There are two types of hypertrophic cardiomyopathy (HCM): nonobstructive hypertrophic cardiomyopathy (nHCM) and obstructive hypertrophic cardiomyopathy (oHCM).

Hypertrophic cardiomyopathy is a heart disease that causes the heart muscle to thicken. Hypertrophic means enlarged, and cardiomyopathy refers to diseases of the heart muscle. Knowing the key differences between the two types of HCM can help you better understand your symptoms, treatment options, and outlook.

Heart Muscle Changes in Nonobstructive vs. Obstructive HCM

HCM usually causes the septum, the wall between the left and right ventricles, to thicken. As the heart muscle thickens, the heart has to work harder to pump blood. This extra work can strain the heart.

Both types of HCM change the structure of the heart muscle. Similar changes in nHCM and oHCM can cause:

• Thick, stiff heart muscle walls
• A smaller cavity (opening) inside the left ventricle
• Damage to the small blood vessels that carry oxygen-rich blood to the heart muscle
• Arrhythmias (irregular heartbeats)

However, the two types of HCM also affect the heart in different ways.

In nHCM, the thickened, stiff heart muscle makes it harder for the lower chambers of the heart to expand normally. This limits their ability to fill with blood and reduces blood flow in people with nHCM.

In oHCM, the heart muscle thickening is more severe and blocks or reduces blood flow from the left ventricle. This blockage limits blood flow through the aortic valve and into the aorta, the body’s main artery. The aorta carries oxygen-rich blood to organs and tissues throughout the body.

Symptom Patterns in Nonobstructive and Obstructive HCM

At first, people with either type of HCM may not have symptoms. Because symptoms can be mild or absent early on, HCM is believed to be underdiagnosed. Both types of HCM are progressive, meaning they worsen over time, and symptoms may become more severe.

Similarities in Symptoms

In general, symptoms of nHCM and oHCM are similar because the heart can’t pump blood efficiently.

In obstructive HCM, the heart muscle thickening is more severe and blocks or reduces blood flow from the left ventricle.

Common symptoms of both types of HCM can greatly affect quality of life and include:

• Shortness of breath, especially during exercise or physical activity
• Fatigue (extreme tiredness that doesn’t improve with rest)
• Dizziness or lightheadedness
• Fainting
• Chest pain
• Heart palpitations (feeling like the heart is pounding, racing, or beating irregularly)

Differences in Symptoms

Obstructive HCM usually causes worse symptoms than nHCM, especially in the early stages. This is because the blockage limits blood flow more.

However, symptoms of nHCM can also worsen over time. In some cases, symptoms can become as severe as those of oHCM.

One study found that many symptoms overlap between oHCM and nHCM. However, people with oHCM had more symptoms at once, and their symptoms happened more often and lasted longer.

As a result of more severe symptoms, people with oHCM also have higher rates of mental health conditions such as depression compared with people who have nHCM.

Diagnosis of Nonobstructive and Obstructive HCM

Diagnosing HCM usually starts with a family history and physical exam. A heart murmur can be a sign of a blood flow problem linked to HCM. When listening to your heart, your doctor may hear a whooshing or swishing sound that suggests a murmur.

In general, symptoms of both nHCM and oHCM are similar because the heart can’t pump blood efficiently.

If your doctor suspects either type of HCM, they’ll likely recommend imaging tests to look for thickening of the heart muscle and check heart function. Tests used to diagnose HCM include:

• Electrocardiogram (ECG or EKG), which measures electrical activity in the heart
• Echocardiogram, an ultrasound that shows the structure of the heart
• Cardiovascular magnetic resonance imaging, which provides detailed images of the heart
• Cardiac catheterization, a procedure that checks blood flow and pressure in the heart

If these tests show HCM along with blocked blood flow, the diagnosis is considered oHCM.

A stress echocardiogram is an ultrasound performed while you exercise. This test may also help determine whether HCM is obstructive. Genetic testing may also be recommended.

Treatment Options for Nonobstructive and Obstructive HCM

Fortunately, treatment options for both types of HCM continue to improve. Your cardiology care team can tell you more about new and emerging therapies that may be right for you, depending on the type of HCM you have.

Medications

Standard treatment for both types of HCM includes medications that slow the heart rate and help the heart pump blood more easily. These include:

• Beta-blockers
• Calcium channel blockers
• Heart rhythm medications
• Blood thinners

Standard treatment for both types of HCM includes medications that slow the heart rate and help the heart pump blood more easily.

Cardiac myosin inhibitors (CMIs) are a newer type of medication used to treat oHCM. CMIs can help relieve symptoms, reduce obstruction in the heart muscle, and improve heart function. Two CMIs are approved to treat oHCM: aficamten (Myqorzo) and mavacamten (Camzyos).

Invasive Procedures and Surgery

Procedures and surgeries that may help manage HCM include:

• Septal myectomy — Open-heart surgery to remove part of the thickened septum (wall between the heart’s chambers)
• Septal ablation — A procedure that uses alcohol to reduce the heart muscle wall thickness
• Implantable cardioverter-defibrillator — A device implanted in the chest to detect irregular heart rhythms and deliver electrical shocks to restore a normal heartbeat

Future Treatments

Researchers are working on promising new treatments that may improve heart structure and function in both types of HCM.

Gene therapies are also being studied. Researchers are looking into the genetic differences between oHCM and nHCM to help develop more targeted treatments.

With new therapies in the pipeline, treatment for HCM continues to advance. Talk with your cardiologist about treatment options that may be most appropriate for your type of HCM.

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