Hi Jarvis1! Sounds like you and your kitty are having a bit of rough go of it right now. Along with the excellent advice RUSTYcat and Love4himies gave you, I'd also like to suggest that you look into a supplement called Transfer Factor Plus
for Jarvis. 1 or 2 capsules a day mixed into wet food should help boost his immune system and hopefully prevent secondary health conditions such as ECG from developing.
For the stress that he's likely experiencing, maybe a Feliway
diffuser plugged into his room will help him feel a little calmer. Another one for the rest of your cats, if you aren't already using them, might help them be more accepting of him.
And lastly, I swear by the benefits of feeding a raw diet. There are some great commercial frozen products available that make it as easy as opening a can, or if you're up for the challenge, you can make your own from scratch. Some good info at this link on the why's and how's: http://feline-nutrition.org/
All the best to you and Jarvis. Crossing my fingers that his ECG gets resolved and that you can eventually integrate him into the rest of your household.