For patients too old or frail for open heart surgery, a diagnosis of aortic stenosis often is akin to a death sentence: The mortality rate for some is 40 percent or higher.

But a surging worldwide trend to replace diseased aortic valves through a less invasive procedure is increasingly proving safe and effective. On Monday, Medtronic added more momentum, releasing study results that show its CoreValve aortic valve has some of the highest one-year survival rates yet for such procedures.

The CoreValve Advance Study also showed significant improvement in the quality of life at one month and six months after the procedure, compared to what their life was like before getting the valve replaced. The study tracked nearly 1,000 people from 44 centers in 12 countries. Study results were presented Monday at the Transcatheter Cardiovascular Therapeutics conference in Miami.

Called transcatheter aortic valve replacement or implantation, the procedure allows doctors to use a catheter to snake a valve up to the heart through an artery in the leg or near the shoulder after making a small incision. Previously, the only way to replace an aortic valve was with open heart surgery.

Many with condition die

An estimated 300,000 people worldwide suffer from aortic stenosis, a dangerous narrowing of the aortic valve that prevents the aorta from properly opening and closing. As many as half of those with aortic stenosis die within a year. Yet, one-third of those with the disease are deemed to be in danger of dying during open heart surgery.

Initial results of the CoreValve Advance study showed one-year mortality for all causes at less than 18 percent and one-year mortality due to cardiovascular causes at less than 12 percent, said Dr. Axel Linke, the Advance study's principal investigator.

"This is showing the quality of the treatment," said Linke, a medical doctor at the University of Leipzig in Germany.

The study also looked at health-related quality-of-life measures at one and six months. Patients reported significant improvement when compared to their lives before getting the new valve. One-year quality-of-life results will be reported next year.

Medtronic's CoreValve is not yet approved for use in the United States. Edwards Lifesciences, based in California, is the first medical technology company to have a transcatheter valve approved here with its Sapien valve.

Used in 60 countries

Medtronic's valve, which received European approval in 2007 and has been implanted in more than 30,000 patients in more than 60 countries outside the United States, is expected to gain approval by the Food and Drug Administration in 2014.

St. Jude Medical is expected to introduce its own transcatheter aortic valve soon. Boston Scientific expects to gain European approval for its valve in late 2013.

Thomas Gunderson, a senior analyst with Piper Jaffray & Co., said growing competition and promising results are speeding development and investment in the technology. More patients around the world are turning to the procedure. Twenty percent of all heart valve replacements in Germany are done in this way, he said.

"It's still relatively early in the overall adoption of this," Gunderson said, adding that it could grow to a $1 billion business in the United States alone -- especially if studies such as Advance continue to show promising results.

"What do you want to know about this?" he said, referring to investors. "You want to know how those patients are doing a month, two months, a year, five years from now."

James Walsh • 612-673-7428