In the first analysis of mass commercial use of a new minimally invasive therapy for a narrowed heart valve, researchers reported Tuesday that nearly 24 percent of patients died within a year of treatment.

That mortality rate is higher than some researchers would like for the approach, known as transcatheter aortic valve replacement (TAVR) therapy. All of Minnesota's big device companies either have TAVR devices on the market or in development.

But the study's result was complicated by the fact that right now TAVR is only supposed to be used for high-risk patients. Often that means the patients are at least 85 years old and have other chronic diseases that complicate their long-term outlook.

"Transcatheter aortic valve replacement has become transformational for patients who need a new valve and are at high risk for surgery or inoperable. But we have been lacking long-term data for this group of patients who are considering this procedure," said a statement from Dr. David Holmes Jr., the interventional cardiologist at the Mayo Clinic who was lead author of the study in the Journal of the American Medical Association.

TAVR is a relatively new therapy, and medical device companies are projecting it will generate billions of dollars in new sales in coming years because it is less traumatic for patients than traditional open-chest surgery to replace a ­diseased aortic valve.

Typically, the only incision required is in the leg, where the femoral artery is opened to receive a long catheter that is snaked through the circulatory system. The new valve is precisely delivered to the heart on the end of the catheter, eliminating the need for traumatic chest surgery that some frail patients can't tolerate.

Fridley-based Medtronic Inc. was second to market with its CoreValve TAVR device last year, following California's Edwards Lifesciences device, Sapien. Major Minnesota employer Boston Scientific Corp. projects U.S. approval for its TAVR therapy Lotus in 2017, and St. Jude Medical Inc. in Little Canada hasn't updated the timeline for its Portico TAVR valve since pausing its clinical trial late last year.

The mortality study published Tuesday examined 12,182 Medicare patients with Edwards valves at 299 hospitals between 2011 and 2013. The study used data from a national registry of all U.S. TAVR patients, which was mandated in 2012 by the Centers for Medicare and Medicaid Services following concerns that the new procedure could be ripe for overuse.

Dr. Paul Sorajja, a cardiologist with Allina Health and researcher with the Minneapolis Heart Institute Foundation, said in an interview that one-year mortality data were informative, if not surprising.

"Our treatment of aortic stenosis with TAVR is lifesaving. But despite that, one in four patients still die. And the reason why they die is because they have other conditions that drive their prognosis. Those other conditions are things that, as physicians, we have to consider in our decisionmaking and not just focus on aortic stenosis," said Sorajja, who was not one of the JAMA study's 14 authors.

Earlier studies on TAVR found that aortic stenosis patients faced a 50 percent risk of death without any treatment, and their chances of survival grew to about 70 percent with the procedure. Sorajja said the TAVR mortality rate in those older studies was roughly equivalent to mortality seen in traditional open-chest surgery.

"If the long-term outcomes are the same, then choose the less-invasive approach," ­Sorajja said.

But only in those patients who will benefit. Tuesday's study said that some patients' other diseases raise questions about whether TAVR will benefit them, even if it fixes a diseased valve. For example, a group of 77 men over 85 who were undergoing dialysis had a mortality rate of 54 percent one year after TAVR.

"Before this study, we only had 30-day information," Holmes said in the Mayo news release. "This is a milestone and will help us better guide patients and learn as physicians."

Twitter: @_JoeCarlson