Thank you so much for your kind words when I was freaking out last week.
Since my last email, I've been increasing the dose of atenolol (beta blocker) under vet's advice. I've noticed that Oscar is having far fewer facial twitches, and seems a lot more relaxed and less jumpy. This makes me agree with the cardio that the problem might be heart, rather than epilepsy.
She's prescribed clopidegrel (1/4 tablet daily) just in case there is a risk of clots, which wasn't obvious from the ECG and echo. However, it's not arrived yet (grrr!) so I'm on the phone chasing it up.
Thanks again for all of your help, and for calming me down somewhat. Big hugs to you and your kitties.