Introduction

As indicated by the name, left atrial enlargement (LAE) is a clinical pathology where the left atrium (one of the heart chambers) is abnormally enlarged.¹ It usually presents as a result of an underlying cardiovascular condition, such as raised blood pressure (hypertension), and, if identified, can be a useful warning sign to the development of other serious cardiovascular events. Therefore, early recognition, particularly in children, is essential for the maintenance of good heart function and the management and prevention of potential disease.

Anatomy and Function of the Left Atrium

The heart has four chambers which are divided into the left and right side of the heart.² Each side has an atrium and a ventricle, with the right side functioning to carry deoxygenated blood from the body to the lungs for oxygenation, and the left side functioning to carry oxygenated blood from the lungs to the rest of the body. Because the left side requires a higher force of contraction, both the left atrium and ventricles have thicker muscle walls compared to their right counterparts. 

Structure of the heart

On either side of the heart, when blood enters it first travels into the atria which contracts and squeezes the blood into the ventricles. Separating the two chambers are atrioventricular valves, which close when the ventricles contract and force the blood out of the heart. Both sides of the heart contract in synchrony, with the atria contracting at the same time, followed by simultaneous contraction of the ventricles. These are the fundamentals of what is known as the heart beat. Normal functioning hearts have a regular heart rate and rhythm when beating. 

How LAE Disrupts Normal Heart Function

As mentioned previously, LAE can be an indicator of underlying cardiovascular disease in children. When a child is affected by LAE and another pathology, they increase the risk of an atrial arrhythmia known as atrial fibrillation (AF), where the atria contract irregularly at an abnormally fast rate.^3,4 The most alarming risk that atrial fibrillation gives rise to is the formation of blot clots, which can cause serious cardiovascular events, such as heart attacks, stroke, and pulmonary embolism.⁵ For these reasons, children with diagnosed LAE must be monitored and managed accordingly. 

Causes of Pediatric Left Atrial Enlargement

Hypertension 

Although high blood pressure is rarely seen in children, hypertension has been correlated to LAE, even in paediatric patients.⁶ It is believed to develop due to pressure increasing in the left atrium, resulting in the remodelling of the cardiac muscle. The ventricle is unable to accommodate for this change, which causes more blood to remain in the atrium, eventually increasing the pressure and forcing the chamber to enlarge over time. 

Atrial Septal Defect 

Atrial septal defect is a cardiac birth defect where there is a hole in between the left and right atria.⁷ In patients where the hole is particularly large, more blood is forced into the right atrium, causing increased blood flow to the lungs and in turn, increases the volume of blood entering the left atrium. This overload of blood stretches out and remodels the cardiac muscle of the left atrium, eventually causing its enlargement. 

Valvular heart diseases

In a normal cardiac cycle, the atrioventricular valves close when the ventricles contract, then reopen when they relax. Valvular heart disease describes when the valves are stiff and fail to open properly (stenosis), or when the valves become « floppy » and are unable to close properly (regurgitation).⁸ Children can be born with these defects or develop them later on in life.^8,9 In cases with stenosis, the narrowed opening between the left atrium and ventricle causes a backup of blood, resulting in increased pressure in the left atrium, causing it to enlarge.¹ Similarly, regurgitation of the valve also causes an abnormal increase in pressure in the left atrium, due to blood flowing back in through the unclosed valves when the ventricles contract.

Diagnosis of Pediatric Left Atrial Enlargement

Clinical Presentation

Most cases of LAE present with no, or very few symptoms.¹ Signs and symptoms usually present as the underlying cause. 

Symptoms:

• Fatigue and chest discomfort: due to insufficient heart function in more severe cases 
• Shortness of breath, cough or haemoptysis: due to increased blood pressure in the lungs 
• Dizziness, feeling faint and palpitation: signs and symptoms of atrial fibrillation (AF) 

Physical signs: 

• Heart murmurs: these are heard as “whooshing” sounds when listening to the heart using a stethoscope,¹⁰ caused by abnormal blood flow and are indicators of valvular heart disease
• Cyanosis: sign of low oxygen in the body, where the skin appears blue or purple¹¹ and may be indicative of an atrial septal defect or impaired heart function 
• Oedema: swelling of the legs and back can be signs of developed heart failure in severe cases of LAE¹
• Signs of stroke: although incredibly rare in children, AF can cause blood clot formation, which can travel from the heart and up to the brain, blocking an artery and causing an ischaemic stroke and presents as weakness, seizures, poor feeding or excessive sleeping¹²

Diagnostic Imaging and Tests

• Echocardiogram: the gold standard investigation to diagnose suspected LAE following an examination¹ and is characterised by an ultrasound scan of the heart that can measure the size and volume of the heart chambers, identify any diseased valves and measure the blood flow 
• Electrocardiogram (ECG): a non-invasive investigation to measure the electrical activity of the heart and can be used to identify signs of LAE such as AF and prolonged electrical activity of the atria, which suggests a larger atrium

Management of Paediatric Left Atrial Enlargement

There is currently no medical intervention able to reverse LAE.¹ The focus of management is to investigate potential underlying causes and symptoms and to treat accordingly. In the case of children, investigating congenital heart diseases such as ASD and valve diseases is imperative to prevent progression of LAE and worsening cardiac function. Some treatments include: 

• Surgical repair of ASD and valvular disease: to prevent LAE progression and to stabilise blood flow and pressure in the lung¹³
• Anticoagulation therapy for children with underlying AF: more commonly known as “blood thinners”, these medications are used to reduce the risk of blood clot formation.¹⁴ However, children with AF need to be seen by a specialist as there are various types of anticoagulation medication which need to be dosed and selected appropriately depending on the severity of AF and the child’s age 
• Lifestyle and diet changes: to manage hypertension and pressure overload of the left atrium 
• Oxygen and fluids: to treat symptoms of heart failure
• Antihypertensive medication: under specialist care, children with hypertension may be prescribed medication to lower and manage their blood pressure¹⁵

Summary

• LAE in children is the abnormal enlargement of the left atrium 
• It is usually caused by an underlying cardiovascular or cardiac condition which causes pressure or fluid overload in the left atrium, causing it to remodel and enlarge overtime 
• LAE can increase the risk of arrhythmias, heart dysfunction (heart failure), blot clot formation and stroke in very rare incidences
• Signs and symptoms include shortness of breath, chest discomfort, poor feeding and cyanosis
• An echocardiogram is the gold standard method for diagnosis
• Management focuses on the prevention of disease progression and treating the underlying cause, however, there is no treatment available to reverse LAE 
• Specialist care is needed for appropriate management of cardiac disease in children