Introduction

A plethora of different conditions can threaten the livelihood of our hearts, the vital organ that is necessary for sustaining life. Congenital heart conditions, cardiomyopathies, cardiac tumours and diseases of the heart valves can all interrupt the way in which our heart functions, leading to the necessity of cardiac imaging. 

Cardiac imaging can help physicians visualise the extent of the issue, differentiate it from other conditions and determine the correct course of treatment. In the last decade, cardiac magnetic resonance imaging (MRI) has emerged as an imaging technique that can elucidate the cause behind cardiac discomfort more clearly than ever before.¹ The following article will therefore explore the role of cardiac MRIs and weigh the benefits they offer against other imaging modalities.

Causes and consequences of heart enlargement

Heart enlargement, also known as cardiomegaly, is not a disease itself but a symptom of underlying cardiovascular conditions. As such, its diagnosis is important and it plays a valuable role in the diagnosis of other serious conditions such as Chronic Obstructive Pulmonary Disease (COPD). 

Commonly, hearts enlarge because the body is trying to compensate for other issues caused. High blood pressure, also known as hypertension, can force the heart to enlarge so it still has the capacity to push blood around the body against the existing resistance in the blood vessels. As this takes more effort, the heart muscle increases (hypertrophy) and then the chambers of the ventricles enlarge as this increased pressure is faced over time.²

Enlargement can also be caused by respiratory issues, such as COPD or scarring in the lungs from long-term infections (e.g. Long COVID-19), and as the blood cannot efficiently get oxygen, the heart works harder to push blood faster and at higher pressures around the body to get limited oxygen supplies to the cells around the body. Over time, this can also cause heart enlargement, as well as different cardiomyopathies can weaken the heart’s ability to pump blood efficiently, causing irregular heart rhythms (arrhythmias) and possibly even heart failure.⁴ Cardiomyopathies can be inherited or caused by various other lifestyle/ environmental factors.

Diseases of the heart valves, especially where they don’t open or close properly, can also cause heart enlargement due to the interactions of the blood flowing improperly through the heart. This valvular disease can develop during our lives or be present from birth (congenital), along with a host of other congenital heart problems that can lead to heart enlargement. Infections in the heart can also lead to improper pumping, which in turn can lead to compensation in the form of heart enlargement.

Heart enlargement in general can be dangerous, with consequent arrhythmias and inability to pump (fibrillations), possibly leading to heart failure. As such, treatment is necessary for both the underlying cause and the enlargement itself, where possible. Imaging of the heart is the best way for physicians to prepare for diagnosing and treating enlarged hearts. With a variety of different imaging modalities available, each has its advantages, and the following will look at each method in more detail to ascertain which is best used in specific circumstances. Tumours or cancer of the heart can also cause heart enlargement, such as angiosarcomas.

Imaging modalities for heart enlargement

Below is a detailed overview of different imaging techniques that can assist in the diagnosis and treatment of heart enlargement, with a discussion on the benefits and limitations that they offer.

Chest x-ray

Chest x-rays pass small doses of ionising radiation through the body and thus create a 2D image of the heart in the chest with its accompanying organs. As the x-rays are absorbed at different rates by different types of tissues, completely solid substances appear whiter, whereas very hollow areas, such as the lungs, appear darker. This forms an image which can be used to analyse the thickness of different structures, and it is very quick.⁵ 

It is not costly and widely available, and thus is used as one of the first imaging modalities to try to visualise any issues within the chest cavity. However, as only the relative thickness of each structure is identified with overlapping organs present in the chest cavity, a lot of detail cannot be gained from this, but it can show if the heart is generally larger than it should be. Other imaging techniques may be used to confirm whether another issue is involved.

Echocardiography

Echocardiography is an ultrasound of the heart. It uses high-frequency waves of energy to produce real-time images of the heart. A probe is placed directly on different parts of the body and emits the waves, which can then bounce off internal structures, like parts of the heart, and can then be converted into an image. Because the image can be produced very quickly, it can produce a moving image of the heart and the ejection of blood through the different ventricles can be visualised in real-time.⁶

The image produced gives details about the thickness of the heart muscle, heart size and valvular function. However, because it focuses on producing images based on waves bouncing back, in patients with lung issues or obesity, it can be difficult to accurately read the image produced, especially because the image is of low quality, making it unclear.

Computed Tomography (CT)

CT uses special computer algorithms to convert X-rays into an image of a cross-section of the heart. Contrast dye can be injected into the patient’s blood vessels to make the individual structures of the heart more visible. However, the muscle of the heart is less distinctly visualised than with an MRI, and the iodine dye used for CT contrasts can cause allergic reactions in many patients.⁷

As X-rays are used, the patient is exposed to ionising radiation, which can alter DNA and potentially cause illness. Therefore, the number of CTs performed within a year must be limited to decrease the risk of DNA damage, but due to the speed at which the CT can be performed makes it very useful in emergencies. An example of this could be when a cardiac tumour that has caused heart enlargement breaks off and causes a stroke or block blood supply to other vital areas.

Magnetic Resonance Imaging (MRI)

Although the above methods are good for specific purposes, MRI stands out as one of the best imaging modalities, especially when preparing for surgical intervention. The clarity and resolution of the heart muscle (myocardium) and the other heart structures can never be visualised more clearly than with an MRI, making surgical planning easier as the margins of tumours, scarring and valvular disposition can be visualised, especially with gadolinium-dye (to which most people don’t have allergies).³

This greater clarity can also result in better accuracy when diagnosing cardiac issues, allowing physicians to differentiate between heart enlarging issues in a non-invasive manner, such as myocarditis (inflammation of the heart muscle) or amyloidosis ⁹ (a protein called amyloid can build up in different parts of the body, causing those parts to dysfunction and possibly leading to heart enlargement in some cases).

Unlike other types of imaging, MRI uses magnetic rays which aren’t ionising, so can be safely used, even during pregnancy. The contrast dyes are also safer than those used for CT, except for those with severe kidney disease, in which case an MRI without the dye may be more useful. Previously, MRI imaging would be blurred when an image was taken of a moving heart, but now, with technical advancement, accurate images are being produced.⁸ 4D MRIs can now also image blood flow in 3 different directions, making the visualisation greater than that of echocardiography.

However, it is important to consider that a typical MRI can take anywhere from 30-90 minutes, whereas CT scans can produce images within seconds. Another aspect to consider is the fact that metallic objects, such as a hip replacement, shouldn’t be present in the patient during MRIs, in which case another imaging modality may need to be considered. However, detailed diagnostic and surgical images cannot be created as accurately with any other imaging technique, as MRIs remain unparalleled in this respect.

The cost of an MRI is higher due to the superior nature of the image produced, but the accuracy of the images produced is also unmatched. The time taken for your healthcare physician to interpret and convey your results may depend on various factors, such as whether comparison is required with previous scans or if other tests also need to be considered.

Summary

Ultimately, MRIs offer many benefits over other imaging modalities when imaging enlarged hearts, with the only limitations being metallic object prohibitions and the time taken to produce a scan. The detail produced can help diagnose many complicated pathological conditions, including those present from birth and those developed over time. As such, they are used the world over to diagnose and help patients with many different types of heart conditions.