Hypertrophic Cardiomyopathy

What Is Hypertrophic Cardiomyopathy & What Causes It?

HCM is one of many genetic heart problems that individuals may not realise they are at risk of inheriting or passing on, or that they may even currently be affected by. It’s estimated that HCM affects 1 in 500 adults. 

In HCM, heart muscle hypertrophies (becomes thicker and/or enlarged), making it more difficult for your heart to pump blood. HCM usually affects the interventricular septum (a muscular wall) separating the two ventricles (the lower chambers of your heart) but can affect any wall of the heart. When the septum and outer walls of the ventricles become thicker and stiffer, your left ventricle (the main pumping chamber) is able to hold and send out less blood with each beat. In the case of hypertrophic obstructive cardiomyopathy, the thickened muscle of your upper septum may also restrict blood from flowing out of the heart. 

The heart muscle thickening in HCM is also abnormal in that the muscle cells are not arranged properly (myofiber disarray), and there is scarring (myocardial fibrosis) between muscle cells. This scarring can trigger potentially harmful arrhythmias (dangerous heartbeats) which can be life-threatening.

In general, hypertrophic cardiomyopathy is inherited. This is where a genetic mutation can be passed down through parents to children, or occurs spontaneously at conception. The mutations in certain genes cause the heart muscle to thicken. Many genes associated with HCM have already been identified, but not all are yet known; scientists and specialists are working to identify and understand exactly which other genes and mutations are responsible for HCM. 

If a parent has a mutation in a gene associated with HCM, they have a 50% chance of passing it on to their child. If the child has inherited the mutation, they are at risk from birth (and even in the uterus during pregnancy) of developing HCM. Similarly, the mutation can occur spontaneously at conception with neither of the parents carrying a mutation that is associated with HCM (this is called a ‘de novo’ mutation).

At this point in time, if an individual has a mutation in a gene associated with HCM, there is no way of reversing this mutation and totally removing the possibility of developing HCM. However, because HCM is very treatable, early diagnosis is vital in improving life expectancy and quality of life. This is why it is important to be aware of what the symptoms of hypertrophic cardiomyopathy are, so you can respond appropriately.

Do You Have Hypertrophic Cardiomyopathy Symptoms?

If you have HCM, you may find you experience some or all of these symptoms to varying degrees:

• Lack of energy, fatigue or exercise intolerance
• Swelling in feet and ankles
• Shortness of breath, especially when exercising or lying down
• Fainting (syncope), especially during or right after exercise
• Chest pain (angina), especially during exercise
• Irregular heartbeats (arrhythmias)
• Heart palpitations (fast, fluttering or pounding heartbeats)

While the above are symptoms of HCM, many can also indicate other genetic heart conditions, like dilated cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy. Similarly, their severity also differs between people. Some people may develop progressive heart issues, while others remain stable or have only minor changes that require a skilled cardiologist to spot. Further, you may not experience the above symptoms all at once or all the time either. Instead, they may only occur in certain circumstances, like exercising. Additionally, while you have risk of HCM from birth, the symptoms may not appear until later. Typically, symptoms occur in early adult years, but some people will not see symptoms until they are mid-life.

If these symptoms are not treated, however mild, complications can occur. These include:

• Atrial fibrillation, where structural changes to the heart lead to fast and irregular heartbeats. This increases your likelihood of blood clots and strokes.
• Reduced blood flow out of the heart as obstruction increases. You may experience dizziness and fainting, shortness of breath, and chest pain as the obstruction worsens over time. 
• Mitral regurgitation (leaking of blood through the mitral valve). HCM can stop the mitral valve (between your left atrium and left ventricle) from closing properly and therefore blood can leak back into the left atrium. If this occurs, you’ll likely find your other HCM symptoms becoming worse.
• Progressive weakness of your heart muscle, and severe heart failure that leads to fluid accumulation in the lungs, abdomen and legs. 

Unfortunately, for some people affected by HCM the first sign of the condition is sudden death. Sudden death usually occurs due to a dangerous heart rhythm (ventricular arrhythmia or ventricular fibrillation) causing a cardiac arrest. If these rhythms occur in risky situations, for example swimming alone or behind the wheel of a car, they can be life-threatening. Sudden death can also happen to young active people who seem otherwise healthy. HCM is a major cause for sudden cardiac death in people younger than 35 years of age. This, therefore, highlights the importance of early diagnosis and accurate treatment to ensure that this catastrophic outcome is avoided. 

Further, as the condition is genetic, the sudden death of a family member can be an indicator to yourself and your family that you all need to be checked for HCM.

How Do You Get a Diagnosis of Hypertrophic Cardiomyopathy?

If you have symptoms of HCM, there are different tests your general practitioner or cardiologist may recommend in order to see exactly what is occurring with your heart. These can include: 

• An ECG (electrocardiogram) to check your heart’s electrical activity and detect abnormal rhythms.
• An echocardiogram (echo) to check how well your heart pumps blood and identify abnormalities, like thicker walls.
• An MRI scan of the heart that can detect more subtle signs of muscle abnormalities.
• A stress test or exercise test to check for dangerous heart rhythms and how well your heart responds to stress.

It is possible for people to have no obvious or only minor signs and symptoms of hypertrophic cardiomyopathy present. Genetic testing is therefore very helpful in accurately determining if someone is at risk of hypertrophic cardiomyopathy. As part of this, your family health history must be evaluated for the possibility of HCM. Often, there are markers in a family history that point towards not just HCM but other inherited heart diseases, such as dilated cardiomyopathy, ARVC and long QT syndrome, because all these conditions can manifest first as sudden unexplained death.

Genetic testing is crucial when considering a diagnosis of HCM. However, you want to be working with an appropriately specialised service that understands the nuances of cardiac genetics. They need to know how HCM can differ between people and how serious it is. Similarly, they need the specialist expertise to choose the most appropriate genetic test and then correctly interpret them for the best prognosis. This specialisation and nuance is why Progenics was created.

How Genetic Testing Can Help

While your physician can build up a strong case for an HCM diagnosis through clinical tests, genetic testing is needed to complete the picture. This is because the specialised testing can reveal which mutations are at play, thereby guiding your treatment and management plans to be as effective as possible. Without genetic testing, your medical evaluation is incomplete.

Further, as HCM can be inherited, your genetic tests can help diagnose family members who are also at risk. While complex clinical evaluations can still help to provide a more accurate picture of their health, and if and how the disease is affecting them, your test results are a compelling reason to have them tested too. As a result, they probably will be diagnosed with HCM more quickly, helping to improve their prognosis.

Are There Signs of Hypertrophic Cardiomyopathy in Your Family Tree?

Genetic testing for hypertrophic cardiomyopathy is a vital tool to confirm that the condition runs in your family, but it is not always the first starting place. Discussing your family’s health history, particularly in regards to heart conditions and issues, and potential symptoms of HCM, your general practitioner or cardiologist can indicate if genetic testing is the appropriate next step.

It can be useful to come prepared for this discussion with your general practitioner or cardiologist with relevant information. Outline your family tree and make a note of any family members who have been diagnosed with HCM, or have had issues that suggest the possibility of an inherited heart condition (for example, sudden unexplained death or unexplained deaths in car accidents).