As it works to resolve issues with federal regulators, Medtronic Inc. has been forced to hold off on launching a highly anticipated new pacemaker that was designed to be compatible with most MRI scans.

Although Medtronic's Revo MRI Pacemaker System won the recommendation of a Food and Drug Administration advisory panel earlier this year, a warning letter the agency issued to its Mounds View-based pacemaker and defibrillator business last year has held up final approval -- as well as the product's U.S. introduction.

The product is unique because patients treated with the silver-dollar sized device are generally warned against getting magnetic resonance imaging procedures because of potentially risky complications. Each year, about 200,000 pacemaker recipients are denied MRIs because of those risks, according to the Fridley-based medical technology company.

But lingering FDA warning letters such as the one Medtronic received often prevent companies from introducing the most-sophisticated and lucrative medical devices (also known as Class III products) until issues are resolved.

"The FDA has completed the reinspection of the Mounds View facility, and we are awaiting results," said Medtronic spokesman Christopher Garland.

When (and if) that will occur is anyone's guess -- FDA spokesman Dick Thompson said Tuesday the agency couldn't comment on the Medtronic situation.

So for the time being, the Revo pacemaker remains on hold, as well as another promising product, a heart defibrillator called Protecta, which minimizes inappropriate shocks to patients. Studies have shown that about 20 percent of patients with defibrillators may experience unnecessary shocks, often described by patients as swift and painful blows to the chest.

Implanted in the chest, pacemakers and defibrillators generally control the heart's rhythm using electrical impulses. A pacemaker "paces" the heart, while a defibrillator shocks the heart when it detects an abnormal heartbeat.

Both new products could help boost Medtronic's $5.3 billion cardiac rhythm business, which accounts for roughly a third of the company's annual revenue. The $7.9 billion U.S. business for these products includes competitors St. Jude Medical Inc., based in Little Canada, and Boston Scientific Corp., whose pacemaker business operates out of Arden Hills.

The problem stems from an inspection of Medtronic's Mounds View Cardiac Rhythm Disease Management headquarters last year, when the FDA found problems with the company's procedures for preventing and identifying potential issues with devices, and in the way those problems are documented and communicated to the agency.

Phil Nalbone, an analyst with Wedbush Securities, said the warning letter is a big obstacle for Medtronic as it attempts to revitalize its cardiac rhythm business. St. Jude Medical will likely benefit from the [warning letter] delay, he said.

While the investment community has focused largely on the Revo product, Nalbone said the new Protecta line of defibrillators is more of a workhorse product.

"It's not a game-changer, but [it's the] freshest new product offering in the [defibrillator] space for Medtronic in several years," Nalbone said. The product feature that prevents unnecessary shocks "spares patients needless suffering and saves the health care system a fair amount of money."

Janet Moore • 612-673-7752