Coronary Heart Disease Risk Factors and Hospital Mortality

An observational study of patients who had their first myocardial infarction (MI) found that there was an inverse relationship between the number of coronary heart disease (CHD) risk factors a patient possessed and in-hospital mortality. The findings from the National Registry of Myocardial Infarction’s (NRMI) recent study were published in the Journal of the American Medical Association [2011;306(19):2120-2127].

Other studies have examined the prevalence of CHD risk factors in patients with MI; however, many of those studies have been limited to specific populations or regions. In addition, according to the study’s authors, limited research has been done focusing on inpatient mortality rates. In this study, researchers used the NRMI, a national registry that collects and analyzes hospital data from 2,160,671 patients with confirmed MI who were admitted at 1977 hospitals from 1994 to 2006.

Using this registry, researchers wanted to determine whether there was an association between hospital mortality and the number of CHD risk factors in patients who presented with their first MI and had no previous cardiovascular disease. The study’s authors assessed hospital data to determine whether patients possessed 5 major CHD risk factors identified as smoking history, diabetes, hypertension, dyslipidemia, or a family history of CHD. The risk factors were identified in the patient’s medical record and had been determined using previous medical records, self-report from the patient, or through information from the family.

The primary outcome of the study was all-cause, in-hospital mortality. Researchers found that 85.6% of the 542,008 patients included in the study had at least 1 CHD risk factor, with the most common risk factor being identified as hypertension (52.3%), followed by smoking (31.3%), dyslipidemia (28.0%), a family history of CHD (28.0%), and diabetes (22.4%). As the number of CHD risk factors increased, the median age of patients declined (P for the trend <.001). Researchers reported mean ages varying from 71.5 years with 0 risk factors to 56.7 years with 5 risk factors.

There was also an inverse relationship between the number of CHD risk factors and in-hospital mortality rates. According to overall crude mortality figures, the all-cause hospital mortality was 14.9%, 10.9%, 7.9%, 5.3%, 4.2%, and 3.6% for 0, 1, 2, 3, 4, and 5 CHD risk factors, respectively. The trend continued even after researchers adjusted for age and other clinical factors. Once these adjustments had been made, the study’s authors still noted a significant inverse association between CHD risk factors and in-hospital mortality and reported a hospital mortality-adjusted odds ratio of 1.54 (95% CI, 1.23-1.94) among patients with 0 versus 5 risk factors (P<.001).

During the study, researchers also found that patients who had few or no risk factors were less likely to receive evidence-based medications during the first 24 hours or undergo invasive cardiac procedures (P for trend <.001). According to the researchers, there were several limitations to the observational study. First, patients without CHD have a high prevalence of the same risk factors as well, which researchers said may decrease the study’s discriminatory power to predict which patients would experience an MI. In addition, researchers did not have access to some patient information, such as level of blood pressure or blood glucose control, and did not examine CHD mortality specifically.

Finally, due to its observational design, the study could be limited by bias, unmeasured confounders, or residual confounding. The researchers concluded their report by highlighting the need for additional research to gain more insight into the possible explanations for the inverse relationship observed in the study.