I'm sorry no one has responded to your post. I think your baby may possibly have MVD - tiny little shunts that can't be surgically repaired, rather than one large shunt that can. I am no vet and your vet can explain the difference. Here is a quick link that may be helpful. I think with MVD, babies can be medically managed with diet and medication. I would suggest that you go to a specialist so you don't waste any money on tests that won't give you answers.
MVD
Thoughts and prayers for Samson.......