The good news, the Apple Watch 0 will still report the heart rate, when it sees it. The difference, no notification and the Apple Watch 0 will not be specifically looking for this condition. My Apple Watch 0 infact did report a very high random heart rate, I had to look at the Health App history, figure out what time of day it was, what was I doing, and report this to my Doctor. I share this persons success story with my Apple Watch 0, even if a bit more mechanical with my Apple Watch 0. Now updated to Apple Watch 3.
Look at tour Apple Watch heart rate in the Health App, select the year tab at top, will show you low and high for the year. If high like 200, drill down to see what day and time the events happened. Long explanation, for you were not left behind, the New Apple Watch easier and it taps you on the wrist when a problem occurs. Have this or other heart related problems, and upgrade would be prudent.