Hypertrophic Cardiomyopathy (HCM) Complications: What to Know
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Complications of Hypertrophic Cardiomyopathy (HCM)

Complications of Hypertrophic Cardiomyopathy (HCM)
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Updated on October 9, 2025
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Hypertrophic cardiomyopathy (HCM) is a genetic condition in which the heart muscle thickens abnormally, increasing one’s risk of several serious heart complications. The muscle thickening disrupts heart function, obstructing blood flow out of the heart and reducing the amount of blood pumped to the body, which causes the heart to need more energy and oxygen to work. If you have HCM, you may have complications such as arrhythmias and heart failure. It’s critical that you check in with your cardiologist regularly, even if your symptoms are mild or barely noticeable.

Arrhythmias

Arrhythmias, or irregular heart rhythms, are common complications of HCM. The thickened heart muscle disrupts the electrical pathways that coordinate heartbeat, leading to arrhythmias.

Atrial fibrillation (afib) is the most frequently encountered arrhythmia in people with HCM, occurring in over 25 percent of cases.

 Afib causes the upper heart chambers to beat rapidly, irregularly, and out of sync with the lower chambers. Symptoms may include palpitations, lightheadedness, and chest discomfort, but afib can be “silent” as well. It can also increase your risk of blood clots that can lead to stroke.

Additionally, people with HCM often experience arrhythmias of the ventricles, or the lower heart chambers, including nonsustained ventricular tachycardia (short pulses of rapid ventricular beats) and ventricular premature beats (extra heartbeats that disrupt the regular heart rhythm). Ventricular arrhythmias can inhibit effective blood pumping, cause symptoms similar to afib, and lead to sudden cardiac death.

Embolic Phenomena

When arrhythmias like afib develop in people with HCM, the irregular heart rhythm may allow blood to pool in the atria, promoting clot formation. These clots can break free and travel to other parts of the body, including the brain, causing embolic phenomena like stroke.

Anticoagulant medications (blood thinners), including vitamin K antagonists like warfarin, are key to reducing this risk if you have HCM and afib. Treatment with alcohol septal ablation, a procedure in which alcohol is injected into the heart’s artery to shrink thickened tissue, can also address an obstruction in the atria, though it doesn’t directly address afib.

Heart Block

The abnormal muscle thickening in HCM can also interfere with the heart’s electrical conduction system. In rare cases, it can lead to heart block, also known as atrioventricular block, which occurs when electrical signals are delayed or blocked as they travel through the heart.

Once considered benign, first-degree atrioventricular block (when the electrical signals are just slowed) may not cause symptoms.

 However, it may still be associated with an increased risk of death from causes like arrhythmia, sudden death, heart failure, and stroke.

 Complete atrioventricular block, or third-degree atrioventricular block, typically causes symptoms like dizziness, fainting, and fatigue, and it requires immediate treatment with a pacemaker.

Endocarditis

HCM can change the structure of the heart valves, the mitral valve in particular, which separates the left atrium and ventricle. This change, combined with turbulent blood flow, can create sites where bacteria like streptococcus can attach and grow, leading to an infection of the inner layer of heart tissue called endocarditis.

Infective endocarditis typically causes symptoms affecting the heart and respiratory systems that are similar to other HCM symptoms. While it’s an uncommon complication, endocarditis can severely damage the mitral valve, leading to severe regurgitation (blood that normally flows from the left atrium to the left ventricle leaks back into the atrium), progressive heart failure, shock from lack of blood in the body, and sepsis (bloodstream infection).

The bacteria responsible for the infection often come from the mouth, typically after dental procedures. Maintaining good dental hygiene and promptly treating infections are important preventative strategies.

Heart Failure

Heart failure, or congestive heart failure, occurs when the heart is unable to pump blood efficiently. In HCM cases, heart failure usually develops from left ventricle outflow tract obstruction, a condition in which blood flow from the left ventricle is blocked due to thickened heart muscle. Common symptoms include difficulty breathing, fatigue, chest pain, dizziness, and fainting.

Heart failure can also develop from diastolic dysfunction, an inability of the left ventricle to fill with blood properly. This condition, known as heart failure with preserved ejection fraction or diastolic heart failure, causes many of the same symptoms as other types of heart failure, including shortness of breath with exertion or when lying flat, fatigue, and swelling in the legs and ankles.

End-Stage HCM

While many people with HCM live for decades, about 3 percent progress to end-stage HCM, also known as burnt-out HCM. During this stage, the thickened heart muscle starts to thin and large areas of scar tissue develop, replacing functioning heart muscle. These changes weaken the heart, and its ability to either fill with blood or pump blood to the rest of the body declines significantly.

People with end-stage HCM often experience symptoms of advanced heart failure. They’re also more likely to experience other complications like afib and blood clots.

Risk factors that increase a person’s likelihood of progressing to end-stage HCM include:

  • Advanced age
  • Being male
  • Increased atrial enlargement
  • Reduced amount of blood being pumped out of the heart

Sudden Death

Sudden death or sudden cardiac death (SCD) occurs when the heart abruptly stops beating, causing a person to collapse, lose consciousness, stop breathing, and die within minutes. It’s usually caused by ventricular arrhythmias, sometimes in people with HCM who had no previous symptoms.

The overall annual risk for sudden death in HCM patients is approximately 1 percent. The risk of SCD is higher in younger individuals (under 35 years old) with HCM, particularly athletes. Some additional risk factors for SCD include:

  • Abnormal blood pressure response during exercise
  • Family history of SCD or fainting
  • Massive heart muscle thickening
  • Recurrent fainting episodes
Risk calculators are available from organizations like the American Heart Association to help you determine your specific risk of HCM-SCD within five years.

Avoiding Complications With HCM

The good news is that many risks of HCM complications can be managed and, in some cases, prevented.

Seeing your cardiologist for regular, comprehensive evaluations and understanding warning signs like fainting, new palpitations, or unexplained breathlessness can help you and your healthcare provider detect complications early. The best way to prevent complications is to manage your condition through various interventions, including:

  • Anti-arrhythmic drugs
  • Drugs that affect muscle contraction, such as beta-blockers, calcium-channel blockers, and sodium-channel blockers
  • Implantable cardioverter-defibrillators, which monitor and correct abnormal heart rhythms
  • Lifestyle changes, such as not smoking, following a heart-healthy diet, and getting regular physical activity
  • Permanent pacemakers
  • Surgery to reduce thickened heart tissue or treat issues like mitral valve abnormalities

The Takeaway

  • Hypertrophic cardiomyopathy is a genetic condition in which the heart muscle thickens abnormally, increasing your risk of serious complications like arrhythmias, heart block, and heart failure.
  • One of the most common complications of HCM is arrhythmia, which can lead to atrial fibrillation and ventricular arrhythmias and increase your risk of stroke.
  • HCM can also lead to other issues such as an infection of the heart’s inner layer called endocarditis and, in rare cases, a progression to end-stage HCM, in which the heart muscle thins and weakens.
  • Your risk of HCM complications can be managed with regular check-ins with your cardiologist and interventions such as medication and lifestyle changes.
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Chung Yoon, MD

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Chung Yoon, MD, is a noninvasive cardiologist with a passion for diagnosis, prevention, intervention, and treatment of a wide range of heart and cardiovascular disorders. He enjoys clinical decision-making and providing patient care in both hospital and outpatient settings. He excels at analytical and decision-making skills and building connection and trust with patients and their families.
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