I had my initial Class 1 at Gatwick where this (RBBB) was picked up - the nurse said it wouldn't be a problem, and their cardiologist signed it off the same day leaving me with an unrestricted Class 1 - it all seemed like a bit of a non-event from start to finish.
I didn't have to have a Holter monitor or stress echo. Nothing more has been said about it.
Viral pericarditis is another battle entirely, though
