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PubMed This is a summary of 24 peer-reviewed journal articles Updated
Cardiology

What Are the Risk Factors for Needing an ICD in HCM?

At a Glance

Most people with hypertrophic cardiomyopathy do not need an ICD. Your doctor may recommend one if you have high-risk features for sudden cardiac death, including heart wall thickness of 30mm or more, unexplained fainting, extensive heart scarring, or a family history of sudden cardiac death.

In this answer

3 sections

01

The Major Risk Factors

02

How Doctors Calculate Your Risk

03

Making the Decision Together

In hypertrophic cardiomyopathy (HCM), an implantable cardioverter-defibrillator (ICD) is a small device placed under the skin to protect you from sudden cardiac death (SCD). While most people with HCM have a normal life expectancy and a low risk of SCD, a small percentage are at higher risk. An ICD does not cure HCM, prevent abnormal rhythms from starting, or act like a typical pacemaker (which speeds up a slow heart rate); instead, it acts as a safety net to deliver a shock that restores a normal rhythm if a dangerous arrhythmia occurs. Determining if you need this safety net involves identifying specific high-risk features in your medical history and imaging tests. The major risk factors include massive thickening of the heart muscle, a family history of sudden cardiac death, unexplained fainting, the presence of an apical aneurysm, and extensive heart muscle scarring [1][2].

The Major Risk Factors

When assessing your need for an ICD, your cardiology team will look for these primary risk factors:

  • Massive Wall Thickness: In HCM, the heart muscle (myocardium) becomes abnormally thick. If the maximum thickness reaches 30 millimeters (mm) or more, your risk of dangerous heart rhythms increases [1][3].
  • Family History of Sudden Cardiac Death: If a close blood relative (like a parent, sibling, or child) passed away suddenly and unexpectedly—especially at a young age—this is considered a significant risk factor [2][4].
  • Unexplained Fainting (Syncope): While fainting can happen for many harmless reasons (like dehydration), sudden, unexplained fainting episodes—especially recent ones occurring within the last 6 months—can be a warning sign of an underlying dangerous heart rhythm [5][6].
  • Apical Aneurysm: This is a condition where the tip (apex) of the heart’s lower left pumping chamber becomes thinned and bulges outward. The presence of a left ventricular apical aneurysm is a strong indicator of increased risk [7][1].
  • Extensive Scarring (LGE): Doctors use a cardiac magnetic resonance imaging (MRI) scan to look for late gadolinium enhancement (LGE), which is the medical term for scar tissue in the heart muscle. Having extensive scarring (typically 15% or more of the heart muscle) significantly raises the risk of sudden cardiac events [8][9][10].

Additional Risk Markers

In addition to the primary factors, doctors also evaluate other elements to complete your risk profile:

  • Non-sustained Ventricular Tachycardia (nsVT): These are brief, self-stopping runs of a very fast, abnormal heart rhythm typically captured on a wearable heart monitor [1][11].
  • Left Ventricular Systolic Dysfunction: This occurs when the heart’s squeezing function becomes weak, generally defined as an ejection fraction (a measure of pumping efficiency) dropping below 50% [1][12].

How Doctors Calculate Your Risk

Your care team does not look at these factors in isolation. Instead, they use comprehensive risk assessment tools to estimate your personal risk. For example, the American Heart Association (AHA) and American College of Cardiology (ACC) guidelines use a checklist of these clinical risk factors to guide decisions [9][13]. In Europe, doctors often use a formula called the HCM Risk-SCD score, which calculates an estimated 5-year risk percentage [14][15].

Because these tools evaluate risk slightly differently, it highlights why combining them with advanced imaging—like a cardiac MRI to check for scarring—is essential for making an accurate, individualized recommendation [16][17]. While an MRI is a standard recommendation for most HCM patients, if you haven’t had one recently, you should feel empowered to ask your doctor if you are a candidate for it.

Making the Decision Together

Deciding to get an ICD is not purely a mathematical calculation; it requires shared decision-making between you and your doctor [18][19]. An ICD provides a life-saving therapy [20]. However, living with an ICD also carries risks and lifestyle implications. You might experience temporary driving restrictions (especially if you have received a shock), be advised to avoid certain high-contact sports, or face complications related to the device itself (like inappropriate shocks when the device fires unnecessarily or issues with the wires connecting it to your heart) [21][22].

Because getting an ICD is a major physical and emotional event, the decision must align with your personal values, lifestyle, and how you view the balance of risk versus peace of mind [23][24].

Common questions in this guide

What makes a person with hypertrophic cardiomyopathy high risk for sudden cardiac death?
High-risk factors include a heart muscle thickness of 30 millimeters or more, extensive scarring on an MRI, an apical aneurysm, unexplained fainting, and a family history of sudden cardiac death.
How does an ICD help with hypertrophic cardiomyopathy?
An implantable cardioverter-defibrillator acts as a safety net for your heart. If it detects a dangerously fast or abnormal heart rhythm, it delivers a shock to restore a normal heartbeat and prevent sudden cardiac death.
Does everyone with HCM need an ICD?
No, most people with hypertrophic cardiomyopathy have a normal life expectancy and a low risk for sudden cardiac death. An ICD is only recommended for the small percentage of patients who show specific high-risk features.
What is late gadolinium enhancement (LGE) on my cardiac MRI?
Late gadolinium enhancement is the medical term for scar tissue in the heart muscle, which can be seen on a cardiac MRI. Having extensive scarring (typically 15% or more of the heart muscle) significantly increases your risk for dangerous heart rhythms.
Will getting an ICD restrict my daily activities?
Living with an ICD may come with some lifestyle changes, such as temporary driving restrictions if the device delivers a shock and avoiding certain high-contact sports. Your doctor will help you understand how an ICD fits into your specific lifestyle.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is my current maximum wall thickness in millimeters, and how has it changed over time?
  2. 2.Has my cardiac MRI shown any late gadolinium enhancement (LGE) or an apical aneurysm? If I haven't had an MRI recently, should I get one?
  3. 3.What is my calculated risk score for sudden cardiac death based on the current guidelines?
  4. 4.If an ICD is recommended, what specific lifestyle changes, such as driving restrictions or sports limitations, should I expect?
  5. 5.Am I a candidate for a subcutaneous ICD (S-ICD), or would I need a traditional transvenous device?

Questions For You

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Related questions

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References

References (24)
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This information explains the risk factors for needing an ICD in hypertrophic cardiomyopathy for educational purposes only. Always consult your cardiologist or electrophysiologist to assess your personal sudden cardiac death risk.

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