Vader just found out an Imperial Officer tried to have him assassinated. So he had the Emperor call the upper elites (the generals, moffs, and admirals) of the millitary in Corsuant to a meeting. Vader introduced himself, before picking five random names. He then forced choked them to death as a message to the mastermind.
I think it's symbolism. Vader is wrecked abomination of vast darkside power, but there's still traces of light within him. Hence when he commits this horrible deed, the next panel shows True!Vader crushing one of the floating butterflies (the remnant of his light) above him.
It seriously reminds me of Aboleth.