D. E. Larsen, DVM
I pushed the winch out to the end of the track and jumped up on the truck’s bed. I secured a chain around the hocks of the dead horse. With the shackle secure, I connected the hook on the winch cable to the chain and lifted the horse up and pushed it into the necropsy room.
This was the summer of my sophomore year in vet school. I was lucky enough to land this job as a necropsy technician in the Colorado State Veterinary Hospital. Up to this point, it was proving to be a tremendous learning experience.
There was a joke in the profession that had a punch line something like; a veterinarian can eat his mistakes. I was never good at remembering jokes. This summer, I got to see the mistakes and the pathology associated with the profession.
I positioned the dead horse in the middle of the necropsy room and lowered it to the floor. I unhooked the winch and removed the shackles, before rolling the winch to the side, out of the way for now.
Dr. Norrdin was on duty as the necropsy pathologist this week. I enjoyed working for him because I got to do most of the necropsy, and he was always challenging my knowledge, usually in a game-like manner.
“Okay, let’s look this guy over closely, read the notes and then come up with a possible diagnosis before we start the necropsy,” Dr. Norrdin said. “You have to be prepared to defend your suspected diagnosis. Then we will find out who was closest to the actual diagnosis.”
This was a young horse, less than four years old. Found dead in the paddock this morning. He was never observed to be sick, ever. Looking over him, there was hardly a mark on him. The only thing evident was his front teeth were punched through his upper lip and protruding out of that lip.
Dr. Norrdin quizzed the resident first, the junior technician next, and finally came to me.
“What is your diagnosis, Larsen?” He asked.
“Cardiac Tamponade,” I said.
“Cardiac Tamponade!” Dr. Norrdin remarked. “How in the world do you arrive at that diagnosis from looking at a young, healthy horse?”
“A young, healthy, dead horse,” I corrected. “This young heathy horse, who has never been sick a day in his life, was dead when he hit the ground. His death was sudden. We know that, not because he was unexpectedly found dead in the morning, but because his front teeth are punch through his upper lip. He hit the ground nose first. Who has seen a horse, standing in a paddock, fall nose first? This had to be a sudden cardiac event.”
“But Cardiac Tamponade,” Dr. Norrdin said, “I have not seen a Cardiac Tamponade in the horse. You know the saying, when you are in a barn and hear hoofbeats, you look for a horse, not a zebra.”
“And, the proof is in the pudding,” I said as I stuck my knife into the dead horse’s ventral midline on his chest.
“If I am correct, we will know in a minute or two,” I said as I sliced open the skin from the end of his sternum to his jaw’s angle.
With the junior technician lifting up the right front leg, I severed all the muscle attachment to the ribs, and we reflected the front leg over the horses back to expose most of the ribs. Then I severed the lower cartilage attachments of the ribs to the sternum. The other technician, standing at the horse’s back, pull up several ribs as I cut the intercostal muscles.
There is was, the pericardium, that sack around the heart, distended with blood. I was vindicated, my diagnosis was spot on. Cardiac Tamponade occurs when the pericardium fills with fluid, usually blood. That constricts the hear’s function. If it is a slow accumulation, it can be recognized and corrected. If it is sudden, it results in sudden death.
“I’ll be damn,” Dr. Norrdin said. “Now, let’s find out just what happened to allow Larsen to win the game.”
“Verminous arteritis,” I said.
“Now you are really sticking your neck out,” Dr. Norrdin said. “But this time, I think you are probably correct.”
We opened the pericardium and drained a surprising amount of blood. The heart was small in appearance because it had not been able to fill with blood. And there it was, a hole in the aorta, right where it came out of the heart. This hole, the size of a match stick, would have filled the pericardium with blood in seconds. A very sudden death would have resulted.
“You guys pull the heart and lungs with the aorta attached,” Dr. Norrdin said. “Try to keep the aorta intact all the way down to the mesenteric artery.”
In the horse, one of the critical intestinal parasites, a large strongyle, Strongylus vulgaris, has a larval stage that causes severe damage and inflammation to the mesenteric artery, the main artery to the gut. This is one of the leading causes of colic in the horse.
We opened the aorta from the heart to the mesenteric artery. There were lesions the entire length of the aorta. The root of the mesenteric artery was swollen and heavily involved with verminous arteritis. This is the standard location of those lesions. The fact that lesions were also located along the entire length of the aorta was an indication of a massive infestation with this dangerous parasite.
“If this horse did not die from this cardiac tamponade, he would have died from severe colic before long,” Dr. Norrdin said. “This is as extensive of an arteritis as I have ever seen.”
“Do you think the rupture of the aorta was caused by the parasite?” I asked.
“Oh, most definitely! This owner needs to get his horses on a rigorous parasite control program, or he will be losing a lot of horses,” Dr. Norrdin said.
“And Larsen, don’t be too smug,” Dr. Norrdin said. “You will never see another case like this in your life. These once in a lifetime cases, just happen, early in your career and later in mine, but only once. Had this been on a test, all of your answers would have been marked wrong. You just had a lucky guess here today.”
Of course, Dr. Norrdin was correct. I never saw another case like this. I never read of another case like this. But having seen the damage from uncontrolled parasitic infections, it is much easier to make strong recommendations to horse owners about their parasite control programs.