Cardiologists at Children’s of Alabama are using exercise training to measure Fontan patients’ health.
Children born with single-ventricle heart disease undergo multiple surgeries before age 6, ending with the Fontan procedure, which redirects blood from the inferior and superior vena cava to the pulmonary arteries. This allows blood returning from the body to skip the overworked single ventricle and instead flow directly to the lungs to receive oxygen. While the surgeries have improved survival for these patients, long-term outcomes are still poor. Now, clinicians at Children’s of Alabama are honing in on exercise as an important way to track and improve their quality of life.
“The Fontan operation is one of the most complicated congenital heart procedures we do,” pediatric cardiologist Camden Hebson, M.D., said. “Even with the best outcomes, there’s a shortened lifespan. Many patients start to have major complications by the time they’re in their 20s and 30s, such that it’s pretty unusual for patients to be still living, especially symptom free, in their 50s.”
The fundamental challenge lies in the procedure’s physiology. In normal hearts, the right side actively pumps blood to the lungs. Because the Fontan operation eliminates this pump, it creates a passive flow system that, while life-sustaining, leads to increased venous pressure throughout the body, particularly in the abdomen and legs.
“The pie in the sky for these patients is getting some sort of pump into them to better push the blood to the lungs,” Hebson said. “There’s all sorts of ideas out there of how to do that, like mechanical implantations and valves. But human beings have our own intrinsic pump that we can maximize: the skeletal muscle pump in our legs, which push venous blood out of the legs back up toward the lungs.”
People who don’t exercise a lot have weak skeletal muscle pumps, he said, which increases the blood pooling and pressure on vital organs, resulting in complications and early mortality. “People who have the strongest legs, the most physically fit legs, the best muscle tone are going to actuate their skeletal muscle pump as much as possible,” he said.
Yet, families and medical teams have traditionally taken a protective approach with these children and limited physical activity, Hebson said. “In some ways, that’s actually a negative, because then these kids are less active than the other kids their age,” he explained. “They exercise less, and then it actually makes the problems of the physiology more likely to occur in their 20s and 30s.”
The link between exercise and better outcomes comes from studies on long-lived Fontan patients called “Super-Fontans.” While the exact reasons for their success aren’t fully understood, physical fitness appears to play a crucial role.
To better understand the effects of exercise on the cardiovascular system of Fontan patients, Hebson and his team use metabolic exercise testing to track heart rate and blood flow during physical activity. This not only helps identify potential treatment targets and provide reassurance about exercise safety, but serves as an early warning sign for complications. For instance, it can reveal issues that aren’t usually apparent at rest, such as the need for stenting the Fontan conduit based on limitations shown in exercise capacity.
“Sometimes, you just need to take the car out on the road and see how it drives,” he said, comparing traditional resting assessments to testing patients during exercise. “For most patients, in particular Fontan patients, your cardiovascular system is what limits your ability to exercise. So how much exercise you can do at any given time is really just feedback on how well the heart works.”
“So we need to encourage our patients to be ahead of the curve on how much exercise they do to keep their legs strong,” Hebson continued. “Not only are they getting the benefits that everybody gets from exercise, they are actually improving the venous return to their heart and their cardiac output as a result.”
“Anything that can be done to improve these patient’s lives and long-term outcomes would be a big deal,” he added.