Can wearing your heart (monitor) on your sleeve save your life?

ON THE MORNING of March 28th, the owners of newish Apple Watches in 19 countries woke up to find their timepiece was now a medical device. Two new features arrived. One monitors the wearer for an irregular pulse. The other allows a brief but detailed electronic portrait, or ECG, to be captured and inspected for signs of a common heart arrhythmia called "atrial fibrillation", or AFib. Americans have had these options since December, but their global expansion puts the technology squarely within t...