What is heart enlargement and why is imaging important?

Heart enlargement is an increase in the physical size of the heart through either dilation (where cardiac muscle becomes thinner) or hypertrophy (where the cardiac muscle becomes thicker). Whilst heart enlargement can be found in healthy individuals due to pregnancy or athletic demands, these abnormalities can also indicate the presence of many different cardiac diseases.¹ 

Once the heart is enlarged to a diameter that is greater than 50% of the transverse diameter of the chest, it is categorised as Cardiomegaly which often leads to heart failure. Left untreated heart failure can often be fatal with transplants necessary for severe cases. Alternatively, milder cases can be treated through a combination of lifestyle changes, specific enzyme inhibitors, beta-blockers, diuretics and by addressing underlying causes.

 To determine the probable cause and most effective treatment plan for patients, the extent of enlargement needs to be accurately determined, emphasising the importance of high-quality imaging techniques in this situation.²

Conventional imaging techniques

There are several imaging techniques that can be used to assess the extent of heart enlargement including:

• Echocardiography
• Cardiac MRI
• Chest X-Ray

2D echocardiography uses ultrasound waves emitted by a probe which are reflected back when they come into contact with matter of different densities. Reflected waves are then detected and form live images of a cross-section of the heart in two dimensions.³ Transthoracic or transesophageal echocardiography can be used with different benefits and downsides. 

Transthoracic echocardiography is a non-invasive method as images are taken of the chest from outside the body making the process quick and comfortable. However, images may not be of the highest quality due to waves having to pass through the chest to reach the heart. Alternatively, transesophageal echocardiography can be used by inserting a probe down the esophagus. This is a much more invasive procedure, usually requiring mild sedation, but produces much higher quality images due to proximity to the heart.⁴ 

These 2D images can then be used to generate a measurement of heart enlargement using geometric assumptions. This can be a source of inaccuracies as hearts may have abnormal shapes or change shape during imaging leading to incorrect results.⁵

Cardiac MRI (Magnetic Resonance Imaging) is an alternative, highly effective method of measuring heart enlargement using radio waves inside a magnetised tunnel. This is non-invasive and produces 3D images of the heart, which are both highly desirable features.⁶

On the other hand, the quality of images produced can be affected by slight movement, so it is crucial to remain as still as possible whilst the process is taking place. Furthermore, irregular heartbeat or other abnormalities can also impact the images, causing inaccuracies in results. Being more time-consuming and at a higher financial cost may also discourage patients from this method of imaging.⁷
Chest X-rays can also be used to identify heart enlargement by projecting x-rays onto a photographic plate with that patient between the two. This will form a basic image that can visualise the extent of heart enlargement but will not accurately measure the size or shape of the heart so is often done as a preliminary to other imaging techniques.⁸ Despite a low image quality, this is a quick and cost-effective method of initially assessing issues with heart size.

What is 3D echocardiography?

Developing technology has made way for the use of 3D echocardiography to now become an emerging imaging technique.⁴ This technique is a modified version of 2D echocardiography using a sample of matrix-array transducers to form 3D images, independent of plane positioning and without making geometric assumptions. 

This reduces some of the errors that are encountered when using 2D echocardiography, allowing more accurate images to be formed whilst maintaining a high level of efficiency and low costs. More complex features can be distinguished, and further abnormalities are also easily detected using this method, proving useful if the cause of enlargement needs to be diagnosed.⁹ 

3D speckle-tracking echocardiography

Speckle-tracking is a technique developed and used specifically to identify enlargement of the left ventricle. Unique patterns that appear in the images produced by an echocardiograph can be tracked throughout frames using specially designed software. The development of 3D echocardiography has improved this technique as the movement of these specks in 3D space can also now be tracked in any plane and direction. This is particularly successful at showing an increase in twisting and confirming complex shapes of deformation.¹⁰

AI enhancement

There are large databases, for example, the National Echocardiography Database Australia, which lend themselves to the involvement of Artificial Intelligence to improve echocardiography as an imaging technique. The analysis of 3D methods can be much more time-consuming due to greater complexity, so automating this process could improve efficiency and reduce human errors when processing these images. Using large banks of data can inform this automation to provide accurate results.¹¹

FAQ’s

What are the risks involved in echocardiography?

There is no radiation involved in this form of imaging, compared to chest x-rays which can pose a risk of irradiation. Transthoracic echocardiography is extremely low risk as it is non-invasive and simply consists of taking an ultrasound externally across the chest. However, transesophageal echocardiography is highly invasive as a probe is inserted into the esophagus and sedation is needed, which will always involve some risk.

Which method produces the highest quality images?

Chest x-rays give the poorest quality images and can only indicate the rough size of the heart. 2D echocardiography gives a better result but still does not produce as high quality images as 3D echocardiography and cardiac MRIs. Cardiac MRIs do give the highest quality images, but this may be outweighed by the financial and time cost.

How accurate is 3D echocardiography compared to other methods?

2D echocardiography makes several assumptions about the geometry of the heart, which can often be incorrect and can cause major discrepancies between the images produced and the actual size of the heart. Particularly, 2D imaging is very bad at showing twisting, something that 3D echocardiography, alongside speckle-tracking, can show to a much higher degree of accuracy. Whilst cardiac MRIs do produce the most high quality images, 3D echocardiography still images to a high level of accuracy necessary to make a correct assessment of heart enlargement. Additionally, 3D echocardiography is less costly ,faster, with no exposure to magnetic fields and images are less easily disrupted by movement or heartbeat irregularities.

Which method should be used?

To roughly assess the extent of heart enlargement, chest x-rays can be used. However, to further understand the extent of issues, further testing must be done using 2D or 3D echocardiography or cardiac MRI. 3D echocardiography produces high quality images whilst also having much lower time and financial costs compared to cardiac MRIs.

Summary

Changes in the physical size of the heart can indicate heart failure or other cardiac complications. These changes can be diagnosed using images formed through various techniques, including chest X-rays, cardiac MRIs and echocardiography, however each has advantages and disadvantages with some techniques producing higher quality images than others and some being much more costly and time-consuming.

3D echocardiography is a novel technique that aims to combat some of the negatives encountered in 2D echocardiography and produce high quality images to rival that of costly MRIs. As opposed to 2D echocardiography, 3D echocardiography methods do not rely on geometric assumptions to form images and so far more accurately measure the volume of the heart. 

Other developing imaging techniques can be used alongside 3D echocardiography to further improve the accuracy of imaging, such as speckle tracking and AI enhancement. Speckle tracking can further improve the accuracy by using specially designed software to trace distinct marks on cardiac walls and produce complex 3D images. Artificial Intelligence has been shown to be highly promising in automating image production and analysis to accelerate the efficiency of using these techniques.

3D echocardiography is being increasingly used by cardiologists, and a combination of these novel techniques may soon be commonplace in assessing heart enlargement.