Sleep apnoea in CKCS with MMVD & CHF

RE: Sleep apnoea in CKCS with MMVD & CHF

Dave Dickson — Thu, 30 Sep 2021 21:15:39 GMT

I find that whilst most dogs lose sinus arrhythmia when they go into CHF, once this is controlled they generally get it back, especially when not in the clinic environment. We see plenty of dogs in CHF on medication who have a resting/nocturnal sinus arrhythmia when at home with a Holter on. In clinic, sinus arrhythmia is much less common when in CHF but I wouldn’t use sinus arrhythmia to exclude CHF especially when being noted at home.

in most dogs it is absence of vagal tone, not the sympathetic drive, that causes loss of sinus arrhythmia. They lose the brake of the parasympathetic system rather than sit on the accelerator pedal of the sympathetic system. Not that the difference is helpful clinically, I just find the physiology fascinating because I’m a geek!

Dave

RE: Sleep apnoea in CKCS with MMVD & CHF

David Mills — Mon, 27 Sep 2021 17:09:07 GMT

I've always thought that the sympathetic drive that comes with true CHF would override any increase in vagal tone (caused by whatever mechanism)? That is, most CHF will continue to have a relatively metronomic heart rate. So if these episodes are happening it would make me revisit the diagnosis of CHF (especially on lung ultrasound, as I consider CHF to be a radiographic diagnosis).

Just some thoughts.

RE: Sleep apnoea in CKCS with MMVD & CHF

Dave Dickson — Mon, 27 Sep 2021 13:35:31 GMT

Hi Holly

This is an interesting question. I get asked about sleep apnoea occasionally but I have to say it's not something I have diagnosed myself. My main worry is that owners have an awareness of the condition in people and are then labelling dogs as getting this condition when we don't actually know (well, I don't actually know!) if it really exists.

My own dog will go 10-12 seconds between breaths when asleep (I know this because I counted her sleeping resp rate for a study I was doing). Equally, in brachycephalic breeds like CKCS, I think there will inevitably be some effect of vagal stimulation from URT obstruction slowing heart rate.

So possibly the owners are just noticing a "normal" slow heart rate during a period of high vagal tone? We run a lot of Holters and in most healthy dogs, the HR will get to 40/min and stay there for hours during sleep, with normal pauses of up to 5 seconds.

Having said all that, if you or the owners are worried, run a Holter (you can rent them from us and other companies online). This will help answer the question of "is this bradycardia significant". I agree, PHT is a possibility however most cases of significant PHT show signs especially during exercise (dyspnoea, weakness, collapse, cyanosis) so if she isn't showing clear signs, this is less of a concern.

Of course, it's hard for me to say don't get the echo - I'd always want to echo these prior to GA. If funds are that limited, I'd do the echo over the Holter as that gives more immediate information about GA risk. If the owner's main concern is the apnoea/bradycardia, do the Holter.

Hope that helps.

Dave