Having fewer coronary heart disease risk factors associated with higher risk of in-hospital death following first heart attack

This issue is being released early online to coincide with the American Heart Association Scientific Sessions.

Previous studies have examined the prevalence of coronary heart disease (CHD) risk factors, such as hypertension, smoking, dyslipidemia, and diabetes, in patients with myocardial infarction (MI; heart attack). "Most of these studies did not focus on inpatient mortality during hospitalization for first MI. However, a recent study from a quality improvement initiative reported a modest but surprising inverse association between number of CHD risk factors and mortality in patients with non-ST-segment elevation MI [a certain pattern on an electrocardiogram following a heart attack] only," according to background information in the article.

John G. Canto, M.D., M.S.P.H., of the Watson Clinic LLP, Lakeland, Fla., and colleagues conducted a study to examine the presence and absence of 5 major traditional coronary heart disease risk factors (hypertension, smoking, dyslipidemia, diabetes, and family history of coronary heart disease) and hospital mortality among 542,008 patients with first heart attack and without prior cardiovascular disease. For the study, the researchers used data from the National Registry of Myocardial Infarction, 1994-2006.

The researchers found that 14.4 percent of patients in the study had no risk factors identified at hospitalization; 81 percent had a clustering of 1 to 3 CHD risk factors; and 4.5 percent had 4 or 5 risk factors. The most common risk factor among patients with initial MI was hypertension (52.3 percent), followed by smoking (31.3 percent), dyslipidemia (28.0 percent), family history of CHD (28.0 percent), and diabetes (22.4 percent). Age varied inversely with the number of CHD risk factors, from an average age of 71.5 years with 0 risk factors to 56.7 years with 5 risk factors.

The total number of in-hospital all-cause deaths was 50,788. Analysis of the data indicated that there was an inverse relationship between overall crude mortality and the number of CHD risk factors determined at presentation to the hospital: 0 risk factors, a 14.9 percent mortality rate; 1 risk factor, 10.9 percent; 2 risk factors, 7.9 percent; 3 risk factors, 5.3 percent; 4 risk factors, 4.2 percent; and the mortality rate for 5 risk factors was 3.6 percent. "After adjusting for age and other important outcome-associated factors at presentation, there was a significant inverse relationship between adjusted mortality and number of CHD risk factors present at hospitalization," the authors write.

This association was consistent among several age strata and patient subgroups.

The researchers note that the absence of CHD risk factor exposure should not necessarily be viewed as a guarantee of a favorable prognosis. "There may be multiple explanations for our finding of an inverse association between number of risk factors and mortality. These explanations can be grouped into methodological issues of ascertainment and other biases that limit useful inferences regarding causality vs. real differences in pathophysiology, medical management, or both across groups with different numbers of risk factors."

"Future studies should seek to gain insight into the possible explanations of such an association."