People with the warning signs of heart disease, such as high blood pressure and cholesterol, are more likely to survive their hospital stay for a first heart attack than those with a cleaner bill of health, a US study said.
The analysis, which covered more than 500,000 people, found that even when taking into account influences such as age and weight, the more heart-related risk factors that patients had, the lower their chances of dying.
"After adjusting for age and other clinical factors, there was an inverse association between the number of coronary heart disease risk factors and hospital mortality adjusted odds,"study leader John Canto wrote in the Journal of the American Medical Association.
"The association was consistent among several age strata and important patient subgroups."
While it may seem counter-intuitive, researchers said one possible explanation for the finding is that people who already had known heart problems might have been on medications, including statins and beta blockers, that helped protect them after a heart attack.
Data for the analysis came from a national US registry of close to 500,000 first-time heart attacks between 1994 and 2006. During their hospital stays, doctors noted whether patients had some of the standard risk factors for heart disease, including high blood pressure or cholesterol, diabetes, smoking and a family history of heart disease.
Among all patients, more than 85 per cent had at least one of those risk factors - and people with more of them had their heart attacks younger, on average.
Just over 50,000 of the patients died in the hospital.
After taking into account the fact that people with no risk factors were often older, and adjusting for weight, race and gender, the study found that non-smokers who did not have diabetes, a family history of heart disease, or high cholesterol and high blood pressure, were still 50 per cent more likely to die in the hospital than people with all those signs.
One in seven of those with none of the heart warning signs died after suffering a heart attack, compared to one in 28 patients who had all the risk factors.
Canto and his colleagues noted that patients with more risk factors were also more likely to get medications within the first 24 hours of their stay, or to have heart surgery.
"It certainly shows clinicians that if you don't have risk factors but you've had a heart attack, don't assume that they're going to do well," said Carl Lavie, from the John Ochsner Heart and Vascular Institute in New Orleans, who was not involved in the study.
"On the other hand, it's not doomsday for the person that has all the bad risk factors - they can actually end up doing well."
Those with pre-existing warning signs may have been on heart-protection medication before the heart attack, or had more regular contact with their doctors, but there was no way to know that based on the data, Canto said.
It is also possible that people without the traditional risk factors may have had other, unmeasured health risks that caused their heart attacks in the first place and raised the chance of death, or that something about their blood flow was different.
"The general population really needs to identify these risk factors so they can potentially be treated, and these treatments will improve your outcome," Canto said.
"As one ages, just because you have no risk factors doesn't mean you shouldn't be seeing a doctor on a regular basis."