A landmark product trial that helped establish implantable defibrillators as devices to help guard against sudden death from heart failure also showed they have continued benefits out to eight years, according to data released Thursday.

The original "Madit II" trial results were released early this decade. The study helped fuel growth in a now $6 billion global market for implantable cardioverter defibrillators, or ICDs, shared by Medtronic Inc. (MDT), St. Jude Medical Inc. (STJ) and Boston Scientific Corp. (BSX).

Boston Scientific sponsors the Madit II study by way of Guidant Corp., which Boston Scientific purchased three years ago.

The new long-term results, unveiled at the Heart Rhythm Society's annual scientific sessions, showed an expanded survival benefit for patients with ICDs. Such data could help manufacturers defend the market for the devices priced at roughly $25,000, which are often used in Medicare-aged patients. It comes amid a search for ways to wring savings from the U.S. health-care system.

The study looked at patients who had prior heart attacks that did some damage and put them at risk of sudden-cardiac death based on certain measurements of heart performance. ICDs are designed to provide shocks when needed to jolt hearts back into proper rhythms.

Among the 1,232 patients originally enrolled, the study showed a 31% relative reduction in risk of death at 20 months of follow-up for patients who had an ICD plus medication compared with patients on just drugs. Over an average follow-up period of about two years, ICDs extended patient lives by about two months.

The eight-year results from Madit II showed a probability of death by any cause of 45% among patients with an ICD, as compared with a 61% probability for patients without one. The numbers indicate that these are patients who face significant risks, and many will die with or without protection from ICDs. Still, the difference at eight years corresponds to an expanded 1.2 life-years saved among ICD patients, according to a release from the Heart Rhythm Society.

The results also indicate a 37% lower chance of death from any cause at eight years among ICD patients.

Boston Scientific noted that at eight years in the study, one life is saved for every six patients who received an ICD. That compares with saving one life for every 17 patients with an ICD at the two-year point.

-By Jon Kamp, Dow Jones Newswires; 617-654-6728; jon.kamp@dowjones.com