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