Medicine has made great strides in lowering the rate of death caused by heart attacks and coronary heart disease. Not so much with sudden cardiac arrest — the malady that strikes more than 300,000 people in the United States each year, such as actress Carrie Fisher and the husband of Facebook executive Sheryl Sandberg.

A key reason: It is hard to tell who is at risk. But a  recent study led by a University of Pennsylvania physician may help.

In the journal Circulation, Penn's Rajat Deo and coauthors reported that they could estimate the risk of sudden cardiac death based on 12 patient characteristics — potentially identifying people whose families should be trained in CPR.

No  single indicator was a red flag. But when combined into a composite score, the traits helped identify people who had up to a 12 percent risk of dying of sudden cardiac arrest in 10 years, the authors reported.

Among the dozen indicators was one measurement that is not part of a standard doctor visit: levels of a protein called albumin.

Another surprise was that the list did not include something that is typically associated with a risk of sudden cardiac arrest: a low ejection fraction, or how much blood leaves your heart each time it contracts.

The risk prediction model was developed by studying thousands of patients with no known heart disease or inherited  heart rhythm condition.

Though a promising start, the tool is not yet ready for widespread use, said Deo, a cardiac electrophysiologist and an assistant professor at Penn's Perelman School of Medicine.

That is partly because the results would not significantly change what your doctor tells you to do. In addition to high albumin levels, other factors associated with a higher risk of sudden cardiac death included smoking, blood pressure, and diabetes, which have long been on the medical radar screen.

Deo wants to refine the prediction model further, to identify those at the very highest risk.

"We still want better discrimination," he said.

In one group of patients, average age 54, the model identified a subset of people who had a 5 percent risk of sudden cardiac death over a 10-year period — equivalent to a  0.5 percent chance of dying of that cause in any one year. This subset represented the top tenth of more than 13,000 people in terms of sudden cardiac death risk.

In another patient group with an average age of 72, the model identified a top tenth of people whose risk was 12 percent — a risk of death by sudden cardiac arrest in any one year of just over 1 percent.

That is not high enough to warrant implanting a defibrillator, a significant medical procedure. But it is high enough to consider lower-cost interventions, he said.

"Maybe that person should go see his doctor sooner rather than later," Deo said. "That person's family should potentially be trained in CPR."

People who can afford it might even buy a wall-mounted defibrillator, some of which cost under $1,000, he said.

In more than half of the sudden cardiac deaths in the United States, there is some degree of underlying heart disease, though it may be undiagnosed. An additional 20 percent can be explained by inherited arrhythmia, such as the cardiomyopathies that sometimes strike young athletes out of the blue. The remaining quarter of sudden cardiac deaths are unexplained, Deo said.

Sudden cardiac arrest patients have the best chance for full recovery when resuscitation efforts are started within the first minute.

But too often that does not happen. In another recent Penn study, physicians found that patients at highest risk for sudden cardiac death are least likely to live in households where someone knows how to perform CPR.

People who are older, who have less education, and who have lower household incomes are less likely to have been trained in the lifesaving procedure, yet they are more likely to be stricken with a sudden cardiac arrest, the authors reported in November at a meeting of the American Heart Association.