Management of CHF in cats

RE: Management of CHF in cats

David Mills — Sat, 14 Nov 2020 18:23:58 GMT

Yes I agree the evidence for making decisions is lamentably poor, but my view is that the evidence we do have indicates that it appears to be safe, and efficacious, across a range of CMs. It also has somewhat of a 'happy dog' effect in canines, due to some action on inflammatory mediators. I wasn't saying everyone should treat the same way as myself, merely that the discourse around pimobendan and cats within cardiology often quickly invokes the spectre of LVOTO/SAM and it is not as simple as that.

Clopidogrel vs aspirin is another perpetual one. The evidence we have is that clopidogrel is better at preventing a recurrence of ATE than aspirin, but we do not know if it is better at preventing the first occurrence (whether it is ethical to treat to prevent recurrence is another interesting question). Aspirin of course has the advantage of reducing total tablet load, and clopidogrel tastes awful to cats.

I suspect most CMs are related and the descriptors we are using are actually describing a narrower range of CMs at different stages of pathology. Whenever an unclassified form of a disease exists we know we're miles away from consistency and being able to prognosticate, and, relatedly, knowing what therapy works best.

Re licensing - the last time I checked, the only medication that was licensed for use in cats for CM was diltiazem. Pimobendan, of course, is licensed in dogs.

RE: Management of CHF in cats

Dave Dickson — Sat, 14 Nov 2020 15:44:09 GMT

Hi David

You raise some good points. There are some recent studies that have looked at this (for those following along) -

https://pubmed.ncbi.nlm.nih.gov/30778391/

and

https://pubmed.ncbi.nlm.nih.gov/33026124/

and

https://pubmed.ncbi.nlm.nih.gov/30778391/

All support the argument that pimo appears to improve LA function and isn't dangerous from increasing outflow tract velocity.

What we are lacking are prospective trials that look at outcome. Until we have those, this all remains fairly speculative, but I agree that we can't dismiss pimobendan outright, particularly as it has potential to be really beneficial. I think you can argue that it's dangerous to advise treating all cats with CHF with off-license pimobendan without providing at least some qualifying statements. There is a difference between saying "this is what I do" versus "this is what everyone should do".

My clinical practice is to use pimobendan in cats cautiously with mind to the fact that you can't treat all cardiomyopathies in cats (or even the same cardiomyopathy in different cats) as one disease. And that once you add a third medication in (assuming cats are going to be on a diuretic and most will be on clopidogrel), the rate of compliance drops precipitously and this will affect outcome more than most other factors.

Dave

RE: Management of CHF in cats

David Mills — Sat, 14 Nov 2020 15:27:11 GMT

The pimobendan theory often gets trotted out in these discussions, but it's important to remember it's a theory, based on mechanistic reasoning. The latter has a poor record in the history of EBM. Anti arrhythmics in asymptomatic humans is perhaps the most famous example.

The physiological effects of LVOTO are poorly understood where SAM is involved. Whole theses have been written on the subject and there is some thinking it relates to the Bernoulli effect (like a shower curtain) but this is by no means a perfect fit for a complex 3D dynamic structure. It may be that the opposite is true. Pimobendan is lusitrophic meaning more rapid rate of ventricular relaxation and therefore filling a greater ejection fraction may therefore reduce the effects of LVOTO.

Its also worth bearing in mind the generally benign nature of LVOTO. In the RVC data these cats survived as long as cats without LVOTO provided there was no other CM. it doesn't seem to affect survival times as far as we're aware.

The only published evidence we have is that pimobendan does not cause issues in cats with LVOTO. It is dangerous to start dismissing this evidence based on tying oneself to theory or anecdote.

The studies published also use a relatively high dose of pimobendan. There is pharmacological data showing the half life in cats is about twice as long as dogs, meaning it can be given once a day.

Most cardiomyopathies have a significant systolic dysfunction.

So for cats with CHF I use frusemide 2mgkg bd and pimo 1.25mg per cat sd. I haven't seen any deleterious side effects of the latter.

RE: Management of CHF in cats

Rob Loxley — Fri, 13 Nov 2020 22:46:32 GMT

If there’s not a loud murmur, how likely is significant lvoto- I’ve had some good successes with cats on pimo but do worry about those cases it might worsen. Maybe the answer is to improve my echo skills?!

RE: Management of CHF in cats

Dave Dickson — Fri, 13 Nov 2020 18:27:49 GMT

I wasn't involved with the study(ies?) that looked at this but I've heard the results presented. Basically yes I think LVOTO is the problem, though I don't know enough to say more. I think that there is still a good argument to use it in some cats with systolic dysfunction without obstruction - that's what I do currently.

I had a case with confirmed hypotension on pimobendan - we gave the cat pimo and an hour later it was clinically hypotensive (subdued, stumbling) and systolic BP was 80mmHg or so I think. I wasn't convinced so I kept the cat in, checked BP later that day and it was 140mmHg or so and the cat was much better. I gave another dose of pimo the next day and the same thing happened. That cat did have bad DLVOTO due to SAM and I think the pimo pushed it over the edge - totally my fault - but I was convinced from that point on that pimo is not benign in all cats.

Dave

RE: Management of CHF in cats

Roger Wilkinson — Fri, 13 Nov 2020 17:27:22 GMT

I understand you might not be at liberty to tell us, but what were the potential harms associated with pimo?

and were they associated with LVOTO? The hypothesis that pimobendan is contraindicated in LVOTO in cats or dogs is theoretical rather than based on evidence is it?

RE: Management of CHF in cats

Dave Dickson — Fri, 13 Nov 2020 15:51:38 GMT

I think that reflects the fact that honestly, we don't really know much more than that. Frusemide (and torasemide) work, clopidogrel works but is hard to give to some/many cats, the rest is guesswork.

Dave

RE: Management of CHF in cats

Bibs — Fri, 13 Nov 2020 15:41:01 GMT

That's very helpful thanks. I'm coming from a position where on a good day I'd be able to get a LA:Ao ratio but need to work on my echo skills beyond that. There doesn't seem to be much easy to access info on what else to use apart frusemide, so your outline does clear up a lot of questions for me for cases that can't be referred.