Ask Your Veterinarian: What Heart Scans Can Tell You, And What They Can’t

by | 05.21.2018 | 6:34pm

Secretariat, who was known for having an abnormally large heart

QUESTION: Some buyers at the upper end of the auction market are now including heart scans as part of their pre-sale vetting process. What can these scans tell buyers, and what don’t they tell us?

ANSWER: Heart scans, also known as echocardiograms, are used to create ultrasonographic images of the heart. Echocardiography allows visualization of the entirety of the heart. This includes the cardiac walls and interventricular septum (composed of cardiac muscle), the valves and chambers within the heart, and the large vessels that carry blood to and away from the heart.  Ultrasound facilitates accurate measurement of these cardiac structures and can be performed at different phases of the cardiac cycle (such as systole and diastole). By examining the heart throughout the cardiac cycle, determination of cardiac function indicators can be made. Some of these indicators of cardiac function include stroke volume, cardiac output, fractional shortening, and end-diastolic volume.

Many of us are familiar with racehorses storied to have famously large hearts—Secretariat and Eclipse being two primary examples. It has been theorized that the successes of these two legendary horses can be credited to the size of this organ. And there is reason to conclude that this is the case. The left ventricle is the most muscular cardiac chamber and is responsible for pumping oxygenated blood coming directly from the lungs out through the aorta to be delivered to the rest of the body. In human athletes that are trained for either endurance or strength, there is evidence that thickening (hypertrophy) of the left ventricular wall can occur with training. This structural change can lead to increases in stroke volume and cardiac output, which ultimately enhance a person’s oxygen carrying capacity. Studies have also demonstrated that these structural changes can occur in equine athletes in response to training. Electrocardiography was used in the 1970s to demonstrate that increased cardiac size is related to enhanced athletic performance.

Heart scans have become an important component of the sales process. The veterinarians who perform these scans have measured a large number of equine hearts and have as such amassed a large database of information. This information can be used to make recommendations on both the athletic and breeding potential for a horse. Because much of this data is proprietary information, there is a paucity of recent peer-reviewed literature available on the subject. However, many who have pursued this purchasing strategy have encountered success in using it. It must be emphasized that evaluating the heart in isolation from the rest of the body is really just “one piece of the puzzle”. The athletic potential of a sales horse often includes analysis of other factors, including genetics and musculoskeletal conformation, before a recommendation is made.

The use of echocardiography in horses is not limited to assessing athletic potential. Echocardiography is a critical tool in evaluating a horse’s heart for cardiac pathology. When performed for this reason, a heart scan is typically completed by a cardiologist or internal medicine specialist. The aim of an echocardiographic examination in this scenario is to gather information that will allow for diagnosis and treatment recommendations. Common indications for this type of heart scan include valvular leakage, stretching of the cardiac walls, and congenital defects. While any of these abnormalities can certainly affect athletic potential, they can also interfere with a horse’s longevity and even a horse’s safety to ride due to a potential for collapse. Just as in heart scans performed in a sales setting, the echocardiogram can be used by a specialist as “one piece of the puzzle”. Other diagnostic tools, such as physical examination, electrocardiography, and exercise testing, will aid a veterinarian in tracking progression of disease and formulation of a treatment plan.

Dr. Bill Gilsenan received his veterinary degree from the University of Pennsylvania in 2008. Following an internship at Colorado State University, he completed a residency in large animal internal medicine at the New Bolton Center—University of Pennsylvania. He became board certified in large animal internal medicine in 2012. He held a faculty position at the Virginia-Maryland College of Veterinary Medicine until joining the staff at Rood and Riddle Equine Hospital as an internal medicine specialist in 2015.