Medtronic says the first 50 patients in a pilot study of its experimental minimally invasive mitral valve replacement device, the Intrepid, are showing positive early experience for treatment of their severe mitral regurgitation.

Mitral regurgitation happens when blood flows backwards through the mitral valve in the heart, leaving the patient out of breath and unable to exercise normally. Several companies including Medtronic are designing devices that can replace a damaged mitral valve without requiring open-heart surgery.

In a presentation at an industry conference last week, researchers reported that Medtronic's Intrepid mitral valve was successfully implanted in 48 of 50 consecutive patients enrolled at hospitals in the U.S., Europe and Australia. The median deployment time was 14 minutes, according to the data, which were simultaneously published in the Journal of the American College of Cardiology.

After roughly six months, 79 percent of the patients had mild or no mitral regurgitation, putting their symptoms in Class I or Class II of the New York Heart Association heart-failure classification system, the data show. Before the study, 86 percent of the patients were in Class III or Class IV categories, meaning their heart failure symptoms notably or completely limited their physical abilities.

"These early outcomes with the Intrepid TMVR System are encouraging as we investigate a minimally-invasive alternative to surgical mitral valve replacement," Dr. Paul Sorajja of the Minneapolis Heart Institute Foundation said in a news release.

The severe mitral regurgitation patients had an average age of 73. The mortality rate was 14 percent after 30 days, with no disabling strokes or repeat interventions, the data show.

Last month, Medtronic announced that it has already launched a pivotal study of the safety and effectiveness of the Intrepid valve in up to 1,200 severe mitral regurgitation patients. That study includes one group of patients who will be randomized to either the Intrepid or conventional mitral valve surgery, and a second group of patients who are considered inoperable who will get the valve and be compared to statistical performance goals.