Your Horses Health:

Diagnosing Equine Cardiovascular Disease

By Anne Desrochers, DMV, Diplomate ACVIM

A horses heart may be the most important muscle in its entire body. As the pump for the cardiovascular system, the heart supports a closed system of arteries, veins, and capillaries. These blood vessels are responsible for the rapid delivery of nutrients and oxygen to all of the horses tissues and organs. In addition, the cardiovascular system plays a crucial role in the elimination of waste products, distribution of hormones, immune response, blood clotting, and body temperature regulation.

Heart disease can affect horses of all ages and breeds. It can be congenital (present at birth) or acquired (developed later in life). The most common abnormalities involve the valves and muscle of the heart. Cardiac problems can manifest in different ways, including poor performance, exercise intolerance, presence of a heart murmur or murmurs, irregular heartbeats, distended veins, limb swelling, poor growth, weakness, or collapse. The most frequently diagnosed cardiac abnormalities in equine medicine include congenital anomalies, degenerative or infectious valve disease, diseases of the muscle or external envelope of the heart (pericardium), congestive heart failure, and irregular heart beat (arrhythmias).The importance of the heart cannot be overstated, and any disease affecting it should be promptly diagnosed and monitored carefully.

In-depth evaluation of horses suffering from heart disease typically requires specialized diagnostic aids to determine the underlying problem and to recommend appropriate treatment. Evaluation of horses for cardiac conditions includes a complete examination, including a physical examination to detect the presence of heart murmurs and a resting electrocardiogram (ECG), a resting electrocardiogram (ECG) to examine the electrical activity of the heart. Sometimes radiographs (x-rays) are taken to examine the size and shape of the heart. A complete cardiac ultrasound evaluation (echocardiogram) can also be performed to examine the valves, muscle, and heart function.

The echocardiogram uses realtime ultrasound techniques to examine the size, structure, shape, and function of the heart in motion. Color-flow ultrasound and other Doppler technologies are also used to evaluate speed and patterns of blood flow within the heart and large vessels connected to the heart, such as the aorta and pulmonary artery. With digital image storage of the echocardiogram evaluation, veterinarians can easily review cases and follow their progression over time. Archiving of the cardiac examinations also allows the medical experts to share this information with others involved with the case.

Cardiac monitors allow veterinarians to acquire continuous electrocardiographic recordings over a 24-hour period or several 24-hour periods. This technique is used with critically ill patients for identification and monitoring of arrhythmias that only occur a few times during the day, quantifying the severity of an arrhythmia, or for evaluation of the efficacy of drug therapy. Cardiac evaluations may also be performed on horses that exhibit poor performance. Although musculoskeletal and respiratory system diseases are more common causes of reduced athletic performance, certain heart conditions can also lead to exercise intolerance. In some cases, an exercise test is crucial for the detection of exercise-induced cardiovascular dysfunction. Electrocardiography using a radiotelemetry unit can be performed during a high-speed treadmill examination or an under saddle evaluation to learn about the heart rate and rhythm during exercise. A functional assessment of the heart can then be performed in the immediate post-exercise period with echocardiography. Treatment for some arrhythmias are available, and monitoring heart function can be essential for horses with murmurs to make sure they are not a safety risk for themselves or their riders.Appointments for cardiology consultations are usually made on an outpatient basis. Patients with acute or more severe cardiac conditions require immediate attention. Contact your veterinarian with any questions or concerns you have with regard to your horses heart health.Dr. Desrochers is a clinical assistant professor in equine internal medicine at Virginia Techs Marion duPont Scott Equine Medical Center, which is a premier, full-service equine hospital located in Leesburg that offers advanced specialty care, 24-hour emergency treatment, and diagnostic services for all ages and breeds of horses. One of three campuses that comprise the Virginia-Maryland Regional College of Veterinary Medicine, the Center and its team of equine specialists are committed to providing exceptional treatment to patients, superior service to clients, and cutting-edge research to the equine industry. For additional information, visit www.equinemedicalcenter.net.