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Researchers found that the majority of victims have symptoms in the days and weeks before the emergency.
Most had chest pains between four weeks and one hour before a sudden cardiac arrest when the heart stops abruptly, the study found. Others had noted shortness of breath, while a small percentage experienced dizziness, fainting or heart palpitations.
The study authors said that although middle-aged people are considered to be in the prime of life, they are not immune to cardiac emergencies.
Electrical system failure
"At least a third of cardiac arrests in men are happening in middle age," said study lead author Dr Sumeet Chugh, a cardiologist at Cedars-Sinai Medical Centre in Los Angeles.
The recent death of The Sopranos star James Gandolfini at the age 51 highlighted the fact that sudden cardiac arrest can affect relatively young people.
The study was scheduled for presentation Tuesday at the annual meeting of the American Heart Association, in Dallas.
Sudden cardiac arrest occurs when the heart suddenly starts beating either very quickly and erratically, or extremely slowly, due to a failure of its electrical system, said Dr Gregg Fonarow, a cardiologist at the University of California, Los Angeles. "That's different than a heart attack, where there is a blockage that injures the muscle," he said.
About 360 000 out-of-hospital cardiac arrests are reported each year in the United States, according to the American Heart Association. Less than 10% of those who have a cardiac arrest outside the hospital survive.
For the study, the scientists focused on the population of Portland, Oregon., assessing every man between the ages of 35 and 65 who had a sudden cardiac arrest within a period of almost 12 years. Of the more than 800 total cases, 31% of the medical records did not have enough information to identify whether symptoms were present before the attack.
Recognising symptoms
The researchers also reviewed the accounts of family members, witnesses, emergency medical personnel and medical records from the time period around the cardiac arrest.
In the remaining cases, 53% had symptoms that ranged from episodes of chest pain to feeling like they had the flu.
Although the data helps point to the importance of recognising symptoms and seeking help, Chugh said, there are still more questions than answers. For many people with early symptoms of potential heart problems, doctors' exams may not show anything definitive.
"We're trying to improve the scope of a complete [cardiac] work-up, but there are big gaps in what we know," Chugh said. "What happens in the hour before cardiac arrest? What about in the 24 hours before, the week before or the month before?"
Preliminary conclusions
Part of the challenge is that a variety of problems may trigger sudden cardiac arrest. Depending on genetic, anatomical and other factors, people may respond differently.
"We are teasing out a million different variables at this point," Chugh said. "The nature of heart disease isn't so different from cancer. There's a genetic component... and then there are clinical factors and some lifestyle factors."
The study results do not apply to women, and more research is needed, Chugh said. "Women are different in so many ways," he said.
The research supports current recommendations for anyone having these kinds of symptoms, especially chest pain, shortness of breath and dizziness to seek medical attention, UCLA's Fonarow said. "Many people don't follow these recommendations and they delay," he said. "Their health may really be at stake."
Chugh agreed. "We have not educated men in middle age very much, and we need to do that," he said.
More information
Learn more about sudden cardiac arrest from the US National Heart, Lung, and Blood Institute.
