Hypertrophic Cardiomyopathy (HCM)

What happens in hypertrophic cardiomyopathy

In HCM the muscle cells of the left ventricle, the main pumping chamber, are enlarged and arranged in a disorganized pattern, with scarring between them. The wall becomes thick (often 15 to 30 mm instead of about 10 mm) and stiff. This causes problems in three ways:

1. Stiffness: the ventricle cannot relax and fill well, so pressure backs up into the lungs. This causes breathlessness, especially with exercise.
2. Obstruction: in about two-thirds of people, the thickened septum and the mitral valve narrow the exit from the heart, either at rest or with exertion. This is called hypertrophic obstructive cardiomyopathy (HOCM). See hypertrophic obstructive cardiomyopathy for obstruction-specific treatment.
3. Electrical instability: the disorganized, scarred muscle can trigger dangerous ventricular rhythms and atrial fibrillation.

The pumping strength is usually normal or even above normal. That makes HCM different from other forms of cardiomyopathy, where the heart is weak and enlarged.

Symptoms

Many people with HCM have no symptoms and are diagnosed after a murmur, an abnormal ECG or family screening. When symptoms occur, they are often triggered by exercise, heavy meals, dehydration or alcohol:

• shortness of breath on exertion, the most common symptom
• chest pain or tightness, because thick muscle needs more oxygen than the coronary arteries can supply
• palpitations, from extra beats or atrial fibrillation
• dizziness or fainting, especially during or right after exercise
• tiredness and reduced exercise capacity
• swollen ankles in later stages

Symptoms can start at any age, from infancy to old age. They often appear in adolescence or early adulthood.

Causes: is hypertrophic cardiomyopathy genetic?

Yes, in most cases. HCM is usually caused by a variant in a gene that codes for a sarcomere protein, the contractile machinery of heart muscle cells. The most common are MYH7 and MYBPC3. Inheritance is autosomal dominant: each child of an affected parent has a 50% chance of inheriting the variant.

Not everyone who carries the gene develops thickening, and severity varies a lot even within one family. Genetic testing finds a cause in about 30 to 60% of people.

Other conditions can mimic HCM and need different treatment, including cardiac amyloidosis, Fabry disease, Danon disease and the "athlete's heart" seen in highly trained athletes.

Diagnosis

1. Physical exam: a murmur that gets louder when standing or straining (Valsalva) suggests obstruction.
2. ECG: abnormal in most people with HCM, showing thick muscle or deep inverted T waves.
3. Echocardiogram: measures wall thickness and checks for obstruction at rest and during exercise or Valsalva. A gradient of 30 mmHg or more counts as obstructive.
4. Cardiac MRI: measures thickness precisely and shows scarring (late gadolinium enhancement), which helps predict risk.
5. Ambulatory heart monitor (24 to 48 hours or longer): looks for ventricular tachycardia and atrial fibrillation.
6. Exercise test: checks blood pressure response, symptoms and provoked obstruction.
7. Genetic testing: confirms the cause and allows cascade testing of relatives.

Screening relatives

First-degree relatives (parents, siblings, children) should have an ECG and echocardiogram, and genetic testing if a variant has been found in the family. Children are usually screened from diagnosis in the family or from early childhood, and gene carriers are rechecked every 1 to 3 years, because thickening may develop in the teens or later.

Treatment

Medicines

• Beta-blockers (such as metoprolol) or non-dihydropyridine calcium channel blockers (verapamil, diltiazem): slow the heart so it fills better, easing symptoms and obstruction.
• Cardiac myosin inhibitors (mavacamten): reduce excessive muscle contraction and obstruction in symptomatic obstructive HCM. They require regular echocardiograms because they can lower pumping strength too far.
• Disopyramide: an older drug that reduces obstruction.
• Diuretics, used carefully, for fluid buildup.
• Anticoagulants for anyone with HCM and atrial fibrillation, because stroke risk is high regardless of other risk scores.

People with obstruction should avoid dehydration and be cautious with medicines that widen blood vessels or reduce filling, such as nitrates and some blood pressure and erectile dysfunction medicines. Check with your cardiologist first.

Septal reduction procedures

For severe symptoms from obstruction despite medicine:

• Surgical septal myectomy: removes part of the thick septum through open-heart surgery. It is the most durable option and is best done at an experienced HCM center.
• Alcohol septal ablation: a catheter procedure that injects alcohol into a small artery to create a controlled scar that thins the septum.

Preventing sudden cardiac death

An implantable cardioverter-defibrillator (ICD) shocks the heart back to a normal rhythm if a dangerous arrhythmia happens. It is recommended after a cardiac arrest or sustained ventricular tachycardia, and considered for people with risk factors:

• a close relative who died suddenly from HCM
• unexplained fainting
• very thick walls (30 mm or more)
• extensive scarring on MRI
• a weakened pumping function (ejection fraction below 50%)
• an apical aneurysm
• runs of non-sustained ventricular tachycardia, especially in younger people

Advanced HCM

A small number of people develop end-stage HCM, in which the muscle thins and weakens. They are treated like heart failure, and heart transplant is an option.

Living with HCM

• Exercise: most people can and should do regular moderate exercise. Current US guidelines allow some people to take part in competitive sports after a thorough evaluation and shared decision-making with an HCM specialist.
• Stay hydrated and avoid very large meals and heavy alcohol, which can worsen obstruction.
• Pregnancy is usually well tolerated but should be planned with a cardiologist and genetic counselor.
• Regular follow-up every 1 to 2 years with echocardiogram and monitoring, sooner if symptoms change.
• Family members should learn CPR, and you can discuss whether an AED at home makes sense.

Outlook

With current care, the yearly risk of HCM-related death has fallen below 1% at specialized centers, and most people have a normal or near-normal life expectancy. Many people remain free of symptoms for decades. The main ongoing issues are atrial fibrillation, which affects about 1 in 4, and gradual heart failure symptoms in some.

Frequently asked questions

What is the life expectancy with hypertrophic cardiomyopathy?

Most people with HCM who receive specialist care have a normal or near-normal life expectancy. Risk assessment, ICDs for those at high risk, anticoagulation for atrial fibrillation and septal reduction for obstruction have made HCM-related deaths uncommon.

Can hypertrophic cardiomyopathy cause sudden death?

Yes, but it is uncommon. HCM is one of the known causes of sudden cardiac death in young people and athletes. Doctors estimate each person's risk from family history, fainting episodes, wall thickness, MRI scarring and heart rhythm monitoring, and offer an ICD to people at high risk.

Is hypertrophic cardiomyopathy genetic?

Usually, yes. It is most often caused by a variant in a heart muscle protein gene, inherited in an autosomal dominant pattern, so each child of an affected parent has a 50% chance of carrying it. First-degree relatives should be screened with an ECG, echocardiogram and, where available, genetic testing.

Can you exercise with HCM?

Most people with HCM benefit from regular moderate exercise such as brisk walking, cycling or swimming. Avoid sudden bursts of very intense effort and dehydration unless your cardiologist has cleared you. Decisions about competitive sport are made individually with an HCM specialist.

What is the difference between HCM and HOCM?

HCM is the overall condition of abnormally thick heart muscle. HOCM, hypertrophic obstructive cardiomyopathy, is the form in which the thick septum blocks blood leaving the heart, at rest or with exertion. About two-thirds of people with HCM have obstruction at some point.

Can hypertrophic cardiomyopathy be cured?

There is no cure, but treatment controls it well. Medicines and procedures relieve symptoms and obstruction, and ICDs prevent sudden death. Research into gene-targeted therapies is ongoing.