Are you talking 'now', or 'back then' ?
What you describe is obviously the ideal, and how it very often is. However, I was thinking/talking mainly about manipulation of pacing wires within the heart. As you imply, it very often only required a fairly small number of seconds of screening, in short bursts, to get that done. However, sometimes the wires were stubbornly reluctant to go where one wanted them to go, so one had to do a lot of 'fiddling about', under more-or-less continuous screening.
I can't remember whether the machines told them this, or whether they had some sort of 'stop watch', but the radiographers were constantly aware of the accumulated amount of screening time, frequently updated us on that amount, and started becoming increasingly 'concerned' if/when the total got to more than a minute or two.