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Hypertrophic Cardiomyopathy (HCM) is an inherited disease of the heart muscle in which a portion of it is inappropriately hypertrophied (thickened) without any obvious, systemic cause.
A cardiomyopathy is a disease that primarily affects the muscle of the heart. With hypertrophic cardiomyopathy (HCM), the normal alignment of muscle cells is disrupted, a phenomenon known as myocardial disarray. HCM also causes disruptions of the electrical functions of the heart. 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 defined as obstructive or non-obstructive. The obstructive variant of HCM, hypertrophic obstructive cardiomyopathy (HOCM) has also historically been known as idiopathic hypertrophic subaortic stenosis (IHSS) and asymmetric septal hypertrophy (ASH).
Genetics of HCM
HCM is due to a mutation in one of many genes that results in altered sarcomere proteins: critical components of the heart cell architecture. About 50-60% of patients with a high index of clinical suspicion for HCM will have a mutation identified in at least 1 of 9 sarcomeric genes. Approximately 45% of these mutations occur in the ß myosin heavy chain gene on chromosome 14 q11.2-3, while approximately 35% involve the cardiac myosin binding protein C gene. These are transmitted in an autosomal dominant pattern: boys and girls are equally affected & each child of an affected parent has a 50% chance of inheriting the alteration. New molecular & genetic techniques allow for the early detection of potential defects—in turn, identifying patients & family members who are at risk for HCM.
HCM is recognized as relatively common: the incidence is thought to approach 1/500 individuals, approximately 0.2-0.5% of the population across all ethnic & age groups, without gender predilection. It is also one of the leading causes of sudden death in young people & athletes…
This syndrome is often undetected prior to death & is not recognized as the cause of death. HCM is treatable and, with the correct diagnosis & appropriate intervention, most deaths are preventable.
Individuals with HCM have some degree of left ventricular hypertrophy. Usually this is an asymmetric hypertrophy, involving the inter-ventricular septum of the left ventricle (LV). This is in contrast to the concentric hypertrophy seen in longstanding hypertension. About two-thirds of individuals with HCM have asymmetric septal hypertrophy. About 25% of individuals with HCM demonstrate an obstruction to the outflow of blood from the left ventricle during rest. In other individuals obstruction only occurs under certain conditions (if dehydrated, standing suddenly, or with exercise). This is known as dynamic outflow obstruction, because the degree of obstruction is variable & is dependent on the amount of blood in the LV immediately before ventricle systole (contraction).
Symptoms of HCM are variable - they may include shortness of breath (dyspnea), temporary loss of consciousness (syncope) & rapid heart rate (palpitations). These events of HCM may occur without warning; they often occur during physical exertion or emotional excitement. Why?
People with HCM develop arrhythmia following normal adrenaline surges of excitement. This phenomenon occurs when an electrical impulse triggers a new heartbeat before the ventricles have fully recovered from the previous beat. When this occurs, the heart muscle cannot contract effectively. Blood is not pumped out to the body and the individual faints within seconds. If the heart does not return to a normal rhythm on its own, it may switch into deadly arrhythmia called ventricular fibrillation. Without immediate emergency treatment, death follows within minutes.
Fainting/syncope or palpitation are high risk symptoms—and may be the only warning sign of HCM. About 60% of patients exhibit symptoms, therefore, the lack of symptoms does not exclude a person or family from having HCM. Patients may also experience intermittent chest pain. Unfortunately, as mentioned, HCM often goes undetected & untreated.
If there is a family history of unexplained syncope or sudden death, including a death in an otherwise healthy person, you should seek further evaluation & refer family members for basic screening.
Typically, a consultation will last sixty to ninety minutes & will take place at the Heart Rhythm Center at the NYU Langone Medical Center. This will involve a thorough directed history, family history, & physical examination. Simple procedures are likely to be requested—primarily to further evaluate the heart under different physiologic conditions (exercise, rest, on/off medications, etc.) These may include:
- An Electrocardiogram (EKG)
- An Echocardiogram (ECHO) or Magnetic Resonance (MRI)
- A Holter Monitor (24-hour EKG monitor)
- An Exercise Stress Test (treadmill test)
- Genetic Testing (blood test)
The ECHO is of particular importance, as it has the ability to visualize the septal hypertrophy, which serves as a hallmark of HCM. Maneuvers performed during the exam may also delineate & quantify any obstructive component of the disease.
Patients should also expect to have at least one visit with our clinical geneticist to evaluate the full family history & to discuss potential genetic testing. Once a family member is identified with HCM, it is extremely important that other family members be screened for the syndrome. Records from prior work-up [hospital admission, EKG, treadmill stress test, Holter, etc.] are encouraged for review.
All symptomatic patients should receive treatment. All asymptomatic patients with HCM should also be treated, as the first manifestation of the syndrome may be sudden arrest. It is not possible to predict which person is destined to have symptoms—thus, preventative treatment is required in all HCM patients.
Treatment options for patients with HCM include lifestyle modification, medical therapy & possible device therapy. Lifestyle modification involves the avoidance of potential triggers & adaptation of exertional activity/athletics. Medications, like beta-blockers & calcium channel blockers, serve to reduce the excitatory effect on the heart muscle tissue & are effective in limiting the obstructive component of symptoms. Device therapy (Implantable Cardioverter-Defibrillator) is reserved for select high risk cases and should be reviewed with your doctor—it serves as a safety net for potential lethal events in those treated for HCM. In severe HOCM, patients may also surgery to remove some of the septal tissue of the LV to alleviate obstructive symptoms.
Overall, early recognition and guided therapy by a trained specialist is the key to the best outcome for both you & your family!
Our HCM patients have access to cutting-edge testing & research only available through the Cardiovascular Genetics Program at NYU Langone Medical Center. It is one of the reasons we can help.
For information on how you can help support this program, please contact our Development Office at (212) 404-3569.
For a consultation, simply speak to your doctor or call (212) 263-3612.