Staff reviewers for the U.S. Food and Drug Administration did not recommend approval of Abbott Laboratories' implantable heart device MitraClip, citing a lack of ``valid scientific evidence'' of safety and
effectiveness.

In briefing documents posted on the regulator's website on Monday, the FDA reviewers said the device's approval would not be appropriate at the time as major questions of safety, efficacy and overall benefit-risk profile for the device remained unanswered.

MitraClip Clip Delivery System (CDS) is a percutaneously implanted mechanical clip for the reduction of mitral valve insufficiency - a heart disorder in which the mitral valve does not close properly when the heart pumps out blood, allowing blood to flow backward into the heart.

Abbott is seeking approval of MitraClip to reduce mitral valve insufficiency in patients who have been determined by a cardiac surgeon to be too high risk for open mitral valve surgery.

The proposed use for the device was changed by Abbott after the FDA had expressed concerns that there was a lack of evidence to support the device's approval for use in patients with significant mitral valve insufficiency, the reviewers said in the documents.

However, the reviewers recommended that MitraClip CDS continue to remain available to the high-risk patient population as an investigational device so that Abbott can conduct its trials in an optimal manner. 

Shares of the company were down 1% at $33.81 in early trading on the New York Stock Exchange.