Congenital heart defects (CHDs), also known as congenital anomalies, are structural and/or functional problems of the heart and its vessels, preventing the organ from functioning correctly from birth. As the most common type of birth defect, 1 in 100 babies are born with a congenital heat defect in the UK. Congenital heat defects do not always have an obvious cause, and no two heart defects are the same in a baby. These defects may include but are not limited to holes in the heart, underdevelopment in key structures, or narrow valves and vessels. 

The severity of the malformations depends on when the symptoms present: straight from birth or develop later in childhood and adulthood. 

Consequently, these defects are associated with a condition called cardiomegaly, in which the heart is bigger than usual (enlargement). An enlarged heart indicates that the heart, or a portion of it, has grown thicker or more stretched out. As a result, this may make it difficult for the heart to pump blood efficiently, as the heart would work twice as hard. This can also lead to an abnormal blood flow pattern. Many defects, including patent ductus arteriosus (PDA), ventricular septal defect (VSD), and atrial septal defect (ASD), can also strain the heart and cause it to expand in an attempt to compensate for the increased workload. If left untreated, this can eventually result in cardiac failure.¹

Immediate detection of these issues enables medical professionals to take immediate action to prevent the development of any long-term issues. Not only does cardiomegaly cause heart failure, but it also causes delayed development in children, as well as difficulty in breathing and stunted growth if unaddressed. An early intervention, with medication or surgery, can avoid these grave outcomes, lowering stress on the heart and improving its function.¹

Types of congenital heart defects associated with heart enlargement

Ventricular septal defect (VSD)

Ventricular septal defect (VSD) is the most common congenital birth defect in children. This condition entails having a hole in the intraventricular septum - the walls that separate the left and right ventricles (the heart’s lower chambers).² 

Having a hole in that specific region means that the hole permits blood to flow from the left side of the heart to the right, increasing blood pressure as it travels to the lungs and forcing the heart to work harder, which may lead to enlargement of the right ventricle. 

Although the precise reason for why ventricular septal defects occur is not exactly known, these anomalies are more likely to emerge during embryonic development. When a foetus is growing inside the womb, no septum or wall divides the left and right ventricles. This wall of separation is formed as the baby grows. Thus, the ventricular septal defect is enabled when the muscular wall does not form completely.³

You may wish to imagine this as building an actual wall - if there are air bubbles in the cement of a wall, the whole structure may be reduced in strength and durability. Similarly, a hole in the ventricular chambers results in an increased blood flow to the lungs, which can potentially result in the right side being more enlarged than the other. 

Atrial septal defect (ASD)

Similarly to ventricular septal defect, atrial septal defect (ASD) is among the third common birth defect. This condition involves the formation of a hole in the septum between the heart’s atriums (upper chamber). This defect causes excessive blood flow from the left to the right atrium, leading to enlargement of the right side of the heart.⁴

The size of the hole determines how ventricular and atrial septal abnormalities are treated. A smaller hole that causes no symptoms or a strain on the heart means that no further treatment is required, as this is resolved on its own during childhood. However, with a larger hole, surgical interventions are needed to seal the hole.⁵

Patent ductus arteriosus (PDA)

Patent ductus arteriosus (PDA) is a condition that arises when the connection between the blood vessel ductus arteriosus (which is linked to the pulmonary artery) and the aorta artery remains open after birth. In the womb, the foetus receives oxygen from the mother’s placenta as its lungs are still developing. Blood is transported from the lungs to the body through the ductus arteriosus. This is no longer required when a newborn breathes and uses its lungs, and it often shuts on its own during the first two days of life.

A patent ductus arteriosus occurs when the ductus does not seal completely. In the pulmonary artery, the PDA allows deoxygenated blood to mix with oxygenated blood from the aorta, causing an overabundance of blood to enter the lungs, straining the heart and raising blood pressure in the pulmonary arteries. Consequently, the heart is enlarged and weakened by the overload of blood in the lungs.⁶

Treatment

In most cases of PDA, medications can be used straight after birth to induce the closure of the ductus. These are ibuprofen in a particular form, and indomethacin may be used to encourage closure shortly after birth. If the medicine is unable to close the PDA, catheter-based procedures with a coil or plug may be used to seal the duct through a keyhole surgery.⁶

Tetralogy of fallot (TOF)

Tetralogy of fallot (TOF) is a combination of four congenital cardiac structural defects. This includes: ⁷

• Ventricular septal defect
• Pulmonary stenosis: a constriction at, under, or above the valve between the right pumping chamber (right ventricle) and the blood vessel that delivers blood to the lungs to pick up oxygen (pulmonary artery)
• Right ventricle hypertrophy: due to the narrowed pulmonary artery, the heart works harder to excessively pump blood, causing the right lower heart chamber muscle to thicken⁸ 
• Overriding aorta: the aorta is the primary artery in the body, which transports blood from the heart to the rest of the body. In this condition, the aorta is incorrectly positioned above a ventricular septal defect instead of the left ventricle, which permits deoxygenated blood to enter and flow from the aorta to the lungs 

Treatment

Depending on the baby's health, weight, and the severity of the defects and symptoms, doctors may choose to do open heart surgery to treat tetralogy of Fallot shortly after birth or later in infancy.⁷

Coarctation of the aorta

About 5% to 7% of all congenital heart illnesses are coarctations of the aorta, a congenital heart abnormality that is more common in people assigned male at birth than assigned female. It is characterised by the narrowing of the aorta, which leads to increased pressure in the heart, particularly in the left ventricle. It often leads to left ventricular hypertrophy (thickening of the left ventricle) because the heart works harder in the narrowed aorta if untreated, and ultimately results in heart failure.⁹

Treatment

There are surgical and non-surgical methods for treating aortic coarctation. Reconnecting the two ends of the aorta after removing the narrow segment is one of the most popular methods for treating coarctation. Physicians may perform balloon dilations (also known as balloon angioplasty) to dilute the constricted area.⁹

Diagnosis and detection 

Congenital heat defects with heart enlargement can be detected during pregnancy or after birth through a wide range of modalities. This includes the following:¹

• Foetal echocardiography: a non-invasive ultrasound test that produces moving images of the heart’s structure and function without any pain. It can be used to track movement over time or assist in diagnosing a cardiac abnormality
• Chest X-Ray: an X-ray is ideal to examine heart size, whether the heart is enlarged, as well as overseeing the blood flow in the lungs and heart
• Genetic testing: a genetic test can indicate gene mutations associated with specific congenital conditions, particularly in families with a history of congenital heat defects
• Electrocardiogram (ECG): This measures the rhythm of the heartbeat through the heart’s electrical activity
• Cardiac MRI: an MRI of the chest allows a visualisation of the heart to follow or diagnose any congenital defects 
• Pulse oximetry: This measures the amount of oxygen in the blood to identify issues with oxygenation

Alongside this series of tests, a doctor or practitioner may refer to the clinical symptoms that the baby exhibits. The severity and extent of these symptoms depend on the CHD and the individual. However, some general signs may comprise of:

• Cyanosis (characterised by having a blue or grey tinge in the face) 
• Difficulty breathing
• Trouble with gaining weight, growth and development 
• Extreme fatigue 
• Sweating during feeding
• Swelling in the limbs

Importance of early intervention

Early diagnosis and treatment are essential to reduce the risk of long-term complications such as heart failure, developmental delays, and breathing difficulties. The prognosis is good with proper care, and over 97% of children who had congenital heart defects live to adulthood. However, research has indicated that the first four years are key to monitoring and observing symptoms due to the mortality rate. Therefore, it is important to intervene and seek medical attention if there is any doubt.¹⁰

Summary

Congenital heart defects associated with heart enlargement, also known as cardiomegaly, arise when structural abnormalities in the heart increase pressure or blood flow, causing the heart to work harder. Common defects include ventricular septal defects, atrial septal defects, patent ductus arteriosus, and aortic coarctation. In these conditions, the heart chambers eventually grow as a result of inefficient blood circulation, a way of making up for the increased strain. These disorders force the heart to work harder and, if untreated, may result in heart failure, poor oxygenation, and developmental abnormalities. Early detection and treatment are imperative to improve outcomes and support healthy growth and development.