What is HCM?

Definition

Hypertrophic cardiomyopathy (HCM) is a chronic and progressive disease¹ characterized by thickening of the left ventricular muscle tissue in the absence of other causes².

HCM is largely caused by dysfunction of the sarcomeres (highly organized subcellular structure that form the basic units of muscle tissue), leading to an excess of cross-bridges between myosin and actin. This results in hypercontractility, reduced relaxation and compliance^3-4, disorganized sarcomeres, and increased cardiac stiffness⁵.

Quick fact

HCM is a chronic, progressive disease that can lead to serious, long-term health problems^1-2. Next to progressive heart failure, sudden cardiac death is a major cause of mortality in HCM⁶, with risk higher at younger ages. (e.g., ≤40 years)^7-8.

Understanding Hypertrophic Cardiomyopathy

Healthy cardiac muscle

In a healthy sarcomere, myosin binds to actin and forms cross-bridges that regulate myocardial contraction and relaxation³.

Heart with Excess Actin-Myosin Cross-Bridges in HCM

In HCM, there is an excess of actin-myosin cross-bridges⁴, with fewer myosin heads in the inactive state⁹. This can have the following effects:

Increased contractility: The physiological alteration of the protein filaments, and indirectly the disruption of calcium regulation within the sarcomere, lead to a state of hypercontractility^14-15.
Reduced relaxation: Increased calcium sensitivity in cardiomyocytes leads to deficits in sarcomere relaxation^{3; 15}.
Reduced efficiency: More energy is used during sarcomere contraction, which can decrease mechanical efficiency^{4; 15}.

The excess actin-myosin cross-bridges can increase myocardial stiffness and reduce the volume of blood pumped out¹¹.

Hypertrophic cardiomyopathy is defined as increased left ventricular wall thickness that is not solely explained by abnormal loading conditions (such as hypertension or valvular disease).

Typically, a wall thickness ≥15 mm in one or more LV segments is diagnostic in adults, or ≥13 mm when there is a positive family history or genetic confirmation¹².

Hypercontractility and the subsequent hypertrophy of the ventricular walls are key features of HCM¹³.

The thickening of the left ventricular wall cannot be explained by other cardiac or systemic diseases^{2; 14; 15}.

Prevalence & symptoms

HCM is more common than generally thought. Although it is the most common inherited heart disease, HCM is often recognized and diagnosed late, or not at all, in many people^{16; 3; 17}.

Discover more about HCM by downloading the Cardiomyopathies Matter Roadmap.

In adult population-based cohorts, the prevalence of HCM is approximately 1 in 500 (0.2%)¹⁶.

Contemporary data suggest prevalence may be as high as ~1 in 200 in some cohorts¹⁸.

80–90% of people with HCM are likely undiagnosed^19-20-21.

Symptoms of HCM can resemble those of other conditions, making diagnosis challenging. Among diagnosed patients with obstructive HCM (oHCM), 33% were NYHA Class I, 50% Class II, 16% Class III, and 1% Class IV²².

Distinction between obstructive (oHCM) and non-obstructive HCM(nHCM)

Obstructive HCM (oHCM)

Hypertrophy of the ventricular septum causes obstruction of the LVOT, reducing blood flow from the left ventricle^{3; 23}.
Peak instantaneous LVOT gradient is ≥30 mmHg at rest OR with provocation (Valsalva or exercise). Severe obstruction is typically defined as ≥50 mmHg (rest or provoked)^{12; 23}.

Non-obstructive HCM (nHCM)

Left ventricular hypertrophy is present, but with little or no obstruction of blood flow from the left ventricle¹⁴.
Peak instantaneous LVOT gradient is <30 mmHg at rest and with provocation (Valsalva or exercise)^{12; 23}.

In patients with HCM, LVOT obstruction is an important and independent predictor of progression to severe symptoms such as heart failure or death²⁴.

Family history & genetics¹²

HCM is most often inherited in an autosomal dominant manner. In clinically diagnosed HCM, a pathogenic sarcomere‑gene variant is identified in up to 60% of patients.

HCM is commonly hereditary; when a pathogenic variant is present, each child has a 50% chance of inheriting it
The genes involved code for either a contractile sarcomere protein or a protein regulating contraction. The principal sarcomere genes most commonly implicated include MYH7 and MYBPC3; less commonly TNNI3, TNNT2, TPM1 and MYL3. Genetic testing is recommended in probands to enable cascade screening of relatives.
Determining family history over three to four generations can help confirm a genetic origin of HCM and identify family members at risk.

Q&A

What is hypertrophic cardiomyopathy (HCM) and how does it affect the heart?

How common is HCM?

What are the typical signs and symptoms of HCM, and why can diagnosis be challenging?

How do family history and genetic testing influence the management of HCM?

Patient Resources

Clear and accessible materials are available to support your patients in understanding hypertrophic cardiomyopathy and finding trustworthy guidance. From personal stories to a dedicated website and detailed brochures, each resource is designed to deepen understanding and encourage informed conversations.

Patient website

Clear, reliable online information about HCM, its symptoms, and practical tips for patients and families.

Patient stories

Testimonials from people living with HCM, sharing their experiences and how they manage daily life.

Patient brochures

Concise guides for patients with obstructive hypertrophic cardiomyopathy (oHCM), covering the disease, symptoms, treatments, and everyday advice.

Next step: Treatment options

Learn more about the role of cardiac myosin inhibition
within today’s therapeutic landscape for HCM.

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Learn more: Imaging modules

Learn how to apply imaging techniques to identify
and assess HCM in clinical practice.