blood pressure (mm Hg) | 142.7 ± 31.5 | 146.3 ± 33.7 | 146.7 ± 30.8 | 149.5 ± 33.8 | 146.4 ± 30.4 |
| Heart rate (beats/min) | 84.5 ± 22.9 | 90.8 ± 24.2 | 83.4 ± 22.0 | 87.5 ± 24.0 | 83.3 ± 21.8 |
| Symptom onset to arrival, hours | 5.3 ± 8.9 | 6.4 ± 10.1 | 5.6 ± 9.0 | 5.9 ± 9.5 | 5.6 ± 9.2 |
| Killip class | |||||
| I | 87.1% | 74.9% | 87.5% | 80.1% | 88.2% |
| II | 8.4% | 15.4% | 8.2% | 12.8% | 7.9% |
| III | 3.3% | 8.3% | 3.5% | 5.9% | 3.1% |
| IV | 1.2% | 1.4% | 0.8% | 1.1% | 0.8% |
| Initial electrocardiographic findings | |||||
| ST-segment elevation | 49.8% | 36.1% | 42.3% | 37.1% | 45.5% |
| ST-segment depression | 31.4% | 26.4% | 30.4% | 27.8% | 30.3% |
| Nonspecific | 26.7% | 33.9% | 30.1% | 32.9% | 29.4% |
| Q wave | 11.8% | 10.6% | 11.1% | 10.0% | 11.7% |
| Left bundle branch block | 2.0% | 5.0% | 2.8% | 4.4% | 2.6% |
| Myocardial infarction location | |||||
| Anterior/septal | 25.2% | 24.7% | 24.0% | 24.3% | 25.7% |
| Inferior | 41.8% | 30.0% | 37.1% | 31.1% | 38.5% |
| Posterior | 6.2% | 3.9% | 5.6% | 4.5% | 5.8% |
| Lateral | 13.8% | 12.2% | 13.1% | 12.7% | 13.8% |
| Right ventricle | 1.1% | 0.7% | 0.9% | 0.7% | 0.9% |
| Unspecified | 29.7% | 42.7% | 35.2% | 41.5% | 32.0% |
Results
A total of 542,008 patients fulfilled study criteria for initial MI presentation. The most common risk factor in patients with initial MIs was hypertension (52.3%), followed by smoking (31.3%), dyslipidemia (28.0%), family history of CHD (28.0%), and the least common traditional risk factor, diabetes mellitus (22.4%) ( Table 1 ).
The mean age was highest in patients with hypertension, followed by those with diabetes, and lowest in smokers. Whites had a greater prevalence of family history of CHD, but blacks and Hispanics had relatively higher proportions with diabetes and hypertension. Asians were the least likely to smoke. Among patients with diabetes, the next most common risk factor in combination with diabetes was hypertension, followed by dyslipidemia. In patients with family histories of CHD, almost half had hypertension, and 1/3 had dyslipidemia. Despite family histories of CHD, >40% smoked. In patients with hypertension, 1/4 had diabetes, >1/4 had dyslipidemia, 1/4 had smoking histories, and 1/4 had family histories of CHD. Smokers were most likely to have hypertension or family histories of CHD but least likely to have diabetes. More than 2/3 of the population with initial MI was either overweight or obese. The proportion of population with either obesity or morbid obesity was highest in patients with diabetes and lowest in smokers.
Patients with diabetes were more likely to delay hospital presentation (46 minutes more on average) compared to those without diabetes. Also, patients with diabetes were most likely to present in Killip class >1, although patients with diabetes or smoking histories were more likely to be in cardiogenic shock. Smokers and those with family histories of CHD were more likely to have ST-segment elevation on initial electrocardiography and inferior or posterior MI location compared to the other risk factor groups, and patients with MI with diabetes or hypertension had a slightly higher prevalence of left bundle branch block.
Overall, men with MIs tended to have a greater prevalence of smoking, to have family histories of CHD, or to be either overweight or obese ( Table 2 ). Women with MIs had more diabetes and hypertension and were more likely to be underweight, normal weight, or morbidly obese. Smokers tended to present with initial MIs at a much younger age, a finding seen in men and women. Similarly, patients with MI with family histories of CHD were more likely to present at an earlier age. In contrast, in those with MIs, hypertension appeared to increase in prevalence with advancing age and was especially notable in those aged >55 years old in either gender. Gender differences in diabetes were more apparent in younger age groups (greater in women), and these differences appeared to attenuate with increasing age.
| Risk Factor | Age <45 Years | Age 46–55 Years | Age 56–65 Years | Age 66–75 Years | Age >75 Years | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| Women | Men | Women | Men | Women | Men | Women | Men | Women | Men | |
| n (%) | 11,369 (2.1%) | 38,214 (7.0%) | 24,102 (4.4%) | 73,761 (13.6%) | 36,182 (6.7%) | 75,004 (13.8%) | 54,011 (10.0%) | 66,531 (12.3%) | 98,629 (18.2%) | 64,205 (11.8%) |
| Smoking | 61.6% | 63.5% | 53.4% | 54.4% | 40.2% | 39.3% | 22.6% | 23.1% | 7.2% | 10.4% |
| Diabetes mellitus | 21.9% | 11.7% | 26.3% | 16.5% | 29.5% | 21.6% | 29.4% | 25.5% | 22.0% | 23.0% |
| Dyslipidemia | 24.1% | 31.1% | 32.9% | 35.4% | 34.7% | 33.6% | 31.3% | 27.7% | 19.5% | 16.8% |
| Hypertension | 38.8% | 32.8% | 49.7% | 41.1% | 56.4% | 47.4% | 62.2% | 52.4% | 65.9% | 53.8% |
| Family history of CHD | 41.9% | 46.1% | 40.5% | 40.9% | 33.6% | 33.2% | 25.0% | 23.8% | 14.3% | 13.7% |
| Body mass index (kg/m 2 ) ⁎ | ||||||||||
| <18.5 | 2.2% | 0.8% | 1.7% | 0.8% | 2.4% | 1.1% | 4.4% | 1.8% | 8.5% | 4.0% |
| 18.5–24.9 | 23.8% | 17.6% | 22.2% | 17.1% | 25.2% | 19.3% | 31.0% | 25.1% | 45.5% | 43.2% |
| 25–29.9 | 25.8% | 37.6% | 28.1% | 40.9% | 29.6% | 42.1% | 31.4% | 44.6% | 28.3% | 38.1% |
| 30–39.9 | 34.9% | 37.7% | 36.0% | 35.7% | 33.6% | 33.4% | 28.2% | 26.1% | 15.8% | 13.8% |
| ≥40 | 13.2% | 6.3% | 12.1% | 5.4% | 9.2% | 4.1% | 5.0% | 2.4% | 1.8% | 0.9% |
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