On July 9, a human interventional cardiologist and an equine veterinarian in Lexington, Ky., successfully completed the first step of a landmark procedure to repair a heart problem in a 5-month-old Thoroughbred colt called a ventricular septal defect (VSD). At best, the problem could cost him his athletic career if not corrected. At worst, it could cost him his life.

The colt's defect involves a hole in the wall (called the septum) between the left and right ventricles, or lower chambers of the heart, between the origins of the aorta and pulmonary artery. The septum stopped growing before the area could close up during fetal development (the defect is not inherited). Normally, there is no communication between these two chambers so no blood flows between them, but this foal's defect allows a certain percentage of blood flow to be shunted from left to right instead of all of it passing out into the aorta as in the normal heart.

The defect disturbs pressures in the chambers and causes a loud heart murmur, which was detected when the foal was being evaluated for a fever caused by an unrelated problem. John Gurley, MD, associate professor and director of the University of Kentucky catheterization lab, used a heart catheter (passed through the jugular vein) and a special ultrasound probe to view the colt's heart from the inside (an intracardiac procedure). Debbie Creighton, of Siemens Medical Solutions, provided the equipment for the procedure and gave assistance.

Fairfield Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, the veterinary internist who is treating the foal at Hagyard-Davidson-McGee veterinary hospital, asked Gurley if he would attempt a procedure to correct the problem. Bain says he sees about eight to 10 horses a year with this type of defect. While some have successfully performed with these defects, the great majority eventually show the long-term effects of heart failure.

In horses, just as in children, VSDs can sometimes self-repair, but this colt's hole is in a non-muscular area of the septum and is highly unlikely to close on its own, says Bain.

Gurley notes, "The (heart) catheter and imaging skills do not currently exist in veterinary cardiology." He viewed the hole with the foal sedated and standing, the first time this has been done in a horse; the hole measured about 1 cm in diameter. (Transesophageal ultrasounds, via the esophagus, the tube that leads from the mouth to the stomach, have been done, but not intracardiac exams.) Gurley and Bain think that installing a closure device via catheter to "plug" the hole would be feasible without interfering with the nearby valves that prevent backflow of blood. Open-heart surgery to correct heart problems is impossible in a horse due to its narrow-chested anatomy.

Engineers will decide what type and size closure device, called an amplatzer, will suit the foal. Amplatzers are made of a nickel-titanium alloy and fabric, and once installed, heart tissue covers the margins of the device, creating a smooth wall of endothelium (organ lining) where the hole once was and sealing the defect. In humans, holes up to 38 mm (about 1 1/2 inches) have been repaired.

Gurley and Bain hoped to install the device soon, because the colt is growing quickly and these operations are more successful on younger, growing individuals. The device will likely cost about $3,000. Each ultrasound probe (a new one must be used for each procedure to avoid contamination) costs around $2,500. "Fortunately, the animal's value and potential are of the level that the owners are willing to pursue cutting-edge technology in an effort to correct the problem. It may not work, but they are willing to give it a try," says Bain. For more images and video, visit www.TheHorse.com/ViewArticle.aspx?id=2589.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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