A puppy born with a rare heart condition—Tetralogy of Fallot—got a second chance at life, thanks to a collaboration involving a visiting veterinary heart surgeon and the cardiology and surgery teams at the University of Illinois Veterinary Teaching Hospital.
Odyssey, an Australian shepherd, was only three months old and newly placed in a foster home when he started showing signs of a problem. After exercising, he began breathing heavily and had trouble standing up on his own. He would lean up against the fence just to stay standing and was having uncontrollable tremors.
Dr. Todd Sumerfield, a resident pursuing specialization in veterinary cardiology at the College of Veterinary Medicine, explains how the Illinois team diagnosed Odyssey’s condition and arranged for his surgical intervention—a modified Blalock-Taussig shunt—that had never before been performed at the university hospital.
Diagnosing Tetralogy of Fallot
Noticing Odyssey’s post-exercise behaviors, his foster owners took him to their veterinarian, who identified a loud heart murmur and referred the case to the cardiology team at Illinois in August 2023.
“An echocardiogram was performed, as well as a packed cell volume,” Dr. Sumerfield says.
An echocardiogram allows doctors to visualize the heart as it beats within the patient. In Odyssey’s case, the echocardiogram identified all the defects associated with a condition known as Tetralogy of Fallot.
Tetralogy of Fallot is an uncommon, congenital heart disease. It occurs when the patient has four—thus ‘tetralogy’—concurrent abnormalities.
Dr. Todd Sumerfield | Cardiology Resident
Packed cell volume measures the amount of red blood cells within the blood of the patient. When an animal has a heart condition leading to decreased oxygen in the blood, as in Tetralogy of Fallot, the body produces more red blood cells in an attempt to deliver more oxygen to the body’s tissues. Although the echocardiographic signs of Odyssey’s condition were severe, his packed cell volume was within the normal range, at 44%.
Dr. Sumerfield points out this normal finding “underlines that Odyssey was doing better than most dogs with this condition at the time of his diagnosis.”
What Is Tetralogy of Fallot?
“Tetralogy of Fallot is an uncommon, congenital heart disease,” Dr. Sumerfield says. “It occurs when the patient has four (thus ‘tetralogy’) concurrent abnormalities.”
To understand these abnormalities, it helps to recall how blood flows through the body. Blood is pumped from the heart’s right atrium to its right ventricle and then, via the pulmonary artery, to the lungs. After receiving oxygen from the lungs, the blood then travels back to the heart into the left atrium. From there it is pumped to the left ventricle, which pushes the blood into the large blood vessel called the aorta and on to the rest of the body.
After delivering its oxygen to tissues and organs, the deoxygenated blood travels back to the right atrium, where the cycle begins again.
In a Tetralogy of Fallot case, the animal is born with a narrowing of the pulmonary valve, which controls blood flow from the right side of the heart to the lungs. The animal also has a ventricular septal defect, which is an inappropriate opening in the septum, or wall, that separates the left and right ventricles. Additionally, the aorta, instead of being positioned over the left ventricle, sits over the left and right ventricular outflow tracts. In that location, the aorta accepts blood from both the left and right ventricles, sending a mixture of oxygenated and deoxygenated blood to the body’s tissues. Lastly, the right ventricle of the heart is abnormally thickened.
Heart Defects Lead to Low Oxygen
Dr. Sumerfield continues, “The narrowing of the pulmonary valve obstructs the outflow of the blood to the lungs. As a consequence, the right ventricle must pump harder to force the same volume of blood through a narrowed orifice.” Because the right ventricle functions just like any other muscle, as it “works out” harder, the muscle grows and thickens.
The ventricular septal defect means deoxygenated blood found in the right ventricle can flow into the left ventricle, where it is pushed into the body without having passed by the lungs to take on oxygen.
All four abnormalities are interrelated and contribute to the problem of low oxygen levels in circulating blood. Abnormally low circulating oxygen led to Odyssey’s exercise intolerance: he was unable to oxygenate his body properly while playing in the yard, making him easily tired.
In response to low oxygen in the body, the bone marrow receives instructions to produce more red blood cells. “When there are inappropriately high numbers of red blood cells in circulation, the blood can become more viscous, or thick. This change, in turn, can impair blood flow to the brain and lead to neurologic signs and even seizures.” Or, in Odyssey’s case, tremors.
Surgery: Modified Blalock-Taussig Shunt
Once Odyssey had a diagnosis, the next step was to determine a treatment approach. It is not typical to treat a patient with Tetralogy of Fallot with medications until there is evidence of heart failure. Phlebotomy (physical reduction of the number of red blood cells) and balloon valvuloplasty (a minimally invasive procedure to widen the pulmonary valve) were considered but both approaches had limitations.
Another option was surgical intervention using the modified Blalock-Taussig shunt. “This surgery involves redirecting mixed arterial blood flow back to the lungs for another pass at oxygenating the red blood cells,” explains Dr. Sumerfield. “The procedure is performed under general anesthesia via a left thoracotomy. A synthetic tube is placed to allow arterial blood to flow to the lungs. The goals of the procedure would be to improve forward flow through the lungs and have a higher percentage of oxygenated blood circulating at any one time.”
A shunt can be thought of as an alternate path, or a turn in the road. It provides the blood with somewhere else to go. Shunts that arise naturally may be present at birth or may be “acquired” by the body after certain stressors. However, in this surgery, an artificial shunt is placed to redirect blood from where it was going into the body (with no oxygen supply) back to the pulmonary artery (which feeds into the lungs) so it can receive its oxygen load.
Odyssey Still Going Strong
Although Odyssey’s clinical signs were not severe, they were getting progressively worse. After his fosters decided to pursue the modified Blalock-Taussig shunt surgery, the University of Illinois cardiology service conferred with surgeons across the country, and Dr. Brian Sutherland, a veterinary cardiothoracic surgeon from the University of Georgia, agreed to perform the surgery. The modified Blalock-Taussig shunt surgery was performed at the Veterinary Teaching Hospital in September 2024, when Odyssey was 1 year, 4 months old. The surgery was successful and Odyssey recovered well.
After two days in the hospital, Odyssey was sent home with pain relievers, sedation, and a strict exercise restriction for two weeks. He was also given six months of blood thinners to decrease the risk of a clot forming in the newly implanted synthetic shunt.
“If left untreated, most dogs with Tetralogy of Fallot will die before reaching one year of age,” says Dr. Sumerfield. “There is limited information regarding life expectancy in dogs who have had the modified Blalock-Taussig shunt procedure, but one journal article found that patients lived for an average of 7 years after the procedure.”
Odyssey is currently almost two years old and continuing to improve. His ability to exercise has improved significantly and his tremors have resolved. Recent rechecks have shown that Odyssey’s shunt is still working.
His fosters have formally adopted Odyssey and are hoping Odyssey lives a long and happy life.
By Lauren Bryan
