The Dutch National guideline on the prevention of thromboembolic complications in pediatric patients with congenital and acquired heart disease

In the developing heart of a child, blood must flow with a precise rhythm to deliver oxygen and sustain life. When a child is born with a heart that does not form correctly, or when the heart is damaged by disease, doctors often intervene with surgery or devices to restore that flow. These interventions are life-saving, but they introduce a new challenge: the risk of blood clots. A clot is a solid mass that forms when blood thickens and sticks together, much like a traffic jam in a river. If this jam occurs in a delicate heart chamber or a narrow vessel, it can block blood flow entirely or break loose and travel to the brain or lungs, causing a stroke or a lung blockage. For decades, doctors have used medicines to thin the blood and prevent these clots, but the rules for giving these medicines to children have been unclear. Most of what doctors knew came from studies on adults, yet a child's body processes drugs differently, and their heart conditions are often unique. Without clear, shared rules, a child in one hospital might receive a different treatment than a child in another, creating a patchwork of care that leaves families and doctors guessing.

To address this uncertainty, a team of experts in the Netherlands came together to create a single, national guide for preventing blood clots in children with heart disease. This group included heart specialists for children, blood experts, surgeons, and even a parent who has lived with congenital heart disease. They did not simply gather opinions; they conducted a rigorous search for every piece of scientific evidence available, looking for studies that compared different treatments in children. When they found high-quality evidence, they used it to build their advice. When the evidence was missing or weak, as it often was, they relied on careful reasoning and the collective experience of the group to fill the gaps. The result is a set of clear instructions designed to ensure that every child in the country receives the same, best possible protection against clots, regardless of which hospital they visit.

The team focused on seven specific situations where children are most at risk. The first situation involves children who need a temporary bridge to help blood reach their lungs. These bridges, called shunts, are surgically created connections that allow blood to flow from the body to the lungs. The experts found that as soon as a child wakes from this surgery, they should receive medicine to thin the blood immediately. This is usually done with an injection until the child can eat and drink again, at which point they switch to a daily pill. The goal is to keep the blood flowing smoothly through the new connection for as long as the shunt remains in place.

For children who have undergone a more complex series of surgeries to create a single pumping chamber for their heart, the rules become more nuanced. In the second stage of this repair, known as the Glenn procedure, the blood from the upper body flows directly to the lungs. Here, the experts recommend starting with an injection to thin the blood, then switching to a daily aspirin pill. However, if a child has other factors that make clots more likely, such as an irregular heartbeat or a history of clots, the doctors may choose a stronger type of medicine to thin the blood more aggressively.

The final stage of this single-ventricle repair is called the Fontan circulation, where the blood from the lower body is also connected directly to the lungs. This creates a unique environment where blood moves slowly and is prone to clotting. For the first six months after this surgery, the risk is highest, so the experts recommend using a strong blood-thinning medicine, either a traditional pill that requires regular blood tests to monitor its strength or a newer type of pill that does not. After six months, if the child has no other risk factors, they can often switch to a milder daily aspirin. If the child still has high-risk factors, they should continue with the stronger medicine.

When a child has a heart muscle disease, the advice depends on how hard the heart is pumping. If the heart is pumping with less than thirty percent of its normal strength, the risk of a clot forming inside the heart is significant. In these cases, the experts recommend a daily aspirin to prevent clots. If the heart's pumping strength improves and stays above thirty percent for three months, the daily aspirin can be stopped. This distinction is crucial because it avoids giving unnecessary medicine to children who are no longer at high risk.

For children who have had a hole in their heart closed with a device inserted through a vein, the risk is temporary. The metal mesh of the device can attract clots while the body heals around it. The experts recommend giving a blood-thinning injection or an aspirin pill immediately after the procedure, followed by six months of daily aspirin. This covers the period while the body grows a smooth layer of tissue over the device, making it safe from the inside.

Stents, which are tiny metal tubes used to hold open narrow blood vessels, also require careful management. The advice here depends entirely on where the stent is placed and how fast the blood is flowing. In areas where blood rushes quickly, such as the main arteries, a single daily aspirin for three months is usually enough. However, in areas where blood moves slowly or where the stent is very narrow, the risk is higher. In these cases, the experts suggest using two types of anti-clotting medicines together for a period of time to provide extra protection. For stents placed in critical areas like the ductus arteriosus, which connects the heart to the lungs, the two-medicine approach is continued until the stent is removed.

Finally, for children with artificial heart valves, the type of valve dictates the treatment. If a child has a mechanical valve, which is made of metal and plastic, they must take a strong blood-thinning medicine for the rest of their lives. The dose is carefully adjusted based on regular blood tests to ensure it is strong enough to prevent clots but not so strong that it causes bleeding. If a child has a biological valve made from animal tissue, the need for strong medicine is usually temporary. For valves in the lower part of the heart, strong medicine is recommended for three months while the tissue heals. For valves in the upper part, a daily aspirin or the strong medicine is used for the same three-month period. After that, most children with biological valves do not need long-term blood thinners.

Despite these clear recommendations, the authors are honest about the limits of their work. For many of these situations, there are very few studies that directly compare different treatments in children. Much of the advice is based on what is known about adults or on the logical understanding of how blood flows and clots. The experts acknowledge that while their guidelines provide a much-needed standard, they are built on a foundation that is still being strengthened. They call for more research to find the best treatments for every specific child, hoping that future studies will replace these careful estimates with solid proof. Until then, this guide serves as a vital map, ensuring that children with heart disease receive consistent, thoughtful care that balances the danger of clots with the safety of the medicines used to prevent them.