If both are 11 probably you wont have any problem changing only the shifters. If the athena is 10 speed (i doubt it is) you might have a problem because the 10 sp rd and 11 sp rd are different from what I red, almost the same cable pull but not the same exactly. But at the same time I heard that 10 speed rd works fine too.

Is it the shifter itself that determines this? <-- yes, but 11 speed cogs are all the same spacing so change for another brifter shouldn't be a problem.