Overview 

The heart is divided into four compartments or chambers: two atria (upper chambers) and two ventricles (lower chambers). Conditions that affect the shape, size, heartbeat, or function of any of these compartments are diverse, and some of them fall under the category of cardiomyopathies.¹

Cardiomyopathies are diseases of the heart muscle. These conditions can affect how the heart develops and functions, altering its shape, the way it pumps blood, and the electrical system that controls the heartbeat. The causes are diverse and include infections, exposure to toxins, genetic mutations (changes in the DNA sequence), tachycardias (irregularly fast heartbeat), or can be symptoms of metabolic or neuromuscular disorders.²

These heart conditions in children are rare and occur in approximately 4.8 out of 100,000 infants and 1.3 out of 100,000 children under 10 years old.³ Children under the age of two are especially implicated, with this being the age group with the highest incidence. Although heart conditions are generally rare in children, understanding the signs and symptoms at an early stage can improve outcomes. 

This article will explore various types of paediatric cardiomyopathies, the signs and symptoms, diagnosis and treatment.

What is cardiomyopathy in children?

The heart is the pump that drives blood through blood vessels. Cardiomyopathies can weaken, thicken, or stiffen the heart muscles due to fibrosis, which creates scar-like tissue, hindering the heart's ability to pump blood effectively.

In children, there are various types of cardiomyopathies, with the most common being dilated and hypertrophic cardiomyopathies. Other types, like restrictive and left ventricular non-compaction cardiomyopathies, are less common.² Possible causes of altered heart function in children include genetic predisposition and infections, among others. If the doctor suspects cardiomyopathies, they may order some tests such as:

• Blood tests
• Chest X-rays
• Electrocardiogram (ECG)
• Cardiac magnetic resonance (CMR)
• Exercise ECG or ‘stress test’

Cardiomyopathy types in children

Dilated cardiomyopathy

In this type of cardiomyopathy, the main pumping chamber of the heart, the left ventricle, and sometimes also the right ventricle, becomes dilated (stretched bigger) and therefore weaker. Because of these changes, the heart can not pump blood as strongly as it should to the rest of the body.

Causes

Dilated cardiomyopathies are the most common type in children and occur in 1 in 156,250. In most cases, the causes are unknown or ‘idiopathic’. Some possible causes for this condition are genetic. Approximately 40% are inherited, resulting from mutations in around 110 genes that control the heart’s muscle function.

Other possible causes of dilated cardiomyopathy include infections like viral myocarditis, autoimmune diseases, systemic disorders, toxins (including those from chemotherapy),  metabolic and nutritional alterations, and neuromuscular diseases (such as Duchenne/Becker muscular dystrophies).^4,5

Symptoms and signs 

Most children with dilated cardiomyopathy show signs of heart failure.^4,2 This can look like:

• Breastfeeding difficulties
• Swelling of the lower limbs (oedema)
• Difficulties breathing
• Tiredness 
• Poor growth (sometimes called growth faltering)
• Racing heartbeat (tachycardia)

Diagnosis and outcomes

Children with a family history of heart conditions can be diagnosed in routine screening before any symptoms appear. Dilated cardiomyopathy is the most prevalent reason for heart transplantation in children because of its link to heart failure.

Hypertrophic cardiomyopathy

In this type of cardiomyopathy, the heart’s muscles become thickened (hypertrophic), making the heart less contractile and therefore harder for it to pump blood to the entire body. Hypertrophy of the left or both left and right ventricles is observed at diagnosis. 

Causes

Hypertrophic cardiomyopathy in children is found in 25 - 42% of cases and is the second most common subset of cardiomyopathy. In 60% of cases, genetic mutations are observed.⁴ 

The severity of disease presentation can vary in grade between individuals in the same family with this heart condition. There are some syndromes associated with this cardiomyopathy, like Noonan syndrome and Friedrich’s ataxia.⁵

Symptoms and signs

Common symptoms observed in hypertrophic cardiomyopathy include:

• Intolerance to exercise
• Chest pain (angina)
• Palpitations
• Fainting
• Excessive sweating (hyperhidrosis)
• Abnormal heart rhythm (arrhythmia)

In very rare cases, the first sign can be sudden cardiac arrest.⁴

Diagnosis and outcomes

Because of the connection between genetics and this form of cardiomyopathy, physicians often prioritise the family's medical history. Children will undergo a physical exam, an electrocardiogram (ECG) to assess their heartbeat, imaging studies, and laboratory tests. During diagnosis, it is observed that the left ventricle (primary pumping chamber) is significantly thicker than anticipated based on the child's age and body size.⁴ 

Restrictive cardiomyopathy

Restrictive cardiomyopathy is less common, accounting for approximately 3.2% of cardiomyopathy cases.³ In restrictive cardiomyopathy, the ventricular chambers (the lower, pumping ones) retain their usual size. However, the atria (upper chambers) are enlarged to compensate for the increased effort needed for blood to flow through stiff ventricles, resulting in restrictive cardiomyopathy.

Causes

About 25% of children with restrictive cardiomyopathy have relatives with the condition. In most cases, restrictive cardiomyopathies have no clear cause and are idiopathic. Sometimes this condition develops due to another problem, such as an infection in the heart tissue, or as a consequence of medical treatments.⁶

Additional factors include inherited mutations in genes that constitute the portion of the heart muscle fibres responsible for their contraction and relaxation (the sarcomere). 

Symptoms and signs

Early symptoms of this condition are not specific and heavily overlap with symptoms associated with heart failure. These can include: 

• General fatigue
• Feel usually exhausted after mild activities
• Chest pains
• Dizziness
• Swelling in the abdomen or feet (oedema)

Diagnosis and outcomes

This type of cardiomyopathy is more frequent with increasing age; only 10% of cases are diagnosed during the first year of life. ² More than half of the children diagnosed with this condition will require a heart transplant. All children with this heart condition should undergo frequent evaluations to monitor their pulmonary vascular resistance (PVR), which measures the difficulty of blood flow through the blood vessels in the lungs.⁶

Left ventricular non-compaction

This type of cardiomyopathy is sometimes referred to as ‘spongy heart’. Usually, the wall of the heart muscle is smooth, but in this condition, there are too many trabeculations (ridges) in the left ventricle. These prevent the muscle wall from being smooth, making the heart look ‘spongy’ and function less efficiently.⁷

Causes

The condition is rare, often hereditary, and is commonly diagnosed in infants presenting with various symptoms.²

Symptoms and signs

Sometimes this cardiomyopathy is found by chance during routine heart checks, but other symptoms and signs which may indicate left ventricular non-compaction (LVNC) include: 

• Abnormal heart rhythms (arrhythmias)
• Blood clots (thrombosis)
• Heart failure

Symptoms and signs can vary among children, and some may show signs of other cardiomyopathies as well.²

Diagnosis and outcomes

Sometimes it can be challenging to differentiate between dilated cardiomyopathy and LVNC.  Cardiac magnetic resonance (CMR) is the most effective method for differentiating between disease morphologies in these cases. As an alternative, cardiac computed tomography (CT) can help in diagnosing this condition.⁴ 

Treatment options for cardiomyopathies in children

Children with cardiomyopathies should undergo regular evaluations as recommended by their healthcare providers. Treatment options depend on the type and cause of the cardiomyopathy and any other co-existing conditions.  

Treatment options for children with cardiomyopathies include:

• Beta blocker therapy (to lower blood pressure)
• Diuretics (to prevent fluid buildup in the body)
• Anticoagulants (to prevent the formation of clots)

Moreover, surgical treatment can also be considered in some cases that have been previously evaluated by specialists. Surgical treatment can be diverse and specific for a heart condition; these may include:

• Cardiac resynchronisation therapy (CRT) is recommended in some severe cases of dilated cardiomyopathies
• Palliative surgeries, like cardiomyoplasty, can be an alternative to heart transplantation
• Alcohol septal ablation as an alternative for hypertrophic cardiomyopathy 
• Defibrillators and pacemakers implantation
• Heart transplant

Summary

The heart has four chambers, two atria and two ventricles, and various conditions can affect their shape, size, and function. One group of these conditions is called cardiomyopathies, which are diseases of the heart muscle that impact its ability to pump blood. Causes vary and can include infections, genetic mutations, and metabolic disorders. Early detection of symptoms in children may improve outcomes, despite heart conditions being rare in this age group. Cardiomyopathies can lead to weakened, stiffened, or thickened heart muscles, which impede blood flow. The common types in children include dilated and hypertrophic cardiomyopathies. Dilated cardiomyopathy, the most common form, results in an enlarged left ventricle, often linked to genetic factors. Symptoms typically involve heart failure signs, including difficulties in breathing and poor growth. Diagnosis might involve family history, blood tests, and imaging. Hypertrophic cardiomyopathy involves thickening of the heart muscles, making it harder to pump blood. Genetic mutations are often a factor, and symptoms can include chest pain and fainting. Restrictive cardiomyopathy, though less common, features enlarged atria and can have genetic roots or be idiopathic. Symptoms often overlap with heart failure. Left ventricular non-compaction is rare, having a spongy heart muscle wall. Diagnosis may sometimes be challenging, requiring specialised imaging. Treatment options for cardiomyopathies include medications to manage symptoms and, in severe cases, surgical interventions or heart transplants. Regular evaluations by a doctor are crucial for children with these conditions. Parents should look out for and be aware of typical symptoms such as tiredness, chest pain, dizziness, feeding difficulties, swelling, and breathing problems, especially if a family history of heart problems is present. Parents should seek urgent medical attention if a child faints or collapses suddenly or presents severe shortness of breath.