"While it may be expected that the presence of coronary heart disease risk factors would further increase the risk of mortality among patients with acute myocardial infarction [heart attack], multiple studies have shown the opposite is true," Fonarow said. "This has been referred to as the 'risk factor paradox' or 'reverse epidemiology.'"
The new study did look at obesity and found "a direct association between obesity and increasing numbers of risk factors." Obesity rarely occurred in isolation.
Although the reasons for the paradox are not fully clear, Fonarow said, age might contribute. He noted that study patients "without risk factors, presenting with acute myocardial infarction, were over 15 years older than those with multiple risk factors -- and age is a major determinate of in-hospital mortality."
Of those with zero risk factors, the average age for first heart attack was about 72 years, while patients with five risk factors had their first attack at about 57.
"It's not just age. We did adjust for age and stratified results [according to] age," Canto said. For the zero-risk-factor patients, "it might take longer to form significant disease," Canto said, or their biology might be different. Higher-risk patients might have gradually adapted to their disease, perhaps by forming collateral circulation (using other channels) to compensate for clogged arteries.
Another possible explanation: "People with risk factors may also be more likely to be on treatments to modify their risk of dying, such as higher use of aspirin, statins and other cholesterol-lowering meds, blood pressure meds, all treatments known to improve CHD outcome," Canto said. "It might be that these patients are encour
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