Understanding Your Risk of Sudden Cardiac Arrest With Hypertrophic Cardiomyopathy (HCM)

If you’ve been diagnosed with hypertrophic cardiomyopathy (HCM), you probably have lots of questions about what the future will bring. You might’ve heard that HCM raises your risk of sudden cardiac arrest — a medical emergency in which the heart suddenly stops beating. And now you’re wondering whether that’s true and how worried you should be.

So, let’s get straight to the facts.

HCM does make you more likely to have sudden cardiac arrest than someone without the condition. But that’s only if the condition goes untreated.

Cardiologist Milind Desai, MD, explains why HCM can lead to this life-threatening complication, which factors put you at a higher risk and what you can do about it.

Why HCM raises your risk of sudden cardiac arrest

HCM is a type of heart disease that thickens areas of your heart muscle, in turn disrupting blood flow out of your heart. There are four main features of HCM that create conditions where sudden cardiac arrest could occur:

• Thickened muscle: The muscles that make up your heart can become too thick (hypertrophied). This may affect your heart function, including the way electrical signals travel through the muscles. Disrupted signals may lead to abnormal heart rhythms (arrhythmias) that can cause sudden cardiac arrest.
• Disorganized muscle: “When you have HCM, your heart’s muscles are in a state of disarray,” Dr. Desai explains. “Think of a house with evenly arranged bricks versus an older church where the bricks are all over the place. This disorganized pattern forces your heart to work harder to pump blood.”
• Fibrosis: It’s also common to have scarring (fibrosis) in between the thickened, disorganized muscles. To continue the brick house analogy, it’s like there’s damage to the mortar that holds the bricks together.
• Abnormal coronary arteries: Your coronary arteries supply blood to your heart muscle. “With HCM, those vital vessels are dysplastic, meaning they’re abnormal,” he says. “This may keep your heart muscle from getting enough blood, which adds to the scar formation.”

Having one or more of these features raises your risk for a dangerous type of heart rhythm called a ventricular arrhythmia.

“Ventricular arrhythmias can stop your heart from pumping blood, meaning you go into cardiac arrest,” Dr. Desai explains. “Instead of beating effectively, your heart quivers.” When this happens, you need immediate medical care. Cardiac arrest can be fatal within minutes.

This can all sound pretty scary. But there’s an important caveat. These HCM features are most dangerous when they’re unrecognized and untreated. Once you have a diagnosis and your care team is monitoring and treating the condition, you’re in a much safer place.

How your risk is determined

Imagine a large room filled with people who have HCM. Each person’s risk for cardiac arrest is slightly different. That’s because many other factors play a role besides the four features common to everyone with HCM.

“We have tools that we can use to identify your individual level of risk,” Dr. Desai says. “This is called risk stratification. We look at your medical history, your family history and the condition of your heart to understand the odds of sudden cardiac arrest happening in the next year.”

You can expect these risk assessments on a yearly basis. Your cardiologist will tell you if you need any tests as part of each year’s assessment. For example, you’ll likely have an echocardiogram every year and a cardiac MRI every three to five years. 

He continues that there are certain “high-risk” features that cardiologists look for. These include:

• You have a first-degree family member (parents, siblings or children) who died suddenly of heart-related causes.
• You’ve gone into cardiac arrest in the past.
• You have a fast, abnormal heart rhythm called a ventricular tachyarrhythmia.
• There’s scarring on at least 10% of your heart muscle.
• You have left ventricular dysfunction, meaning your heart’s ejection fraction is less than 50%.
• There’s a weak, bulging area at the bottom tip of your heart called an apical aneurysm.

“Having one or more of these factors heightens your risk above others with HCM,” Dr. Desai says. “This might sound frightening. But we use this knowledge to take action and protect you. With the right treatment plan, we can get your risk down to a much safer level.”

How to lower your risk

Your cardiologist will determine if you have any high-risk features. If you do, they’ll talk with you about next steps, which may include placement of an implantable cardioverter defibrillator (ICD).

An ICD is a device that a surgeon places in your chest. It constantly monitors your heart rhythm. If it detects a dangerous rhythm, it sends an electrical shock to your heart to restore a normal rhythm. This prevents you from going into cardiac arrest.

That means even if you’re at a high risk of cardiac arrest, you’re not powerless or alone. An ICD can be lifesaving — and give you peace of mind.

“If you don’t have high-risk features at this time, take comfort in that knowledge,” Dr. Desai encourages. “But because HCM is a lifelong condition, it’s important to be aware that your risk may change over time.”

What does that mean for your day-to-day routine? Stay vigilant — but don’t let the worry consume you. Be proactive in managing HCM by:

• Taking your prescribed medications: These might include myosin inhibitors, if you have obstructive HCM. If you have the nonobstructive form, your cardiologist might prescribe other medications that help your heart work better.
• Making lifestyle changes: From heart-healthy foods to moderate-intensity exercise, there’s a lot you can do to give your heart some extra love. Even small changes can help reduce your risk of coronary artery disease. “People with HCM can still get heart attacks,” Dr. Desai cautions. “So, a heart-healthy lifestyle is key.”
• Going to your follow-ups: You’ll see your cardiologist each year for a risk evaluation. They’ll review your medical history, run tests and determine if your risk for cardiac arrest has changed. They’ll adjust your treatment plan accordingly.

Final thoughts

Having HCM is by no means a guarantee that you’ll have sudden cardiac arrest someday. In fact, many people live long, healthy lives with HCM and never experience serious complications. But it’s important to understand the factors that doctors consider when determining your risk and planning your treatment.

Dr. Desai offers some reassuring advice as you continue to navigate life with HCM: “If your HCM is well-managed, your risk for sudden cardiac death matches that of someone your age and sex who doesn’t have HCM. That risk is less than 0.5% per year, which is pretty amazing compared to where we started.”

He understands that many people with HCM fear the unknown. “But in 2026, thanks to robust testing and treatment, there should be nothing left unknown. We can measure your risk and map out a plan to protect you. So, you can worry less and live more.”