225 means one of two things:
1) You are some sort of genetic freak. Hitting anything over 200 is unbelievable
2) The powerlines or something were interfering with the wireless transfer between your HRM and the heart rate sensor itself.
I'm betting on #2. My wireless speedometer flips out every now and then and claims I'm hitting 80+ mph for a second or two before calming back down. I'm betting HRM's are subject to the same interference.