Medina Spirit Teleconference: Scientists Explain Why Sudden Deaths Are Hard To Pinpoint by Natalie Voss|02.11.202202.11.2022|4:33pm5:07pm Medina Spirit When the California Horse Racing Board (CHRB) released a summary of the necropsy report from Medina Spirit on Feb. 11, people had a lot of questions — particularly as to why the necropsy could not pinpoint a specific cause of the 3-year-old's death. Medina Spirit died suddenly after the conclusion of a workout at Santa Anita Park in early December. The CHRB hosted a media teleconference after the report's release, with California Animal Health and Food Safety director Dr. Ashley Hill alongside University of California-Davis veterinarians Drs. Benjamin Moeller and Dr. Francisco Uzal to help give some context to the findings. A few key takeaways: It's not uncommon for sudden death cases to have no cause of death identified after necropsy. Sudden deaths among racehorses have proven challenging to pathologists and researchers around the world for some time. Uzal estimated that in a case like Medina Spirit's, where the horse drops dead with no apparent musculoskeletal injury, the exact cause remains unknown about half the time. In one 2011 study published in the peer-reviewed Equine Veterinary Journal, a research team looked at 268 sudden death incidents in Thoroughbred racehorses around the world and found a definitive cause of death in only 53 percent of them. A presumptive cause of death was identified in another 25 percent, with 22 percent remaining completely unexplained. That's partially because it's really hard to uncover a heart condition in a horse whose heart is no longer beating. We've written before about how horses don't have “heart attacks” the way people do. In humans, the condition we call a “heart attack” is a blockage of a coronary artery that supplies the heart, which results in tissue death in the heart muscle. Dead tissue is pretty easy to see in an autopsy, as it will be discolored and often dark. According to Hill, researchers currently believe that athletic horses probably don't experience that kind of tissue death that leaves behind evidence. Instead, the heart problems they suffer are likely misfirings of the electrical impulses that travel through the heart, regulating its beat. Once the heart is no longer beating, there's no good way to test how electrical signals were passing through it.”Looking through the microscope at the tissues doesn't give you information about the electrical conduction through the heart,” Hill said. “There are no gross or microscopic lesion specific to that condition,” echoed Uzal. “That's why we go by indirect indicators like pooling of the blood in the lungs. When we see that, we think that the heart stopped pumping.” [Story Continues Below] But what about the congestion and bleeding in the lungs and spleen? Those are typical for a sudden or suspected cardiac death in a horse. Once the heart suddenly becomes unable to pump blood to or from other organs, it gets stuck wherever it is. “Congestion” cited by pathologists in this context refers to the presence of lots of blood inside the vessels (rather than the mucus you're used to thinking of when you have a head cold). Sometimes, pathologists find that organs with a large blood supply, like the horse's lungs or spleen, may have small amounts of blood leak out of those vessels around the time it stops pumping normally. Are there other issues that could cause those findings? Yes. Uzal said pulmonary hemorrhage in the lungs could cause similar findings in a horse's organs. Certain types of allergic reactions also could produce the same thing. Are racehorses the only ones who suffer from these sudden cardiac deaths? No, but we know more about the frequency of occurrence in racehorses because of how many of them have necropsies done. Several racing jurisdictions have programs in place that require them to perform necropsies on horses who die in racing and training, so racehorses are necropsied more broadly and consistently than other types of horses, but Hill said we've seen these kinds of deaths in other sports and breeds, too. “I think one of the reasons we have as much information about this in racehorses as we do is the CHRB necropsy review program we've had in place since 1990,” said Hill. “That's not true for other types of equine performance, so it doesn't mean it doesn't happen, but it means we're able to see the horses and do the work on necropsies.” Researchers are trying to determine whether there is a genetic link with these electrical issues in the equine heart. Uzal and Hill said that both UC-Davis and the University of Minnesota are collecting samples on sudden death cases and analyzing those to see if they can find any genetic commonalities. Similar electrical disorders in humans can sometimes be passed genetically. Samples from Medina Spirit's body were archived for this purpose. What about the drug testing done on the horse's body? Urine, blood, and hair samples were taken on the horse in the minutes after his death at the track. The CHRB is in charge of testing the samples collected at the racetrack to look for any violations of drug rules. Blood and urine samples are also taken from the horse's body upon arrival at the pathology lab, and those were tested as part of the necropsy process. There was some confusion on the call about whether hair was tested and by who, but it seems the CHRB did perform hair testing on samples collected at the track, with no positives for prohibited substances detected. Hair samples were collected upon the horse's arrival at the pathology lab, and those samples have been stored for future testing, should it become necessary. Necropsy sample testing did find furosemide and omeprazole, which matched veterinary records submitted to the CHRB. It seems the UC-Davis lab did test for EPO and several EPO mimetics, but while some testing was refereed by other laboratories, Hill said they were unable to find another domestic lab willing to accept the liability to do referee EPO testing in this case prior to the release of the report. About that thyroxine testing… A Cornell laboratory performed testing for thyroxine and found no abnormalities. This does come with the caveat that while the lab's thyroxine testing method has been validated, it's designed for the testing of thyroxine levels in living animals. Most of the time, thyroxine testing is done in veterinary patients to decide whether they're hyperthyroid or hypothyroid and need medication. Only in rare instances are people testing samples from dead horses, so there is no test that is engineered for this specifically. The test also cannot tell the difference between naturally-occurring thyroid hormones and synthetic hormones. Scientists on the call said they spent about three years ordering thyroxine tests on sudden death cases submitted for necropsy, hoping to find some connection between elevated thyroxine levels and sudden deaths. Elevated levels could be indicative of either a horse receiving synthetic thyroid hormones, or an individual having naturally-elevated levels. It's also known that regularly-exercised animals probably have higher natural levels of thyroid hormones.Those tests over a three-year period did not result in any significant findings. The scientists don't know if that's because the tests were designed for living animals and were unable to correctly capture elevated thyroid hormones from post-mortem samples, or if the horses submitted really didn't have elevated thyroid hormones — or if it's there's not an association between elevated thyroid hormones and sudden death risk. No, betamethasone probably didn't have any impact on the horse's death. The veterinary team said that the typical length of action for injected betamethasone is about a week from administration. Of course, in the case of Medina Spirit, his connections insist he was exposed to the drug via a topical administration. We know less about the way topical, skin-based administrations of betamethasone are metabolized, but Hill and Moeller agreed there was no reason to suspect that kind of administration in May could be having an appreciable impact on the horse in December. Blea's removal from the death investigation wasn't hugely impactful to the necropsy process, according to the UC-Davis team. Much has been made of the removal of CHRB equine medical director Dr. Jeff Blea from the Medina Spirit necropsy process, after the state veterinary board issued an emergency suspension of Blea's veterinary license. But for those unfamiliar with the process, Blea was never going to be involved in the actual dissection of a horse's body nor the testing process in the event of an on-track death — that is left to pathologists and toxicologists. The equine medical director's role has always been to assemble the necropsy and toxicology reports and present them to the CHRB while answering questions about the veterinary jargon included there. Those on the media teleconference said that while other processes normally undertaken by Blea have been impacted by his suspension by the university, death investigations like this one were not among them. This robust process is pretty standard for the CHRB necropsy program. Although the decision to send some samples to outside laboratories and ask for peer review of the report and necropsy photos was specific to this case, the level of post-mortem testing is standard for all fatalities in California — including the extensive testing for foreign substances. So, what's next? An official veterinarian, safety steward, and member of the board of stewards will review the necropsy as well as other evidence collected in the death investigation and issue their own report, which will also be distributed to the public. If any CHRB rule violations are uncovered, they will be adjudicated at that point.