Bristol-Myers Squibb is discontinuing a Phase 1 clinical trial proof of concept study for a proposed atrial fibrillation drug from Icagen, Icagen said Thursday.

However, the drug giant is “currently considering alternative trial designs,” Icagen said in a statement.

Bristol-Myers Squibb cited “slow enrollment” of test subjects as the reason for its decision, Icagen added.

“While we are disappointed that enrollment in this proof-of-concept study was difficult, we are pleased that Bristol-Myers Squibb is considering alternative trial designs,” said P. Kay Wagoner, Icagen’s chief executive officer.

According to the American Heart Association, 2.2 million Americans suffer with the atrial fibrillation disorder. It occurs when the heart’s two upper chambers, known as the atria, quiver instead of beating effectively. Some 15 percent of strokes occur in people with atrial fibrillation.