Introduction

Measuring the size of the left atrium (LA) is important for understanding heart health. An enlarged LA can be an early sign of problems including high blood pressure, heart failure, or irregular heart rhythms such as atrial fibrillation. It is crucial to assess the size of LA, which helps healthcare professionals predict the risk of cardiovascular conditions, such as a stroke, or assess how well a treatment is working.¹ Imaging techniques such as cardiac magnetic resonance (CMR) are used to assess the structure and sizing of the heart.² Other imaging modalities used to measure LA size include echocardiography and computed tomography (CT). Early diagnosis of heart related conditions and recognition of abnormal changes in size of LA are important in preventing life-threatening conditions and to make better decisions about management and treatment. This article will discuss the role and advantages of CMR and why this method of imaging is opted for measuring LA size. 

Anatomy and function of the left atrium 

The left atrium is one of the four chambers of the heart, which is located on the left side of the heart. It receives oxygen rich blood from the lungs and delivers it to the left ventricle, which then pumps it out to the rest of the body.³ The left atrium has three main physiological functions including reservoir, conduit, and booster pump, which work together in phases for functioning the heart; this allows oxygen to be delivered around the body and maintains the blood pressure, and changes to the LA can indicate signals of an underlying heart problem.

• Reservoir phase: The reservoir function refers to the volume of blood collected in the atrium when blood returning from the lungs, while the left ventricle is contracting⁴
• Conduit phase: This phase passively allows blood to flow into the left ventricle from the pulmonary veins when it relaxes
• Booster pump phase: The booster pump phase actively contracts LA to push blood into the left ventricle before the next heartbeat

There can be limitations to physical examination when there is a change in size of LA. Physical examination has low sensitivity and specificity when identifying pulmonary congestion which is essentially fluid buildup in lungs.⁵ Physical examination will include listening to the lungs with a stethoscope which doesn’t reliably show how much pressure is building up in the heart.

Also people affected with heart failure often feel less short of breath which can affect measurements during examination. Prediction of systemic congestion which is essentially how much fluid is in the rest of the body can vary a lot from patient to patient. For example, it is difficult to spot small amounts of fluid buildup with people who are overweight. Therefore, non-imaging techniques have several limitations making it difficult to detect changes in LA. 

Overview of cardiac magnetic resonance imaging (CMR)

Cardiac magnetic resonance (CMR) uses the same technology as magnetic resonance imaging (MRI), however, it is specific to the heart and is used to assess ventricle function, cardiovascular function, and state of tissues.⁶ CMR is one of the best ways of detecting changes in LA due to many advantages of this technique in comparison to other techniques: It is a noninvasive procedure that produces high-resolution images of the heart in any spatial plane, without being restricted by acoustic windows as in echocardiography. Unlike computed tomography, it does not involve exposure to ionizing radiation or require iodinated contrast agents.⁷ These advantages have made CMR a valuable tool for assessing heart structure and function, analysing myocardial tissue, evaluating both coronary vessels and the vascular system.

Techniques used in CMR to measure LA size

Imaging sequences commonly used are steady-state free precession (SSFP) in CMR. It's a highly accurate and precise method for assessing the volume and dimensions of the left atrium. SSFP images provide high temporal resolution, allowing for detailed visualization of the LA throughout the cardiac cycle.⁸ Nevertheless, the measurement of LA size can be obtained with the volume of LA using images captured from CMR. The pre-atrial contraction volume, maximum and minimum LA volume is measured and techniques used to measure are either area-length or Simpson's method.⁹ 

Two dimensional (2D) and three dimensional (3D) volume assessments can be completed to measure LA size. 3D assessments are seen to be more accurate and reliable specifically, in echocardiography, 3D volume assessments have improved accuracy in measuring atrial volume, especially in cases of enlarged atria in comparison to 2D echocardiography.¹⁰ This method can be very useful in diagnosing dysfunction of the heart and other cardiovascular conditions. However, monitoring LA size in patients with heart failure is usually done using CMR as outcome can be predicted, the prognosis of the condition can be predicted, and risks of stroke can be measured.  

Advantages and disadvantages of CMR in LA assessment

There are many advantages to the use of CMR in assessing LA, including high spatial resolution and accuracy, which provides in depth imaging that uses 3D technology to view the soft tissues characteristics.¹¹ It is a non-invasive procedure that does not require a long time to complete and is a standard imaging technique used worldwide. Nevertheless, it is non-toxic and does not harm the human body with ionizing radiation like other imaging techniques, such as x-rays and CT scans. On the other hand, there are a few disadvantages of CMR including long waiting lists for scans, and some people that carry pacemakers and defibrillators are not suitable for CMR use because it interferes with the machine.¹¹ These safety concerns are associated with CMR because the magnetic field interacts with ferromagnetic materials and electronic circuits, which could produce theoretical heating of ferrous material and damage.¹² It is important to be aware if the patient has fitted cardiac pacemakers, or similar devices, to prevent the risk of injury to both patient and damage to the devices. 

Other patient-related challenges of CMR include claustrophobia, with some patients refusing treatment due to the claustrophobic nature of CMR. Approximately 2 million CMR scans worldwide cannot be performed annually because patients are claustrophobic and, in this case, a mild sedation can be applied to patients to complete the scan.¹³ However, if this limitation cannot be overcome, then these patients can be referred to other procedures such as an electrocardiogram, which does not require a tight space and is performed quickly by placing electrodes on the surface of the skin. 

FAQs

How do you assess left atrial enlargement?                                                                                

Imaging techniques including CMR or other techniques such as ECG can be used. 

Can losing weight help left atrial enlargement?                                                                  

Reductions in body weight could be useful to prevent the enlargement. 

What should you avoid if you have an enlarged heart?                                                              

You should avoid trans fats, high salt intake, and high caffeine intake.  

How serious is left atrial enlargement?                                                                                             

This is generally not a serious condition, however, it can be if there is an underlying heart condition. 

Can anxiety cause left atrial enlargement?                                                                                 

Yes, anxiety can be a factor that causes atrial enlargement.

Summary 

It is very important to accurately assess changes of size in LA as this could be a sign of a more serious underlying issue of the heart. CMR is one of the best suited technologies to measure changes in LA size and other health conditions. It is a cutting-edge, highly advanced, and rapidly evolving non-invasive tool that is used for the assessment of a wide range of cardiovascular conditions. In healthcare, CMR continues to establish itself as a leading imaging modality with the amount of advantages outweighing other imaging techniques. Therefore, patients affected with LA enlargement and many patients who are affected with other conditions are suitable for CMR imaging.