I have not been following this thread and am just responding to last
sentence posted by Enfilade....I didn't
know cats could have pacemakers, but if Steve's cat w/
tachycardia has a pacer (otherwise, my post is irrelevant)
I can tell you from hospital employment that people come
in quite frequently to have their pacemakers adjusted as
to timing and other factors of efficiency, so if this is true
for hoomins, why not for veterinary care?
Hoomins get distinctive symptoms when their pacers need adjustment, but of
course cats can't talk...your vet
sounds very expert and knowledgeable about the matter.
Best wishes for your kitty Steve.

Right. It would also make a difference if it's fairly constant (the fast
pacemaker), or what is called PSVT -- paroxysmal supraventricular
tachycardia, where there are sudden bursts, more likely to cause
dizziness or fainting.  This is sometimes due to hyperthyroidism.

As DP suggested, atrial tachycardia is relatively benign.  Atrial
fibrillation would be more of concern -- where the upper chambers beat
erratically. Again, atrial phenomena are far less dangerous than
ventricular problems.

Thanks. Back when Dr Haney first diagnosed Sammy with a heart murmur I
was kind of freaked. So far all Dr Haney thinks she needs is a
healthier diet than the Iams she used to eat. When the diagnosis was
first made we were going to do ECGs every quarter. I think that's
mainly to get a baseline on how her heart is working.  He skipped the
ECG in January, deciding she was doing well enough that we would
switch to ding them once every six months. Now I just view it as
something that needs to be monitored.