Understanding Pediatric Cardiomyopathy: How Does Cardiomyopathy Affect Children?

Pediatric cardiomyopathy is a rare but dangerous disease of the heart muscle that may lead to life-threatening events. It affects approximately one out of 100,000 children under the age of 18, but remains the leading cause of heart transplant in children.

For every child diagnosed with cardiomyopathy, another is believed to suffer from it but remain undiagnosed — since not everyone develops symptoms. Even without symptoms, a child still has a risk of premature death. In cardiomyopathy, the heart muscle suffers structural changes that may reduce its ability to pump blood, which can lead to complications like heart failure or sudden cardiac death.

Which types of cardiomyopathy affect children and what causes them? 

Cardiomyopathy (CM) can have many possible causes, ranging from gene mutations to viral infections, toxins, and underlying diseases such as diabetes mellitus. However, in 67 percent of CM cases in children, the cause remains unknown (also called idiopathic CM). Regardless of the cause, in the majority of cases in both children and adults, changes of the heart muscle are consistent with one of four main types of CM: dilated, hypertrophic, non-compaction or restrictive.

Dilated cardiomyopathy (DCM)

Symptoms can vary significantly, ranging from asymptomatic to cardiogenic shock. However, most of the children and infants (between 75 and 80 percent) present with symptoms of heart failure. 

For infants and young children, symptoms include:

• Irritability
• Poor feeding (prolonged feeding time, consuming smaller volumes or vomiting)
• Growth failure
• Persistent cough
• Short and shallow breathing (tachypnea)
• Increased liver (hepatomegaly)
• Pale skin (pallor)

Older children have more prominent abdominal symptoms like increased liver and ascites (accumulation of fluid in the abdomen), abdominal pain, shortness of breath and difficulties with physical activity.

Unfortunately, treatment for DCM in children is limited and the prognosis is often poor. Around 40 percent of children with DCM undergo heart transplantation or die within two years of being diagnosed. 

One study that analyzed 1400 cases of pediatric DCM found that 66 percent were of unknown cause. Other causes included viral infections, genetic causes, inborn errors in metabolism and neuromuscular disorders such as Duchenne and Becker muscular dystrophies. Among those, children with neuromuscular disorders had the highest risk of complications and death. 

Being male or African American is a risk factor for DCM associated with worse outcomes. Additionally, children under the age of six are three to four times more likely to recover. Unlike adults, up to 45 percent of children regain normal heart function. Registries from the United States, Australia, and Europe show that the transplant-free survival rate is between 60 and 75 percent.

Hypertrophic cardiomyopathy (HCM)

In many cases, children and infants with HCM have no symptoms. If they do show symptoms, they might be one of the following:

• Excessive sweating in infants 
• Poor appetite and/or growth failure
• Fatigue
• Wheezing
• Abdominal pain
• Fainting (syncope)

In some cases, complications like sudden death can occur. However, overall survival and transplant-free survival is better for children with HCM than all other types of CM.

Restrictive cardiomyopathy (RCM)

The ventricles are the lower chambers of the heart that fill with blood coming from upper chambers. Heart chambers fill with blood in their relaxed state, while a contraction causes the blood to be pumped out of the chamber. When the ventricle becomes stiff it can’t fully relax, which means that it can’t fully fill with blood. In other words, the blood flow through the heart is restricted. 

Compared to other types of CM, RCM has the highest mortality rate in children. The cause is unknown in most cases, while some known causes include amyloidosis (a disease in which amyloid fibers accumulate and cause damage), inborn errors of metabolism, sarcoidosis (inflammatory disease that affects many organs in the body, but mainly lymph glands and lungs) and scleroderma (hardening and tightening of the skin and connective tissues).

Left ventricular noncompaction cardiomyopathy (LVNC)

LVNC is still a somewhat controversial question in the medical community since not all doctors agree that the changes happening in LVNC are a distinct type of CM. For this reason, there is still no official diagnostic criteria or treatment for this cardiomyopathy. There are seven different subtypes, associated with different outcomes.

Trabeculations in the ventricle walls can disrupt normal electrical signaling in the heart and lead to life-threatening arrhythmias (irregular heartbeats). The largest study of LVNC in children showed that nearly 40 percent of the patients were infants, while 25 percent had a family history of cardiomyopathy. One-third of patients had some type of arrhythmia, while one-fourth had a history of cardiomyopathy in the family.

How is pediatric cardiomyopathy treated?

Treatment of cardiomyopathy depends on the type, its cause, how far the disease has progressed, and the symptoms that the child is showing. The main goal of treatment is to ease the symptoms, prevent complications, and stop the disease from progressing further. While some children just need consistent monitoring and lifestyle changes, others will require medications that can significantly improve their quality of life.

Most children who are hospitalized for cardiomyopathy present with heart failure. In children with heart failure who are also at risk of dangerous arrhythmias, implantable devices might be considered. If heart failure has progressed too far for medications and implantable devices to be effective, heart transplant presents as the last option.

In secondary cardiomyopathies, where CM happens as a result of another underlying disease, the condition improves with treatment of the underlying disease. More research is needed to establish effective therapy designed especially for children, especially now when it's becoming apparent that the molecular mechanisms and gene expression are different than in adult CM.