Veterinary Vertex
Veterinary Vertex is a weekly podcast that takes you behind the scenes of the clinical and research discoveries published in the Journal of the American Veterinary Medical Association (JAVMA) and the American Journal of Veterinary Research (AJVR). Tune in to learn about cutting-edge veterinary research and gain in-depth insights you won’t find anywhere else. Come away with knowledge you can put to use in your own practice – along with a healthy dose of inspiration to remind you what you love about veterinary medicine.
Veterinary Vertex
Heart Rate Variability Derangements in Dogs with Chagas Disease
Dr. Roy Madigan joins us to uncover the hidden danger of Chagas disease, a parasitic infection transmitted by "kissing bugs" that's far more prevalent than most veterinarians realize.
Contrary to outdated beliefs that Chagas is a "third world disease," this silent killer affects up to 18% of dogs across the southern United States, with millions of cases going undiagnosed. Dr. Madigan shares how his journey began with one fateful case named Max, whose unexplained death led to a 25-year quest to understand this misunderstood condition. What he discovered changes everything we thought we knew about cardiac disease in dogs.
The most alarming revelation? Heart rate variability analysis shows that dogs with Chagas disease develop serious autonomic nervous system dysfunction long before showing any symptoms. This explains the devastating phenomenon of sudden death in apparently healthy dogs—a tragedy Dr. Madigan has witnessed countless times. Through sophisticated monitoring techniques, veterinarians can now detect these dangerous irregularities early, potentially saving lives.
Perhaps most concerning is the One Health implication. Dogs serve as sentinels for human infection, with Dr. Madigan noting that several dog owners have tested positive for Chagas only after their pets were diagnosed. The disease doesn't discriminate based on neighborhood or housing quality—these bugs readily infiltrate modern homes regardless of socioeconomic factors.
For veterinarians, the message is clear: implement thorough cardiac assessments and consider Chagas when arrhythmias are detected. For pet owners, especially those in the southern states or who've adopted dogs from these regions, ask your veterinarian about testing. Your vigilance might save not only your dog's life but potentially your family's health as well. Listen now to understand the heartbeat irregularities that could be your first warning sign of this emerging threat.
JAVMA article: https://doi.org/10.2460/javma.24.12.0773
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This is Veterinary Vertex, a podcast of the AVMA Journals. In this episode we chat about heart rate variability derangements in dogs with Chagas disease with Roy Madigan.
Speaker 2:Welcome listeners. I'm Editor-in-Chief Lisa Fortier, and I'm joined by Associate Editor Sarah Wright Roy. Thank you so much for taking time out of your busy schedule to be with us here today.
Speaker 3:Thank you, Lisa and Sarah. It's a pleasure to be here.
Speaker 1:All right, let's dive right in. So, roy, your JABMA article discusses how heart rate variability analysis may enhance early detection and management of Chagas disease, which is an emerging One Health issue, by addressing underdiagnosed autonomic and cardiac dysfunction in dogs. Please share with our listeners the background on this article.
Speaker 3:Thanks, sarah. Yeah, so for those listeners that don't know much about Chagas disease, or if you're like me and you kind of slept through that section in parasitology, just a brief background Chagas disease is a parasitic disease. Okay, it's caused by a protozoal organism called Chapanosoma cruzii. So you know, not a virus, not a bacteria, but a little tiny, little microscopic bug similar to toxoplasma leishmania, if you're over in Europe, and so it's. It's pretty widespread as far as Southern United States. The Southern 26 states, including Texas, which is where I practice, is just inundated with it, and it's mainly because we have the vector, and that vector is called the kissing bug or the triadamine bug. So it's a little bit bigger or probably in similar in size, depending on where you are, to a cockroach, but it's like a giant mosquito it crawls, it flies and it takes blood meals, and so wherever we find that vector, you know we're going to find the disease. Generally, we're taught in veterinary school that it's a disease of third world countries, and so you know, central America, south America, but we have quite a bit of it. Essentially, what happens is the parasite is in the hindgut of this kissing bug, so it's actually not transmitted through the bite of the bug like heartworm disease, but it's spread through the feces. So when this kissing bug takes a blood meal from its host, whatever mammal it decides to do, it'll actually defecate, and in that feces the parasite is transmitted into the bite wound and then gets into circulation. That's the classic transmission. Other methods are a little bit more effective in our companion animals because they eat everything. If you have a dog, you know how it goes. They eat everything smaller than themselves, especially when these bugs have a nice crunchy center with blood in it right. So major reinforcement there. And so these kissing bugs are commonly ingested through the oral route. Other methods of transmission include vertical transmission, so from the bitch to the babies we also had through blood transfusions. Obviously that's much less common than on the human side, and we also have carrion ingestion, so eating stuff they're not supposed to, which I'm sure your dog's never done before, and so those are pretty common methods of transmission.
Speaker 3:The parasite is very, very effective at getting into all tissues. So one common misconception with Chagas disease is that it only goes to the heart. We tend to look at the heart a lot because any amount of myocarditis is bad, but it causes inflammation in any tissue that it goes to including the heart for myocarditis, and so the disease that it causes is pretty simple. Okay, it generally causes a progressive chronic myocarditis. Okay, if you think of it that way, there's kind of like three pillars that it operates in, okay, so by presence of the parasite we cause tissue damage, so when those cells get ruptured they die, right, regardless if it's in the liver, the brain, the heart.
Speaker 3:The second thing that it does is it causes inflammation, or what we call the host immune response, and so the body's response to the disease or the parasite itself causes damage. And then the last thing that it does is it causes some microvascular disturbances, so tiny little microclots and all the wonderful things that those do in tissues, okay, but the end result, when we're talking about the heart, is generally systolic dysfunction, eventually electrical disturbances, which is huge, okay, and then you know, over time we can get these autonomic disruptions. So our paper really focused on these autonomic disruptions that happen. So more of a nervous system effect. It really hasn't been looked at in dogs, and so that's what kind of drove us to do this paper and gather this data, because we wanted to see, you know, we know it happens in humans, but does it happen in dogs, and so it's very, very fun to explore that.
Speaker 1:Yeah, thanks. That was a great review. Appreciate that. So what are some of the important take-home messages from this article?
Speaker 3:Yeah, I think the biggest thing that I'd like to share with veterinarians you know we obviously in private practice don't do too many Holter monitors, right, but certainly everybody has access to EKGs, ECGs, and hopefully most of you are using those now. You know, back when I graduated a long time ago, not too many of us had ECGs for surgical monitoring, but that can be your most reliable indicator of early detection for Chagas, you know. You know, classically this disease is diagnosed through serology. So we're going to be checking the body's response to the parasites. We're not looking for direct parasites, necessarily. We're looking for the antibody response, right.
Speaker 3:But the biggest red flag, at least in our hospital, probably a third of the cases that we diagnose are under anesthesia, with arrhythmias, and so there's a lot of papers out there that look at arrhythmias. You know the types, the frequencies, all that. But the biggest surprise for me with this was that heart rate variability analysis, which is just a fancy term and a set of tools that measure autonomic function in the heart, so sympathetic versus parasympathetic, and there's these distinct markers that have a lot of abbreviations. There's a lot of math involved with it, but essentially, at the end of the day, these just reflect the function of that autonomic nervous system. Okay. So the the big take home is, you know, let's, let's kind of expand our knowledge when we're looking at these Holter reports, when we're looking at HRV analysis, instead of just glossing over it and ignoring it.
Speaker 3:You know, kind of really give us some thought there. If I see a derangement, if, if I live in an area that's endemic for Chagas disease again, it's like if you're South of Oregon and south of Pennsylvania, you're in that region, Okay. Or if you have a dog with a travel history, maybe they adopted the dog from the south, you know, maybe maybe you're in like I've got a dog in Singapore right now that we're treating. I mean, how did that happen? Right, so people travel around the world and so if I'm, if I have an abnormality in my physical exam, I'm doing a Holter monitor, or maybe the cardiologist is, you know, give some extra thought to that and consider maybe I'm dealing with Chagas and I need to do a test for that.
Speaker 2:Yeah, fascinating. We recently did a podcast on Rocky Mountain Spotted Fever and how it's creeping its way into places that it never was before either, and I think that podcast and your article and this podcast also really highlight how important the role of the veterinarian is in these One Health situations, to recognize it in the animals as well as in people.
Speaker 3:Yeah, lisa, you bring up a fantastic point. You know, dogs are sentinels for this disease across the world. We know that. So when we look at dogs with Chagas disease, it's always associated with a higher risk of infection in their human counterparts, right, and you know, let's face it. You know, when we were growing up, dogs lived outside. Now they live in our bedroom, right, and so they bring in all kind of fun creatures, including kissing bugs. You know these little vectors and we see them, and you know our clients see them in their bedrooms, you know, and they don't live in thatched huts, right, and so I don't know about you guys, but we were incorrectly taught in vet school, and still are to this day, that this is a disease of third world countries. This is not. You know, you can live in a gated community and that gate won't stop these kissing bugs, right, and so we've got to be aware of that. So the one health implications are huge.
Speaker 3:Years of, you know, diagnosing and treating this disease. I've only and we're talking thousands of dogs, okay, but I've only had six people that tested positive. However, they would not have gotten tested if their dogs didn't have it, and so hopefully, you know, their physicians were able to intervene and help these people and, as far as I know, they're all alive still. So. But dogs, dogs can help, you know, dogs can help us. Dogs can help us diagnose other mammals in the pack.
Speaker 3:We've had a lot of cats, we've had a lot of horses and again they would have gone undiagnosed. In fact, in my own pack here I have three dogs. I know that's weird, a veterinarian with only three dogs. One of our dogs, our golden retriever, during her surgical procedure at two and a half, we noticed an arrhythmia that triggered us to test. She almost died. She was in VTAC on the table. That's not fun, but we diagnosed Chagas disease on her and that triggered me to test the other dogs and they were also positive. So you know, early detection is key. You know, and I think this particular set of indices, this heart rate variability, looking for arrhythmias on your EKG or Holter, is huge and it's going to help us diagnose more patients for sure.
Speaker 2:What sparked your interest in Chavez disease?
Speaker 3:Yeah, that's a hilarious question because, as you know, I literally did sleep through this and parasitology, because I said I'm never going to practice in South America. So I apologize, dr Craig, at Texas A&M, it just it kind of fell in my lap and my staff's lap. I mean I have to include. I have an amazing team at work. They're very, very loyal and have stuck with me a long time through this and have kind of experienced this. But you know, long story short, we had a dog, one-year-old dog, come in from the Humane Society actually His name was Max, I'll never forget him. He was my gateway drug and he came in with a tachyarrhythmia and we were unable to save him. Any drug we gave didn't work. He succumbed and so I couldn't sleep.
Speaker 3:The next morning I came in and I was like God, you know, we, we've got to figure out what's going on here. So we did an e-cropsy. The shelter was kind enough to let us do that and we we stopped tissues, looked at everything. Dog had a giant, dilated, purple heart, heavy, heavy, heavy on on on the cut surface. We sent it in for histopath. It took them weeks and weeks and weeks, lots of internal meetings. This is about 25 years ago, about 23 years ago, and the end result a month later was hey, this dog had T cruzi infection.
Speaker 3:I guess what I had to go dust off my head went to how many cases, how many dogs have I been seeing with heart disease or not heart disease and been missing these? So that started that process of you know it's the old adage, right? It's like if you don't look for it, you never find it, so you never think you have it Right. So we started looking for it. Find it, so you never think you have it right, so we started looking for it. And one thing that I would advise veterinarians as you go into the Chagas world it's like the matrix right, once you take the red pill, you're toast. You can never go back. So, fair warning, I warned you.
Speaker 3:If you want to find Chagas disease, the easiest way to find it is and we all have these cases just go back to your heart disease patients that you're managing right now. So do a little. Who Got on your inventory and your practice management software and look at Pimobendin? Whoever gets that. You need to go test them. Okay, this disease is a great mimicker. We've got plenty of dogs with mitral valve disease with Chagas. We've got plenty of dogs with DCM with it. Okay, and that's not even going into the realm of cats, but that's the easiest way to start looking for Chagas disease. So that one little dog, max. That's what started the whole journey and unfortunately haven't looked back yet.
Speaker 2:So well done, max. You said it's, you know, like 23, 25 years ago, and then you write this fabulous article and, oh, even though you're a key opinion leader with all that experience, we always find something surprising when we're putting a manuscript together. Was there anything that stuck out in this manuscript that's surprising to you?
Speaker 3:Yeah, that's a great question, Lisa. I never cease to be amazed. I think that's why I still love my job. You know, 24 years later, you know you can always find some things to challenge you on a daily basis.
Speaker 3:The biggest surprise for me was how widespread this autonomic dysfunction is. Okay, and the second key point is it didn't matter if the dog was asymptomatic versus symptomatic. Okay, there, we're going to find that same amount of or not the same amount, but we're going to still find arrhythmias. We're going to still find the same amount of autonomic disruption in there. And it and it precluded, you know, symptoms. You got to understand these. Like historically, people come in and they're like my dog's fine, okay, I'm only testing, because you know my other, my fourth dog, has Chagas and sure enough, you know they have Chagas.
Speaker 3:And I go through the history again. Are you sure you know are we are? We are we, you know, lethargic, you know decreased activity, collapse, anything, nothing, nothing, nothing. My physical exam is normal, my ClinPath is normal, my imaging is normal, yet here we go, right, and then you run the Holter and you get back these derangements and you're like, wow, you know, and it affected so many of the dogs, and you know, in human medicine again, this is kind of new stuff for us in veterinary medicine, but in human medicine we know it's a well established fact that derangements in HRV analysis, so autonomic disruption, is a direct predictor of number one progression of the disease and number two mortality.
Speaker 3:So this is kind of important stuff. But it explains why dogs with chagas drop dead Okay, and I've lost count of how many dogs I've heard about from owners. Is you know? I gave my dog a bath they're doing the zoomies, you know, in the yard after the bath and then they drop dead, okay. Or I went to bed and the dog was fine and now he's dead, okay, that happens very, very frequently, especially here in the South, and so those are the biggest surprises for me for sure.
Speaker 1:You have me thinking back now to all my cardio cases.
Speaker 3:I'm like, hmm, I wonder if any of them had chagas? Yep, yep, and you know, if we don't look for it again, we don't find it right, but we tend to kind of get into the weeds, right. So that's another soapbox I have. But, like you know, we start looking at things like diet, you know, and we're like, well, what about lentils and grain free and stuff like that? Yeah, but you're missing the point, right? You know we have prevalence rates of Chagas in Texas in companion animals and this is a grossly underdiagnosed number because of the test platforms that they've used in the papers 18%, so 18% of dogs in Texas have Chagas disease companion animals, compared to about 16 and a half with shelter dogs. That we're talking millions of dogs that are underdiagnosed and the average, like our reference lab, we have a couple of them that do the testing, serology but the state lab, which is kind of the tried and true, you know, set one, those guys test probably, you know, a thousand dogs a year. So how many are we missing, right? Yeah?
Speaker 1:So crazy to think about, wow. Well, thank you for doing this podcast episode with us. Hopefully this is pretty enlightening for folks.
Speaker 3:Yeah, I hope so, thank you.
Speaker 1:Yeah, of course, for those of you just joining us, we're discussing heart rate variability, derangements and dogs with Chagas disease with our guest Roy.
Speaker 2:Roy, again back to you know 20, 25 years. How has all that previous training and experience prepared you to help write this article?
Speaker 3:previous training and experience prepared you to help write this article.
Speaker 3:Yeah, and again, I kind of alluded to that earlier about our training, right, formal training.
Speaker 3:You know we were kind of given a little bit different story about Chagas disease. I think the majority of my just experience, you know, seeing it on a, on a, literally I'm not exaggerating literally on a daily basis when I'm in the hospital multiple cases of Shiga's disease. I think you know it's the grunt work on the daily basis that we see in our hospitals that trains us to recognize these patterns of disease. And also, I think, on the human side, you know we've got an international team that we work with for this kind of stuff and they've been huge in opening up my eyes. So, again, drawing from their experience, um, connecting with physicians, connecting with researchers that are doing this, and then taking all the pieces of the puzzle and putting them together, um, I think that's been my biggest um help with education. For myself is just just the wide variety of people in the field that have helped me do that People way smarter than me and they've really done a good job of giving me their information so we can help out with it.
Speaker 1:So, roy, this next set of questions is going to be really important for our listeners and you've given us a wealth of information today about this disease. But if you can really narrow it down to like one piece of information that the veterinarian needs to know when they walk into the door to see that client that may have a pet with Chagas disease, what's one piece of information the veterinarian should know about heart rate variability derangements in dogs with Chagas disease?
Speaker 3:Sarah, I would say that the biggest one thing that they could focus on is do your cardiac assessment and look for those arrhythmias. Okay so you're going to know you're obviously not slapping a halter on everybody as soon as they walk in the door, but you're going to be able to detect, through your physical exam, those variabilities. Okay so you may not be able to get it down to the millisecond right Like the AI can do on the halter, but you're going to be able to detect those abnormalities in there. So just do your auscultation, pay attention to that, and then if you see anything abnormal, you know, think about Chagas.
Speaker 2:Good old physical exam.
Speaker 3:That's right.
Speaker 1:Tried and true. And on the other side of the relationship, what's one thing clients should know about Chagas disease? The relationship.
Speaker 3:What's one thing clients should know about Chagas disease? Yeah so, because there's this is kind of an emerging disease. Right, it's an important one, but it's an emerging disease and so you know, your veterinarian, you might not have had very much experience with it yet. Okay. So, as as a patient, as a client, you are your dog or cat or whatever your companion animals number one advocate. Okay.
Speaker 3:So, if you have information, if you're listening to this podcast, ask your veterinarian about Chagas. You know we're generally nice people, okay, so we'll, we'll do what you want us to. So just just say hey, I'd like to have my dog tested for Chagas disease. Now, if you're living in Canada, okay. Or you're living in Alaska and you've never seen one of these and then you don't have it, don't worry about it, okay. But if you adopted your dog from here, you know, in the South, you know you're traveling, you're doing agility work, you're at the dog shows, you know I mean, you're getting exposed, your dog's getting exposed, so so just just ask your veterinarian and we'll, we'll look for those things. You know, like I said, I learn things every day. My clients educate me a lot, so please don't feel bad about asking your veterinarian to test for this.
Speaker 2:I can see Sarah smirking. One of my favorite sayings is every day is a school day.
Speaker 3:That's right Every day and it never stops right.
Speaker 2:That's what keeps us interested in our wonderful profession.
Speaker 3:That's right.
Speaker 2:You read my mind, Lisa. I know I can see the smirk.
Speaker 3:I call those growth opportunities. You know another growth opportunity Great, super, here I go again.
Speaker 2:I should be much taller than I am.
Speaker 3:That's right.
Speaker 2:Roy, thank you again, and as we wind down, we always like to ask something just a little more personal. So for you, we'd like to know what's the first concert you attended.
Speaker 3:Oh yeah, that's a great question, lisa. So 1992, I was in high school and I'm dating myself the very first concert I ever went to was U2 in Houston, so that set the bar really really high. It's an amazing concert. But yeah, a long time ago I think Bono was like the size of a piece of sand. That's how high up we were, but it was amazing.
Speaker 2:Did you get a chance to see them in the sphere?
Speaker 3:I did not. Oh gosh, I was thinking about it. Oh, it was so hard to resist, but I would have loved to see them. You know, a lot of years later for sure.
Speaker 1:Yeah, very cool, it's a fun question. We actually haven't had that one in a while, so thanks for picking that one.
Speaker 3:Yeah, you're welcome. Well, you asked me about puzzles and I was like I don't do puzzles. That would be a boring answer.
Speaker 1:Yeah, that's an interesting one. We have this theory where, like, internists do puzzles a certain way and surgeons do it a certain way. So, yeah, so, thank you so much, roy. We appreciate you being here with us today and sharing information, too, about your manuscript with our listeners. So thank you.
Speaker 3:Thank you, sarah Lisa.
Speaker 1:Appreciate you guys and to our listeners you can read Roy's article on JAPMA. I'm Sarah Wright with Lisa Fortier. Be on the lookout for next week's episode and don't forget to leave us a rating and review on Apple Podcasts or whatever platform you listen to.
