Gallop Heart in 6yo male cat

Hi! 2 weeks ago I (26F) took my cat in for an annual checkup and the vet noticed gallop rhythm.
I was shocked by it as this was never mentioned in any of his wellness checkups before. He also went through anaesthesia last year and he had prior checkup to make sure he is not at risk. Everything was completely fine.

I went for a second opinion to a different vet. It’s confirmed - he has gallop heart.

We are getting a referral to a cardiologist, but the wait times vary from several weeks to a month. We will be getting an echocardiogram which is expensive, but luckily I have some savings.

I am devastated. The vet mentioned it is unlikely that the sound is benign and that it is likely a symptom of an underlying issue - probability is - it’s HCM.

He is a young 6 year old neutered seemingly heathy boy that I love more than anything in this world. I know we don’t have a definitive diagnosis yet, but it feels like I’m going to lose him.

I am looking for guidance on what tests need to be done in addition to echocardiogram. I read about pro-BNP blood test, but the vet said it’s better to get an echocardiogram. Should I push for the blood test?

Bloodwork came back normal. Some elevated blood cells and ALT, likely this is connected to his skin issues and not the heart. T4 is normal.

He is acting normal. Eating, using litter box, but I am terrified every day that when I come back from work he will be gone.

Side note:
He was sneezing and had runny nose 2 weeks ago - the vet prescribed h a round of antibiotics and he seems better now. I am not sure if it’s connected.

He is a Devon Rex. He has skin problems - environmental and food allergies.

I would appreciate any stories from anyone who went through the same experience.

We live in Canada, BC

Thank you.