U.S.
reviewers said a Medtronic Inc device was effective for treating a common heart
rhythm disorder, but they raised concerns about its safety.

Medtronic’s Cardiac Ablation System is designed to treat
persistent atrial fibrillation, a major cause of strokes. But, in documents
released on Tuesday, Food and Drug Administration staff expressed concerns
about the high rate of stroke found in patients treated with the device.

Atrial fibrillation, which affects more than 2 million
Americans, is the most prevalent heart rhythm disorder. It describes the rapid
and irregular contraction of the heart’s upper two chambers, which allows blood
to pool. This can form clots that travel to the brain and cause strokes.

Medtronic is seeking approval for the device as a treatment
for persistent atrial fibrillation, which lasts for more than seven days or
recurs for as long as four years. The company said just over half of patients
have persistent atrial fibrillation, but there are no FDA-approved devices to
treat this condition.

In a clinical trial, five people out of 176 had a stroke
within a month of getting the Medtronic device, and 38 people had at least one
serious problem such as low blood pressure or swelling of the covering around
the heart, FDA reviewers said.

The device helped some people in clinical trials; 55.8
percent of patients had regular heartbeats within six months of using
Medtronic’s device, compared to 26.4 percent of patients who used the typical
treatment of anti-arrhythmic drugs to treat atrial fibrillation.

A panel of outside experts will consider the device at a
meeting on Thursday, with the FDA set to make a final decision.

Given the FDA’s safety concerns, Sanford Bernstein analyst
Derrick Sung said he sees a 50 percent chance of the panel recommending the
device for approval.

“We would emphasize that investor expectations are
low,” Sung said in a research note.

Anti-arrhythmic drugs such as beta-blockers can help restore
a normal rhythm. However, Medtronic and other companies such as Johnson &
Johnson and Boston Scientific are turning to ablation devices to treat atrial
fibrillation.

While such ablation devices are still a relatively small
part of the multibillion atrial fibrillation market, analysts expect it to
grow.

Ablation is a non-surgical technique used to neutralize the
cells within the heart muscle that are responsible for starting or maintaining
these abnormally fast, and sometimes lethal rhythms.

The Medtronic device uses catheter ablation, which involves
inserting a thin tube into a blood vessel, usually through a site in the upper
leg or neck, then threading it though the body until it reaches the heart.

When it reaches the area causing abnormal rhythms, a device
emits radiofrequency energy to destroy the tissue.

Medtronic received FDA approval in December 2010 to sell a
different ablation device for treating paroxysmal atrial fibrillation, which is
intermittent — meaning it lasts for less than seven days — but recurring.

Medtronic shares fell 1.5 percent to $34.19 in trading on
the New York Stock Exchange, below a 1.1 percent drop in the S&P Health
Care Equipment index.

(Reporting by Anna Yukhananov in Washington; Editing by Gerald E. McCormick
and Robert
MacMillan)