Fewer cardiac arrests in Portland and the surrounding county may be the result of the Affordable Care Act, new research suggests.

In a study of emergency medical services in an urban Oregon county before and after the Affordable Care Act, researchers found the incidence of cardiac arrest fell 17 percent among middle-aged adults after they gained health insurance through the health care law, primarily through Medicaid expansion.

Incidence, however, remained the same among older adults with consistently high rates of health insurance coverage, primarily through Medicare.

“Cardiac arrest is a devastating and under-recognized cause of premature death for both men and women older than 45 years,” the study’s lead author Eric Stecker, M.D., said in a news release.

“Health insurance allows people to engage in regular medical care, which is crucial for the prevention of cardiovascular disease and the diagnosis and treatment of conditions that can cause cardiac arrest,” said Stecker, associate professor of cardiology at Oregon Health & Science University’s Knight Cardiovascular Institute in Portland.

Each year in the United States, more than 350,000 cardiac arrests occur outside a hospital. Cardiac arrest occurs when the heart’s regulatory system suddenly malfunctions, causing an abnormal heart rhythm.

In the study, researchers used records for emergency medical services in Multnomah County, Oregon, to identify patients with out-of-hospital cardiac arrest. They compared this information to U.S. Census Bureau data for the county’s adult population in the years before (2011-2012) and after (2014-2015) implementation of the Affordable Care Act.

“These findings underscore the important role of prevention,” said senior author Sumeet Chugh, M.D., director of the Heart Rhythm Center at Cedars-Sinai Heart Institute in Los Angeles. “Less than 10 percent of these patients make it out of the hospital alive.”

Researchers, however, are quick to caution that the small study shows only an association between health insurance and lower rates of cardiac arrest, and does not prove cause and effect. To do so, larger studies that control other possible influences and include more diverse groups of patients are necessary.

Even so, “it is critical to more comprehensively identify the health benefits of insurance and to carefully consider public policies that affect the number of uninsured Americans,” Stecker said.

The study appears in the Journal of the American Heart Association.