Cardiogram last week announced that it has developed a preliminary algorithm to use with the Apple Watch and Android Wear devices to detect atrial fibrillation with higher accuracy than previously validated detection methods. Atrial fibrillation, or AF, affects about 2.7 million Americans, and increases the risk of stroke by five times. Overall, it causes about 15 percent of strokes. Cardiogram trained a deep neural network using heart rate readings taken from Apple Watches. The company sent 200 AliveCor mobile electrocardiogram devices to people diagnosed with AF.