Hypertrophic cardiomyopathy

Template:Short description Template:Redirect Template:Cs1 config Template:Infobox medical condition (new) Hypertrophic cardiomyopathy (HCM, or HOCM when obstructive) is a condition in which muscle tissues of the heart become thickened without an obvious cause.<ref name=Raja2020>Template:Cite book</ref> The parts of the heart most commonly affected are the interventricular septum and the ventricles.<ref name=":0">Template:Cite book</ref> This results in the heart being less able to pump blood effectively and also may cause electrical conduction problems.<ref name=NIH2016What>Template:Cite web</ref> Specifically affected are the bundle branches that conduct impulses through the interventricular septum and into the Purkinje fibers, as these are responsible for the depolarization of contractile cells of both ventricles.<ref name=NIH2023>Template:Cite journal</ref>

People who have HCM may have a range of symptoms. People may be asymptomatic, or may have fatigue, leg swelling, and shortness of breath.<ref name="NIH2016Sym" /> It may also result in chest pain or fainting.<ref name="NIH2016Sym">Template:Cite web</ref> Symptoms may be worse when the person is dehydrated.<ref name=":0" /> Complications may include heart failure, an irregular heartbeat, and sudden cardiac death.<ref name="NIH2016What" /><ref name="SCD2011">Template:Cite journal</ref>

HCM is most commonly inherited in an autosomal dominant pattern.<ref name="NIH2016Ca">Template:Cite web</ref><ref name=":0" /> It is often due to mutations in certain genes involved with making heart muscle proteins.<ref name="NIH2016Ca" /> Other inherited causes of left ventricular hypertrophy include Fabry disease and Friedreich's ataxia.<ref name="Fer2018">Template:Cite book</ref> Other considerations for causes of enlarged heart are athlete's heart and hypertension (high blood pressure).<ref name=":0" /> Making the diagnosis of HCM often involves a family history or pedigree, an electrocardiogram, echocardiogram, and stress testing.<ref name="JACC2011" /> Genetic testing is recommended for affected people and their family members.<ref name="Braunwald 2025" /><ref name="JACC2011">Template:Cite journal</ref> HCM can be distinguished from other inherited causes of cardiomyopathy by its autosomal dominant pattern, whereas Fabry disease is X-linked, and Friedreich's ataxia is inherited in an autosomal recessive pattern.<ref name=":0" />

Treatment depends on symptoms and other risk factors. Medications may include beta blockers, verapamil or disopyramide.<ref name=Raja2020/> An implantable cardiac defibrillator may be recommended in those with certain types of irregular heartbeat.<ref name="JACC2011" /> Surgery, in the form of a septal myectomy or heart transplant, may be done in those who do not improve with other measures.<ref name="JACC2011" /> With treatment, the risk of death from the disease is less than one percent per year.<ref name="Mar2014">Template:Cite journal</ref>

HCM affects up to one in 500 people.<ref name=Raja2020/> People of all ages may be affected.<ref name=NIH2016Type>Template:Cite web</ref> The first modern description of the disease was by Donald Teare in 1958.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Signs and symptoms

Many people with HCM are asymptomatic or mildly symptomatic, and many of those carrying disease genes for HCM do not have clinically detectable disease.<ref name="Mar2002"/> The symptoms of HCM include shortness of breath due to stiffening and decreased blood filling of the ventricles, exertional chest pain (also known as angina) due to reduced blood flow to the coronary arteries, uncomfortable awareness of the heart beat (palpitations), lightheadedness, weakness, fainting and sudden cardiac death.<ref>Template:Cite journal</ref><ref name=":1">Template:Cite book</ref>

Shortness of breath is largely due to increased thickness of the left ventricle (LV) wall and interventricular septal wall, which impairs the filling of the ventricles, but also leads to elevated pressure in the left ventricle and left atrium as a result of increased thickness. This impaired heart filling can cause blood to back up in the lungs' circulation, causing further symptoms<ref name="Braunwauld 2005">Template:Cite book</ref> Often, symptoms of HCM are due to congestive heart failure (especially activity intolerance and dyspnea), but also lower extremity edema.<ref name="Braunwald 2025" />

Major risk factors for sudden death in individuals with HCM include prior history of cardiac arrest or ventricular fibrillation, spontaneous sustained ventricular tachycardia, abnormal exercise blood pressure and non-sustained ventricular tachycardia, unexplained syncope, family history of premature sudden death, and left ventricular wall thickness greater than 15 mm to 30 mm, on echocardiogram.<ref name="Maron, McKenna et al. 2003">Template:Cite journal</ref><ref>Template:Cite journal</ref>

HCM also presents with a systolic ejection murmur that increases in intensity with decreased preload (as in the Valsalva maneuver or standing), or with decreased afterload (as in vasodilator administration). On the other hand, the murmur decreases in intensity with increased preload (as in squatting) or increased afterload (as in the handgrip maneuver).<ref name=":1" /> "Spike and dome" pulse and "triple ripple apical impulse" are two other signs that can be discovered in physical examination.<ref>Template:Cite book</ref> Pulsus bisferiens may also be found during examination.<ref>Template:Cite book</ref>

Genetics

Genetic basis
Gene	Locus	Type
MYH7	14q12	CMH1 (Template:OMIM)
TNNT2	1q32	CMH2 (Template:OMIM)
TPM1	15q22.1	CMH3 (Template:OMIM)
MYBPC3	11p11.2	CMH4 (Template:OMIM)
?	?	CMH5
PRKAG2	7q36	CMH6 (Template:OMIM)
TNNI3	19q13.4	CMH7 (Template:OMIM)
MYL3	3p	CMH8 (Template:OMIM)
TTN	2q24.3	CMH9 (Template:OMIM)
MYL2	12q23-q24	CMH10 (Template:OMIM)
ACTC1	15q14	CMH11 (Template:OMIM)
CSRP3	11p15.1	CMH12 (Template:OMIM)

Familial hypertrophic cardiomyopathy is inherited as an autosomal dominant trait which is attributed to mutations in one of several genes that encode for the sarcomere proteins, and most diagnosed individuals will have an affected parent. Occasionally, both copies of the gene will be defective, a condition that may lead to a more severe manifestation of the disease.<ref>Template:Cite journal</ref><ref name=":0" />

Currently, about 40–60% of people with HCM will have a mutation identified in at least one of nine sarcomeric genes.<ref name="Braunwald 2025" /> Approximately 40% of these mutations occur in the β-myosin heavy chain gene on chromosome 14 q11.2-3, and approximately 40% involve the cardiac myosin-binding protein C gene. Since HCM is typically an autosomal dominant trait, children of a single HCM parent have a 50% chance of inheriting the disease-causing mutation. Whenever such a mutation is identified, family-specific genetic testing can be used to identify relatives at risk for the disease, although clinical severity and age of onset cannot be predicted.<ref>Template:Cite book</ref>

An insertion/deletion polymorphism in the gene encoding for angiotensin converting enzyme (ACE) alters the clinical phenotype of the disease. The D/D (deletion/deletion) genotype of ACE is associated with more marked hypertrophy of the left ventricle and may be associated with a higher risk of adverse outcomes.<ref name="Doolan, Nguyen et al. 2004">Template:Cite journal</ref><ref name="Marian, Yu et al. 1993">Template:Cite journal</ref>

Over 1400 mutations have been identified in genes known to lead to HCM.<ref>Template:Cite journal</ref> Some mutations could have more harmful potential compared to others (β-myosin heavy chain). For example, troponin T mutations were originally associated with a 50% mortality before the age of 40. However, a more recent and larger study found a similar risk to other sarcomeric protein mutations.<ref name="Pasquale et al. 2012">Template:Cite journal</ref> The age at disease onset of HCM with MYH7 mutations is earlier and leads to more severe symptoms.<ref name="Sedaghat-Hamedani F et al. 2017">Template:Cite journal</ref> Moreover, mutations on troponin C can alter Ca⁺² sensibility on force development in cardiac muscle, these mutations are named after the amino acid that was changed after the location in which it happened, such as A8V, A31S, C84Y and D145E.<ref>Template:Cite journal</ref>

Pathophysiology

Ventricular hypertrophy causes a dynamic pressure gradient across the left ventricular outflow tract (LVOT), which is associated with further narrowing of the outflow during systole. Pulling of the mitral valve leaflets towards the septum contributes to the outflow obstruction. This pulling is thought to occur by several proposed mechanisms, including the flow of blood through the narrowed outflow tract resulting in a higher velocity, and less pressure via the Venturi effect.<ref name=":1" /> This low pressure then causes the anterior leaflet of the mitral valve to be pulled into the outflow tract, resulting in further obstruction.<ref name=":2">Template:Cite web</ref>

The hypertrophied (thickened) left ventricular wall in HCM requires a greater oxygen demand. This increased oxygen demand of the enlarged heart muscle, combined with fibrosis (scarring) of the heart muscle and a reduced flow through thick-walled coronary arteries results in an oxygen deficit to the heart muscle. These pathophysiological changes result in the anginal (exertional chest pain) symptoms sometimes seen in HCM.<ref name="Braunwald 2025" />

Diagnosis

A diagnosis of hypertrophic cardiomyopathy is based upon several features of the disease process. While there is use of echocardiography, cardiac catheterization, or cardiac MRI in the diagnosis of the disease, other important considerations include ECG and genetic testing. Genetic testing is recommended for those affected by HCM and their family members.<ref name="Braunwald 2025" /> In about 60 to 70% of the cases, cardiac MRI shows thickening of more than 15 mm of the lower part of the ventricular septum. T1-weighted imaging may identify scarring of cardiac tissues while T2-weighted imaging may identify edema and inflammation of cardiac tissue which is associated with acute clinical signs of chest pain and fainting episodes.<ref>Template:Cite journal</ref>

ECG is the most sensitive diagnostic test.<ref name=":1" /> The combination of left ventricular hypertrophy, and right atrial enlargement on ECG strongly suggests HCM.<ref name=":1" />

Variants Template:Anchor

Depending on whether the distortion of normal heart anatomy causes an obstruction of the outflow of blood from the left ventricle of the heart, HCM can be classified as obstructive or non-obstructive.<ref name="pmid33215931">Template:Cite journal</ref> The obstructive variant of HCM is hypertrophic obstructive cardiomyopathy (HOCM).<ref>Template:Cite book</ref> The diagnosis of left ventricular outflow tract obstruction is usually made by echocardiographic assessment and is defined as a peak left ventricular outflow tract gradient of ≥ 30 mmHg.<ref name="pmid33215931" />

Another, non-obstructive variant of HCM is apical hypertrophic cardiomyopathy (AHCM or ApHCM),<ref name=pmid8685759>Template:Cite journal</ref> also called Yamaguchi syndrome. It was first described in individuals of Japanese descent. Sakamoto was the first to report the condition's ECG pattern in 1976. Yamaguchi was the first to characterize the syndrome and its ventriculargrophic feature in 1979.<ref>Yamaguchi H, Ishimura T, Nishiyama S, Nagasaki F, Nakanishi S, Takatsu F, Nishijo T, Umeda T, Machii K. Hypertrophic nonobstructive cardiomyopathy with giant negative T waves (apical hypertrophy): ventriculographic and echocardiographic features in 30 patients. Am J Cardiol. 1979 Sep;44(3):401-12. doi: 10.1016/0002-9149(79)90388-6. PMID 573056.</ref> Yamaguchi syndrome is an infrequent variant of HCM in the European population. ApHCM is thought to be autosomal dominant, with the majority of mutations occurring in the genes encoding for the sarcomere.<ref name="Arad 2005">Template:Cite journal</ref> ECG findings in Yamaguchi syndrome may mimic those of a heart attack. Yamaguchi syndrome has a more favorable prognosis than classic HCM, and it is more common in Asian populations.<ref name="Dasari 2023">Template:Cite journal</ref>

Cardiac catheterization

Upon cardiac catheterization, catheters can be placed in the left ventricle and the ascending aorta, to measure the pressure difference between these structures. In normal individuals, during ventricular systole, the pressure in the ascending aorta and the left ventricle will equalize, and the aortic valve is open. In individuals with aortic stenosis or with HCM with an outflow tract gradient, there will be a pressure gradient (difference) between the left ventricle and the aorta, with the left ventricular pressure higher than the aortic pressure. This gradient represents the degree of obstruction that has to be overcome to eject blood from the left ventricle.Template:Citation needed

The Brockenbrough–Braunwald–Morrow sign is observed in individuals with HCM with an outflow tract gradient. This sign can be used to differentiate HCM from aortic stenosis. In individuals with aortic stenosis, after a premature ventricular contraction (PVC), the following ventricular contraction will be more forceful, and the pressure generated in the left ventricle will be higher. Because of the fixed obstruction that the stenotic aortic valve represents, the post-PVC ascending aortic pressure will increase as well. In individuals with HCM, however, the degree of obstruction will increase more than the force of contraction will increase in the post-PVC beat. The result of this is that the left ventricular pressure increases and the ascending aortic pressure decreases, with an increase in the LVOT gradient. Those with a dynamic obstruction across the aortic valve (those with HOCM) will also have a decrease in the pulse pressure in the beat after a PVC.<ref name="Cui 2018">Template:Cite journal</ref>

Screening

Template:Main

Although HCM may be asymptomatic, affected individuals may present with symptoms ranging from mild to critical heart failure and sudden cardiac death at any point from early childhood to seniority.<ref name=Mar2002>Template:Cite journal</ref><ref name="Behr & McKenna">Template:Cite journal</ref> HCM is the leading cause of sudden cardiac death in young athletes in the United States, and the most common genetic cardiovascular disorder.<ref name=SCD2011/> One study found that the incidence of sudden cardiac death in young competitive athletes declined in the Veneto region of Italy by 89% from an unusually high baseline rate since the 1982 introduction of routine cardiac screening for athletes.<ref name ="Corrado et al. 2006">Template:Cite journal</ref> As of 2010, however, studies have shown that the incidence of sudden cardiac death, among all people with HCM, has declined to one percent or less.<ref name="Critoph & Elliot">Template:Cite journal</ref> Screen-positive individuals who are diagnosed with cardiac disease are usually told to avoid competitive athletics.<ref>Template:Cite journal</ref>

HCM can be detected with an echocardiogram (ECHO) with 80%+ accuracy,<ref>Template:Cite journal</ref> which can be preceded by screening with an electrocardiogram (ECG) to test for heart abnormalities. Cardiac magnetic resonance imaging (CMR), considered the gold standard for determining the physical properties of the left ventricular wall, can serve as an alternative screening tool when an echocardiogram provides inconclusive results.<ref name="magnetic res. imaging">Template:Cite journal</ref> For example, the identification of segmental lateral ventricular hypertrophy cannot be accomplished with echocardiography alone. Also, left ventricular hypertrophy may be absent in children under thirteen years of age. This reduces sensitivity of pre-adolescents' echocardiograms.<ref name=Mar2002/>

United States

The American Academy of Pediatrics recommends screening questions for all children (both athletes and non-athletes) to assess the risk of congenital heart disease, inherited cardiac disorders (including HCM) and suddent cardiac arrest or death. The questions assess symptoms such as syncope (passing out) or seizures in the child, exercise related chest pain or shortness of breath, having a family member with sudden cardiac death before age 50, having a family history of HCM, HOCM, or a family member requiring a pacemaker or implantable cardiac defibrillator before the age of 50.<ref name="Erickson 2021">Template:Cite journal</ref> The role of universal EKG or non-invasive cardiac imaging in amateur or recreational athletes is not well established.<ref name="Petek 2020">Template:Cite journal</ref>

There are several potential challenges associated with routine screening for HCM in the United States.<ref name="Maron-2010">Template:Cite journal</ref> First, the U.S. athlete population of 15 million is large compared to other countries.<ref name="Maron-2010"/> Second, these events are rare, with fewer than 100 deaths in the U.S. due to HCM in competitive athletes per year, or about 1 death per 220,000 athletes.<ref name="Maron-2009">Template:Cite journal</ref> Lastly, genetic testing may suggest a diagnosis of HCM; however, due to the numerous HCM-causing mutations, this method of screening is complex and is not cost-effective.<ref name=Mar2002 />

Canada

Canadian genetic testing guidelines and recommendations for individuals diagnosed with HCM are as follows:<ref name="Canada Gen Test">Template:Cite journal</ref>

The main purpose of genetic testing is to screen family members.
- According to the results, at-risk relatives may be encouraged to undergo extensive testing.
Genetic testing is not meant to confirm a diagnosis.
Genetic testing is not intended for risk assessment or treatment decisions.
- Evidence only supports clinical testing in predicting the progression and risk of developing complications of HCM.

For individuals suspected of having HCM:

Genetic testing is not recommended for determining other causes of left ventricular hypertrophy (such as "athlete's heart", hypertension, and cardiac amyloidosis).
- HCM may be differentiated from other hypertrophy-causing conditions using clinical history and clinical testing.

Treatment

Asymptomatic people

A significant number of people with hypertrophic cardiomyopathy do not have any symptoms and will have a normal life expectancy, although they should avoid particularly strenuous activities or competitive athletics. Asymptomatic people should be screened for risk factors for sudden cardiac death. In people with resting or inducible outflow obstructions, situations that will cause dehydration or vasodilation (such as the use of vasodilatory or diuretic blood pressure medications) should be avoided. Septal reduction therapy is not recommended in asymptomatic people.<ref name=JACC2011/>

Medications

The primary goal of medications in the treatment of HCM is to relieve symptoms such as chest pain, shortness of breath, and palpitations. Beta blockers are considered first-line agents, as they can reduce the outflow obstruction, reduce heart strain and relieve anginal symptoms.<ref name="Braunwald 2025" /> Beta-blockers can also slow the heart rate and decrease the likelihood of ectopic beats. For people who cannot tolerate beta-blockers, nondihydropyridine calcium channel blockers such as verapamil can be used, but are potentially harmful in people who also have low blood pressure or severe shortness of breath at rest. These medications also decrease the heart rate, though their use in people with severe outflow obstruction, elevated pulmonary artery wedge pressure, and low blood pressure should be done with caution. Dihydropyridine calcium channel blockers should be avoided in people with evidence of obstruction. For people whose symptoms are not relieved by the above treatments, disopyramide can be considered for further symptom relief. Diuretics can be considered for people with evidence of fluid overload, though cautiously used in those with evidence of obstruction.<ref name=":1" /> Intravenous phenylephrine (or another pure vasoconstricting agent) can be used in the acute setting of low blood pressure in those with obstructive hypertrophic cardiomyopathy who do not respond to fluid administration.<ref name=JACC2011/>

Cardiac myosin inhibitors reduce left ventricular contractility by inhibiting cardiac ATPase to decrease the number of active actin–myosin cross-bridges within the myocyte sarcomere.<ref name="Braunwald 2025" /><ref>Template:Cite journal</ref> Mavacamten was shown to reduce left ventricular outflow tract gradient (a measure of obstruction) and improve symptoms in patients with obstructive hypertrophic cardiomyopathy, and was approved for medical use in the United States in April 2022.<ref>Template:Cite press release</ref> Mavamectin was also shown to reduce left ventricular wall thickness in those with HCM and was associated with a lower need for septal reduction surgery.<ref name="Braunwald 2025" /> Aficamten, which has a shorter half life compared with mavacamten, achieves steady state within 2 weeks, and appears to have a wide therapeutic window, was shown to improve peak oxygen uptake during cardiopulmonary exercise testing in patients with New York Heart Association (NYHA) functional class II or III heart failure and decreased exercise capacity.<ref>Template:Cite journal</ref>

People who continue to have symptoms despite drug therapy can consider more invasive therapies.

Surgical septal myectomy

Template:Main Surgical septal myectomy is an open-heart operation done to relieve symptoms in people who remain severely symptomatic despite medical therapy. It has been performed successfully since the early 1960s.<ref name="Maron, McKenna et al. 2003"/> Surgical septal myectomy uniformly decreases left ventricular outflow tract obstruction and improves symptoms, and in experienced centers has a surgical mortality of less than 1%, as well as 85% success rate.<ref name="Behr & McKenna" /> It involves a median sternotomy (opening the chest) and removing a portion of the interventricular septum.<ref name=Mar2002/> Surgical myectomy resection that focuses just on the subaortic septum, to increase the size of the outflow tract to reduce Venturi forces, may be inadequate to abolish systolic anterior motion (SAM) of the anterior leaflet of the mitral valve. With this limited resection, the residual mid-septal bulge still redirects flow posteriorly; SAM persists because flow still gets behind the mitral valve. It is only when the deeper portion of the septal bulge is resected that flow is redirected anteriorly away from the mitral valve, abolishing SAM. With this in mind, a modification of the Morrow myectomy termed extended myectomy, mobilization and partial excision of the papillary muscles has become the excision of choice.<ref name="Sherrid Chaudhry et al. 2003">Template:Cite journal</ref><ref name="Messmer 1994">Template:Cite journal</ref><ref name="Schoendube, Klues et al. 1995">Template:Cite journal</ref><ref name="Balaram, Sherrid et al. 2005">Template:Cite journal</ref> In people with particularly large redundant mitral valves, anterior leaflet plication may be added to complete separation of the mitral valve and outflow.<ref name="Balaram, Sherrid et al. 2005"/> Complications of septal myectomy surgery include possible death, arrhythmias, infection, bleeding, septal perforation/defect, and stroke.<ref name="Behr & McKenna" />

Alcohol septal ablation

Template:Main Alcohol septal ablation, introduced by Ulrich Sigwart in 1994, is a percutaneous technique that involves an injection of alcohol into one or more septal branches of the left anterior descending artery. This is a catheter technique with results similar to the surgical septal myectomy procedure but is less invasive since it does not involve general anesthesia and opening of the chest wall and pericardium (which are done in a septal myectomy). In a select population with symptoms secondary to a high outflow tract gradient, alcohol septal ablation can reduce the symptoms of HCM. In addition, older individuals and those with other medical problems, for whom surgical myectomy would pose an increased procedural risk, would likely benefit from the less-invasive septal ablation procedure.<ref name=Mar2002/><ref>Template:Cite journal</ref>

When performed properly, an alcohol septal ablation induces a controlled heart attack, in which the portion of the interventricular septum that involves the left ventricular outflow tract is infarcted and will contract into a scar.

Alcohol septal ablation has a risk of secondary complete heart block as well as a greater need for repeated procedures due to persistent outflow tract obstruction.<ref name="Braunwald 2025" /> Septal reduction surgery and alcohol septal ablation have a similar risk of death related to procedural complications.<ref name="Braunwald 2025" />

Mitral clip

Template:Main Since 2013, mitral clips have been implanted via a catheter as a new strategy to correct the motion of the mitral valve in people with severe obstructive HCM (= oHCM). The device fastens together the mitral valve leaflets to improve the heart's blood outflow. The mitral clip has not yet established the same long-term reliability as septal myectomy or alcohol septal ablation, but HCM specialists are increasingly offering the clip as a less-invasive treatment option.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Implantable pacemaker or defibrillator

Template:Further The use of a pacemaker has been advocated in a subset of individuals, to cause asynchronous contraction of the left ventricle. Since the pacemaker activates the interventricular septum before the left ventricular free wall, the gradient across the left ventricular outflow tract may decrease. This form of treatment has been shown to provide less relief of symptoms and less of a reduction in the left ventricular outflow tract gradient when compared to surgical myectomy.<ref name="Ommen, Nishimura et al. 1999">Template:Cite journal</ref> Technological advancements have also led to the development of a dual-chamber pacemaker, which is only turned on when needed (in contrast to a regular pacemaker which provides a constant stimulus). Although the dual-chamber pacemaker has been shown to decrease ventricular outflow tract obstruction, experimental trials have found only a few individuals with improved symptoms.<ref name="Coats & Elliot">Template:Cite journal</ref> Researchers suspect that these reports of improved symptoms are due to a placebo effect.<ref name="Behr & McKenna" />

The procedure includes an incision on the anterolateral area below the clavicle. Two leads are then inserted; one into the right atrium and the other into the right ventricular apex via the subclavian veins. Once in place, they are secured and attached to the generator which will remain inside the fascia, anterior to the pectoral muscle.<ref name="Behr & McKenna" /> Complications of this procedure include infection, electrical lead, and generator malfunction which will require replacement.<ref name="Behr & McKenna" />

For people with HCM who exhibit one or more of the major risk factors for sudden cardiac death, an implantable cardioverter-defibrillator (ICD) or a combination pacemaker/ICD all-in-one unit may be recommended as an appropriate precaution.<ref name=JACC2011 /><ref name="Maron, McKenna et al. 2003" /><ref>Template:Cite journal</ref><ref>Template:Cite web</ref> In 2014, European Society of Cardiology suggested a practical risk score to calculate that risk.<ref>Template:Cite web</ref>

Cardiac transplantation

Template:Further In cases that are unresponsive to all other forms of treatment, cardiac transplantation is one option. It is also the only treatment available for end-stage heart failure.<ref name="Coats & Elliot" /> Studies have indicated a seven-year survival rate of 94% in people with HCM after transplantation.<ref name="Coats & Elliot" />

Prognosis

The annual mortality rate in those with HCM is 1%.<ref name=Mar2002/> 70% of those with HCM have a left ventricular outflow tract obstruction (HOCM).<ref name="Braunwald 2025" />

A family history of sudden cardiac death, left ventricular wall thickness greater than 30 milimeters, an aneurysm at the left ventricular apex, unexplained syncope (passing out) multiple episodes of sustained ventricular tachycardia, late gadolinium enhancement on cardiac MRI (a marker of heart muscle fibrosis or scar formation) and a left ventricular ejection fraction of less than 50% are all risk factors for sudden cardiac death in HCM. The incidence of sudden cardiac in those older than 60 with HCM is rare.<ref name="Braunwald 2025">Template:Cite journal</ref>

About 25% of those with symptomatic HCM have atrial fibrillation (in which the atrial chambers of the heart beat irregularly, and sometimes rapidly). Those with HCM and atrial fibrillation have a worse prognosis, partly due to the loss of the contribution of atrial contractility to heart function and the fast heart rate impairing ventricular filling.<ref name="Braunwald 2025"/>

Children

Even though hypertrophic cardiomyopathy may be present early in life and is most likely congenital, it is not commonly seen in pediatric cardiology, largely because the presentation of symptoms is usually absent, incomplete, or delayed into adulthood. Most of the current information pertaining to HCM arises from studies in adult populations, and the implication of these observations for the pediatric population is uncertain.<ref name="Colan 2010 433–444">Template:Cite journal</ref> Nonetheless, recent studies in pediatric cardiology have revealed that HCM accounts for 42% of childhood cardiomyopathies, with an annual incidence rate of 0.47/100,000 in children.<ref>Template:Cite journal</ref> In asymptomatic cases, sudden death is considered one of the most-feared complications associated with the disease. Consequently, the recommended practice is to screen children of affected individuals throughout childhood to detect cardiac abnormalities at an early stage, in the hope of preventing further complications of the disease.<ref name="Colan 2010 433–444"/>

Generally, the diagnosis of HCM in a pediatric population is made during assessment for murmur, congestive heart failure, physical exhaustion, and genetic testing of children of affected individuals.<ref name="Colan 2010 433–444"/> Echocardiography is used to assess left ventricular wall thickness, ventricular size, systolic and diastolic heart function, and outflow tract obstruction to diagnose HCM in children.<ref name="Colan 2010 433–444"/>

For children with HCM, treatment strategies aim to reduce disease symptoms and lower the risk of sudden death.<ref name="Maskatia 2012 84–92">Template:Cite journal</ref> Due to the heterogeneity of the disease, treatment is usually modified according to individual's needs.<ref name="Maskatia 2012 84–92"/> β-blockers improve left ventricular filling and relaxation and thereby lessen symptoms. In some children, β–blockers were shown effective in reducing the risk of sudden death.<ref name="Maskatia 2012 84–92"/> Calcium channel blockers (verapamil) and antiarrhythmic drugs may be used as an adjunct therapy to β-blockers in symptomatic children.<ref name="Maskatia 2012 84–92"/> Septal myectomy, if required for treatment, is considered safe in children.<ref name="Braunwald 2025" />

Epidemiology

The prevalence of HCM in the general population globally is 0.2% (1 in 500 adults), as determined by echocardiographic studies.<ref name=":1" /> HCM is more common in males than females.<ref name=":1" /> The most common presentation of HCM is in the third decade of life, though it can present at any age, from newborns to the elderly.<ref name=":1" />

Other animals

Saddle thrombus in the feline aorta. 1 opened Aorta with thrombus, 2 A. iliaca externa, 3 common trunk for both Aa. iliacae internae, 4 A. circumflexa ilium profunda, 5 A. mesenterica caudalis, 6 Colon descendens.

Cats

Feline hypertrophic cardiomyopathy (HCM) is the most common heart disease in domestic cats;<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> the disease process and genetics are believed to be similar to the disease in humans.<ref name="Cornell">Template:Cite web</ref> In Maine Coon cats, HCM has been confirmed as an autosomal dominant inherited trait.<ref name="Kittleson, Meurs et al. 1999">Template:Cite journal</ref> Numerous cat breeds have HCM as a problem in the breed.<ref>Template:Cite web</ref> The first genetic mutation (in cardiac myosin binding protein C) responsible for feline HCM was discovered in 2005 in Maine Coon cats.<ref name="Meurs, Sanchez et al. 2005">Template:Cite journal</ref> A test for this mutation (A31P) is available.<ref>Template:Cite web</ref> About one-third of Maine Coon cats tested for the mutation are either heterozygous or homozygous for the mutation, although many of the cats that are heterozygous have no overt evidence of the disease on an echocardiogram (low penetrance).

Some Maine Coon cats with clinical evidence of hypertrophic cardiomyopathy test negative for this mutation, strongly suggesting that another cause exists in the breed. The cardiac myosin binding protein C mutation identified in Maine Coon cats has not been found in any other breed of cat with HCM, but more recently another myosin binding protein C mutation has been identified in Ragdoll cats with HCM.<ref name="Meurs, Kittleson et al. 2007">Template:Cite journal</ref><ref>Template:Cite web</ref> As in humans, feline HCM is not present at birth but develops over time. It has been identified for the first time in cats as young as 6 months of age and at least as old as 7 years of age.Template:Citation needed

Clinically, cats with hypertrophic cardiomyopathy commonly have a systolic anterior motion (SAM) of the mitral valve (see graphic).<ref>Template:Cite journal</ref> Cats with severe HCM often develop left heart failure (pulmonary edema; pleural effusion) because of severe diastolic dysfunction of the left ventricle. They may also develop a left atrial thrombus that embolizes, most commonly, to the terminal aorta creating acute pain and rear limb paralysis (see below). Sudden death can also occur but appears to be uncommon.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Ultrasound of the heart (echocardiography) is necessary to diagnose HCM in cats.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Measurement of circulating cardiac biomarkers, like N‐terminal‐proBNP (NT‐proBNP)<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> and troponin I (TnI) may be used in cats to strengthen the suspicion of cardiac disease.<ref>Template:Cite journal</ref> There is a Point-of-care test for feline NT-proBNP available which can be used at the veterinary clinic when echocardiography is not possible to perform.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

Cats that are tachycardic (>220) and/or have outflow obstruction (SAM) on echo should probably be treated but there is no cure for feline HCM. Many but not all cats have a heart murmur. Many cats that have a heart murmur do not have HCM. Frequently the first signs that a cat has HCM are tachypnea/dyspnea due to heart failure or acute pain and paralysis due to systemic thromboembolism. While medication is commonly given to cats with HCM that have no clinical signs, no medication is helpful at this stage and it has been shown that an ACE inhibitor is not beneficial until heart failure is present<ref name="MacDonald, Kittleson et al.">Template:Cite journal</ref> (at which time a diuretic is most beneficial). Diltiazem generally produces no demonstrable benefit. Atenolol is commonly administered when a severe systolic anterior motion of the mitral valve is present.Template:Citation needed

Feline arterial thromboembolism (FATE) is a relatively common and devastating complication of feline HCM and other feline cardiomyopathies. The thrombus generally forms in the left atrium, most commonly the left auricle. The formation is thought to be primarily due to blood flow stasis. Classically, the thromboembolism lodges at the iliac trifurcation of the aorta, occluding either one or both of the common iliac arteries. Because this split is called the saddle, and is the most frequent location for the thrombus, FATE is commonly known as saddle thrombus.<ref>Template:Cite web</ref> Clinically this presents as a cat with complete loss of function in one or both hind limbs. The hind limbs are cold and the cat is in considerable pain. Emboli may, rarely, lodge in other locations, most commonly the right front limb and the renal arteries.Template:Citation needed

Clopidogrel is used to try to prevent left atrial thrombus formation in cats with HCM and a large left atrium. The FATCAT study at Purdue University demonstrated that it is superior to aspirin for the prevention of a second thrombus from forming in cats that have already experienced a clot. Thrombolytic agents (e.g., tissue plasminogen activator) have been used with some success to break down existing aortic thromboembolism, but their cost is high and the outcome appears to be no better than giving a cat time (48–72 hours) to break down its own clot. Pain management is extremely important. The prognosis for cats with FATE is often poor as they are likely to have significant HCM already and a recurrent bout of FATE is likely.<ref>Template:Cite journal</ref> For this reason, euthanasia is often a valid consideration.Template:Citation needed

Gorillas

In July 2013, Rigo, a 42-year-old western lowland gorilla, resident in Melbourne Zoo and father of Mzuri, the first gorilla born by artificial insemination, died unexpectedly as a result of HCM. The condition is not uncommon in male gorillas over the age of 30, and in many cases, there is no sign of the disease until the individual's sudden death.<ref>Template:Cite news</ref>

References

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External links

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Hypertrophic cardiomyopathy

Contents

Signs and symptoms

Genetics

Pathophysiology