Spinal muscular atrophy (SMA) mainly affects the nerve cells that control movement, causing muscles to become weak and shrink over time. However, SMA can also affect other parts of the body, making it harder to breathe and eat. Some people with SMA may develop heart problems, such as cardiomyopathy, which weakens the heart muscle.

Although heart problems appear more often in severe forms of SMA, doctors have also linked spinal muscular atrophy type 3 (SMA type 3) — also called Kugelberg-Welander disease or juvenile SMA — to cardiomyopathy. This means some people may experience changes in heart function along with the muscle weakness caused by SMA.

When your child receives an SMA diagnosis, it’s natural to worry, but advances in treatments, nutrition, and respiratory care offer hope for longer, healthier lives — including those with more severe forms of the disease.

What Is Cardiomyopathy?

Cardiomyopathy refers to a group of several conditions that affect the heart muscle, making it harder for the heart to pump blood to the rest of the body. In some cases, cardiomyopathy can lead to heart failure.

People may acquire cardiomyopathy from another disease, condition, or contributing factor, or they may inherit it. Although doctors don’t always know what causes the disease, muscle conditions such as muscular dystrophy and spinal muscular atrophy — both neuromuscular disorders — can cause cardiomyopathy to develop.

Heart Problems With Spinal Muscular Atrophy

Research shows that SMA can sometimes affect more than the muscles used for movement. In some cases, the condition may also involve the heart and blood vessels. Scientists are still learning why this happens and which types of SMA are most affected.

How SMA Affects the Body

Spinal muscular atrophy is a genetic condition that weakens skeletal muscles — the ones that help with movement, breathing, and swallowing. SMA occurs because of a change in SMN1, a gene that helps the body make a protein that keeps nerve cells in the spinal cord healthy. Without enough of this protein, nerve cells die, and muscles become weak or shrink over time.

Although SMA mainly affects skeletal muscles, research shows that it may also involve other organs and body systems — including the heart.

How SMA Might Affect the Heart

Scientists who study the brain and nervous system (neurologists) and those who study the heart (cardiologists) are learning more about how SMA might affect the heart. Some studies suggest that the same SMN1 gene that keeps motor neurons healthy may also play a role in heart development. If the gene doesn’t work correctly, it could affect how the heart grows and functions.

However, not all research findings agree. Some studies show clear signs of heart changes in people with SMA, while others do not. The link between SMA and heart problems is still being studied.

Heart Conditions Linked to SMA

Researchers have found several kinds of heart problems in people with SMA. These include:

• Cardiomyopathy — As mentioned above, this condition has been reported in people with Kugelberg-Welander disease, though it’s not common.
• Congenital heart defects — Some people are born with structural problems in the heart, such as hypoplastic left heart syndrome, in which the left side doesn’t develop properly.
• Heart rhythm changes — Researchers have found that people with SMA, especially types 2 and 3, may have arrhythmias (irregular heartbeats) or atrioventricular block, which affects the heart’s ability to conduct electrical signals from one part to another.

In many cases, doctors believe heart problems in SMA may be linked to breathing and oxygen issues caused by weak respiratory muscles, rather than damage to the heart itself.

What Research Says So Far

A 2017 review of studies found that heart structure problems appear more often in people with severe types of SMA, whereas heart rhythm problems may be seen in types 2 and 3. Still, more research is needed to fully understand how and why SMA affects the heart.

For now, doctors recommend that people with SMA have regular heart checkups, especially if they have symptoms such as chest pain, shortness of breath, or irregular heartbeat. Early detection can help prevent serious complications and improve quality of life.

Symptoms of Cardiomyopathy in Spinal Muscular Atrophy

In the early stages, cardiomyopathy may not cause any signs or symptoms. However, as the condition progresses, some people may develop symptoms such as:

• Breathlessness with physical activity or while at rest
• Cough when lying down
• Fatigue
• Rapid, pounding, or fluttering heartbeat
• Chest discomfort or pressure
• Swelling in the legs, ankles, and feet
• Dizziness, lightheadedness, or fainting
• Bloating of the abdomen (caused by fluid buildup)

You should see your doctor if you experience any of these symptoms. Get emergency treatment if you faint, have severe trouble breathing, or experience chest pain that lasts more than a few minutes.

Treatment and Management of Cardiomyopathy in Spinal Muscular Atrophy

Treatment for cardiomyopathy may involve medication, surgically implanted devices, or different procedures, including — in severe cases — a heart transplant. Doctors choose the approach based on the type and severity of cardiomyopathy. Treatment aims to manage signs and symptoms, keep cardiomyopathy from worsening, and reduce the risk of complications. Ask your doctor whether these treatments are appropriate.

Medications

Your doctor might prescribe medication to help:

• Increase blood flow
• Improve the heart’s ability to pump blood
• Lower blood pressure
• Slow heart rate
• Remove excess fluid from the body
• Prevent blood clots

Surgically Implanted Devices

Several types of devices can be implanted into the heart to help improve function and relieve cardiomyopathy symptoms. These devices include:

• Implantable cardioverter-defibrillator — An implantable cardioverter-defibrillator (ICD) monitors for and corrects abnormal heart rhythms, a serious complication of cardiomyopathy. An ICD doesn’t treat cardiomyopathy itself but works by delivering electric shocks as necessary to control abnormal rhythms.
• Pacemaker — This small device is placed under the skin of the chest or the abdomen. Like an ICD, a pacemaker uses electrical impulses to control arrhythmias.
• Ventricular assist device — A ventricular assist device (VAD), which helps blood circulate through the heart, can be used as a long-term treatment or in the short term while waiting for a heart transplant. VADs are usually considered when less-invasive approaches haven’t worked.

Surgery

Surgery to treat cardiomyopathy may include septal myectomy or heart transplant:

• Septal myectomy — This open-heart surgery involves removing part of the thickened septum (heart muscle wall) separating the two bottom ventricles (heart chambers). Septal myectomy improves blood flow through the heart and reduces mitral valve regurgitation, a condition in which the heart’s mitral valve doesn’t close tightly, allowing blood to flow backward in the heart.
• Heart transplant — A heart transplant may be necessary for those with end-stage heart failure for whom medications and other treatments are no longer effective.

Nonsurgical Procedures

Nonsurgical procedures to treat cardiomyopathy include ablation:

• Septal ablation — A small part of the thickened heart muscle is destroyed by injecting alcohol through a long, thin tube (called a catheter) into the artery that feeds that area. This helps the heart pump blood more easily and reduces strain on the muscle, similar to the goal of septal myectomy.
• Radiofrequency ablation — Catheters are inserted through the blood vessels into the heart to treat abnormal rhythms. Electrodes at the tips transmit energy to damage a small spot of the abnormal heart tissue responsible for the arrhythmias.

Work With Your Doctor

Understanding how SMA may affect the heart can help you and your care team monitor symptoms, explore treatment options, and take steps to support your overall health.

Join the Conversation

On mySMAteam, people share their experiences with spinal muscular atrophy, get advice, and find support from others who understand.

Are you managing cardiomyopathy or another heart condition related to SMA? Let others know in the comments below.