WASHINGTON (AP) - A huge study suggests the Apple Watch sometimes can detect a worrisome irregular heartbeat. But experts say more work is needed to tell if using wearable technology to screen for heart problems really helps.

  

More than 419,000 Apple Watch users signed up for the study. An app would alert them if the watch spotted a heart rate problem that might signal atrial fibrillation, a condition that if untreated eventually can trigger strokes.

  

Stanford researchers reported preliminary results Saturday at a cardiology conference.

  

The watch flagged only a small group of people - about 2,100 - for a possible problem. Among those who got rechecked with EKG monitoring, a third had a-fib.

  

Experts say the study may not have included enough seniors, who are at high risk of the heart problem.