TUESDAY, Nov. 15, 2011 (HealthDay News) -- People with more risk factors for heart disease are more likely than healthier individuals to suffer a first heart attack, according to a large new study. No surprise there. But patients with fewer or no risk factors are more likely to die from that heart attack.
"Our data show that patients with multiple risk factors present much earlier in age than patients with fewer or no risk factors. However, patients with fewer or no coronary heart disease [CHD] risk factors overall had higher mortality after the first heart attack," said Dr. John Canto, lead study author and director of cardiovascular prevention, research and education at the Watson Clinic in Lakeland, Fla.
The researchers looked at data on about 540,000 patients with a first heart attack but without previous heart disease, from the U.S. National Registry of Myocardial Infarction (NRMI) for 1994 to 2006. They focused on five major risk factors: high blood pressure, smoking, high blood cholesterol, diabetes and family history of heart disease.
Of these patients, about 14.5 percent had no risk factors for heart disease when admitted to the hospital, 81 percent had one to three risk factors, and 4.5 percent had four or five risk factors.
But of those who died while still in the hospital, nearly 15 percent had no risk factors, while slightly more than 4 percent had four risk factors and about 3.5 percent had all five. With every drop in number of risk factors, the odds of dying rose.
The researchers noted that because the NRMI is an observational study, they cannot prove cause and effect between mortality rate and number of heart disease risk factors.
The study, published in the Nov. 16 issue of the Journal of the American Medical Association, is slated for presentation Tuesday at an American Heart Association meeting in Orlando, Fla.
The inverse relationship between death rates and other risk factors -- notably obesity -- previously has been observed, said Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles, who is familiar with the study findings.
"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 encouraged to go on exercise programs and eat better, and are more likely to be closely monitored and treated by physicians."
Study results notwithstanding, the best bet is to avoid having a heart attack, Fonarow said.
"Acute myocardial infarction is preventable," he said. "Aggressive control of coronary heart disease risk factors including hypertension [high blood pressure], hyperlipidemia [high cholesterol] and smoking can prevent acute myocardial infarction in the vast majority of men and women in the first place."
For people who are at risk, "the clinical implication of our study is that treating CHD factors makes a tremendous difference in reducing CHD mortality, and conversely, absence of CHD risk factors does not necessarily portend a good prognosis after heart attack," Canto said. "We hope the study will motivate people to get evaluated and treated."
The American Heart Association describes how to assess and reduce your own risk.