Podcast: Identifying Arrhythmias in Veterinary Patients with Dr. Estrada

Amara H. Estrada, DVM, DACVIM (Cardiology), University of Florida

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In this episode, host Alyssa Watson, DVM, welcomes back Amara Estrada, DVM, DACVIM (Cardiology), to talk about her recent Clinician’s Brief article, “Identifying Arrhythmias in Veterinary Patients.” Dr. Estrada shares how to effectively use ECG in general practice and reviews a comprehensive list of arrhythmias that veterinarians may encounter, including those that could mean trouble.


Episode Transcript

This podcast recording represents the opinions of Dr. Watson and Dr. Estrada. Content, including the transcript, is presented for discussion purposes and should not be taken as medical advice. No guarantee is given regarding the accuracy of any statements or opinions made on the podcast. The transcript—which was prepared with the assistance of artificial intelligence—is provided as a service to our audience.

Dr. Watson [00:00:09] Welcome back, everyone, to Clinician's Brief: The Podcast where we bring you the conversations behind our Clinician's Brief content. I'm the host, Dr. Alyssa Watson, and today I am joined by returning distinguished guest Dr. Amara Estrada. Dr. Estrada is a professor of cardiology at the University of Florida College of Veterinary Medicine. She is a frequent author for Clinician's Brief, and she has been on the podcast several times before. We have talked about measuring vertebral left heart atrial size in dogs. And we have also talked about the vertebral heart scale in cats and that scale not score because there's no winner. Right, Dr. Estrada?

Dr. Estrada [00:00:50] That's right. No winners, no losers.

Dr. Watson [00:00:53] No winners, no losers. And so today we have asked her back and we're going to talk about her most recent article. And she's here to offer some insights on the clinical significance of varying arrhythmias in veterinary patients. And we are hoping to learn how to quickly and accurately identify some of these arrhythmias, and then also get some crucial steps that we need to take about diagnosing abnormal heart rhythms and what, you know, we can handle as general practitioners. So thank you so much for coming back on the show, Dr. Estrada. It's been a little while. We've got some changes. We're on video now, so if you.

Dr. Estrada [00:01:30] Had to get a little bit more put together quickly.

Dr. Watson [00:01:35] Well we appreciate you.

Speaker 3 [00:01:36] Wet hair, no make up and yeah.

Dr. Watson [00:01:38] And, we're here we're here. So. But could you take just a second and for anybody that hasn't, you know, listened to your previous episodes, just give us a quick introduction again?

Dr. Estrada [00:01:50] So I am a veterinary cardiologist. I did my veterinary school training and my undergrad at the University of Florida. I went to the University of Tennessee for a rotating internship and then to Cornell University for my residency in comparative cardiology. I spent 11 months in specialty private practice before I realized that I was in the wrong place, and I really missed teaching and interacting with students and interns and residents. And I came back to the university probably ten months after I got to private practice. And I've been at the University of Florida ever since. So that's been 21 years now. I'm a full professor with tenure. I do a lot of research. I do a lot of teaching, and I still maintain two days a week in practice.

Dr. Watson [00:02:43] Well, you're definitely a wonderful teacher and a wonderful speaker. And so you really did find your calling there.

Dr. Estrada [00:02:48] Thank you! I love it.

Dr. Watson [00:02:51] Good, good. We love having you so. And I'll be really honest, this is a topic that I feel, you know, I don't often times don't feel like I have a lot of strength with. So I was really excited to have this conversation with you today. And I'm hoping to learn some things, you know, to bring back into my own practice. We're going to talk a lot about ECG characteristics. But before we kind of, like, jump into the nitty gritty of all of those arrhythmias, would you just give us, like, a brief overview or like what how should we be utilizing ECG in our veterinary patients?

Dr. Estrada [00:03:29] Yeah. So an ECG and then it's an easy and a quick tool. And I totally get where you're coming from. ECGs are the scariest thing in the world to general practitioners. Because if you don't do them every day or you're not looking at them or thinking about them every day, it's very foreign to you. What I'm hoping is will maybe help break it down to you not being so scary. And we can talk about things in more generalities. In terms of, like, hemodynamic, compromise that might happen from an arrhythmia. So when to use it? There are a couple of times where it's a really great screening tool. So for some of our at-risk breeds, the breeds that we know have dangerous or malignant arrhythmias as part of their breed, like boxers or Dobermans. Honestly, doing that as frequently when you see those patients as possible and not just doing like a 30-second ECG, more like a 3 or a 5 minute ECG. One VPC in a patient like that is probably indicative of they have underlying cardiomyopathy. So if you can catch it on something as cheap and easy as an ECG and not force your clients to have to go through Holter monitoring and echocardiograms every year for their their pets who are at high risk breeds. That's a really great way to do it, but it can't be just a quick 30 second, it's got to be a full 3 or 5 minutes, which is a lot of paper, but you can do it on electronic devices too. So that was a long answer to your question.

Dr. Watson [00:04:59] No, it was a perfect answer because, you know, that's one of the things that I find there's a lot of confusion about. Like is this a sensitive or a specific screening tool? You know, I see a lot of debate about whether or not we should be running ECGs, you know, prior to anesthesia in all of our patients. And, you know, that can add up to a lot of expense for clients, especially if it's something that's not going to give us, you know, a good, deal of information.

Dr. Estrada [00:05:26] Yeah, you know, I don't know where that recommendation kind of came from, that every patient that has anesthesia needs a pre-op clearance and ECG. To be honest with you as a cardiologist, it makes me want to put my eyeballs out and the number of dogs that I have to look at so that they can have the anesthesia. That's not something they need to come to. Even if they have a murmur, they don't, they really don't need to come to see a cardiologist to get like a blessing that they can have anesthesia. But, you know, if you're going to spend money on a client to get that patient ready for anesthesia, radiographs are going to be like far and away a better tool because you're looking at what you're concerned about, heart size and is there any reason that this patient would decompensate under anesthesia. You know, if you had a high risk patient like a Doberman or a boxer or you heard an arrhythmia, like something fast or something slow, I think that's a really, or a murmur, you know, that's a great time to get an ECG. But I don't think we need to be mandating that all patients that have to have an anesthetic procedure need an ECG beforehand.

Dr. Watson [00:06:40] That's good information. Let's talk about anatomy just for a minute. We'll jump all the way back to freshman year. Freshman year anatomy.

Dr. Estrada [00:06:52] Fortunately, I teach that so I can I can talk about it all day long.

Dr. Watson [00:06:55] Good, good. Can you just give us just a quick refresher on the cardiac anatomy, and you know how that anatomy pertains to kind of each different segment when we're looking at our ECG?

Dr. Estrada [00:07:09] It's a little bit hard without graphics, but I'll try. But, so basically we remember back in Physiology and Anatomy that there are lots of different pacemaking cells in the heart, and the one that beats the fastest is the one that gets to control the rhythm. So that's usually the sinus node. So the sinus node has an inherent rate of like anywhere from 60 to 220. The AV node can only beat 40 to 60 beats per minute. And then in the ventricular myocytes are a bit slower. So the fastest guy wins. And that's usually the sinus node. Fortunately we have video this time, so I can be the sinus node up here beating. So the sinus node will be and it's not actually when the sinus node depolarizes, you don't see anything on an ECG. It's the wave that's traveling through the atria that creates that p wave. So when the wavefront travels through the atria, you get your p wave. At the AV node, those cells are a little bit different. They're not capable of vastly depolarizing and repolarization. So there's a little bit of a lag when that impulse hits the AV node because the AV node kind of has to take its time. And that's what creates that PR interval, is when the impulse hits the AV node and every node has to decide, do I want to conduct this impulse down or am I not ready for it? And that's actually beneficial to the heart that the AV node is like, I don't pay attention to everything that comes my way because for a patient who was, for example in atrial fibrillation, you don't want the heartbeat to be 5 to 600 beats per minute. You want the AV node to protect the heart a little bit. So the PR interval is what happens when the AV node kind of waits and takes its time, and then that impulses very rapidly discharge to the right and left ventricle. And that's what causes the majority of the QRS complex.

Dr. Watson [00:08:58] Excellent. Now, you already talked a little bit about what clinical presentations should prompt us to conduct in ECG. What about just equipment wise, what are kind of like the minimum number of leads we're going to need to diagnose the arrhythmias that we're going to be talking about today?

Dr. Estrada [00:09:16] Yeah. So, when you put, when you hook up your ECG, you're, I mean, the lead system, you get six leads if you do one, two, three, four. So you should really just run it all the time, like, run all six leads because you're going to get you're hooking it up anyhow, so to just run one is kind of silly. The times that the other one lead helps with rhythm diagnosis. So for things like VPCs, APCs, atrial fibrillation, sinus bradycardia, AV nodal block, one lead will pick that up because what you're worried about is just what that rhythm is. But for example, if you couldn't decide if it was atrial fibrillation and if you were having a hard time deciding if you saw P waves or not having those other leads to look at and just see things from multiple different vantage points is really helpful in making that determination. It's kind of like double checking yourself. Like, I think this is a fib. I don't see p waves in lead two, let me go look at lead one, three, AVR, ADL and AVF and see if I see P waves there. So that's what it's helpful for more for double checking yourself. And then it's impossible to do chamber enlargement assessments or mean electrical access without multiple leads because you only have one lead. But the point is, is you're hooking them all up. So just scroll through your machine and like, do one, two, three, AVR, AVL, AVF and just run a minute of each or 30s of each.

Dr. Watson [00:10:46] Excellent. Thank you. And then you kind of alluded to this a little bit earlier too, in that, you know, not all there are certainly some arrhythmias that are benign. But other ones are can be very dangerous or need therapy. And, you know, you talked about that hemodynamicly stable or unstable. So, so in general, how are we going to talk about that with each arrhythmia or is there some is there kind of like a general rule we can follow?

Dr. Estrada [00:11:22] Yeah. So, in general, the way I think about arrhythmias, whether it's, when I think about malignant arrhythmias, I'm thinking about ventricular arrhythmias because that's stuff that can really degenerate and cause sudden death. Supraventricular arrhythmias because the AV node kind of protects the rest of the heart aren't as dangerous because they're kind of protected from beating that fast. Ventricular arrhythmias aren't protected because it just happens. There's no gatekeeper. When I think about ventricular arrhythmias and I'm trying to decide, is this something I need to worry about? That's that's the bottom line is if I see a VPC, just one VPC, my brain is immediately thinking, all right, do I need to worry about this VPC? Is it just like whatever people have VPCs? If I did a Holter on myself, I'd have some VPCs. It's just normal. But what I'm trying to think about is which ones are dangerous. And so I first think about my I call them danger breeds, right, so Dobermans, German Shepherds, boxers, cats with HCM, dogs with some aortic stenosis. VPCs, single VPCs in those breeds are going to be a little bit more concerning to me as a cardiologist because those dogs or cats have a substrate that might coincide with that VPC to cause sudden death. So there are patient breeds, the danger breeds. But then, you know, if I, if I say it's not a Doberman, it's not a boxer, he doesn't have SAS, it's not a cat with HCM, it's a golden retriever. And I'm looking at this golden retriever and it has like you know bigeminy let's say there's a ventricular beat every other beat which is not actually very hemodynamically unstable as long as the heart rate is normal. The things I look at in that situation are, how fast does that VPC happen in relation to the normal beat? Because the faster that VPC happens, the closer it gets to that downslope of the T wave, which is where the vulnerable period is. So the faster that VPC comes, the more dangerous it is to happen right on top of where ventricular fibrillation would occur. The other thing I look for are, if they're occurring in couplets, so not just one. So with bigeminy, it's a normal B, an abnormal beat, a normal beat, an abnormal beat. So I'm looking at timing. But if there are normal beat abnormal abnormal normal beat that's maybe a little bit more dangerous. If those two beats now don't look identical and they look polymorphic, like they might have just taken a different route each time, that's more dangerous. Because if they take a different route in different parts of the myocardium or depolarize, that can also lead to ventricular fibrillation when you don't have the entire myocardium depolarizing and repolarization, and you have these little areas that are doing their own thing, that's very dangerous. So polymorphic runs more than just singles couplets, triplets runs, non sustained versus sustained runs of ventricular tachycardia on a Holter. Obviously if you see ventricular tachycardia, that's dangerous in and of itself. But those are some of the features of malignancy that I'm looking for. And then if you have an animal, let's I think we're going to talk about specific rhythms, but for example, if you have an animal, let's say who has is post-op from a splenectomy and having lots of ventricular arrhythmias, which they often do postoperatively. I tend to look at the rate of those. So if it's even if the heart rate, it's all ventricular rhythm and the heart rate is less than 180 beats per minute, and the dog is just sitting there looking at me and his blood pressure is normal, I'm probably going to tell ICU to turn the monitor off because they're going to get really stressed about looking at that arrhythmia when it's hemodynamically completely just benign, and you just need to stop stressing about it. So those are kinds of things that I look at. Sometimes those kinds of cases, those accelerated idioventricular rhythms in a post-op splenectomy, they get a little fast, they get a little polymorphic, and then the dogs are kind of dumpy because they're post-op and you don't really know, like, is the arrhythmia a factor? Is it just post-op pain? Should I get the pain meds? But I don't want them to be gawked or now I can assess them. Sometimes I do end up putting those dogs on a lidocaine drip or on sotalol. The problem with that is that then I have to. I don't want them on at long term, right? So now I need to go through the entire expense of bringing an owner and a client back and spending another pile of money on doing another echo, another Holter. Can I get this dog off the antiarrhythmic? So I really avoid that situation if I can, mostly because I know I'm going to take the dog off antiarrhythmic and it's going to be a pain in the butt to do.

Dr. Watson [00:16:36] When you were talking about that, I had a flashback to a case I had that was a young German shepherd that came in for a spay. And yeah, we anesthetized her and hooked her up, and it was just VPC, VPC, VPC, VPC, and oh, my heart, my heart stopped. Hers was going.

Dr. Estrada [00:16:52] Well, that that actually, that situation is a pretty dangerous situation because young German Shepherds are very different in the type of arrhythmia that they have. Their arrhythmia gets worse when they're asleep. So when their heart rate is slow, that rhythm gets very dangerous. Versus Dobermans and boxers, the type of arrhythmia that they have, it gets worse when the heart rates are high. So under anesthesia they're great. They have no rhythm abnormalities. But the German shepherd will go nuts under anesthesia.

Dr. Watson [00:17:24] Yeah, I had never seen it before.

Dr. Estrada [00:17:24] Scary.

Dr. Watson [00:17:27] It was. We woke her up and sent her to the cardiologist.

Dr. Estrada [00:17:33] Oh, well you don't have to do that. Next time you can send it to me. I get lots of I get lots of texts like that from students. Ahhh.

Dr. Watson [00:17:42] I will, I will do that. I'm going to get your number after this. You're going to be sorry that you said that.

Dr. Estrada [00:17:47] No, totally okay.

Dr. Watson [00:17:49] So all right. Well let's let's talk let's start talking about some of these, these, rhythms okay. So let's talk about bundle branch blocks. I'm going to kind of go in the order that you presented them in in the article. So we started with bundle branch blocks. And that is a superventricular arrhythmia. So what is the clinical significance of those types? You know, sounds like we have that gatekeeper. So what do you think about these ones?

Dr. Estrada [00:18:19] Yeah. So, let's just talk about bundle branch blocks really quickly. So what it means is that the sinus node fired, it got to the AV node just fine. It got through the AV node. But somewhere in that specialized conduction system, either the right or the left bundle was like, oh, I can't do it. And so it has to travel in a completely different direction. And that's why it changes the way that ECG looks. The important thing, though, is that it still drives the rhythm. There's still a sinus beat that gets through the AV node to cause a ventricular depolarization. So the heart rate and hemodynamics are normal. In people having a bundle branch block can lead to desynchrony because now the right and the left ventricle aren't contracting at the same time, they're contracting differently. And that can lead to systolic dysfunction and heart failure in people. I don't know why that doesn't happen in animals. My theory is that they just don't live as long as people, so they don't develop the degree of desynchrony that will be prolonged enough to develop the systolic dysfunction. So for us, bundle branch blocks are really just a red flag that says, hey, come look closer. I might have heart disease, or there are some electrolyte abnormalities that can cause bundle branch blocks, notably hyperkalemia. So they're kind of a red flag that just says not normal. Don't freak out, but maybe want to look at blood work. Maybe want to look at some chest x rays or an echocardiogram if you're able to do that in practice. I don't think that those animals necessarily need to get like referred immediately for a cardiology workup because most cardiologists' waitlist is about six months right now. I think if practitioners can do some chest x rays or even do a focused ultrasound to make sure that cardiac chambers look normal in size, they can get a really good idea of how to direct the owner or how to direct treatment in general practice. The other thing is don't forget about telemedicine. Like, that's a really great way to improve access to care for your clients. So let's say you have a dog with a bundle branch block, and you took some chest x rays and maybe the heart looks a little big. You have an ultrasound in your practice and you're not very confident on your skills. Just bundle that all together and send it off to somebody versus making them wait six months for an appointment and spending probably like $1,500.

Dr. Watson [00:20:40] Yeah, that's a great tip. So there are the right and the left bundle branch blocks. Does I mean clinically, is there any significant difference between them or is it just the morphology?

Dr. Estrada [00:20:53] Changes the morphology of the ECG and the right bundle is a little bit more superficial. So I can see that in completely normal animals. Not commonly, but I wouldn't say it would like surprise me like, oh my God, why does this dog have an right bundle branch? Like, it just it happens sometimes. It's a it's important to investigate and make sure they don't have right sided heart disease. The left bundle is a bit deeper. So when we see a left bundle branch plot that pretty, I would say I wouldn't bet my life on it, but I'd bet 100 bucks that that dog has underlying heart disease if he's got a left bundle branch block. So, just a little bit difference in terms of what they might mean for a specific patient. A left bundle branch block is definitely pretty significant for underlying heart disease.

Dr. Watson [00:21:42] Okay, that's a good little clinical pearl.

Dr. Estrada [00:21:44] Yeah.

Dr. Watson [00:21:46] Can you explain the different degrees of atrioventricular blocks? How can we determine if those are hemodynamic stable or not?

Dr. Estrada [00:21:55] Right. So again comes down to heart rate and blood pressure. So if they're making a normal heart rate then they're probably making a normal blood pressure. So the first type of AV block would be first degree AV block, and first degree AV block, it just means that that AV node is a little bit slower than it should be. And it's taking a little bit longer for that impulse to get into the ventricle and cause a contraction, but it still causes it. So it's there and there's lots of reasons for first degree AV block. Like I think it's in the article maybe. But it's still the important part is it still drives the rhythm. You still get a completely normal rhythm and a completely normal heart rate. So it's not hemodynamically important. The second type of AV block is called second degree AV block. And there are different levels of secondary AV block. And really don't worry about what they're called. It's just the degree to which P waves don't go through. So you can have second degree AV block that's due to something like high vagal tone or dogs who are under anesthesia where every once in a while one blocks and the PR interval might prolong progressively until you get a block. But most of those p waves are conducted through the cause and impulse. And so oftentimes that's not hemodynamically significance at all. It's when more p waves start getting blocked. So if you start having brachycardias because you have blocked p waves, you can have high grade AV block where maybe every third P wave actually gets conducted and causes a heart rate that's too low for normal cardiac output in a patient and causes clinical signs. And those clinical signs can be collapse, exercise intolerance, and sometimes heart failure, if they have slow enough heart rates or degenerate valve disease in addition to AV nodal block. The the last kind of AV nodal block is third degree AV block, where none of those sinus impulses are getting through. The AV node is like uh uh no way I don't do my thing anymore, rely on somebody else. And so that's somebody else is usually the AV node, the junctional cells or the ventricular myocardium. So it kind of depends on how much of the AV node has become diseased. It's usually a degenerative process. So if it's diseased enough, the entire AV node and the junctional tissues can't fire, and then they're reliant on the ventricular myocytes to only beat 20 to 40 beats per minute at their fastest to kind of rescue the rhythm. So third degree AV block most of the time those patients are going to be symptomatic, collapsing, heart failure, exercise intolerance, that sort of thing. And that's mostly because the heart rates are so low and they don't they physically just don't have the reserve. So they're fine if they're couch potatoes. But the minute they want to get up and go get a drink of water or go out to go to the bathroom, they don't have enough cardiac output.

Dr. Watson [00:24:51] Okay. Let's talk a little bit before the break about premature beats. There's two main categories of premature beats, right?

Dr. Estrada [00:25:01] Mhm.

Dr. Watson [00:25:03] Okay. Yeah. Go ahead.

Dr. Estrada [00:25:05] I didn't know if you wanted me to do it or if you're going to do it.

Dr. Watson [00:25:07] No. You go. You're the cardiologist.

Dr. Estrada [00:25:09] So, when you think about premature beats for me, they can either come above the AV node or below the AV node. And the reason I try to differentiate those is if they come from above the AV node, they can kind of link up to the specialized conduction tissue and cause what looks like a very normal looking contraction. Because even if they happen, let's say from within the left atrium, they can still travel through the atrial myocardium, hit the AV node, cause a PR interval and and a conduction. So they're going to look very, very different from a ventricular premature contraction which is now happening below the AV node. And it can't hop on the specialized conduction tissue to cause contraction. It has to go muscle cell to muscle cell very slowly. And so those are going to look very different. So regardless of where a ectopic beat happens above the AV node, it still uses the AV node. So it's going to look very very similar to a normal sinus beat, in comparison to a ventricular premature beat is going to look very different. bizarre because it can't use any of the specialized conduction system.

Dr. Watson [00:26:17] Okay. Yeah, that makes total sense.

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Dr. Watson [00:27:06] Okay. I want to talk a minute about idioventricular rhythms, and why it's really important to differentiate these from ventricular tachycardia and how we do that.

Dr. Estrada [00:27:19] Yep. So let's just talk a little bit about idioventricular rhythms and what that is. It's pretty it's honestly a fancy name for slow ventricular tachycardia. So if you think about ventricular myocytes we just talked about that their normal inherent rate is 20 to 40 beats per minute. When a ventricular myocyte gets disease or ischemic or angry for any reason, it can beat faster and become more of a driver of the rhythm. So an idioventricular rhythm is usually when a group of cells or one cell becomes angry or ischemia, or there's electrolyte abnormalities and starts behaving like a pacemaker cell. And so now it goes faster than the sinus rhythm and it's driving the rhythm. So even though it's not beating at a rate of a ventricular tachycardia, when we think of ventricular tachycardias we think of 250 300 beats per minute, this ventricular myocytes is now beating faster than normal but still not a ventricular tachycardia. So it might be going 120 140 beats per minute 160, 180 beats per minute. It's supposed to beat at 20 to 40. So it's idioventricular because it's idio ventricular and it's driving the rhythm. But it really is just a slow ventricular tachycardia meaning it's not a dangerous fast polymorphic malignant ventricular tachycardia. And the reason that it's important to identify those is those patients don't need antiarrhythmic agents. They don't need lidocaine. Lidocaine infusions can make an animal nauseous, can actually make them seize at higher values. And what I've seen happen in a lot of ICU cases is that they get very focused on that rhythm instead of looking at the patients, and they're on tons of antiarrhythmic. They've done tons of diagnostics. The echo, the abdominal ultrasound. Why is the rhythm there? Why won't it to go away? Just leave it alone and it's gonna it'll go away when whatever that systemic disease that is causing it is addressed. So people tend to focus too much on it and then don't focus on what's actually causing the disturbance, which is usually something systemic, not cardiac related.

Dr. Watson [00:29:37] Sure. That that makes total sense. And kind of like you said, at the top, so it's driving the rhythm because it's the fastest and the fastest wins. But it's. Yeah, but it's not, you know, making the heart beat so fast that the animal is, is, you know, unstable. So.

Dr. Estrada [00:29:55] Hemodynamically. Like if you are concerned about it, what I always tell the techs in ICU is, well go get a blood pressure. If you're really worried about the rhythm, go tell me what the blood pressure is. And they always come back at 140. It's normal. It's 140. It's like. Okay, thanks.

Dr. Watson [00:30:14] So, the like we said, you said there that this is oftentimes caused by systemic diseases. So electrolyte abnormalities, any other, you know, really common ones that jump to mind?

Dr. Estrada [00:30:25] Post-op GDVs, post-op splenectomy, renal failure, like real bad renal failures, especially acute renal failures. You know, if they're hyperkalemia, especially to, septicemia, splenic masses. IMHA

Dr. Watson [00:30:41] Lots of things.

Dr. Estrada [00:30:43] And tons and tons of things. Yeah. Lymphoma, cancer, all kinds of things. So but you know, the the problem is, is like what happens for us is people will get real focused on it and spend all their money on chasing the arrhythmia. And then it's depleted. And they don't have the funds to either treat the IMHA or work up the IMHA. So it's super important that right at the beginning that you can identify an idioventricular rhythm and distinguish it from ventricular tachycardia, and that it does not need to be treated and chased.

Dr. Watson [00:31:17] Wonderful. Let's talk about sick sinus syndrome. So this oftentimes leads to a kind of like this combination of bradycardia and tachycardia. How does that happen?

Dr. Estrada [00:31:29] So sick sinus syndrome is kind of a it's a name for a clinical spectrum of symptoms. So that sick sinus syndrome is the patient who is exhibiting like collapse, heart failure or clinical signs. Sinus node dysfunction is probably a better term for it, but we kind of lumped them together. What sinus is the true sinus node dysfunction is literally just sinus node or AV node in that they are degenerative. They forget to be or they can't conduct impulses normally. And that's where the slow part comes, is they're just kind of sleeping. They forget that they're supposed to do their job. But the other part of sinus node dysfunction is that a lot of well, not a lot, I would say it's rare to have brady and tachy just the brady is way more frequent. they have atrial arrhythmias. So they might have a long pause, but they might also have a super ventricular arrhythmia that is also happening. And so sometimes becomes difficult to characterize. Are they collapsing and have exercise intolerance from the slow part or from the fast part? And it's hard to tell. So what we often are left with is putting a pacemaker in for the slow part, and then seeing if the animal continues to have clinical signs, and then holtering them and figuring out if they need antiarrhythmic agents to slow that fast part down in addition to treating the slow part. You can't really treat the slow part with antiarrhythmic until you get the pacemaker in because anything that you do for the fast arrhythmia is going to affect the slow part too. So fortunately, most of our dogs with sick sinus syndrome are predominantly bradycardic.

Dr. Watson [00:33:15] And we want to treat the slow first, then the fast, if you need to?

Dr. Estrada [00:33:19] Slow first, then the fast. Yep.

Dr. Watson [00:33:20] Yeah. And which breeds is that most commonly seen in?

Dr. Estrada [00:33:25] Commonly seen in Westies, schnauzers, Cocker spaniels, Boston terriers I see it pretty frequently in and I would say some boxers. Younger boxers I've seen it in.

Dr. Watson [00:33:38] Okay. So let's talk about atrial fibrillation a little bit. I remember being taught, like, if it's really fast and irregular, then it's atrial fibrillation. That's like what I remember about it.

Dr. Estrada [00:33:52] It's literally what I tell my students. I say, if you can convince yourself that it's fast and irregular, I want you to call atrial fibrillation before anything else because 99% of the time, that's what it's going to be. It's just the most common arrhythmia period in people and in companion animals. So and the hallmarks are that really fast rhythm, the irregularity, which kind of sometimes becomes difficult to pick out when it's so fast. And the lack of p waves.

Dr. Watson [00:34:21] Yeah. This is one that, you know, sometimes you pick up on auscultation too. Sometimes, like, it sounds like that shoes in a dryer or, you know, I've always heard people describe it that way.

Dr. Estrada [00:34:34] Yeah. I actually remember the very first time I heard a dog in atrial fibrillation. I was a student at the University of Florida, and I went into the exam room and I listened to the dog, and I was like, I have no idea what that is. And I came out of the room and I told the resident, I'm like I don't know what that is. And so she goes in there and she's like, how long is your dog in atrial fibrillation? I was like oh she's magical. But it is that way, right. Like you hear it the first time. You're like, whoa. But this makes such an impression that you're like, you know what it is every time you hear it. So I always tell students that, like, yes, having just an ECG, it's difficult to maybe diagnose a-fib. But if you put that together with what you heard and meet me in the back of your mind saying, if it's fast and you can't find p waves and it's irregular, it's a fib, like it's usually a fib. So you're going to have that auscultation coupled with the ECG that really after you've seen it once, you're, you're going to know what it is. And I can do a plug for Clinician's Brief cardiac library because I have like, I don't know, 20 different a-fib recordings on there so that if you weren't sure, you could go listen to 20 different animals and convince yourself that it sounds the same.

Dr. Watson [00:35:49] Yeah. I'm so glad you did that because I love the cardiac library. So yeah.

Dr. Estrada [00:35:55] So many people love it. Yeah. I love it too.

Dr. Watson [00:35:58] It's fantastic. Yeah. Yeah, yeah. Anybody at home who doesn't know, yeah, the Clinician's Brief website. Search up the cardiac library. And there are all sorts of different murmurs, and you can slow them down, you know, and listen to them at half speed or quarter speed. It's very, very helpful.

Dr. Estrada [00:36:15] And I, and I put little descriptions on them to tell you what I heard so that you can kind of listen to them go, oh, okay, maybe I hear that, maybe I don't. Most of them you can though. My students say that that's really helpful.

Dr. Watson [00:36:27] Yeah, it is. It definitely is. So with this atrial fibrillation, you know, is this always associated with significant heart disease in dogs and cats?

Dr. Estrada [00:36:38] Yep. So atrial fibrillation, one of the things that, you've probably learned is that, size matters. So the larger your atria, the more critical mass you have. Atrial fibrillation it's an arrhythmia that needs, like, multiple little reentrant circuits to be able to combine and drive that rhythm to be a stable rhythm. And if you don't have a big enough heart to have those multiple reentrant arrhythmias, it might form, but it can't sustain itself. So cats with heart disease hardly ever get atrial fibrillation. But I have seen it. If I see a cat with a fib, I know that that atrium has to be ginormous because it's got to be big enough to sustain that same thing with small breed dogs with mitral valve disease. Very rarely. Well, I wouldn't say rarely, but not common that they go into atrial fibrillation like a Doberman or like a horse who has heart disease. Horses, you know, racehorses that are racing and they have, like, this huge sympathetic tone. And then they stop and they get a big vagal surge because they have that big critical mass that's enough to put them into atrial fibrillation, that big vagal surge and critical mass. So size matters. So small breeds and cats hardly ever go into a-fib. Our Dobermans our Great Danes that develop heart disease. They're pretty, you know, if they if they make it long enough, they're probably going to go into atrial fibrillation at some point.

Dr. Watson [00:38:05] Okay. And then. When we are looking at determining the potential for a ventricular arrhythmia to degenerate into ventricular fibrillation, are there breeds and things that we need to have increased vigilance for when we're diagnosing those arrhythmias?

Dr. Estrada [00:38:27] Yeah. So the Dobermans, for sure. Boxers. So boxers get ARVC and they can be completely normal. And that one VPC that you saw during your three minute ECGs, if you did a Holter on him, you'd probably see hundreds of thousands of VPC. So really significant. Your German shepherd, your young German shepherd that has arrhythmias. So fortunately, they outgrow it by the time they're two years of age. So, any German shepherd that you're going to anesthetize for anything, I would a young German shepherd, I would do an ECG and look for an arrhythmia. And again, just one in a shepherd would be significant for me. Those are probably the biggest breeds that I think about.

Dr. Watson [00:39:11] Oh, that's funny that you brought that up because we actually did wait until that dog I told you about earlier was a two and a half, and I spayed her at that time, but by then she was she was huge and obese. And so it was a much harder spay.

Dr. Estrada [00:39:26] Yeah.

Dr. Watson [00:39:27] But her ECG was normal.

Dr. Estrada [00:39:29] But she lived! Yeah, yeah, yeah, yeah. Well, because the other thing is with those dogs, you know, I will usually have conversation with, we used to have a colony of them at Cornell, and we would have to wait to adopt them out until after two years of age because we didn't want to adopt out a dog that would die suddenly on an owner. But it's a conversation with owners because you kind of want to be like, well, let's wait and see if it gets through, the two year mark because a lot of them do die before two years of age if they have the inherited arrhythmias.

Dr. Watson [00:40:00] Yeah.

Dr. Estrada [00:40:01] So waiting is a completely reasonable option. Just makes it harder surgery.

Dr. Watson [00:40:07] Yeah. It a little bit.

Dr. Estrada [00:40:09] Yeah.

Dr. Watson [00:40:09] That's that's a that's a whole debate right now too. But that's a different podcast.

Dr. Estrada [00:40:12] Yes. That's yeah. That's not mine.

Dr. Watson [00:40:17] Well I think we made it through all of your arrhythmias in in the article. It was fantastic as, as all of your articles are and I'm so glad that we got to talk about them. That brings us to rapid fire, which I know you've played before. Do you want to play again?

Dr. Estrada [00:40:35] Sure. I, I don't remember it, so let's go.

Dr. Watson [00:40:36] Oh, okay. These are those would you rather questions that I just shoot you off at the end of the episode. So, we'll get started. Would you rather go forward in time and practice 100 years in the future, or would you rather go back in time and practice in the mid 1920s?

Dr. Estrada [00:40:55] Forward, for sure. I think it's going to be so many cool advances in cardiology that I like the diseases that piss me off right now are probably going to be so easy to fix.

Dr. Watson [00:41:07] I love it. If you attend a party and all the other party guests are talking about their pets, would you admit that you're a veterinary cardiologist? Or do you make up a different profession?

Dr. Estrada [00:41:19] 100% make up a different profession?

Dr. Watson [00:41:23] I don't want to work at a party either. All right.

Dr. Watson [00:41:28] Would you

Dr. Estrada [00:41:29] I don't want anyone to text me the next day either and ask me questions.

Dr. Watson [00:41:31] Exactly, exactly. Would you rather have a famous TikTok pet as a patient? Or would you rather have a famous Hollywood actor as a client?

Dr. Estrada [00:41:42] Actor as a client.

Dr. Watson [00:41:43] Oh actor as a client, somebody in mind, like anybody in particular?

Dr. Estrada [00:41:47] Oh my God, if I could have Matthew McConaughey as a client.

Dr. Watson [00:41:52] I got that.

Dr. Estrada [00:41:53] That just popped in my brain. That's always the one.

Dr. Watson [00:41:56] Ryan Reynolds for me. So if you're out there, you come like, I'm in Vegas, come on through.

Dr. Estrada [00:42:01] I will come to you if you have dogs. I'm your girl. I am your girl.

Dr. Watson [00:42:07] Okay. Last question. Would you rather be covered in fur or would you rather be covered in scales?

Dr. Estrada [00:42:16] Scales.

Dr. Watson [00:42:18] Scales?

Dr. Estrada [00:42:18] Yes. menopause sucked and I never want to be hot again.

Dr. Watson [00:42:25] That's really. That's a good reason. Also, like, you could get like really beautiful iridescent scales. Like I would be all pretty. Yeah. And sparkly. Yeah. For Ryan Reynolds.

Dr. Estrada [00:42:36] Yeah. Yeah. Matthew McConaughey. I don't know if he likes the iridescent. He's more of a down to earth kind of guy, so. I might just have to go chameleon.

Dr. Watson [00:42:45] I love it. I love it. All right. Well, that was it. I just I want to say thank you again. I know this time of year you're so, so, so busy. And we just really appreciate you taking the time to talk with us and thank you to our audience. I hope you enjoyed this conversation as much as I did. I learned so much. And we hopefully we'll see you again.

Dr. Estrada [00:43:04] Yeah. Any opportunity I get to teach and get people to figure things out where they're not scared is great.



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