What to Know About Hypertrophic Cardiomyopathy in Kids

The human heart is a muscle, but it’s also a kind of complicated balloon—a balloon that fills and empties roughly 60 to 100 times every minute, and several billion times during the course of a lifetime.

Among people with hypertrophic cardiomyopathy, the walls of the heart muscle are abnormally thick. This thickness can interfere with the heart’s normal filling-and-emptying operation. “If you think of a balloon made with super-thick rubber, you have to blow harder to fill it, and it’s the same with a hypertrophic heart,” says Dr. Daphne Hsu, professor of pediatrics and medicine at Pediatric Heart Center of Montefiore/Einstein in New York. 

Hypertrophic cardiomyopathy is the most common form of genetic heart disease in the U.S. and the second commonest heart-muscle disease among children. Roughly 1 out of 500 adults is thought to be living with it. It’s unclear exactly how many American kids have the condition, but experts estimate its prevalence somewhere in the neighborhood of three cases per 100,000 children. That makes it a very rare disease. However, despite its uncommonness, hypertrophic cardiomyopathy is one of the leading causes of sudden death in young athletes. While it’s true that the condition can in some cases be life-threatening, it can also be almost very mild. “A lot of patients do not have many symptoms and their quality of life is good,” Hsu says.

Here, she and other heart experts explain the basics of hypertrophic cardiomyopathy in children—including the different forms of the condition, how it’s identified and treated, and how it affects a young person’s health as they mature into adulthood. 

Types and causes 

Hypertrophic cardiomyopathy, like most other diseases, can range from mild to severe. In some cases, the heart’s functioning is only minimally impaired—if it’s impaired at all. In other cases, however, the heart’s ability to function properly may be significantly disturbed or weakened.

While all cases of hypertrophic cardiomyopathy involve abnormal thickening of the heart muscle, this thickening may or may not cause obstructions (blockages). In some cases, hypertrophic cardiomyopathy leads to heart rhythm problems (aka arrhythmias), and it can also disturb the way blood flows into and out of the heart’s chambers. Put another way, two children who both have hypertrophic cardiomyopathy may nonetheless have very different experiences and require very different types of treatment.

The underlying causes of hypertrophic cardiomyopathy are similarly diverse. In most adults, and likewise in many children, the condition stems from genetic abnormalities. “There are many, many genetic mutations associated with hypertrophic cardiomyopathy,” Hsu says. (They number in the dozens.) While experts have identified a lot of the mutations that cause hypertrophic cardiomyopathy in adults, the condition is not as well-mapped in kids. “We’re learning more about [these mutations] and we’re working on better techniques to measure them, but right now we don’t know most of them,” she says. While these mutations may be inherited from one’s parents, that’s not necessarily the case. “Sometimes genetic mutations occur spontaneously,” Hsu says. “Often if we do testing, we don’t find the [hypertrophic cardiomyopathy] mutations in either of the parents.”

Apart from mutations that specifically cause hypertrophic cardiomyopathy, the condition can also develop as a complication of a metabolic disorder. “Infants and very young children can have it because the heart muscle’s metabolism is not right, meaning there’s an accumulation of things like sugars that make the heart muscle thicker,” she explains. In these cases, hypertrophic cardiomyopathy is often just one aspect of a broader and systemic illness that affects the brain, the liver, and other organs. According to research in the journal Heart, these cases represent less than 10% of all childhood hypertrophic cardiomyopathies, and they’re almost always recognized at birth, as opposed to later on during childhood or adolescence.

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Living with hypertrophic cardiomyopathy

The main symptoms of hypertrophic cardiomyopathy are shortness of breath, fatigue, chest pain, heart palpitations (a fluttering feeling), and light-headedness (often just after standing or sitting up). These symptoms may be mild or unnoticeable. They may also be moderate or severe. “What life looks like depends on whether a child has signs of heart failure or arrhythmia, but heart failure is not very common,” Hsu says. In many cases, symptoms become more noticeable following physical activity; exercise causes the heart to beat faster and pump more blood, and this exertion can make hypertrophic cardiomyopathy worse. 

While sudden cardiac death is possible, the risk of this happening varies from one child to the next. “The risk of cardiac death among all children with hypertrophic cardiomyopathy is approximately 1.5% per year, but some kids are at greater risk than others,” says Dr. Juan-Pablo Kaski, a pediatric cardiologist and director of the Centre for Paediatric Inherited and Rare Cardiovascular Disease at University College London. “There are clinical models we can use to estimate the risk for a particular child.” 

Depending on that risk, some kids with the condition may be advised to avoid sports or strenuous exercise. But that’s not always the case. “Most children can do all the things their peers would do,” Kaski says. “The only difference is they need to come to a clinic every six months to a year for a checkup.” 

There was a time when pretty much all children with hypertrophic cardiomyopathy were advised to avoid vigorous exercise, but the thinking on that has changed. “There’s been a trend to have more freedom for sports participation,” says Dr. Jeffrey Geske, a cardiologist and hypertrophic cardiomyopathy specialist at the Mayo Clinic in Minnesota. This shift has happened in part because experts have become more adept at identifying the people who are most at risk for sports-related complications or death. “We also know that sports and activities are good for people,” Geske adds. “So it’s about balancing the risks and the benefits.”

Hsu echoes these sentiments. “It’s not healthy for a child’s body or mind to be restricted from normal activities and sports,” she says. “There are many kids with hypertrophic cardiomyopathy who play sports, but the decision to allow a child to play requires extensive discussion between the cardiologist and family.”

It’s also worth noting that sudden cardiac death does not always occur as a result of exercise. “Most children who die don’t die during exercise,” Kaski says. “They die during normal day to day activities.” Again, while the risk of sudden death is elevated in kids with the condition, it is nonetheless uncommon.

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Diagnosis and treatment

Hypertrophic cardiomyopathy is usually identified and diagnosed in one of three ways. “One is through family screening,” says University College London’s Kaski. In these situations, a child’s parent or relative is diagnosed with the condition, and follow-up screening reveals that the child also has it. “The second way is that a child has symptoms—so things like breathlessness during exercise, chest pain or palpitations, or near-fainting episodes—and that triggers a referral [to a heart specialist],” he says. “The third way is through incidental finding.” In these cases, health care providers spot the condition while performing routine medical exams, or while looking for something else. 

Once the condition is diagnosed, Mayo’s Geske says that treatment is often dictated by a person’s symptoms. “If somebody has no symptoms, then often no treatment is needed beyond some lifestyle modifications,” he says. These lifestyle changes may or may not include avoiding heavy exercise. Kids (and adults) with the condition are also usually advised to drink plenty of water or fluids because dehydration can make symptoms worse, Geske says. A healthy diet and regular exercise are also recommended. 

The symptoms of hypertrophic cardiomyopathy, whether mild or severe, tend to stem from two particular complications: heart arrhythmias and heart failure. Heart failure happens “when the heart can’t fill or pump out as well as it should, and the heart can’t supply the body with the blood it needs,” Hsu says. Heart arrhythmias happen when the hypertrophied muscle causes electricity to travel through the heart in an abnormal way, and as a result the heart may have unusual rhythms.”

Doctors treat these complications with medications, surgical procedures, and/or implanted heart devices. “So if there’s heart failure, we have drugs that help the heart fill and empty better,” she says. These include beta blockers, calcium-channel blockers, and other drugs that are also used to treat heart failure in adults. Medications tend not to work well for heart rhythm problems, she says, and so these arrhythmias—if severe—may require surgical intervention or the implantation of a pacemaker. (Hsu says this isn’t as common in kids as it is in adults.) 

Hypertrophic cardiomyopathy can also block the flow of blood through the heart. These blockages usually require surgical intervention. In rare cases, a heart transplant may be necessary. “The ultimate treatment is taking out the heart and giving a new one, and this works well—people do well after a transplant,” Hsu says. 

Long-term outlook

Experts say the long-term prognosis for a child with hypertrophic cardiomyopathy can be hard to pin down. Some go on to live long lives free of major symptoms. “The vast majority, I would say, have a good quality of life and good life expectancy,” Kaski says.  

However, complications such as heart failure or arrhythmias, even if mild during childhood and adolescence, can grow worse during adulthood. “The progression [of heart complications] seems to be more quick when hypertrophic cardiomyopathy is diagnosed in childhood,” he says. “So the thickening of the heart muscle or abnormal heart rhythms—all that tends to happen more quickly.” 

Hsu says that kids with the condition may be at greater lifelong risk for heart trouble, although she says this is more a matter of educated guesswork than established fact. “We don’t have a database going back 50 or 100 years, so we really don’t know a lot about long-term outcomes,” she says. “In general, we know if you have heart disease as a child, you usually have more severe disease as you get to 40 or 50 and beyond.” But every patient is unique. 

Overall, experts say the situation for a majority of kids with hypertrophic cardiomyopathy is far from dire. In fact, a lot of kids who have it may never even know about it. “When a patient is first diagnosed, you go and Google this condition and a lot of scary stuff shows up,” Geske says. “But most people with this disease have a normal life span.”

Experts are learning more and more about the condition every day. While prospects for most kids with hypertrophic cardiomyopathy are already good, they’re sure to improve as medical science’s understanding of this disease expands and deepens in the years to come. “We now have the ability to recognize people at high risk, and we have more effective interventions,” Geske says. Things are all moving in the right direction.