UPDATE 2-US FDA panel narrowly supports stroke device

* FDA advisors recommend approval in 7-5 vote

* Some panelists still questions safety, effectiveness

* Panel says more study needed if approved (Adds comments from panel, background on device)

By Susan Heavey

WASHINGTON, April 23 (Reuters) - A U.S. Food and Drug Administration advisory panel on Thursday narrowly backed Atritech Inc's experimental device to prevent strokes in patients with irregular heart beat.

In a 7-5 vote, the FDA panel of outside experts said the device, called the Watchman, should be approved despite some lingering concerns over some of the data as well as possible complications.

The privately held device maker is seeking U.S. approval to market its coin-sized, cage-like device as a competitor to the widely used blood-thinning drug warfarin. It aims to prevent harmful blood clots that can enter the blood stream and cause stroke in patients with abnormal heart beat, or atrial fibrillation.

If its device is successful, the Minnesota-based company could become an acquisition target by larger medical technology companies, some stock analysts have speculated.

Warfarin, available as a generic and as Bristol-Myers Squibb Co's (BMY.N) branded drug Coumadin, is relatively inexpensive but can cause significant bleeding risk and patients must be frequently monitored. Several drugmakers, including Johnson & Johnson (JNJ.N) and Bayer AG's BAYG.DE, are also developing alternatives.