Atrial fibrillation (AFib) is a common irregular heartbeat that can lead to blood clots, strokes, heart failure, and other problems. It affects up to 6 million Americans, but many people don’t even know that they have it.

An app for the Apple Watch might help change that. The app uses light-sensor technology to measure blood flow. It can also detect slight changes that might indicate an irregular heartbeat.

If the sensor detects five out of six repeat episodes of an irregular pulse within a 48-hour period, the app sends wearers an “irregular pulse” notification.

Stanford University researchers conducted a trial of more than 419,000 self-enrolled Apple Watch users. Of those, 0.5 percent received an irregular pulse notification. Those who got a notification were advised to contact the study doctor, who then decided whether the participant should wear an electrocardiogram patch for follow-up monitoring.

Of the 658 participants who were sent a patch, 450 returned it, and about one-third of them were found to have AFib.

“We are witnessing the evolution of how health care will be provided,” said Dr. Laurence Epstein, who directs electrophysiology at Northwell Health in Manhasset, N.Y. “[There is] no doubt that in the very near future this is how we will be monitoring patients for a wide range of diseases.”