Editor’s note: This is one in a 10-part series of the top medical research advances of 2016 as determined by the American Heart Association.

One of the most important cardiovascular-related studies of 2016 established that there isn’t much difference between two of the main ways to treat carotid artery disease, a common cause of strokes. But the study’s lead investigator said results from an even more important trial on the subject are still a few years away.

The goal is to prevent strokes by clearing blockages in the carotid arteries, the two major blood vessels in the neck that carry blood to the brain. Carotid stenosis, or narrowing of a carotid artery, is a major risk factor for ischemic strokes, or strokes caused by clots that block blood flow.

For decades, surgeons have opened carotid arteries by cutting into them and removing accumulated plaque, which is called endarterectomy. More recently, carotid stenting has emerged as an alternative treatment. This less invasive approach involves threading a catheter from the groin to the neck and implanting an expandable wire mesh stent to keep the artery open.

A study comparing the procedures known as CREST – short for Carotid Revascularization Endarterectomy versus Stenting Trial – was named one of the American Heart Association’s top 10 heart and stroke science advances of 2016. The trial tracked stroke risk over a decade among 2,502 U.S. and Canadian patients who had one procedure or the other.

“The results showed that both methods of treatment were safe, effective and durable,” said Thomas Brott, M.D., the lead investigator of the CREST study. “The question that remained open was what about the third therapy, which is medical therapy.”

That has led to a new study, called CREST-2, which will track the long-term results of patients receiving only medical therapy, combined with improved diet and more exercise, as well as patients combining medical therapy with endarterectomy or stenting. The medical treatment primarily involves aspirin to prevent clots and drugs to lower blood pressure and LDL, the “bad” cholesterol.

Brott, who is professor of neurology at the Mayo Clinic in Jacksonville, Florida, said he and his fellow CREST-2 investigators are still recruiting participants who have carotid stenosis but no stroke symptoms. He hopes to complete the study by 2022.

In the meantime, he said, “Treatment guidelines for asymptomatic patients vary around the world, because of differences in treatments and lack of good evidence.”

Walter Kernan, M.D., professor of medicine at Yale University, said the CREST study was very important “because it helps us understand we have options. We’ve known that if you fix a carotid artery surgically, that repair tends to last a very long time. The study confirms that stenting is comparable in long-term durability. It’s an anecdotal observation, but I’ve seen clinicians feel more confident about stenting as a result,” said Kernan, who was not involved in the study.

He stressed that the procedures are clearly warranted for patients who have exhibited stroke symptoms, such as mini-strokes, temporary numbness or slurring words. For asymptomatic patients, Kernan said, “There is a lot of uncertainty in the medical community about the benefits of revascularization in 2017. Since those asymptomatic trials were done, we’ve begun to use statin therapy differently, we control blood pressure differently and we know more how to prevent vascular disease in general.”

That, Kernan said, makes CREST-2 “an incredibly important next step in the carotid revascularization story.”

Both doctors said the studies come against an encouraging backdrop of declining mortality rates from stroke, thanks in large part to new medication, better treatments and fewer Americans smoking cigarettes. The AHA reports that stroke death rates have fallen 29 percent in the past decade, and the actual number of stroke deaths are down 11 percent. But an estimated 795,000 Americans still suffer a stroke each year, and about 133,000 die, making it the No. 5 cause of death in the United States.

“While I can be very happy we’ve had this dramatic decrease in mortality, it’s still a major killer,” Brott said. “So we’ve got to pull out all the stops when it comes to prevention.”

In the United States, Brott said, endarterectomies remain much more common than stenting. One reason for the disparity is that Medicare and most private insurers traditionally have covered endarterectomy, but would only cover stenting if the risk of surgery were too great. When the CREST study was published in the New England Journal of Medicine last February, some experts predicted that Medicare might change that policy in view of the new findings.

That has not happened, Brott said. “All we can do is report the facts and leave it to others to do the interpretation,” he said.