Introduction
The human heart is split into four main chambers: two chambers at the top (atria) receive blood from the body, which has been oxygenated by the lungs, and the two chambers at the bottom (ventricles) that pump blood to different parts of the body. Left atrial enlargement (LAE) is a condition that happens when there is a large, abnormal change in the size of the left atrium of the heart. This expansion can lead to serious heart conditions, one of them being cardiomyopathy.
The heart
In the cardiac cycle, the left atrium has three main functions:1
- Receives oxygenated blood
- Passively pushes that oxygenated blood to the left ventricle
- Acts as a booster pump that actively empties blood into the left ventricle
The heart is the most important organ in the human body; a failure of one of its sections is catastrophic for the body, especially the left side of the heart, which deals with oxygenated blood.
Several clinical conditions can happen because of this, with one of the most important ones being a stroke, because the blood supply is being cut off from the brain. Another serious problem would be atrial fibrillation, which is when the heart rhythm is irregular and the atrial chambers beat rapidly and out of sync to the ventricles, causing other problems such as stroke, palpitations and shortness of breath.
Left atrial cardiomyopathy happens when the atrial chamber walls become thick or stretched, stopping it from pumping blood to various parts of the body. This prevents the affected parts of the body from working efficiently, as well as having a greater risk of heart failure. Since the left atrium receives oxygenated blood, which the body needs to function, a reduction in efficiency in this chamber can be catastrophic for the organs and muscles.2
Causes and risk factors
Left atrial enlargement (LAE) is not caused by one specific factor but can result from various reasons that force the chamber to exert more effort due to the pressure and/or volume of blood. Conditions that add extra stress and pressure to the atrium can be:
Some problems can add extra blood volume to the atrium, such as:
One of the most important risk factors that affects atrial enlargement is hypertension.
Characterised by elevated pressure within the arteries, this condition forces the left ventricle to exert more effort as a response. Consequently, this results in diastolic dysfunction, which creates a buildup of volume and pressure in the left atrium, leading to its enlargement.3
The left atrium and its function
The normal mean atrial diameter is around 3.9cm-4cm in women, and around 4cm-4.1cm in men. This size enables the chamber to efficiently deliver oxygenated blood to the left ventricle while also allowing it to contract and expand, thereby actively pushing the blood like a pump. This is done as part of the cardiac cycle, which is divided into two categories:
- Diastole: is the relaxation period, where the heart muscles relax, allowing blood to enter the atria and then the ventricles
- Systole: is when the muscles contract, pushing blood out of the heart
The muscles in the atrial chambers are generally thinner than the ventricles, as the distance from the atrium to the ventricles is much shorter compared to the distance between the ventricles and the rest of the body. However, this distance is still crucial, and a failure in this area can be disastrous.4,5
Atrial assessment
Atrial dimensions and activity can be assessed through echocardiograms, cardiac computed tomography (CCT), and cardiac magnetic resonance (CMR). While echocardiograms are the most appropriate tool for these purposes due to their widespread availability, safety, versatility, and capacity to provide real-time imaging with excellent temporal and spatial resolution, CCT and CMR serve as complementary options in particular clinical situations.
The dimensions of the left atrium (LA) are typically assessed using M-mode and 2-dimensional echocardiography (2DE). Among these assessments, the maximum left atrial volume (LAV) has the strongest correlation with cardiovascular disease and is most sensitive to change.
LAVs can be accurately assessed from 3D datasets obtained through CCT. However, due to the radiation exposure and the requirement for iodinated contrast medium, CCT is primarily used as an important supplementary method in LA ablation procedures. In addition, CCT's relatively low temporal resolution may hinder precise measurements of phasic LAVs and atrial function.
CMR, which is regarded as the “gold standard,” offers accurate LAV measurements with adequate temporal resolution, but its use is restricted by its high costs, limited availability, an inability to measure phasic volumes using gated 3D sequences, as well as complications related to gadolinium contrast and the inability to scan patients with intracardiac devices.6,7
Transition to cardiomyopathy
Enlargement of the atrium itself is not a disease; however, when the walls of the atrium or ventricles change shape and become stiff, thick or stretched, it can lead to cardiomyopathy. One of the changes that occurs is chronic atrial remodelling, which is the long-term change in the function and shape of the atrium. It is often caused by internal or external stimuli and heart conditions such as atrial enlargement.
Classified by the stretching followed by stiffening of the atrial chamber, the atrium's performance is compromised, leading to a reduction in its efficiency. If remodelling of the atrium occurs in an acute situation and is detected early on, it can be reversible. In some cases, when the cause is not particularly severe, the remodelling may also be reversed. Nevertheless, once the remodelling turns chronic, the chances of reversing it become minimal, resulting in the atrium operating below optimal efficiency.
Stretching of the atrial walls is not the only visible damage during cardiomyopathy. Scarring of the heart muscles happens in a process called fibrosis, which is due to a sudden or even chronic injury of the heart. This can lead to heart failure and atrial fibrillation, a serious heart problem in which the heart beats irregularly and not in sync. The longer that the heart remains fibrillated, the harder it is to maintain a normal heartbeat, and that can lead to chronic remodelling and thus an irreversible atrial enlargement and cardiomyopathy. In this case, it is possible to reverse the enlargement of the atrium; however, it is rare.8,9
Prevention
The focus and attention are on the underlying causes rather than the actual enlargement itself. By putting less pressure on the blood vessels and, in turn, on the heart, it is possible to prevent or slow down the enlargement. For example, people who have high blood pressure can make changes to their lifestyle choices, such as:
- Fixing their diet
- Exercising
- Managing stress
- Sleeping more effectively
- Blood pressure medication in some cases
People with heart valve issues can also experience atrial enlargement. In addition to surgical options to repair or replace dysfunctional valves, dietary adjustments can be implemented, quitting smoking is advisable, and if necessary, medications like beta-blockers and anticoagulants may be prescribed to alleviate pressure on the heart.
Routine medical checkups are essential for individuals with heart issues, particularly if there is a family history of similar conditions. Prolonged negligence can place excessive strain on the heart, especially the atrium, posing severe risks that could result in arrhythmias, blood clots, and, in extreme cases, heart failure leading to cardiac arrest. Those diagnosed with cardiomyopathy often face greater challenges in life, which include frequent hospital visits and a heightened risk of mortality. Nevertheless, significant progress has been made in recent years to enhance both the quality of life and life expectancy for these individuals.10
Summary
To conclude, left atrial enlargement is a very serious and life-threatening heart condition caused by several factors, which lead to the atrium expanding in size and forming stretched, stiff walls that are unable to properly contract and force blood to the left ventricle and then to the body. This happens because of high pressure and/or volume in the atrium, forcing it to work harder and damaging and changing the shape of the chamber in a process called remodelling. This then leads to cardiomyopathy, in which stage the atrium's shape has irreversibly changed and oxygenated blood struggles to leave the atrium and sometimes even returns from the ventricle, massively impacting the body's functions. Early detection of this is crucial, as it is possible to reverse in some cases by targeting the underlying cause; however, this is a time-sensitive task due to the enlargement becoming a chronic case as the situation progresses. With more research and focus being given to this heart problem, it may be easier to detect, reverse and treat, hopefully improving life expectancy.
References
- Patel DA, Lavie CJ, Milani RV, Shah S, Gilliland Y. Clinical Implications of Left Atrial Enlargement: A Review. The Ochsner Journal. 2019;9(4): 191. https://pmc.ncbi.nlm.nih.gov/articles/PMC3096293/
- Wijesurendra RS, Casadei B. Mechanisms of atrial fibrillation. Heart. 2019;105(24): 1860–1867. https://doi.org/10.1136/heartjnl-2018-314267.
- Mills KT, Stefanescu A, He J. The Global Epidemiology of Hypertension. Nature Reviews Nephrology. 2020;16(4): 223–237. https://doi.org/10.1038/s41581-019-0244-2.
- Bouzas-Mosquera A, Broullon FJ, Alvarez-Garcia N, Mendez E, Peteiro J, Gandara-Sambade T, et al. Left atrial size and risk for all-cause mortality and ischemic stroke. Canadian Medical Association Journal. 2011;183(10): E657–E664. https://doi.org/10.1503/cmaj.091688.
- Fukuta H, Little WC. The Cardiac Cycle and the Physiologic Basis of Left Ventricular Contraction, Ejection, Relaxation, and Filling. Heart Failure Clinics. 2008;4(1): 1–11. https://doi.org/10.1016/j.hfc.2007.10.004.
- Hoit BD. Left Atrial Size and Function. Journal of the American College of Cardiology. 2014;63(6): 493–505. https://doi.org/10.1016/j.jacc.2013.10.055.
- Parajuli P, Ahmed AA. Left Atrial Enlargement. PubMed. Treasure Island (FL): StatPearls Publishing; https://www.ncbi.nlm.nih.gov/books/NBK553096/
- Al Ghamdi B, Hassan W. Atrial Remodeling And Atrial Fibrillation: Mechanistic Interactions And Clinical Implications. Journal of atrial fibrillation. 2009;2(1): 125. https://doi.org/10.4022/jafib.125.
- Gutierrez C, Blanchard DG. Atrial fibrillation: diagnosis and treatment. American family physician. 2011;83(1): 61–68. https://pubmed.ncbi.nlm.nih.gov/21888129/
- Maron BJ, Rowin EJ, Maron MS. Advances in the Management of Hypertrophic Cardiomyopathy Leading to Low Disease-Related Mortality in 2023. The American Journal of Cardiology. 2024; https://doi.org/10.1016/j.amjcard.2023.10.073.
