The film gives an abbreviated version of Darth Vader’s exclamation:
The comic adaptation expands his words with:
By the Immortal Gods of the Sith!
Are we to believe Darth Vader was literally appealing to the Expanded Universe “Immortal Gods of the Sith,” which the EU would later over many years prove to literally exist throughout many sources, and actually become a quite plentiful pantheon of immortal gods? Or was he just giving a Sith version of “oh crap?” Support for former might include evidence the EU Vader being a strong proponent or dogmatic adherent of Sith religious beliefs.