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！」][1]
instead of 
[「えっ！」][2]

(So... maybe you'd call it a "thick/gruff/husky(?) voice"?? Or, is this what you'd call "strained", as in @ogicu8abruok's comment?)




  

 


  [1]: http://vocaroo.com/i/s0YZv2DMG8AA
  [2]: http://vocaroo.com/i/s1OamI04IXob