Introduction

Sleep apnoea is a common sleep disorder in which reduced oxygen saturation in the blood may interrupt normal sleep cycles. A reduction in oxygen delivery to the brain promotes awakenings, disrupts sleep patterns, and causes daytime sleepiness and fatigue.¹ 

Sleep apnoea has been associated with a myriad of diseases, from problems with memory, focus, and learning to heart disease. Therefore, addressing it is of great importance in the prevention and improvement of quality of life.¹

Obstructive sleep apnoea (OSA) is the most common type of apnoea and a recognised contributor to heart conditions, one of which is left atrial enlargement (LAE). But how exactly does OSA lead to changes in heart structure?

What is obstructive sleep apnoea?

Sleep apnoea is a common sleep disorder in which reduced oxygen saturation in the blood may interrupt normal sleep cycles. Reduction in oxygen delivery to the brain may promote awakenings and fragmented sleep, which may cause the following symptoms:¹

• Morning headaches
• Daytime sleepiness
• Fatigue
• Memory difficulties
• Mood issues

People usually look for medical attention and get a sleep apnoea diagnosis after concerns related to loud snoring, gasping for air or choking during sleep, frequent toilet visits during the night, and awakenings.¹

People with chronic and untreated sleep apnoea may have a higher risk of developing associated diseases, including:^1,2

• Heart disease
• High blood pressure
• Stroke
• Memory impairment

Sleep apnoea is a complex disorder with multiple potential causes. However, it can be classified into subgroups as follows:¹

• Obstructive 
• Central
• Complex sleep apnoea

Obstructive sleep apnoea (OSA) is the most common form of sleep apnoea. Up to 25%-30% of American men and 9%-17% of American women satisfy the requirement for OSA diagnosis, while the percentage of people with this condition may be even higher among Hispanic, Black, and Asian people.²

As its name suggests, OSA stems from the obstruction of the upper airway during sleep. In that sense, it may be a result of structural features that reduce the upper airway's intrinsic ability to transport air from the outside to the lungs. Examples of structural features affecting the upper airway include:^2,3

• Retrognathic lower jaw
• Excess soft/fatty tissue in the airway
• Increased size of upper airway organs, e.g., big tonsils, tongue, or airway lateral walls

According to earlier studies, a large number of people with OSA may still lack proper diagnosis.⁴

Sleep apnoea affects 2–4% of the middle-aged population. People who have the following risk factors are more likely to suffer from sleep apnoea:⁵

• Obesity
• Assigned male at birth (AMAB)
• Age

What is left atrial enlargement?

The left atrium is one of the 4 chambers of the human heart. It is responsible for collecting the oxygenated blood coming from the lungs and sending it to the left ventricle. Once there, the left ventricle pumps blood out to the rest of the body through the aorta.

The left atrium may grow in size and wall thickness, which is called left atrial enlargement (LAE), when it becomes chronically overloaded with blood and/or the pressure inside it gets too high.⁶

It is unclear when LAE develops, but some research suggests that it may start as early as the late 40s in some. However, LAE is not a normal part of ageing. Instead, it happens due to associated congenital or acquired diseases, including:⁶

• High blood pressure (hypertension)
• Obesity
• Left ventricular hypertrophy or failure
• Left ventricular diastolic dysfunction
• Atrial fibrillation
• Aortic stenosis
• Left atrium mass or myxoma
• Arteriovenous fistulas
• Left-to-right shunt

Up to 20% of athletes may also develop LAE. Competitive athletes undergo chronic intensive training, which promotes left ventricular hypertrophy and, later on, may contribute to LAE.⁶

LAE is linked to a higher risk of death in both men and women and ischemic stroke in women. Some other complications from LAE:⁶

• Atrial fibrillation
• Stroke
• Heart failure

How does obstructive sleep apnoea contribute to left atrial enlargement?

In middle-aged people, OSA is associated with several heart-related diseases, such as:⁷

• High blood pressure
• Stroke
• Heart failure
• Myocardial infarction/heart attack
• Atrial fibrillation

The connection between OSA and these diseases may stem from the chronic and recurrent low oxygen saturation (hypoxaemia) that OSA causes during sleep. Hypoxaemia increases the activity of the sympathetic nervous system and causes low-grade inflammation. Moreover, the pressure inside the thorax may rise during breathing interruptions or apnoeas, which exerts physical stress on the atrium and could alter its endothelial wall function.⁷

These phenomena injure the heart tissue and manifest as changes in size, structure, and, thereby, function.⁷

Evidence from a clinical study including 411 men indicates that OSA is associated with LEA, regardless of body weight or diagnosis of high blood pressure, heart failure, or atrial fibrillation. Indeed, men with severe OSA and none of those other health conditions had larger left atria than those with mild or no OSA.⁷

Risk factors that overlap between OSA and LAE

Obesity may be one of the most common contributing factors to both OSA and LAE. Unhealthy weight may come with excessive tissue in the upper airway and, thereby, its obstruction. Difficult air transport shows up as the typical snoring and awakenings that characterise OSA. Moreover, the extra effort the heart makes to keep healthy blood oxygen levels causes overstrain to the heart muscle that may end up in LAE.⁸ 

Another, often overlooked, risk factor related to OSA and LAE is the obesity-induced hypoventilation syndrome (OHS). Similar to OSA, OHS stems from obesity and causes abnormal breathing during sleep. However, it also has the aggravating factor of slow and/or shallow breathing during the daytime. As a result, removal of carbon dioxide from the blood is inefficient, and its levels may remain constantly high (hypercapnia). People with OHS and OSA may be at a higher risk of developing LAE than people with OSA alone. Additionally, they are at a higher risk of developing atrial fibrillation.⁹ 

Atrial fibrillation is a type of arrhythmia whose link with LAE seems to be bidirectional. While people who first develop LAE may have a high risk of developing atrial fibrillation, those with baseline atrial fibrillation may also be diagnosed with LAE later on. The linking mechanism may be heart dysfunction and overstrain.⁶

Diagnosis and monitoring

Early detection of OSA may be of paramount importance to prevent the chronic changes the heart goes through over the years. Moreover, its proper management has the potential to dramatically improve quality of life.¹

OSA may be easily diagnosed through a sleep test called polysomnography. It is an in-clinic sleep apnoea test that monitors your breathing, oxygen saturation, and breathing muscle activity during one night of sleep. The result is the apnoea-hypopnoea index (AHI) that reveals the number of times you stop breathing properly per sleep hour.¹

People with a high apnoea index may need to use a Continuous Positive Air Pressure (CPAP) machine during the first or a separate test to titrate air and see whether correction of oxygen saturation could be achieved.¹

In case LAE is also suspected, it could be diagnosed using the following techniques:⁶

• Echocardiography
• Electrocardiogram
• Cardiac computed tomography (CCT)
• Cardiac magnetic resonance (CMR)

Considering the potential for LAE to contribute to atrial fibrillation, its diagnosis may improve your prognosis.

Treatment strategies to address both conditions

Based on the risk factors associated with LAE, its development could be approached through:

• OSA management (e.g., through CPAP therapy)
• Blood pressure control
• Weight loss

Studies implementing weight loss strategies and OSA treatment to address LAE show that their impact may be limited and likely conditioned by how much weight is lost. This encourages early obesity management and LEA prevention as the first steps to work on.¹⁰ 

When to see a doctor

OSA is a condition that requires proper management to prevent its long-term complications. Hence, you should talk to your doctor if you have any related symptoms to get a proper diagnosis and target its cause.

Your doctor may recommend examination of your upper airway and a polysomnography to determine the best treatment for your sleep apnoea. Due to the multiple causes for sleep apnoea, its treatment should be individualised and based on its severity.¹

LAE may be asymptomatic in its early stages; therefore, physician-guided monitoring may aid in its early diagnosis and management. A more advanced scenario may lead to symptoms like:⁶

• Shortness of breath
• Fatigue
• Palpitations
• Pain or discomfort in the chest
• Cough 
• Arms and legs swelling
• Dizziness
• Difficulty swallowing

Monitor and follow up with a cardiologist or sleep specialist as needed.

Summary

• Sleep apnoea is a health condition that hinders nighttime breathing, causes fragmented sleep, and thereby worsens quality of life
• Obstructive sleep apnoea is a type of sleep apnoea with potential heart-related consequences, including left atrial enlargement 
• Early diagnosis and management of obstructive sleep apnoea may reduce the risk of developing left atrial enlargement and improve quality of life 

FAQs

Can obstructive sleep apnoea cause structural heart changes?

Yes, obstructive sleep apnoea is associated with heart overstrain and hypoxia, which can lead to structural changes like left atrial enlargement and ventricular hypertrophy.

Is left atrial enlargement dangerous?

Yes, left atrial enlargement increases the risk of atrial fibrillation, stroke, and heart failure.

Can weight loss reverse left atrial enlargement?

Scientific studies indicate that significant weight loss may reverse left atrial enlargement. However, more research in this regard is needed.

What tests are used to detect left atrial enlargement?

Echocardiography is the most common diagnostic tool, often followed by ECG or CMR for further evaluation.

How are obstructive sleep apnoea and left atrial enlargement treated together?

A multidisciplinary approach is ideal—combining obstructive sleep apnoea management (e.g., CPAP therapy), heart care, weight loss, lifestyle changes, and regular monitoring.