What Is Shone's Complex

Overview

Shone’s complex is a rare, congenital (present at birth) combination of heart conditions, specifically affecting the left side of the heart. It was first discovered by Dr. John Shone in 1953, who described the four different heart defects which characterise this syndrome. These four malformations of the heart include: parachute mitral valve, supravalvular mitral membrane, subaortic stenosis and coarctation of the aorta. Other cardiac conditions have been associated with Shone's complex patients since its initial discovery, however they are not considered diagnostic features. This collection of defects results in the blockage of normal blood flow in and out of the left side of the heart, impairing the function of this vital organ.¹

This article will detail the different components of Shone’s complex, as well as how this syndrome is diagnosed and treated. 

How does the heart typically function?

In order to understand what Shone’s complex is and how it affects the heart, let us first consider how the healthy heart works in pumping blood around the body. The heart is split into four chambers²:

• Right atrium - The upper right part of the heart
• Right ventricle - The lower right part of the heart
• Left atrium - The upper left part of the heart
• Left ventricle - The lower left part of the heart

Each of the chambers of the heart play a key role in helping the heart effectively and efficiently pump blood around the body:²

1. Blood vessels pick up oxygen-poor blood from organs around the body (which have used up this oxygen to generate energy to continue their specific functions) and carry it to the right side of the heart, into the right atrium.
2. Blood flows through the right atrium and into the right ventricle, where it is then pushed out the heart and towards the lungs, through blood vessels called pulmonary arteries.
3. The lungs deliver oxygen into the blood from the air breathed in.
4. Blood vessels called pulmonary veins then carry the now oxygen-rich blood back to the heart, this time to the left side of the heart, into the left atrium.
5. Blood flows through the left atrium and into the left ventricle, where it is then pushed out of the heart and into the aorta, which is the largest artery (a type of blood vessel) in the body.
6. The aorta is then responsible for pumping the oxygen-rich blood to all the organs. 
7. The process is repeated.

Also important to note is that the heart contains four valves - two on each side of the heart. These valves are like little trap doors, which open and close to control the amount of blood that flows into each chamber of the heart. These valves are vital in preventing any blood flowing in a backwards direction, hence they maintain the correct flow of blood in and out of the heart. The valves which are important to remember in order to fully understand Shone’s complex are:²

• Mitral valve - This is the little trap door which separates the left atrium to the left ventricle. Hence, it regulates blood flow from the upper left chamber of the heart to the lower left chamber
• Aortic valve - This is the little trap door which separates the left ventricle from the aorta. Hence, it regulates blood flow from the lower left chamber of the heart to the aorta outside of the heart. This is the final part of the heart that encounters the oxygen-rich blood before it leaves the heart to travel around the body

Components of Shone’s Complex

As stated above, Shone’s complex is a rare collection of cardiac complications which uniquely occur only on the left side of the heart. These develop very early on in unborn babies as the heart is developing.¹ The four main conditions included in this syndrome are detailed in the following sections. 

Parachute mitral valve

This condition consists of the malformation of the mitral valve - instead of resembling a little trap door with two flaps, it ends up resembling a parachute (hence the name).³ This deformity of the valve occurs due to there being errors within the structures of the heart that have the role of holding the mitral valve in its place. These structures are called the chordae tendineae and papillary muscles.⁴ 

In a healthy heart, the chordae tendineae attach the two flaps of the mitral valve to the papillary muscles, found in the walls of the left ventricle of the heart. These papillary muscles are important in controlling the opening and closing of the mitral valve, effectively preventing any backflow of blood or too much blood from entering the left ventricle at one time.⁵ In Shone’s complex patients who suffer from parachute mitral valve, all their chordae tendineae are attached to just one papillary muscle, leading to the valve being malformed and not functioning as efficiently.⁴ 

Supravalvular mitral ring

This condition consists of the growth of extra tissue (termed membrane or ridge) from the wall of the left atrium, which ends up obstructing the mitral valve. This membrane can range from being thin to thick - the thicker the membrane is, the more of a problem it becomes. This is because its formation over the top of the mitral valve can lead to the blocking of proper blood flow.⁶ 

Subaortic stenosis

This condition consists of the thickening of the muscles surrounding the aortic valve. When such thickening occurs, it leads to the narrowing of the space given for blood to pass through the aortic valve. This results in the restriction of proper blood flow, and the left ventricle of the heart having to work harder to pump blood out of its chamber and into the aorta.⁷ 

Coarctation of the aorta

This condition consists of the narrowing of the aorta. It’s as if there is a noose tightened around a section of the aorta, narrowing the vessel and in turn restricting the normal flow of oxygenated blood leaving the left ventricle towards all organs around the body which need oxygen. This constriction most commonly occurs in the part of the aorta where it splits into smaller arteries, which carry oxygenated blood to different organs around the body. This occurs due to the aorta not forming properly as the baby grows during pregnancy. Because of this narrowing, the left ventricle has to work harder to pump blood out of the heart through the constricted aorta. This can ultimately damage the heart, as the left ventricle is “overworking” itself.⁸ 

Other cardiac conditions associated with Shone’s complex

Although Shone’s complex was initially associated with only four types of cardiac complications (detailed above), nowadays experts have identified further defects which have been found in Shone’s complex patients: 

• Cor triatriatum - This condition consists of the pulmonary veins failing to connect normally to the left atrium. This results in the failure of delivering oxygen-rich blood to the left side of the heart, in turn meaning this blood cannot be as effectively pumped around the body
• Bicuspid aortic valve and small aortic valve annulus - A normal aortic valve has three flaps (known as tricuspid). In some Shone’s complex patients, their aortic valve only has two flaps. This in turn restricts how wide the valve can open itself (the opening itself being called an annulus). Hence, the bicuspid valve coupled with the smaller annulus together cause an obstruction of proper blood flow 
• Hypoplastic (stiff) left ventricle - This is when the left ventricle is small and stiff, meaning it cannot function as effectively in pumping blood out of the heart and into the aorta
• Small aortic arch - This is when the aorta is small and stiff, which is the opposite of what the aorta should be (wide and elastic). This condition is often found in people who have coarctation of the aorta, which together can lead to chronic high blood pressure

Symptoms of Shone’s complex

The symptoms that Shone’s complex patients may feel depends on how severe their group of conditions are. If their cardiac malformations are mild, then symptoms may not occur at all. However, if they have significant blockages and constrictions within the left side of their heart, then patients can experience congestive heart failure (when the heart is not pumping blood as efficiently as it should).⁹ 

Examples of symptoms patients may feel include:⁹

• Shortness of breath
• Uncontrollably high blood pressure 
• Fatigue
• Rapid breathing
• Wheezing 
• Poor intake of food and drink
• Poor weight gain
• Faster heart rate
• Fluid retention in the legs 
• Anaemia 
• Frequent pneumonia 

Also depending on how severe the cardiac defects are, symptoms related to Shone’s complex can appear from the first week of life (if defects are severe) or when the patient is a child or adolescent (if defects are less severe).⁹ 

Diagnosis of Shone’s complex

In order to be diagnosed with Shone’s complex, you must have at least 3 of the defining 4 heart conditions detailed above. If you have 2-3 of these defects, then they would be diagnosed as incomplete Shone’s complex (which is actually more common than complete Shone’s complex).¹⁰ 

Healthcare providers use a range of diagnostic tests to determine whether a patient has Shone’s complex. Examples of the most common examinations include:

• Echocardiograms - This exam takes an ultrasound to evaluate the heart and its chambers, the nearby blood vessels, and the surrounding chest wall. This allows the healthcare provider to check the structure and the function of the heart. This is considered the most effective way of diagnosing Shone’s complex¹¹ 
• CT scans - This exam takes X-rays of the patient’s heart from multiple angles to create an accurate and detailed image of the organ
• MR angiography - This exam uses magnets, radio waves and computers to assess the heart’s surrounding blood vessels¹²
• Cardiac catheterisation - This exam is invasive, as it involves putting a long, thin and flexible tube called a catheter into a blood vessel of the patient (usually in the arm). This tube is then moved through the vessel to the heart, to assess the structure of the organ¹³ 

Treatment options for Shone’s complex

The most common and effective treatment option for Shone’s complex patients is surgery. In fact, most babies who are diagnosed with the syndrome undergo surgery soon after their birth. The surgery type depends on the defects the baby has, how severe they are, and how extensive their symptoms are. It is often the case that Shone’s complex babies need multiple surgeries to address all their heart defects.¹⁰ 

The most common surgical interventions include the following:¹⁰

• Surgical repair of the aorta coarctation
• Surgical repair or replacement of the mitral and aortic valve
• Removal of the subaortic membrane

Specifically for older or relapsing patients with coarctation of the aorta, balloon angioplasty and placement of a stent is done. This surgical procedure involves using a balloon-like structure to open the narrow part of the aorta, and then using a stent to keep the aorta open.¹⁰  

Adults who have/were born with Shone’s complex are advised to visit a heart specialist doctor (cardiologist) at least once a year to get their heart and any potential symptoms checked. During these visits, patients can undergo various tests, such as:¹⁰  

• Echocardiograms
• CT scans
• Exercise tests 
• Cardiac MRI stress tests  

FAQs

What causes Shone’s complex?

Shone’s complex develops in the very early stages of foetal development, and it occurs equally in both sexes and all races and ethnic groups. The cause for these multiple cardiac defects remains relatively unknown.¹⁴ 

However, a recent study has found that 11% of their Shone complex patient pool were associated with a random change (known as mutation) in their MYH6 gene, which is typically found in cells of the foetus’ heart.¹⁵ However, much more research needs to be carried out to explore this further.  

How rare is Shone’s complex? 

Shone’s complex is very rare - it accounts for less than 1% of all heart diseases present at birth (congenital). 

What is the prognosis of Shone’s complex?

The long-term prognosis of Shone’s complex is typically poor, as it is estimated the syndrome has a mortality rate of 24-27% (meaning 24-27 deaths per 1000 patients).¹⁶ However, the prognosis does depend on the patient’s symptoms and the severity of their defects. For instance, babies who receive surgical treatment early into their life do tend to grow into adults who experience a good quality of life. 

Can I get pregnant if I have Shone’s complex?

For people assigned female at birth  (AFAB) who have Shone’s complex, but have undergone surgery to fix their defects, pregnancies typically have favourable outcomes. However, there are higher risks of any pregnancy complications for both the mother and the baby (e.g. unsuccessful pregnancy).¹⁷ 

How can I prevent my child from having Shone’s complex? 

As the cause of the disease is relatively unknown, there is no guaranteed way to prevent a child from being born with Shone’s complex. However, you can increase chances of your baby being healthy by: 

• Avoiding any substances that could harm your baby’s growth during your pregnancy, such as illegal drugs and alcohol
• Discussing any potential risks of any medications you may take with your healthcare provider
• Making sure you have the rubella vaccination, as rubella is an infection that can affect heart development¹⁸
• Taking prenatal vitamins to aid your baby’s development 

Summary

Shone’s complex is a rare collection of heart defects, present at birth in patients. These multiple cardiac complications restrict normal blood flow, specifically into and out of the left side of the heart. Symptoms to look out for which are tell-tale signs of Shone’s complex include those of congestive heart failure. In order to treat this syndrome and for the patient to live a healthy life, surgery is needed shortly after birth. In their adult years, patients are strongly advised to visit a cardiologist for regular check-ups, to make sure no recurrence of their cardiac defects has happened.