We sometimes write 「な!?」,「なっ!?」or「なっ・・・!?」(These three will be pronounced the same way) to mean 「なにっ！？」or「何！？」. Probably it's like "Wha...!?" or "What the...!?".
We also sometimes write 「え゛っ！」in place of「えっ！」 to add emphasis, but the 「゛」([濁点]{だくてん}) won't change/affect the pronunciation, so it'd be impossible to pronounce 「な゛」or「え゛」 correctly (I don't know what would be "correct" here though).
However, if I were a voice actress and had to read them, I'd probably read them as...
「え゛っ！」
instead of
「えっ！」
(So... maybe you'd call it a "thick/gruff/husky(?) voice"?? Or, is this what you'd call "strained", as in @ogicu8abruok's comment?)