Become a Creator today!Start creating today - Share your story with the world!
Start for free
00:00:00
00:00:01
Dr. Carolyn McKune on Anesthetizing Dogs and Cats with Common Cardiac Diseases: Part 1
217 Plays9 days ago
Get ready to follow your heart straight into another fantastic episode of the North American Veterinary Anesthesia Society Podcast! Host Dr. Bonnie Gatson is back (and pumped as ever) with a special guest who truly gets to the heart of the matter—board-certified veterinary anesthesiologist and owner of veterinary consulting business Mythos Veterinary LLC (great video explanation of what Mythos does), Dr. Carolyn McKune! This month, we’re diving deep into the world of anesthetizing dogs and cats with cardiac disease, and spoiler alert: there’s too much good stuff to fit in one beat! So, we’re splitting this topic into a TWO-PART SERIES to make sure nothing important gets left in vein. In this first episode, Dr. McKune helps us lay the groundwork by walking through the pathophysiology of common degenerative cardiac diseases seen in dogs and cats. What diagnostics will help shine a light on which anesthetic protocols are best for these patients? Which cardiac medications should be continued, and which should be left out prior to general anesthesia? If these are questions pique your interest, then this episode is sure to get your blood flowing!
Part two of this special episode on anesthetizing dogs and cats with degenerative cardiac disease will air the week of June 15th, so stay tuned!
If you like what you hear, we have a couple of favors to ask of you:
Thank you for the FANTASTIC turnout at the NAVAS Virtual Spring Symposium. If you enjoyed the educational content of the symposium, consider becoming a subscriber to NAVAS to access even more anesthesia and analgesia educational and RACE-approved CE content. When you become a subscriber to NAVAS, you'll have access to videos of all the sessions from the 2025 Annual Spring Symposium, as well as, all the other session videos from all 5 years NAVAS has presented the symposium. You can also have access to RACE-approved CE credits after you take a 5 question quiz after watching the videos.
Spread the word. Share our podcast on your socials or a discussion forum. That would really help us achieve our mission: Reduce mortality and morbidity in veterinary patients undergoing sedation, anesthesia, and analgesia through high-quality, peer-reviewed education.
Thank you to our sponsor, Dechra - learn more about the pharmaceutical products Dechra has to offer veterinary professionals, such as Zenalpha.
If you have questions about this episode or want to suggest topics for future episodes, reach out to the producers at education@mynavas.org.
All opinions stated by the host and their guests are theirs alone and do not represent the thoughts or opinions of any corporation, university, or other business or governmental entity.
Recommended
Transcript
Introduction and Episode Preview
00:00:06
Speaker
Hello, Gas Passers. Welcome to another episode of the North American Veterinary Anesthesia Society podcast, the show where we explore the fascinating world of veterinary anesthesia and pain management.
00:00:19
Speaker
Our goal with but this podcast is to advance and improve the safe administration of anesthesia and analgesia to all animals. I'm your host, Dr. Bonnie Gatson, and I hope you're pumped for this episode because we have a lot of ground to cover.
00:00:37
Speaker
In fact, once I started getting into a rhythm with this episode's guest, it became pretty apparent that we were going to need to break this into two episodes to keep up with the pressure of covering everything important related to this topic.
00:00:53
Speaker
So since we skipped the beat on our normal episode release for you should expect two episodes to premiere in June, with the second part of this topic releasing close to the middle of the month.
00:01:06
Speaker
And what are we discussing this month? Well, hopefully our clever listeners haven't missed a beat as they keep dropping these puns so they won't all be out in vain.
00:01:18
Speaker
My heart is all aflutter to talk about anesthetizing dogs and cats with heart disease. But first, as usual, we need to thank the sponsor of this podcast, DECRA, for their generous contribution towards supporting our efforts here at the NAVS podcast and for supporting continuing education efforts in the field of veterinary anesthesia and pain management.
00:01:41
Speaker
please consider visiting www.decra-us.com and checking out their line of veterinary anesthesia products, which includes the novel sedative medication for dogs, Xenalfa.
00:01:55
Speaker
We did an episode about this medication almost two years ago here at the Navas podcast. So if you're interested in learning more about Xenalfa, you can check out Decra's website or you could check out our earlier episodes.
00:02:09
Speaker
Second, we had an amazing turnout at the Navas Virtual Spring Symposium, so thank you to those of you who attended. If you enjoyed the contents of the symposium and you're looking for more anesthesia education, please consider becoming a member of the North American Veterinary Anesthesia Society.
00:02:29
Speaker
As a member, you will get access to even more amazing virtual educational opportunities like VIN rounds and fireside chats, which act like roundtable discussions where you can ask an anesthesiologist or specialty technicians all of your burning anesthesia related questions.
00:02:52
Speaker
If this interests you, please visit www.mynavvass.org to register as a member. And as always, please consider supporting us here on the NavVass podcast by not only liking and subscribing to this podcast on whatever format you use to access podcasts, but please consider telling your friends and coworkers about this podcast too, so we can fill the world with more gas passers.
00:03:18
Speaker
And you know we seriously appreciate all of our listeners and any support you can give us is always greatly appreciated. So thank you again to everyone out there.
Anesthetic Management in Pets with Cardiac Disease
00:03:29
Speaker
So I want to introduce you all to our guest who will be leading us through this discussion on approaching anesthetic management of patients with cardiac disease.
00:03:42
Speaker
She's a boarded veterinary anesthesiologist who has consulted with universities and private practices across the globe through her anesthesia consulting business, Mythos Veterinary.
00:03:54
Speaker
She has a deep passion for patient care and is a wonderful educator, as she even spent a few years teaching anesthesia to veterinary students at the University of Florida.
00:04:05
Speaker
I am so excited to share her insight with all of you as she is such a wonderful voice for patient advocacy and is a wealth of knowledge. So without further ado, my heart, again, is all a flutter to speak with Dr. Carolyn McCune all about the pathophysiology of cardiac disease in dogs and cats and how we're going to prepare these patients for anesthesia.
00:04:31
Speaker
In our next episode, Dr. McCune is going to return and together we are going to talk more about our approach specifically with drug protocols and how we're going to troubleshoot common anesthetic complications that are seen with these patients in particular.
00:04:49
Speaker
So let's get to it right here on the Navas Podcasts.
00:04:59
Speaker
Hi, welcome to the Navas podcast. Do you mind starting by introducing yourself? And why don't you tell me a bit about your experience in veterinary anesthesia and your experience with managing cardiac patients?
00:05:15
Speaker
All right. Well, thank you, Bonnie, very much for having me. My name is Carolyn McCune. i am a board-certified veterinary anesthesiologist. I am physically located here in the state of Florida, but as part of my job at the independent contractorship I run, the Mythos Veterinary LLC, I also offer virtual anesthesia.
00:05:36
Speaker
And so I have had quite a bit of wonderful exposure to cardiac disease, both from things that I do physically in a person, But that is actually one of the most common reasons for people to reach out to me about performing virtual cases what for patients who have either mitral valve disease in the canine patient or HCM for the feline patient. so And so I'm super excited to be here so we can talk more about something I do on a regular basis So to get here, I came through a path that includes the academics, referral hospitals, medical directorships, and now I'm doing independent contractor work.
00:06:13
Speaker
All of that gave me a lot of time to really reflect on what is my personal mission statement. field tomorrow, would be to retire from the field tomorrow. What do I want to know that I have achieved over the course of my career?
00:06:25
Speaker
And so my mission statement is to provide outstanding anesthesia to any animal anywhere. And what is not part of that statement, it doesn't say that I have to provide outstanding anesthesia to any animal anywhere, even if I wanted to, just like yourself, Dr. Gadsden, if you wanted to anesthetize every animal that ever went on for a procedure every day in the United States, we couldn't do it.
00:06:49
Speaker
And so really in reality, A big part of my mission and the mission of Navis is to educate. That is how I can provide outstanding anesthesia to any animal anywhere.
00:06:59
Speaker
And so I thank you for the opportunity to be on this podcast so we can help with the educational mission. That being said, I want to be very clear that although I work with a lot of patients who have cardiac disease,
00:07:11
Speaker
I am not a cardiologist. And so in my secret dream world, yes, I would love to do like a cardio residency or fellowship after all of this. But in reality, this will be an anesthesiologist's approach to cardiac disease.
00:07:23
Speaker
And therefore, there might be something different that a cardiologist might talk about or advise. Please just keep in mind that there's going to be multiple different ways to look at things that we all want the same outcome for, which is at the end of the day, the patient is happy, healthy, safe, and comfortable.
00:07:39
Speaker
I ask all my guests this, or at least I try to what is your favorite thing about veterinary anesthesia? What like really jazzes you about it?
00:07:50
Speaker
oh wow. I think my favorite thing about veterinary anesthesia, and this is going to probably sound weird to a lot of people, but is working with other people. I love people. i enjoy people interactions.
00:08:02
Speaker
I could be equally as happy being a bartender, barista at Starbucks. Well, maybe not. That's not a hundred percent true, but I, I enjoy working with groups of people and I feel like anesthesia is something that many people are aware and peripherally involved in, but don't know to a certain depth. And so I like to be able to provide that information to them. That's really probably my favorite things.
00:08:26
Speaker
I think that's a unique answer. i don't think we've had that one before. I think it's funny because I feel like one of the, I would say for me, a benefit, maybe not for you, is that we get to focus a little bit more on the patients because we don't oftentimes and not always have interactions with clients And so I think it's interesting that you went to like the team sort sort of approach to veterinary anesthesia. Yeah. And I speak to every owner before I anesthetize their animal. And that's actually one of the things I've loved about moving into this job is that I do get a little bit more access to the clients versus when I was in an academic setting or a referral setting with everything. And so, yeah, but I'm sure that there's times where I'm also grateful I don't have to deal with things I just don't know that my teammates protect me from those things. Cool.
Exploring Cardiac Diseases in Pets: Mitral Valve Disease and Hypertrophic Cardiomyopathy
00:09:18
Speaker
cool All right. So we are going to jump into the episode now. And as you alluded to earlier, we are going to focus on the two most common presentations of cardiac disease in aging animals.
00:09:35
Speaker
which is going to be mixomatous degeneration of the mitral valve. We're just going to, for the sake of this episode, we're just going to call it mitral valve disease. I hope you're okay with that, even though, you know, sometimes it affects both of the AB valves, but we're just going to focus on mitral valve disease.
00:09:51
Speaker
And then we're also going to talk about hypertrophic cardiomyopathy. So we're going to start our discussion on mitral valve disease. So how prevalent is this disease in our aging canine population?
00:10:05
Speaker
Yeah, great question. So it's estimated that approximately 10% of all dogs will present to their primary care veterinarian for heart disease. And mitral valve disease is going to be the most common of those cardiac disease.
00:10:19
Speaker
at Roughly 75% of the cases that are seen in veterinary clinics in North America for heart disease is going to be myxomatous mitral valve disease. And as an animal ages, that becomes ah more and more of a likelihood.
00:10:34
Speaker
Can you give a brief description of how the heart structurally changes throughout the progression of mitral valve disease? All right, so the mitral valve is part of an apparatus. I know we like to think of it as operating in isolation, but it has a role to play as part of a team. The mitral valve has two leaflets, which are tethered to the ventricular papillary muscles by the chordae tendineae, and that is anchored to a fibrous left atrioventricular ring of the mitral annulus.
00:11:04
Speaker
The purpose of this whole apparatus, then, is to keep blood moving forward in one single direction, And I kind of think of it like the valves on our anesthesia machines. That's the valves for the circle system are intended to keep flow moving in a one-way direction. That's really what the mitral valves apparatus is intended to do.
00:11:24
Speaker
So that's normal life. In patients who have mitral valve disease, this usually starts out as kind of a nodular disorder and gradual thickening of those mitral valve leaflets.
00:11:35
Speaker
They progress and then eventually those nodules coalesce. And so we begin to start to see that the mitral valve does not have what they call normal coaptation. In other words, the valves do not oppose each other as they normally should and therefore they begin to leak.
00:11:52
Speaker
So now we have this situation where blood flow is no longer just this unidirectional forward flow like we would like it. It moves both forward and backwards. That backwards flow officially is referred to as what we call the regurgitant fraction. And the severity can vary between dogs for how severe that is.
00:12:10
Speaker
As you can imagine, that backwards flow is tough on that left atrium. It normally gets this little break during systole. Now during systole, it's got a jet of regurgitation that is coming backwards.
00:12:22
Speaker
That's going to cause this left atrium to start to dilate as it over distends with its normal blood flow and the regurgitated blood flow. That dilation means that then now there's room for additional blood. And so that additional blood moves forward into the ventricles during the next cycle.
00:12:39
Speaker
So now we have... two chambers who have volume overload, both the atrial and the ventricular chambers. That means during rest or diastole, that pressure is going to begin to increase.
00:12:51
Speaker
And so now over time, we start to see that the ventricle hypertrophies, and so it starts to enlarge and thicken in order to accommodate this new forward flow, which we would call eccentric hypertrophy as opposed to what we'll talk about for kitty cats later on.
00:13:06
Speaker
The stronger heart muscle is meant to move blood out of the heart more efficiently, but because the valves continue to leak, it also becomes more effective at sending blood backwards and and into the left atrium. This is where we start to get this cycle of things that are changing.
00:13:23
Speaker
Eventually, that cycle, because there's going to be a neurohormonal component to all of this, results in a failing heart. So a person can tell us, as their heart is starting to fail, I feel breathless. I don't have as much activity that I... can do anymore that I used to. Animals can't tell us that. I'm feeling breathless or those kind of things.
00:13:40
Speaker
So in veterinary medicine, heart failure is considered the more objective criteria when we start to see things like radiographic signs that correlate with an animal who has an underlying heart murmur and start to show things that we consider as true congestive heart failure, which is characterized by those overloaded vessels and some pulmonary edema.
00:14:02
Speaker
Fortunately, acbim has kind of come up with a way for us to be able to stage where in that degree of progression they are at. ah So speaking of that classification, can you dive into that a little bit more and discuss like why that's important for anesthetic planning?
00:14:23
Speaker
All right. So there are in 2009, an ACBM consensus group kind of came up with this staging organization and they revisited that in 2019. They classified these dogs into four stages. Stage a are dogs who are at a high risk for developing heart disease, but do not have an identifiable structural disorder. I think in the veterinary world, you and I both immediately think of King Charles Cavalier Spaniels, but other small breed dogs, dachshunds, poodles, they can also be predisposed to this.
00:14:54
Speaker
These are dogs where under anesthesia, we might handle them with certain preferences to the way we would manage a patient who does truly have heart disease. In other words, we might use a more conservative protocol.
00:15:06
Speaker
But again, structurally, they're normal. And so if someone doesn't really appreciate that as part of their underlying pathology and treats them as they would any other patient, they will probably be okay. From a cardiologist perspective, they want to keep an eye on these guys because they're probably going to have problems at some point.
00:15:21
Speaker
Stage B dogs are dogs who have structural heart disease, typical murmurs that we would experience for the valve, but they have never developed clinical signs of heart failure.
00:15:32
Speaker
So in 2019, the guidelines were updated that they could reflect this strong evidence supporting initiating treatment for certain one of these patients. And so we divided them further into stage B1 and B2. B1 indicates dogs who are asymptomatic. They may have a heart murmur, but there is no radiographic or echocardiographic evidence of cardiac remodeling in response to their mitral valve disease.
00:15:56
Speaker
And if there is some mild remodeling, the changes are usually not severe. Stage B2 will be dogs who are also asymptomatic but have more advanced mitral valve regurgitation with hemodynamically severe changes that we can see on radiographs and echocardiogram.
00:16:13
Speaker
And they suggest that there is the beginning of left atrial and left ventricular enlargement. And in those cases, there may be a benefit for us to begin treatment and therapy. So, Those dogs usually come into us on some cardiac medication, and we'll talk a little bit more about that that, I'm sure, in a bit, that would be helpful for them to be able to have the best longevity and prognosis.
00:16:35
Speaker
Stage C dogs are dogs who either... currently or in the past have had clinical signs of heart failure caused by mitral valve disease. These are the ones where we start to maybe push the envelope on whether or not elective procedures are a great idea for them because we know that in the past their heart has had some difficulty accommodating. So we want to use a little common sense.
00:16:58
Speaker
when we're anesthetizing those dogs. Stage D dogs are dogs who have end-stage mitral valve disease, clinical signs of heart failure, and they are refractory to our standard treatment. In other words, it's no longer just furosamine and ACE inhibitor and pimobendin anymore. They are refractory to all of that.
00:17:17
Speaker
These are the guys that really should not be anesthetized unless there is some remarkably compelling reason that they must have this anesthesia.
Anesthetic Planning and Considerations for Cardiac Stages
00:17:26
Speaker
at this very moment. So most anesthesiologists, I believe, would prefer never to anesthetize stage D dogs.
00:17:33
Speaker
The classification is really pertinent when it comes to anesthesia because we know that we might alter our anesthetic plan for almost any patient who has cardiac disease. But how we alter that will vary based on that staging. For example, if you're a dog who is a stage B1, my management is often going to be confined to the anesthetic plan that's administered at the hospital. So I might select a different induction drug than I otherwise normally would.
00:17:59
Speaker
Stage B2 dog requires the owner to become part of that plan because oftentimes I want that owner, if possible, to make sure that they have any cardiac medication that they are getting in terms of pimobendin. We'll talk about later things that maybe they shouldn't be getting.
00:18:15
Speaker
But pimobendin is something that there are few select locations, as you are, sure, that happen to have access to injectable Pimobendant, but is a real rarity in the United States in general. And in the future, that might change.
00:18:29
Speaker
But because we don't have an injectable version of Pimobendant, I'm very reliant on the owners giving that medication to the point that because I have a little bit more control over my own schedule, I will ask for the case to be rescheduled if they don't give the Pimobendant in the morning for that procedure, because I do not have another drug to mimic that in its entirety.
00:18:49
Speaker
Yeah, we'll definitely talk about Pimobendin, I'm sure, a little bit more. Yes. And then other things we want the owners to be part of for those stage B2 dogs. We want to make sure that they give gabapentin and triacetone if the animal is anything other than a completely mellow, chill dog. Why? Because I want to offload the other drugs that I'm giving injectably and And so the use of oral anti-anxiety medications prior to the animal coming to the veterinary hospital helps me to do that. And so that to me is kind of some of the differences with that stage B2 that we really need to kind of rope the owner into helping assist to make this outcome the best that it can be.
00:19:27
Speaker
Then, like we said, stage C is a dog that we really should probably have some discussions with the owner because there is more major risk of them going back into heart failure after we provide anesthesia.
00:19:38
Speaker
And then I would prefer, if possible, to avoid anesthetizing any stage D dog. This is probably going to be a very poor prognosis for those animals if they cannot respond normally to the things we classically use for heart failure.
00:19:51
Speaker
Now, the good news about all of this and these stages is that in the world, we like to try and think that, you know, there's a objective timeline that they move along that for the first six months, they're stage A and then they're stage B. After the next six months, it's stage B, too.
00:20:06
Speaker
But in reality, it can take years for this mitral valve disease disease to progress. When I was in vet school, we had a clinician who would show us a series of radiographs over 10 years where it took this dog 10 years to go into congestive heart failure. And keep in mind, when I was in vet school, it pre-pemobendant. So and these dogs can make it sometimes quite a long time. And so these stages aren't meant to have a numeric objective diagnosis.
00:20:32
Speaker
time point, they really are meant for the cardiologist to be able to discuss the progression and what will be impending without necessarily tying a specific numerical value to that.
00:20:45
Speaker
Right. So like you, Carolyn, I also have an independent anesthesia consulting business. And I would say of the high risk patients that I get asked to help manage anesthesia for these patients, I would say a vast majority of them are people who ask me to come help or consult on patients that have heart murmurs.
00:21:11
Speaker
And so I want to just discuss with you briefly that if you are somebody who works in general practice, mean, you could also work in referral practice, I suppose.
00:21:22
Speaker
And you asculpt a heart murmur in a middle-aged or older dog, how likely is it that dog truly has functional cardiac disease?
00:21:37
Speaker
If it is small breed dog, 85% of them are likely to have a valve lesion by the time they are 13, according to work that was done way back in the 1970s by Buchanan and their team.
00:21:49
Speaker
Regardless of breed, 30% of all dogs they as they age develop a degenerative valvular disorder. So it is quite common for them to have these concerns and considerations.
00:22:00
Speaker
I think it's important to know when we talk about, I'm sure we are going to talk about it, kind of anesthetic planning for these patients yeah or pre-anesthetic planning, I should say, for these patients.
00:22:12
Speaker
So just wanted to make sure that we were aware of that. And then beyond a sculpting, heart murmur, what are some other clinical signs that you need to be aware of when you're planning anesthesia for a dog that might have mitral valve disease?
00:22:26
Speaker
So it's important to remember here that the heart, which is just a simple pump system, doesn't act in isolation. That's what makes it special. In the case of the left side of the heart, which is the side that's impacted by mitral valve disease, it's pumping oxygenated blood. And so it's not just the pumping action itself, but the blood that's going through there.
00:22:46
Speaker
So we want to listen to the lungs thoroughly as well and see if there's any adventitious lung sounds, ask about whether or not a cough might be present, and look at the dog's body condition score, which we will definitely see with cardiac disease that they become quite thin over time, which may not be the same.
00:23:02
Speaker
If they have a primary respiratory disease, talk about activity level and whether or not they're being limited in terms of their exercise. And then we want to try and make sure that we're thorough for the whole cardiac examination, making sure we're palpating for pulse quality, making sure we're looking if there's jugular pulsations, all of those things that may not be specific to mitral valve disease, but would be a good idea for us to be thorough about.
00:23:24
Speaker
One the hidden signs that I'll bring up here, and maybe we'll explore a little bit more later, is the possible presence of hypertension, right? And so due to complex neuroendocrine pathway changes, we can oftentimes see a patient who may have cardiac disease that we don't appreciate just on physical exam or clinical signs might have a systemic hypertension or a high blood pressure.
00:23:46
Speaker
So I have different targets for patients who are hypertensive under anesthesia. And so although this is not maybe truly a clinical sign in the human world, this is considered one of the fifth vital signs that we should be taking for people is to measure their blood pressure. And I would advocate that as well for our patients who are going to be anesthetized, that getting some baseline blood pressures in patients who have an underlying heart murmur.
00:24:08
Speaker
is probably going to be helpful. Oftentimes people will say, well, there's trust of the veterinarians, and so I don't know if that blood pressure is representative. We have wonderful things now like gabapentin and trazodone that they can come in on specifically for blood pressure measurements, allow them to acclimatize for a few minutes to the clinic, collect those blood pressure measurements in advance of anesthesia, and we can have a little bit better planning that can be done.
00:24:31
Speaker
Yeah, I take a very similar approach to you with regards to blood pressure management in these patients. So we're going to move to cats now. We're going to give cats some love. And we're going to talk about hypertrophic cardiomyopathy, which is the most commonly encountered degenerative heart disease in that population.
00:24:52
Speaker
So how prevalent is this disease in our aging feline population? yeah Yeah, and I think you and I both agree it's not even just the aging feline that we found that between 14 and 16% of apparently healthy cats that don't have clinical signs have subclinical hypertrophic cardiomyopathy and studies both in the U.S. and the U.K.,
00:25:13
Speaker
So in terms of aging population, as recently as last year, we found that in a group of cats who are aged 7 to 10 who are considered apparently healthy, 22% of them had some form of other disease. Now, i'm not going to say it was always cardiac disease, but might be hyperthyroidism. It might be renal failure, all of these other things that can lead to cardio or vascular disease, including systemic hypertension.
00:25:37
Speaker
And as these same cats from the same study population matured and continued to be screened over a two-year period, 22% of them had abnormal cardiac auscultations.
00:25:48
Speaker
So I think that we can reasonably get behind the numerics that HCM accounts for approximately 60% to 70% of feeling cardiomyopathies, and they become more common as cats start to age.
00:26:01
Speaker
Yes, I had a three-year-old Sphinx cat just last week that had obstructive cardiomyopathy that I was asked to assist with. So I hear you about the aging point.
00:26:13
Speaker
Can you give a brief outline of how the heart structurally changes throughout the progression of hypertrophic cardiomyopathy? Yeah. Hypertrophic cardiomyopathy is a disease of diastolic dysfunction as opposed to mitral regurgitation where the blood is regurgitated during systole.
00:26:30
Speaker
In the case of HCM, the left ventricular muscle begins to thicken and fibrosis and will become a lot stiffer. That thickening can also include thickening of the intraventricular septum as well as the free wall in cases of concentric hypertrophy.
00:26:44
Speaker
All right, and as that muscle enlarges, the chamber opening is going to begin to get smaller and smaller. That means there's going to be less room for blood to fill. That is very problematic in our patients who have this hypertrophied muscle because during diastole is when the heart takes its own perfusion. And so now we have this very thickened tissue, very little amount of blood to try and get oxygen from that blood into the cardiac myocytes itself.
00:27:12
Speaker
All of this can lead to myocardial ischemia and arrhythmias that we can see under anesthesia. In addition, eventually this diastolic dysfunction in cats is going to lead to elevated left ventricular filling pressures and dilation of the left atrium, which will eventually progress to left-sided congestive.
00:27:31
Speaker
heart failure in the cat okay so i was always taught that not every cat with hyperstrophic cardiomyopathy which i'm just gonna start calling hcm from this point on so i was always taught that not every cat with hcm has a heart murmur so can you touch on that a little bit further Sure.
00:27:53
Speaker
And I believe this is what you might be referring to, but please feel free to add anything additional. The murmur that we hear is often what's called systolic anterior motion of the mitral valve.
00:28:05
Speaker
Up to 67% of cats with HCM can develop systolic anterior motion the mitral valve, leading to this left-sided parasternal murmur, which and ironically, in the last cat, I actually heard on the right. Cats are little aliens.
00:28:20
Speaker
But that does mean that there's going to be 33% of cats without the systolic anterior motion who still do have hypertrophic cardiomyopathy or HCM and that they are going to not have a murmur that we can asculpt. But there's other reasons we can sometimes not asculpt the murmurs too.
00:28:37
Speaker
Their heart rate is so darn fast and so that makes it very difficult in the mitral valve systolic anterior motion might not be present. Maybe we're not listening in the correct spot.
00:28:47
Speaker
And so There are numerous reasons for all that. Bonnie, are there other reasons you can think of that that you don't hear that heart murmur, even though we know this cat may have HCM? No, I oftentimes think that the hypertrophy that's occurring with HCM just kind of distorts the mitral valve, but that doesn't always necessarily happen for every case because it really just depends on where the hypertrophy is happening. Like sometimes these animals don't have, I think when you think of like a drawing or if you went to Google and you just said like,
00:29:16
Speaker
show me ah an HCM heart, you know, with a graphical representation of that, like a cartoon picture, you see this like perfectly thickened heart. And I feel like there are some cats where like maybe one part of the ventricle is thickened, but not another.
00:29:29
Speaker
and so all of that can contribute to like various changes in the mitral valve. And so that's what I always think of. And I think we come down kind of to the same thing that the Nuts and bolts are about the impact on the mitral valve leading to that murmur.
00:29:44
Speaker
But again, I think this another great thing where cardiologists probably have this like, you know, down to a science on what they say. I'm not sure they do. But I always tell people, i think that just because an animal doesn't have a heart murmur, doesn't like totally rule out.
00:30:02
Speaker
hypertrophic cardiomyopathy and it can so profoundly impact what we see cardiovascularly with these animals when we anesthetize them. I had a case just a few months ago where I had a cat that just did very badly under anesthesia and we proceeded with the case, but it was not an easy, you know, just didn't go well.
00:30:26
Speaker
And by the time we were done with the case, you know, but I was listening to the cat's lungs and there were crackles. i was like, I'm pretty sure this cat's in heart failure. Like, but it was just completely missed on our pre-anesthetic exam because the cat had you know, a normal auscultation didn't necessarily have a reason that we could think of that the cat would have been in heart failure or, you know, at risk of heart failure before he even started.
00:30:51
Speaker
And so i think that, you know, it just makes cats even the more challenging an animal. That is dead to me is classic cat. Yeah, exactly. So i guess the next question is, you know, beyond auscultating a heart murmur,
00:31:09
Speaker
What are some other clinical signs that maybe we might see in these patients that maybe have what we call subclinical HCM? And so some of those things we may not see much, but definitely when we're listening, we're also going to listen for things like the presence of a gallop beat, which is that extra sound during diastole, either early in diastole or during the atrial systole.
00:31:32
Speaker
That's more common for cats who are in for heart failure. So maybe not in the cats who have no heart murmur, but in the ones that have a heart murmur, if we're starting to hear that, that definitely warrants further investigation.
00:31:44
Speaker
We're also listening for any kind of arrhythmia that might be present as well as palpating for pulses for any kind of arrhythmias, which could be secondary to myocardial ischemia or any other numerous causes.
00:31:55
Speaker
When we palpate those pulses, remember that we're also feeling not just for them to be incongruous, but maybe difficult to feel at all because 12 17% of cass who have might also have arterial thrombus that's forming.
00:32:09
Speaker
And so lastly, we, of course, as you have mentioned, we want to listen to the lungs. And sometimes all we want to do is be able to hear that there are lung sounds because cats can get pleural effusion as well as pulmonary edema when they go into heart failure, which muffles those sounds.
00:32:23
Speaker
But yeah, but we're also making sure we're as thorough as possible about history, keeping in mind that it might come out as completely normal. Here as well, we'll also just mention that if we are hearing things that are abnormal or we know there's other potential comorbidities like hyperthyroidism, we do want a sedated baseline blood pressure for these cats as part of their cardiac evaluation so that we can target some specific hemodynamic interventions to the pressures that they are living with in their normal life.
00:32:54
Speaker
Yeah, I also tend to try to palpate the thyroid and try to feel a thyroid slip as well in these patients. You know, sometimes you pull them out of the carrier and it's like very obvious that they have hyperthyroidism, but not always, you know, so I always try to feel for that as well.
Medication Management and Anesthesia Readiness
00:33:10
Speaker
you Yeah, so what are some red flags in dogs or cats with cardiac disease that should make a veterinarian reconsider or delay anesthesia in your opinion?
00:33:22
Speaker
Yeah, in my opinion, and I'd love to hear yours too, my kind of cutoff for anesthesia is the presence of volume overload, which ultimately can result in congestive heart failure. That is, until that is resolved, anesthesia should not be performed for any of them, but the most version of cases. So elective cases should be rescheduled if we're taking radiographs in our canine patient.
00:33:42
Speaker
And we see that these vessels are large and tortuous. We really should be thinking about whether or not we can stabilize this patient to a better degree before anesthesia. And so therefore, radiographs are really a baseline in my canine patients, even though we don't have pulmonary edema in some of these cases.
00:34:00
Speaker
If we do see these changes to these vessels, we might want to take that a little bit more serious if we're also hearing a heart murmur. And for cats, I try to evaluate for, as we said, any the other comorbidities. I've had cats, as we were talking about the hyperthyroid cat, who have died simply from the restraint for a blood draw. I mean, like that's craziness, you know. And so in those animals, it might even be saying that clinically that animal looks very thin,
00:34:27
Speaker
is showing other signs of hyperthyroidism like agitation at home, vocalization, those kind of things. Maybe they come in with some degree of gabapentin and other sedation before we even try and do things like gip collect blood for additional things. And so if we see patients who have certain comorbidity type of signs or in any canine patient, we try and make sure we're more thorough about that cardiac evaluation so that we know whether or not anesthesia is appropriate.
00:34:54
Speaker
ah about you? Yeah. Yeah. I hear what you're saying. I think the first step is, i think you alluded to this, but deciding like how urgent this procedure is needed. And there's also sometimes other circumstances that are not necessarily like the urgency. So sometimes it's just timing, right? Like,
00:35:13
Speaker
this particular individual, whoever the owner is, like only could take this one day or they had to, you know, to anesthetize their patient or to bring their patient to hospital or like this person traveled a really long way and they're very old and there's no way they're going be able to like...
00:35:28
Speaker
travel again. So not saying that should always supersede patient safety, but sometimes that becomes a consideration whether like I'm going to proceed or not. That's just obviously a conversation to have with each individual owner.
00:35:45
Speaker
So I think the first one is like urgency of case and then other extent, like extenuating circumstances that We have to take it into consideration. And i think you really nailed it, which is like, did I hear a brand new heart murmur that I've never heard before?
00:35:58
Speaker
That's going to be a little bit of a red flag for sure for me. And I'm not saying that we can't like do the case the same day, but maybe we need to get some chest radiographs on that patient beforehand.
00:36:09
Speaker
I would also say that hearing a new arrhythmia that has never been heard before, sometimes that's a bit of a red flag. And a lot of times what I'll just do with those cases, I'll pop on an ECG and see what I'm getting.
00:36:23
Speaker
And if the patient has ah known heart disease, you know maybe that's something that we need to get under control before anesthesia then That's on a case by case basis. But those are just things that that might give me pause outside of what you've already mentioned.
00:36:38
Speaker
Yeah. Yeah. And like you're kind of getting it and fundamentally, it's a communication kind of thing that, you know, at least all of these things gives us a kind of a prompting to have that conversation so that the owner can be fully aware of the condition that their animal is in, because especially as we had said with cats and things, it can be hard to know those things beforehand. Yeah.
00:36:59
Speaker
yeah And the only other red flag I can think of has to do with, you know, preparing the patient for anesthesia and preparing for anesthetic complications. So I guess what I mean by that is if the owner brings their dog in and their dog has, you know, been taking Pimobendan and Lasix regularly and they bring their dog in and the dog never got its medication in the morning and i don't have access to either one of those medications, I oftentimes Tell them, but we'll need to do this on a day where your dog has Pimobendin.
00:37:30
Speaker
And I've had some owners like drive to their primary care, grab you know a single dose of Pimobendin and come back so that we can do the case. Yeah.
00:37:41
Speaker
Good on that. Yeah, so I've had that before. But then also, depending on how advanced the cardiac disease is, and you've already gone through all the stages, there are some places that I've gone to that, you know, they don't have Lasix in their practice, or they don't have a way of medically treating hypotension.
00:38:00
Speaker
through pressers or inotropes. And so those might be practices where we're going to have a discussion before I show up because again, i work at a consulting type of capacity and I might say, you know, maybe we want to buy a bottle of Dibetamine for this case, or, you know, we want to get prepared in case there is problems under anesthesia so that there's a way to address them in a way that it's safe for the patient. So yeah,
00:38:25
Speaker
I've delayed cases based off of just a general lack of the practice to be prepared to deal with complications associated with the patient's cardiac disease. And I would agree that's a really great point because it prompts me to to put in mind that one of the other things we really need to make sure of for the practice is what they have available if things don't go well. In other words, the postoperative period is not just limited to the immediate point till the owner gets home. Sometimes
00:38:57
Speaker
This means making sure that practice has a nearby emergency clinic that could keep that animal overnight on oxygen so that they have around-the-clock care. Even if a clinic might have some things like oxygen cages and support and those kind of things, do they have staffing overnight? And so, yeah, I think that's a great point, Bonnie, is and how is your practice set up?
00:39:17
Speaker
And if there were to be an emergency that ultimately would probably manifest as respiratory in nature, prompted um primarily from the cardiac side to the secondary respiratory distress, could they be able to have that patient successfully managed overnight? And that's a great conversation to have with the anesthesiologist that might be on service or with the owner so that they're aware that sometimes those are going to be separate and different charges.
00:39:43
Speaker
All right, so we're going to jump to pre-anesthetic evaluation and preparation, even though we've like been alluding to that in this conversation so far.
Diagnostic Tools and Techniques for Cardiac Assessment
00:39:53
Speaker
So when preparing to anesthetize a dog or cat with a known or suspected cardiac condition, what diagnostic tools do you feel are the most helpful to assess cardiac function prior to anesthesia?
00:40:09
Speaker
So I think there's a few that we're going to talk about today. And so we can start the discussion off with cardiac biomarkers. A biomarker is going to be a substance that's released from a particular tissue, in this case, the myocardium, in response to disease or injury.
00:40:24
Speaker
For example, we have cardiac troponin 1, which tells us that there's been myocardial injury or necrosis. People are often familiar with that from humans who have heart attacks. In the veterinary field, we're starting to use a lot of B-type natriuretic peptides.
00:40:38
Speaker
Most of the time, what that means we're talking about is going to be a N-terminal pro-B-type natriuretic peptide, or NT-proBNP, which are markers of neurohormonal activation and cardiac wall stress, which Their elevation tends to be somewhat proportional to the severity of the disease.
00:40:59
Speaker
Most of the time when we're using these biomarkers, we're using them to clarify the need for additional diagnostics. In other words, they're very rarely standalone tools. They're usually gateways to tell us what additional diagnostics we might need. In dogs, for example, a cardiologist might use these things more for a predictor of morbidity and mortality and less to guide what recommendations they would give for anesthetic management.
00:41:23
Speaker
But in cats, we're really hoping to have ah value that kind of suggests that animal is normal. And so this is one of the tests that they might be rather expensive to obtain these biomarkers, but we're hoping that test will not come back with any abnormality. We're looking for ideally less than 49 nanograms per mil or 50 100 nanograms per mil to make that cardiac disease less likely.
00:41:48
Speaker
Over that value, it doesn't mean that cat has confirmed cardiac disease. It just means that we really should probably do ah more thorough cardiac workup. Thoughts on that, Bonnie?
00:42:01
Speaker
No, I agree with what exactly what you're saying is, I think is a good screening tool. But, you know, I think it's nice that if you have cats with respiratory signs and you're trying to figure out if it's maybe more leaning more cardiac or leaning more respiratory, you know, cardiac biomarkers are really nice.
00:42:19
Speaker
And we did talk about those like subclinical HCM cases, but I am just not aware of the data to show that like in these subclinical HCM cats that these biomarkers are really detecting, you know, subclinical HCM.
00:42:35
Speaker
Our more standard diagnostic tools that we use, especially for canine patients, would include radiographs. And so they are very valuable for our canine population. It helps us to rule in or out pulmonary edema, to look at the left side of the atrium because that left atrial enlargement is going to precede the presence of pulmonary edema to look at those vessels.
00:42:56
Speaker
And But then you're right, when it comes to cats, the availability of diagnostics is a little bit more conservative because we can have normal radiographs in the feline patient and we can still have cardiac disease present, especially if the left atrium hasn't begun to change. And we talked a lot about how that left atrial change might not be the same for every patient.
00:43:18
Speaker
And so we may see a cat that has a perfectly normal-looking heart on their radiographs but still has enough disease to cause challenges under anesthesia because of their underlying hypertrophic cardiomyopathy.
00:43:32
Speaker
Do you feel that every dog or cat that has a heart murmur needs an echo before anesthesia? Yeah, we'll start with a dog because that's way easier. We can get a lot of value from, honestly, even a true six-lead ECG.
00:43:47
Speaker
Obviously, the ones that are part of our multi-parameter monitors are shielded, and so they're not are going to be our true six-lead ECGs. But there are services that will allow you to run an ECG, and they will look at that six-lead ECG.
00:43:58
Speaker
And they'll be able to tell you a little bit about chamber size and that kind of information that gives us feedback and radiographs. And so for those guys, if it's a brand new heart murmur, I would kind of say that at the very minimum, I like to have thoracic radiographs. If a send out six lead ECG or even in-house six lead ECG is available, that would give me a lot of information.
00:44:18
Speaker
But even if all of that information comes back as this animal looks great, you're good to go for anesthesia, it's still worth the owner getting on the cardiologist schedule. Why? Because the cardiologists are booking out by four to six months. And so what might be a very innocent and mild murmur right now, a year and a half down the road might be much more severe. If you have an established relationship with the cardiologist, it's a lot easier for you to say, hey, we're noticing these changes because and for them to be able to get you in then if you're a brand new patient. And so that information, that new heart murmur, is also a good indication to start looking at when you might be able to get an appointment with a cardiologist to begin these things like yearly echoes and examinations to follow up with all of that.
00:45:02
Speaker
Speaking of that, that if I do have an animal who has had a heart murmur and has seen a cardiologist As an anesthesiologist, I try to abide by those recommendations that if the cardiologist says you should get a recheck echo in six months or a year, i do look at when that was requested and how close that is to the anesthesia procedure that's planned to see whether or not they maybe need to get back in there and get checked out.
00:45:26
Speaker
Cats are a whole different story. I highly value an echo for cats to the point when I was in a rural referral practice with an internist who we had a good working relationship together.
00:45:41
Speaker
we would do what we call the pre-screening echo. It was a echo that took less than two minutes. We charged $75 for and was just a couple of quick money shots, two-dimensional imaging, usually that right parasternal short or long access to determine whether or not that cat needed a full echo. So the purpose of this pre-screening echo based on people out of the UK was not for us to diagnose anything, but to determine whether or not this cat is has enough suggestion that they should go for a full echo. So I am i'm very attached to the echo, if possible, in these cats.
00:46:14
Speaker
But I do appreciate that, again, the cardiologists are booking out by months. And so sometimes it might be unrealistic to get an echo. for every cat. So I am grateful for things that are present nowadays. For example, we have genetic testing that we can do for ragdolls and Maine coons out of either UC Davis or North Carolina State that can tell us whether or not from a simple cheek swab, they have the genetic predisposition to having things like HCM. And again, we're hoping that comes back normal. We're not hoping that it comes back as a potential possibility with all of that. Biomarkers are helpful in those cases.
00:46:50
Speaker
And then having those conversations with owners about the multifactorial concern for when we can get this cat in. For example, if you have a fractured tooth, we probably don't want to wait six months on that till you can get in to see the cardiologist.
00:47:04
Speaker
But if you're there for your dental prophylaxis that we can schedule at a later time, that might be an option that the owner chooses to improve the safety of anesthesia. How about you, Bonnie? How do you feel about that?
00:47:16
Speaker
Love the idea of doing that like quick screen echo in cats. And I and very fortunate in that I actually have my own ultrasound machine and I usually use it to do nerve blocks, but I have used a wonderful free tool called YouTube and I've trained myself to help on how to do quick thoracic flashes so that I could look at left atrial size and compare it to aortic size.
00:47:48
Speaker
And so this is a tool that I love to do. It takes, you know, if you have an ultrasound in your practice, yeah again, go on YouTube and find a few cats who are compliant enough to allow you to do this.
00:48:01
Speaker
And just start training yourself on how to get that view so that you can compare your left atrial size to your aortic size. They should be pretty equivalent. But if you're starting to see large left atria, you know, that should be like a red flag for a cat.
00:48:16
Speaker
And so this is just something you can, I mean, literally takes 30 seconds to just kind of. get your image, take a still shot and just do a quick evaluation. And you can charge like, you know, 50 bucks for it, which is so much cheaper than an actual echo. And you can also bring in, you know, money for your practice doing that and all like that, but it, you know, it helps with patient safety as well.
00:48:37
Speaker
Okay. So we're going to move on to kind of our anesthetic planning and we're going to start with our approach for dogs with mitral valve
Pre-Induction Protocols and Final Considerations
00:48:47
Speaker
disease. Okay.
00:48:48
Speaker
So before we get into like the drug protocol, I want to talk about the initial steps beforehand. And, you know, we talked about getting a blood pressure. so we're going to kind of probably move through that because I do the same thing, getting an ECG. So we'll move through kind of those, you know, pre-anesthetic steps.
00:49:07
Speaker
But beyond that, you know, what are your steps that you're taking to improve the safety of induction in in these patients. And maybe a good place to start with, which we've alluded to already, is like what medications are you informing owners that they should give patients before anesthesia versus maybe cardiac medications that you're informing owner that they should discontinue before anesthesia? Well, starting with those dogs who might have mitral valve disease,
00:49:38
Speaker
When it comes to trying to make things a little bit safer for them, as we have both kind of said, and it bears repeating, I think both you and I agree that Pimobendin, absolutely yes on the Pimobendin.
00:49:49
Speaker
And again, this starts with even the receptionist team. When they call to confirm the surgery, then they remind the owner that Pimobendin is going to be essential part or the case might be. canceled if they cannot do that and that they should probably bring that medication in with the patient just in case they're hospitalized for a longer duration than we think that they might be.
00:50:09
Speaker
Now, as passionate as I am about pimobendan being part of the cardiac patient's case, i I prefer not to have any ACE inhibitors for 24 hours in advance of that The ACE inhibitors do a great job for treating these patients and their systemic hypertension especially, but sometimes they can do such a good job that when combined with our anesthetics, we end up with a patient who becomes very hypotensive.
00:50:34
Speaker
And that to me is one of the limiting factors for how long I can provide anesthesia, that if I have refractory hypotension, I cannot get under control through my basic mechanisms, then I'm going to go ahead and ask to discontinue the anesthesia in the appropriate cases, for example, multi-quadrant dental prophylaxis that we know that we can come back later and with everything.
00:50:53
Speaker
And then we take the other medications that they might be on a case-by-case basis. So for example, patients who are on furosemide and other spironolactomer or other diuretics, we might want to individually reassess through the use of radiographs whether or not that patient should or should not have that as part of this whole preemptive medication strategy.
00:51:14
Speaker
Yeah, we didn't really talk about this much yet, especially when we're talking about pre-aesthetic workup, because I think we were focusing a little bit more on just like the cardiac disease. I think it goes without saying that all of these animals should be getting full CBC chems and lights before anesthesia.
00:51:30
Speaker
And so when you're talking about using diuretics, a lot of times I'm making that decision, at least diuretics before anesthesia. I'm making that decision based off of what their pre-anesthetic renal values and their pre-anesthetic electrolytes look like.
00:51:47
Speaker
I don't know if you agree with this. Generally speaking, I tell owners to give diuretics beforehand unless I'm seeing those changes in their blood work. I've definitely seen cases that have gone both ways. We've had cases and i appreciated the opportunity to maybe talk about a case that was special to me at the end of this podcast.
00:52:04
Speaker
But in that case, the cardiologist had suggested that the owners discontinue the diuretic, but the owner was too nervous to do that. And so that I was kind of the final push to say, no, seriously, just get rid of that.
00:52:17
Speaker
And then I think that helped the owner to feel more comfortable with all that. And so, yeah, you're right. I think we do it on a kind of a case by case basis, because as I think both you and I agree that we can give injectable furosamine. So if it's furosamine that the patient is on,
00:52:30
Speaker
and the owners withheld it, we may have an injectable option to be able to withdraw that. Then there's other cases where the animal is really so precariously balanced in terms of their staging that to not give them that diuretic beforehand could potentially be quite problematic for them even intraoperatively. And so, yeah, case by case basis, I think, is what I feel about that.
00:52:52
Speaker
Yeah. And I also, along with the ACE inhibitors, I personally usually recommend that owners discontinue any kind of blood pressure modifying medication within the 24 hour periods that also includes drugs like amlodipine if they happen to be on that.
00:53:07
Speaker
That's just my personal preference because I do find that it tends to augment their hypotension. one i agree. Yeah, I think that's a great point.
00:53:22
Speaker
Thank you for joining us today.
Community Engagement and Sponsorship Acknowledgments
00:53:25
Speaker
If you enjoyed this episode, we invite you to explore the North American Veterinary Anesthesia Society and consider becoming a member.
00:53:34
Speaker
Membership with Navas provides incredible benefits, including access to anesthesia and pain management CE events, informative blog posts, fireside chats with board certified anesthesiologists and specialty technicians, and much more.
00:53:50
Speaker
Navas members also enjoy VIN rounds, hour long presentations on specific topics in veterinary anesthesia that offer valuable tips to use right away in practice.
00:54:02
Speaker
If you're interested, visit www.mynavas.org to elevate your anesthesia journey today. If you've been enjoying our podcast, We'd love your support. Please consider liking, subscribing, writing a review, or sharing this podcast with friends and colleagues.
00:54:21
Speaker
Every bit of listener support helps us to reach more veterinary professionals like you. For questions about this episode or the podcast in general, or if you want to suggest topics for future episodes, feel free to reach out to us at education at mynavast.org.
00:54:40
Speaker
We'd love to hear from you. Special thanks to our sponsor, DECRA, for making this podcast possible. To learn more about their veterinary anesthesia products, visit www.decra-us.com.
00:54:54
Speaker
And of course, a big thank you to our esteemed guest, Dr. Carolyn McCune, for speaking with us today about anesthetic management of patients with cardiac disease. Dr. McCune will join us again on our next episode to continue exploring this important topic.
00:55:10
Speaker
This episode was produced by Maria Bridges, edited by Chris Webster of Chris Webster Productions, with technical support from Saul Jimenez. Finally, thank you to all our gas passers out there for spending time with us on the Navas podcast.
00:55:25
Speaker
Veterinary anesthesia is a lifelong journey of learning and growth, and we hope you'll join us as we continue exploring it together. I'm your host, Dr. Bonnie Gatson.
00:55:36
Speaker
Thanks for listening and stay tuned for another episode of the North American Veterinary Anesthesia Society that should be coming out shortly.