Place the chicken breasts in the bottom of the slow cooker.
In a medium bowl, whisk together the heavy cream, chicken broth, garlic powder, onion powder, Italian seasoning, salt, and black pepper until combined.
Pour the cream mixture over the chicken breasts in the slow cooker.
Cover and cook on low for 3 to 4 hours, or until the chicken is cooked through and tender.
Remove the chicken breasts from the slow cooker and shred them using two forks.
Turn the slow cooker to high heat.
Add the uncooked fettuccine pasta to the slow cooker, spreading it out evenly.
Return the shredded chicken to the slow cooker and stir gently to combine with the pasta and sauce.
Cover and cook on high for 20 to 30 minutes, or until the pasta is tender, stirring occasionally to prevent sticking.
Once the pasta is cooked, stir in the grated Parmesan cheese and unsalted butter until melted and the sauce is creamy.
Taste and adjust seasoning with additional salt and pepper if desired.
Serve the chicken Alfredo hot, garnished with chopped fresh parsley.