"Based on the results of the Apple Heart Study — which were released at the American College of Cardiology meeting this week — it is now official. The Apple Watch is a serious competitor for the worst heart device ever. What was the Apple Heart Study? It was one of the largest studies of 'digital health' to date. Nearly 420,000 people throughout the U.S. agreed to participate. The participants wore watches that sent intermittent information about the regularity of their heart rhythm to Apple for varying periods of time. During the study, about 2,100 notifications of a heart 'irregularity' were sent. … An analysis by Venk Murthy, MD, PhD, of the University of Michigan, suggests that the Apple device failed to correctly identify atrial fibrillation in a large proportion of people who actually had it."