When researchers compared the number of sudden cardiac arrests in Multnomah County before and after the Medicaid expansion under the Affordable Care Act, they expected to see a decline.

They did – but it was bigger than expected.

"The real surprise is not that it dropped," said Dr. Eric Stecker, a cardiologist at Oregon Health and Science University and lead author on the study. "It was the magnitude – about a 17 percent reduction."

The study, published Wednesday in the Journal of the American Heart Association, confirms other research showing that an expansion of insurance coverage reduces mortality rates.

It comes as the U.S. Senate considers a plan to replace former President Barack Obama's Affordable Care Act. The Senate plan would curtail Medicaid, health insurance for the poor. As many as 22 million could lose coverage within a decade if it passes, according to the Congressional Budget Office.

The researchers looked at sudden cardiac arrests because they're a definable health condition with a high mortality rate that preventive care can lower. Nationwide, about 350,000 people a year die from sudden cardiac arrest out of the hospital, according to the American Heart Association.

Few warning signs typically precede sudden cardiac arrests, but good health habits can reduce their possibility, including no smoking, controlling blood pressure, using cholesterol medication and evaluating high-risk symptoms.

Patients with health insurance are more likely to get that kind of preventive care, Stecker said.

"It's really hard to engage in medical care if you're paying out of pocket," he said.

The study was praised by Dr. Dan Oseran, chief cardiologist for Providence Health and Services.

"It was very well done, provocative and timely," Oseran said. "It speaks to what we in the cardio-vascular community have long felt, which is increased access to health care leads to an opportunity for better primary and secondary prevention."

Under the Affordable Care Act, 22,000 people in Multnomah County gained coverage through the Oregon Health Plan, which oversees the state's Medicaid program. In relative terms, Medicaid coverage rose from 7 percent to 14 percent of the population, Strecker's study found.

Coverage also expanded for others who bought plans through the individual marketplace, but most of the overall expansion came from increased Medicaid, Stecker said.

The study compared the number of cardiac arrests before the Affordable Care Act (from 2011 through 2012) and after (from 2014 through 2015) for people 45 to 64 and people 65 and older. The 65-plus group was used as a control because they're almost universally covered by Medicare, the federal health insurance for seniors.

The number of cardiac arrests for the 90,000 seniors in Multnomah County stayed fairly flat, with 275 cardiac arrests before the Medicaid expansion and 269 after. But in the 45 to 64-year-old group, about 200,000 people, they fell from 102 to 85.

Stecker doesn't know how many people survived. Research has shown that 15 percent of people in Multnomah County usually survive sudden cardiac arrest, compared with about 10 percent nationwide.

Follow-up research is needed to rule out other factors that might have affected the cardiac arrest rate, such as lifestyle changes, like stopping smoking, healthy eating and exercise, Stecker said.

"It is hard to flesh those out," Stecker said. "They could have played some role."

The study is backed up by other research, he said, including a study by the Institute of Medicine that shows that people use insurance for preventive care.

"Our study really is consistent with and reinforces prior studies that show that improved preventive care and decreased death rates come after expanding insurance," Stecker said.

-- Lynne Terry