We’re pleased to welcome Dr Laura back to Eventing Nation with an explanation for “heart attacks” and sudden death experienced by sport horses. When she’s not writing for EN or competing her own two event horses, Dr. Laura is a respected vet at Hagyard Equine Medical Institute in Lexington, Kentucky. If you have anything you’d like Dr her to tackle, please submit your queries in the comments section below. Thank you as always to Dr Laura for sharing her time and knowledge so generously, and thank you for reading. Previous entries: [HITS Thermal], [2013 FEI Veterinary Rules, Treatments, and Kissing Spine]
“Heart Attacks” and Sudden Death in Horses
Dr. Laura Werner
EKG of Ventricular Tachycardia in a horse
With the recent loss of Neveah and other wonderful horses in the event world and international show jumpers, such as Hickstead, sudden deaths during high profile competitions have been brought to our attention again. Heart attacks in humans are usually caused by underlying disease or blockage of the coronary vessels that supply blood to the heart itself, causing a fatal arrhythmia , heart attack or acute myocardial infarctions. Unlike humans, horses fortunately have much healthier diets and usually do not get blockage of these arteries or infarction of the heart muscle itself.
Many of these sudden deaths in horses are caused by aortic rupture or aneurysm. The aorta is the main vessel that carries oxygenated blood from the heart to the rest of the body. Tears or aneurysms can occur in this main vessel in the heart itself, the chest, or the abdominal cavity, causing a sudden, severe drop in blood pressure and death within a few seconds to minutes. Sometimes the pericardium (the sac around the heart), chest, or abdomen is filled with blood. Tears can occur within the vessel walls that can cause the horse to have an electrical disturbance or fatal abnormal rhythm of the heart, with resulting collapse and death. The cause is mostly unknown, but theories of older horses with a weakening of the vessels, copper insufficiency in the diet, and possible parasite migration, have all been proposed. Some horses may have underlying defects or leaky heart valves, for example, that have been previously undiagnosed. Often these events seem to be associated when a horse is jumping an obstacle, can be secondary to trauma from a fall at an obstacle, or even can occur when stallions are breeding a mare.
There are also cases of sudden collapse and death where no aneurysm or aortic rupture is found. The cause is unknown but many researchers believe that the horses may develop a fatal arrhythmia of the heart. Some horses may have underlying heart defects or disease that have been previously undiagnosed. These cases may be similar to young human adults at athletic events that have sudden collapse and death. Many of these human cases also have underlying heart defects or diseases that have been previously undiagnosed.
Researchers of the USEA Cardiovascular and Pulmonary Research program are working on collecting valuable information to help determine any causes and if there are any ways to pre-diagnose any problem before a tragic event occurs. These studies are voluntary at many of the larger three- day events and everyone’s participation is critical to help veterinary researchers find a cause and solution. An EKG (or measurement of electrical activity of the heart), echocardiograms (ultrasound of the heart), as well as drawing a blood sample before and after cross country to look at cardiac enzymes are some examples of the data being collected as part of the research. These tests are non-invasive, but essential for researchers to obtain at all levels of competitions. They are working on developing equipment that can record the rhythm and electrical activity of the heart while horses are galloping and jumping on cross country. Though an unfortunate topic, necropsy (or an autopsy for horses) examinations also provide valuable information to find any predisposing factors or links to horse fatalities.
I spoke with researchers Drs. Catherine Kohn and Mark Hart about the program. They are looking at some larger competitions hopefully over the summer to examine horses of all levels as they finish cross-country and record electrocardiograms or EKG ‘s. The more data that they can obtain, the closer they can get to find a cause. Dr. Mark Hart, a human cardiologist and avid supporter of eventing, said it best when I spoke with him, “ We owe it to our equine partners to try to identify any problems ahead of time.”