Physicians have known for years that black people in the United States are at higher risk than whites of dying from sudden cardiac arrest, but the reasons have been unclear. A large new study identifies what is not causing this racial disparity, for the most part: differences in income, education, diet, smoking, stress and other traditional markers of heart health.

That suggests underlying biological differences are a likely culprit, said lead author Rajat Deo, an associate professor at the University of Pennsylvania's Perelman School of Medicine. The findings, published Monday in the Journal of the American College of Cardiology, came from a six-year analysis of 22,500 people with no history of cardiovascular disease.

Black participants in the study were more than twice as likely as whites to die of sudden cardiac arrest—at a rate of 18 deaths per 10,000 black people each year, compared with seven sudden cardiac deaths per 10,000 white people.

Though the exact reasons for that gap remain unknown, Deo said the study illustrates the need for action in areas with large black populations—including an increase in CPR training and the availability of automated external defibrillators.

"A combination of awareness, education, and resource allocation may help reduce the burden of sudden cardiac death in a city like Philadelphia," said Deo, a cardiac electrophysiologist.

A 2017 study led by a Duke University physician came to a similar conclusion, finding that people in predominantly black neighborhoods were less likely to receive CPR or defibrillation than people living in predominantly white areas.

Another study, led by Jefferson University physician David Gaieski, found that Philadelphia as a whole has a poor record of bystanders coming to the rescue—with CPR attempted in 10.7 percent of cases, less than half the rate in some areas.

Philadelphians used defibrillators even less often in just 1 out of 1,000 cases from 2008 to 2012, said Gaieski, a professor of emergency medicine at Jefferson's Sidney Kimmel Medical College.

Sudden cardiac arrest

Each year in the U.S., more than 350,000 people suffer a sudden cardiac arrest, and most of them die from it, according to the American Heart Association. The condition is defined as an abrupt stoppage of the heart, generally due to an electrical abnormality.

It is not the same thing as a heart attack, though it can result from one. The sudden cardiac arrest also can result from various kinds of cardiomyopathy, in which the heart muscle is enlarged or abnormally thick.

To look at the issue of racial disparity, Penn's Deo collaborated with researchers at the University of Alabama at Birmingham who already was studying that question for a different health problem: strokes. At Deo's suggestion, the stroke researchers agreed that anytime someone in their study died suddenly, they would contact next of kin to determine if the person had suffered a sudden cardiac death.

With funds from the National Institutes of Health, the Alabama team had recruited more than 30,000 participants. Deo and his colleagues focused on a subset of 22,500 people who had no history of cardiovascular disease, following them for a median period of six years.

After calculating that black people were more than twice as likely to die of sudden cardiac arrest, the team then analyzed the results to see what might explain the gap. First, they found the disparity existed regardless of education, income, and level of health insurance.