Hypertrophic Cardiomyopathy (HCM): What Patients Need to Know

Hypertrophic cardiomyopathy, almost always shortened to HCM, is the most common inherited heart condition. It affects roughly one in five hundred people. Many of those people never know they have it, because HCM can be entirely asymptomatic until an echocardiogram incidentally picks up thickened heart muscle. For other patients, it is the reason for unexplained shortness of breath, chest pain, fainting, or, in the most tragic cases, sudden cardiac death in a young athlete.

The last five years have transformed how cardiologists treat HCM. New medications, refined risk stratification, better imaging, and updated guidelines have turned HCM from a feared diagnosis into a very manageable one for most patients. This article walks through the diagnosis, the variants, the risks, and the treatment landscape that patients deserve to understand.

What HCM Actually Is

HCM is defined by unexplained thickening of the left ventricular wall, typically 15 millimeters or greater in maximum diastolic thickness, without another cause. Walls of 13 to 14 millimeters can be diagnostic when a family member has HCM or when a patient carries a pathogenic variant in a sarcomere gene. In children, the diagnosis uses body surface area-adjusted z scores.

Cardiologists confirm the diagnosis with echocardiography or cardiac MRI. MRI is particularly valuable because it shows late gadolinium enhancement, which marks areas of fibrosis within the thickened muscle. The more fibrosis, the higher the arrhythmia risk.

Under the microscope, HCM has a distinctive look. Muscle fibers are enlarged and arranged in disorganized patterns, which cardiologists call myocyte disarray. Interstitial fibrosis fills the gaps between cells, and small intramural coronary arteries can become thick-walled. These microscopic changes are what drive both the mechanical problems and the electrical instability.

The Genetics

HCM is fundamentally a disease of the sarcomere, the molecular machine that makes heart muscle contract. Mutations in genes that code for sarcomeric proteins throw off the contractile apparatus, and the muscle remodels in response.

Two genes account for about half of familial cases. MYH7 codes for beta-myosin heavy chain, and MYBPC3 codes for myosin-binding protein C. Dozens of other sarcomeric and sarcomere-related genes account for smaller fractions of cases. Inheritance is autosomal dominant, meaning each child of an affected parent has a fifty percent chance of inheriting the variant.

Up to forty percent of patients with clinically obvious HCM have no identifiable genetic cause and no affected family members. This nonfamilial HCM is an active research area. Common genetic variants likely act as modifiers, producing both monogenic and polygenic susceptibility patterns.

The Phenotypes: Obstructive, Non-Obstructive, and Apical

HCM is asymmetric in most cases, with the thickest muscle at the basal interventricular septum, just below the aortic valve. When that thickening is severe enough, it narrows the outflow tract and produces left ventricular outflow tract obstruction, often called LVOT obstruction. The mitral valve leaflet can be pulled forward by the narrowed outflow tract in a phenomenon called systolic anterior motion, or SAM, which can worsen the obstruction and cause mitral regurgitation.

About one-third of patients have obstruction at rest, and another third develop obstruction only with provocation, such as standing, straining, or exercise. The remaining third are non-obstructive. The distinction matters because obstructive HCM has more treatment options and different prognostic implications.

Apical HCM is a distinct variant in which thickening is concentrated at the apex rather than the septum. It is more common in Japanese populations and has a characteristic spade-shaped left ventricle on imaging. Obstruction is unusual, and prognosis tends to be more favorable, though apical aneurysms can develop over time.

Diastolic dysfunction is common across all phenotypes. The thickened, fibrotic ventricle does not relax normally, leading to elevated filling pressures, left atrial enlargement, and eventually atrial fibrillation.

What Symptoms Look Like

Many HCM patients are asymptomatic and identified only through family screening or an incidental echo. When symptoms appear, they include exertional shortness of breath, chest pain, palpitations, lightheadedness, syncope, or signs of heart failure. Atrial fibrillation is a common complication and is poorly tolerated because patients with HCM depend on the atrial kick for filling the stiff ventricle.

For most patients, the clinical course is relatively benign. The overwhelming majority of people with HCM live a normal lifespan. The minority who are high risk are precisely the group we focus our most intense monitoring and treatment on.

Sudden Cardiac Death Risk Stratification

HCM is an important cause of sudden cardiac death, particularly in adolescents and young adults. The risk is not evenly distributed across patients. Most of the attention in HCM care, and most of the guideline guidance, centers on identifying the minority of patients whose risk is high enough to warrant an implantable cardioverter defibrillator.

Major risk factors include nonsustained ventricular tachycardia on ambulatory monitoring, unexplained syncope, a family history of sudden cardiac death, and severe hypertrophy, usually defined as maximal wall thickness of thirty millimeters or greater. Late gadolinium enhancement on cardiac MRI refines risk further, with extensive enhancement correlating with adverse outcomes. A large meta-analysis of over seven thousand HCM patients found that carriers of sarcomere gene mutations had earlier disease onset and higher sudden death rates than non-carriers.

The ACC/AHA and ESC each have risk stratification calculators that integrate these factors. The approach in my practice is to discuss risk openly with every HCM patient, monitor closely, and offer ICD placement when the calculated risk crosses guideline thresholds.

Medical Management

For symptomatic obstructive HCM, medications are the first line.

Beta-Blockers

Beta-blockers have been the foundation of obstructive HCM therapy for more than half a century. They slow heart rate, extend diastolic filling, and reduce outflow tract obstruction. Doses are titrated upward as tolerated, balanced against symptomatic bradycardia. Evidence for beta-blockers in HCM is based largely on physiology and clinical experience rather than large randomized trials, but they remain first-line for most obstructive patients.

Calcium Channel Blockers and Disopyramide

Non-dihydropyridine calcium channel blockers, particularly verapamil, are an alternative or additive option. Disopyramide, an older antiarrhythmic with strong negative inotropic effect, is reserved for patients whose symptoms persist on beta-blockers or calcium channel blockers.

Mavacamten (Camzyos)

Mavacamten is a first-in-class cardiac myosin inhibitor approved by the FDA in 2022 for symptomatic NYHA class II or III obstructive HCM. It directly targets the molecular defect in HCM by reducing the number of active actin-myosin crossbridges, lowering hypercontractility and outflow obstruction. In trials, mavacamten improved LVOT gradients, symptoms, and functional capacity in 30 to 60 percent of patients.

The drug carries a Risk Evaluation and Mitigation Strategy in the United States because of the potential for ejection fraction to drop below 50 percent. This happened in 5.7 percent of patients attributable to the drug alone, and up to 7 to 10 percent when other clinical factors were considered. Temporary discontinuation is sometimes required. Regular echocardiographic monitoring is part of the REMS protocol.

Aficamten (Myqorzo)

Aficamten is the next-in-class cardiac myosin inhibitor, approved by the FDA for symptomatic obstructive HCM. It works by the same broad mechanism as mavacamten but has no clinically important drug-drug interactions and is designed to have a shallower dose-response relationship, which makes titration safer. The MAPLE-HCM trial tested aficamten as monotherapy against metoprolol. For patients who cannot tolerate mavacamten's monitoring requirements or drug interactions, aficamten is an attractive option.

Septal Reduction Therapy

When medications do not adequately control symptoms in obstructive HCM, septal reduction therapy becomes the next consideration. There are two options: surgical septal myectomy and alcohol septal ablation. Both remove or inactivate enough septal muscle to eliminate outflow obstruction.

Surgical myectomy is performed through an open-heart approach. In experienced hands at high-volume centers, operative mortality is well under one percent, and symptomatic relief is durable. It is preferred for younger patients, those with concurrent mitral valve pathology, or those needing coronary bypass.

Alcohol septal ablation is a catheter-based procedure in which absolute alcohol is injected into a septal perforator branch of the left anterior descending artery, creating a controlled infarct in the septum. It avoids open-heart surgery, which makes it appealing for older patients or those with significant comorbidities, but it can cause heart block requiring a pacemaker.

Either procedure relieves symptoms but does not alter the underlying genetic disease or prevent progression. Patients remain under lifelong cardiology care.

ICD Indications

Implantable cardioverter defibrillators are the single most effective intervention for preventing sudden cardiac death in HCM. The challenge is deciding which patients need one. Younger patients have higher complication rates but also the most to gain. Current guidelines use integrated risk stratification rather than any single factor. In my practice, ICD placement is a major decision that I walk through carefully with each patient, weighing the risk calculator outputs, imaging findings, family history, and patient preferences.

Exercise and Sports Participation

For decades, patients with HCM were systematically excluded from vigorous exercise and competitive sports on the theory that exertion provokes sudden death. That blanket restriction is shifting. Newer evidence shows that tailored exercise improves functional capacity, quality of life, and cardiovascular and psychological health. Competitive sport has been performed safely in selected low-risk patients without a clear safety signal.

Current ESC and AHA guidelines support shared decision-making between patient and cardiologist. Exercise testing is recommended for HCM patients regardless of symptoms to unmask latent obstruction and assess functional capacity. The blanket ban has given way to individualized recommendations, which most of my patients find a relief.

Family Screening

Because HCM is autosomal dominant, every first-degree relative of an affected patient should be screened. Echocardiography and ECG are the cornerstones. Relatives of patients diagnosed in childhood are reassessed every one to three years; relatives of adult-diagnosed patients every three to five years.

Genetic testing has become more widely available. For phenotype-negative relatives whose family has a known pathogenic variant, a negative genetic test can end the need for repeated imaging. For families without an identified variant, surveillance imaging continues.

In clinic, I emphasize that screening is straightforward and that early identification gives us far more treatment options than waiting for symptoms.

Frequently Asked Questions

Does HCM mean I will have sudden cardiac death?

No. The great majority of people with HCM have a normal lifespan. Sudden cardiac death is concentrated in a minority of patients with identifiable risk factors, and modern risk stratification plus ICDs where indicated have reduced that risk substantially. Most of my HCM patients are doing well on a simple medication regimen and living normal lives.

Should I stop exercising?

Almost certainly not. Tailored exercise improves quality of life and functional capacity, and modern guidelines support individualized recommendations over blanket restriction. High-intensity competitive sport is still a case-by-case conversation, but most everyday activity is safe and recommended. An exercise stress test is usually part of the evaluation to guide specific recommendations.

If I have HCM, should my kids be tested?

Yes. First-degree relatives should have echocardiography and ECG at defined intervals. If genetic testing has identified the family variant, cascade genetic testing can stratify which relatives need continued imaging and which do not. Pediatric cardiology gets involved for children.

What is the difference between HCM and athletic heart?

Trained athletes, particularly endurance athletes, can develop mild physiologic left ventricular wall thickening. Athletic heart typically shows less wall thickness, a larger chamber, normal diastolic function, and regresses with deconditioning. HCM shows more pronounced thickening, often asymmetric, with abnormal diastolic function, and does not regress. Cardiac MRI, family history, and genetic testing help differentiate when imaging alone is ambiguous.

Is mavacamten a cure?

No, but it is the closest we have to disease-modifying therapy for obstructive HCM. It directly targets the molecular defect and provides meaningful symptom relief in most patients. It does not reverse fibrosis or change the underlying genetic disease, so it requires ongoing use and monitoring. For many patients it delays or avoids the need for septal reduction therapy entirely.

Do I need an ICD just because I have HCM?

Not automatically. ICD placement is reserved for patients whose risk stratification meets guideline thresholds, not for every HCM patient. The decision involves history, imaging, ambulatory monitoring, and family history. Many HCM patients never need an ICD.

References

1. Leggit JC, Whitaker D. Hypertrophic Cardiomyopathy: Updated Guidelines From the ACC/AHA. Am Fam Physician. 2022.

2. Ommen SR, Ho CY, Asif IM, et al. 2024 AHA/ACC/AMSSM/HRS/PACES/SCMR Guideline for the Management of Hypertrophic Cardiomyopathy. J Am Coll Cardiol. 2024.

3. Braunwald E. Hypertrophic Cardiomyopathy. N Engl J Med. 2025.

4. Marian AJ, Braunwald E. Hypertrophic Cardiomyopathy: Genetics, Pathogenesis, Clinical Manifestations, Diagnosis, and Therapy. Circ Res. 2017.

5. Fatkin D, Calkins H, Elliott P, et al. Contemporary and Future Approaches To Precision Medicine in Inherited Cardiomyopathies. J Am Coll Cardiol. 2021.

6. Aficamten or Metoprolol Monotherapy for Obstructive Hypertrophic Cardiomyopathy (MAPLE-HCM). N Engl J Med. 2025.

7. FDA Prescribing Information: Mavacamten (Camzyos) and Aficamten (Myqorzo).