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Hypertrophic cardiomyopathy: Optimism tinged with caution

Most people with this genetic condition develop thickened heart muscle but lead normal lives.

“You have a really big heart” is usually a wonderful compliment — except when it comes from your cardiologist and the term cardiomyopathy crops up in the conversation. An oversized heart usually isn’t a good sign.

The heart can enlarge for many reasons. High blood pressure, problems with the valves of the heart, and other “insults” can make the muscular walls of the heart’s lower chambers (ventricles) become thicker than they should be. The most common inherited cause is a condition known as hypertrophic cardiomyopathy — translation: excessive and harmful thickening of heart muscle. Instead of helping the heart pump more powerfully, the extra muscle may interfere with its function.

What is HCM?

Hypertrophic cardiomyopathy (HCM) is a genetic condition. Its main characteristic is thickening (hypertrophy) of the heart muscle. This thickening, along with other changes in muscle composition and function, can sap the heart’s pumping power and can cause problems with its electrical system.

The word “can” in the preceding sentence is important. Some people with hypertrophic cardiomyopathy develop symptoms that limit their activity. Some die from it. For most people, though, hypertrophic cardiomyopathy has little or no effect on life or longevity. Right now it’s impossible to tell how HCM will affect an individual, making this condition fraught with as much uncertainty as potential danger.

What causes HCM?

In order to contract and relax over and over again, muscle tissue must be highly organized and carefully constructed. That’s doubly true for heart muscle, which contracts and relaxes once a second, or 2.5 billion times over the average lifetime. A small change in the size, shape, or activity of muscle cells can hamper contraction and relaxation.

Hypertrophic cardiomyopathy usually arises because of a mutation in one of a dozen or so genes. Each of these genes is involved in the task of making properly functioning sarcomeres, the basic units of a muscle. These genes cause muscle tissue to become disorganized and thicker. It also forms scar tissue, a process known as fibrosis.

About 600,000 Americans (one in every 500) have HCM, many because of a sarcomere mutation. Most inherited the faulty gene from a parent. In a small number, the mutation occurs spontaneously soon after conception, causing the individual to develop HCM even though neither of his or her parents carried a gene mutation.

The mutations that cause hypertrophic cardiomyopathy are dominant. If you carry one, each of your children has a 50-50 chance of inheriting it and very likely developing HCM. However, having the gene mutation doesn’t automatically mean that the disease will affect your life.

“Many as-yet-unknown factors influence the penetrance of these mutations, meaning how they ultimately affect the architecture and function of the heart,” says Dr. Carolyn Ho, a cardiologist and hypertrophic cardiomyopathy specialist at Harvard-affiliated Brigham and Women’s Hospital.

In some individuals, the effect of the faulty gene is apparent early in life; some infants with HCM have profound heart muscle thickening at birth. Sometimes it doesn’t make its presence known until adolescence, which is a common time for hypertrophic cardiomyopathy to be diagnosed. And some people with a sarcomere mutation have seemingly normal hearts — in size and activity — into middle or old age.

Hypertrophic cardiomyopathy

illustration of heart showing hypertrophic cardiomyopathy

Classic signs of hypertrophic cardiomyopathy include thickening of the septum (the muscular wall separating the right and left sides of the heart) and the left ventricle (the heart’s main pumping chamber). Instead of neatly lining up, muscle cells become irregular and disorganized. The thickened septum can restrict blood flow out of the left ventricle or throw off the mitral valve.

How HCM affects heart function

The characteristic physical change associated with hypertrophic cardiomyopathy is thickening of the septum (the muscular wall separating the left and right sides of the heart). In a normal heart, the septum is just under half an inch thick. In someone with hypertrophic cardiomyopathy, it can widen to 2.5 inches. The excess muscle takes up space inside the heart’s chambers that is normally used to collect blood. It can also get in the way of blood flowing out of the heart. This is called obstructive cardiomyopathy. To make matters worse, the extra muscle is usually stiff and has trouble relaxing between beats. All of these factors result in a heart that may not work as efficiently as it should. This can lead to shortness of breath, fainting, and other worrisome symptoms, especially during physical activity. Other problems include these:

  • An enlarged septum can interfere with the function of the mitral valve and hinder the flow of blood from the left ventricle to the aorta. It can also prevent the mitral valve from closing tightly with each contraction, allowing blood to leak backward. Both of these interfere with the delivery of oxygenated blood to all parts of the body.

  • Coronary arteries may not be able to deliver enough blood to the extra muscle tissue. This can lead to chest pain similar to angina caused by cholesterol-clogged arteries.

  • Disorganized muscle fibers and scar tissue can throw off the precise pattern of electrical signals that governs regular heartbeats. This can lead to the most feared consequence of hypertrophic cardiomyopathy — sudden cardiac arrest.

Diagnosing HCM

Hypertrophic cardiomyopathy makes its presence known in one of four main ways:

Symptoms. Fainting spells, unexplained shortness of breath, chest pain, or palpitations can herald hypertrophic cardiomyopathy.

Chance. Sometimes the condition is discovered by accident, on an electrocardiogram done as part of a routine physical exam or when a doctor hears a heart murmur.

Screening. Screening means checking seemingly healthy individuals for a disease. All close relatives of anyone diagnosed with HCM should be screened for the condition. Youngsters and young adults often learn they have HCM when undergoing an exam to check them out for a sports team or competitive athletics.

Cardiac arrest. Sometimes a cardiac arrest — the sudden cessation of heartbeats capable of circulating blood — is the first sign of a problem. HCM is the leading cause of sudden death in youths and young adults, accounting for about one of every four cases.

If your doctor thinks you might have hypertrophic cardiomyopathy, an echocardiogram helps pin down the diagnosis. It uses sound waves to show the size and shape of the heart, as well as the blood flow patterns through it. An MRI scan can not only detect a thickened heart but can also reveal fibrosis, a common feature of hypertrophic cardiomyopathy.

A full genetic test, which costs about $3,000, can help provide a definitive diagnosis. If such a test in an individual with a thickened heart reveals a sarcomere mutation, it proves the person has hypertrophic cardiomyopathy and could pass it to his or her children. More focused genetic testing can then be done for family members to determine if they’ve inherited that mutation. Those carrying the mutation may have or may develop hypertrophic cardiomyopathy, and can also pass the mutation on to their children. If they don’t carry the mutation, they don’t have the condition or the genetic factor that causes it, and so can’t pass it on to future generations. Unfortunately, identifying a genetic mutation doesn’t yield precise information about the age at which hypertrophic cardiomyopathy will appear or how serious it will be.

Managing HCM

The variability of HCM means that treatment or management must be tailored to each individual. If you don’t have any symptoms, then what you need is vigilance and lifestyle changes. If or when symptoms appear, here’s an overview of the main therapies.

Medications. Prescription medications are the first line of defense against shortness of breath, chest pain, and other symptoms of hypertrophic cardiomyopathy. A beta blocker or calcium-channel blocker can reduce the heart’s workload and help the ventricles fill with blood. An anti-arrhythmic drug called disopyramide (Norpace) can help the heart beat less forcefully and reduce the obstruction to blood flow out of the heart.

Surgery. Removing or destroying some of the tissue in an enlarged septum can relieve symptoms. One way to do this is with an open-heart procedure called myectomy. Another way is with a procedure called septal ablation that doesn’t require surgery. Instead, it uses injections of alcohol to shrink the upper part of the septum. Although recovery time is shorter with alcohol ablation, less is known about long-term complications.

Implantable cardioverter-defibrillator (ICD). An important cause of death among people with hypertrophic cardiomyopathy is the unpredictable and sudden onset of fast, erratic contractions in the ventricles. The only treatment is to halt these lethal arrhythmias — called ventricular tachycardia and ventricular fibrillation — with an electric shock. This can be done by implanting an ICD.

Living with HCM

Since hypertrophic cardiomyopathy can range from a condition that never affects health or longevity to one that requires heart transplantation, there’s no single way to live with it. No matter how mild or severe your hypertrophic cardiomyopathy, three keys to living well with it are knowledge, vigilance, and planning: Know how the disease can affect your body and how it may affect your family members. Be alert for warning signs. Plan for the worst and hope for the best. Here are a few general guidelines for living with hypertrophic cardiomyopathy:

Know the warning signs. Fainting, feeling dizzy, finding yourself unexpectedly short of breath, feeling your heart race, or experiencing chest pain that doesn’t go away with rest may be signs of impending trouble.

Make a plan. Talk with your doctor about whom to call if you are experiencing one or more of the warning signs. Put your emergency numbers on the refrigerator or by the telephone. Assemble your medical records and put them where they can be grabbed on a moment’s notice.

Eat, drink, and be healthy. Follow a basic heart-healthy eating plan. Go easy on salt, saturated fat, refined grains, sugary beverages, and alcohol. Emphasize unsaturated fats, whole grains, fruits and vegetables, and lean protein. Drink plenty of fluids, especially when you exercise — dehydration can make it harder for the left ventricle to work efficiently.

Keep moving. For most people with hypertrophic cardiomyopathy, light to moderate exercise is perfectly fine, even healthy. Most experts recommend that people with the condition not participate in competitive sports or intense or physically demanding activities that strain the heart, such as weight lifting.

See your doctor. If you are doing well and have no symptoms, seeing your doctor once a year should be fine. But if you have symptoms or have an ICD, make a point to see him or her more often.

Restore the beat. Sudden cardiac arrest is the most catastrophic consequence of hypertrophic cardiomyopathy. Make sure loved ones, neighbors, co-workers, and coaches know how to do cardiopulmonary resuscitation. It can keep blood circulating through the body until a normal heart rhythm can be restored. Also make sure they know where to find the closest automated external defibrillator, the “shock boxes” that can jolt the heart back into a healthy rhythm.

Posted by: Dr.Health

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