What Is Hypertrophic Cardiomyopathy?
Hypertrophic cardiomyopathy (HCM) is a relatively common, often genetic, heart muscle disease known for its diversity. It was first described in 1963 at the National Institutes of Health (NIH) and is now recognized as a global disease with patients identified in at least 125 countries.
Early on, hypertrophic cardiomyopathy was considered a rare disease. However, based on contemporary population data, HCM is now regarded as probably the most common genetic heart disease. Studies estimate that HCM occurs in 1 in every 200 to 500 people, which suggests that at least 750,000 Americans may be affected in some way by HCM. The disease affects all races, ethnic groups, and both genders, and can be associated with heart failure, atrial fibrillation, and sudden cardiac arrest.
Patients and families should know that HCM is now treatable and is compatible with normal life expectancy with a good quality of life when associated with contemporary treatments. The risks of living with HCM are far less than other cardiac or non-cardiac diseases like congestive heart failure and all cancers combined.
When first diagnosed with hypertrophic cardiomyopathy, many patients may believe their outlook is grim and there are no effective treatment options available. This is simply no longer the case. Comprehensive management strategies have evolved over the past 20 years. Approximately 50% of patients experience a stable course and do not require major treatment. Patients with HCM can live with a good quality of life — into their 70s, 80s, and even 90s — without major symptoms or complications.
Therefore, HCM has emerged as a relatively common disease which for most patients is treatable with low mortality (0.5% per year). The treatment strategies that provide patients consistent relief of symptoms, restoration of sound health, and potential for normal life expectancy were established and promoted by Lahey HCM cardiologists.
An HCM heart typically has increased thickness (“hypertrophy”) of the left ventricular wall, usually of the ventricular septum muscle — the muscle that separates the left and right ventricles. Notably, the HCM heart is thickened (and large) but not dilated. The thickening process involving the left ventricular wall often increases during teenage years and typically stops before the age of 21, although there can be substantial variability.
The clinical identification of HCM is most commonly made with contemporary cardiac imaging (i.e., echocardiography and/or MRI). The basic imaging criteria is a thickened area of the wall of the left ventricle (usually involving the ventricular septum), but without abnormal enlargement of the ventricular cavities. There are exceptions to this rule as the disease spectrum of HCM can be complex and exceedingly diverse. Obstruction to left ventricle outflow may be present at rest, with exercise, or absent.
Many patients with hypertrophic cardiomyopathy will not experience any symptoms at all. If patients do experience symptoms, it typically occurs during mid-life, though symptoms can develop/worsen at any age.
In general, HCM symptoms are similar to other heart diseases, and can occur with or without exertion:
- Shortness of breath (the most common symptom of HCM)
- Fatigue and excessive tiredness
- Sudden and forceful heart beats
- Chest pressure or pain
- Dizziness / lightheadedness
- Loss of consciousness
Often HCM is a familial disease (occurring is several family members). This is known as dominant transmission in which one-half of the relatives in a given generation can be affected and associated with gene mutations found in the contracting elements of the heart (sarcomere). Males and females are affected equally. However, many HCM families do not appear to be “genetic,” when only one relative has the disease, suggesting there are other non-genetic causes. These potential causes are under investigation but are most likely environmental in some way.
Approximately 70% of HCM patients have the obstructive form of the disease. This means the mitral valve makes contact with the thickened septum muscle when the heart contracts, which partially blocks blood flow out of the heart. For some patients, blood flow is obstructed while the heart is at rest. For other patients, blood flow is obstructed only when the heart rate increases during exercise.
Obstructed blood flow creates higher pressures in the heart. We measure these pressures using an echocardiogram. The obstruction causes patients to experience symptoms like shortness of breath, excessive tiredness, chest pain, and occasional dizziness and disability. These symptoms are often managed with drugs, but when medications are not effective, patients may be candidates for more advanced treatments like surgical myectomy or alcohol ablation to relieve the obstruction.
Approximately 30% of HCM patients have the nonobstructive form of the disease in which pressures in the heart are not increased. This means the heart muscle is thickened but blood flows normally at rest and during exercise. Symptoms of nonobstructive HCM are often managed with drugs. Only very occasionally, patients with nonobstructive HCM are candidates for more invasive treatments—such as heart transplant—after symptoms fail to respond to medical treatment.
Sudden death has historically been the most feared element in the natural course of HCM, but for more than 20 years the use of implantable defibrillators (ICDs) has remarkably eliminated most sudden death events in HCM. A process called risk stratification is used to identify, by risk markers, which patients will benefit from an ICD. These markers will help us reliably determine if you are at high risk for developing a rapid abnormal heartbeat that may cause loss of consciousness or cardiac arrest.
It is important to note: a very small number of patients diagnosed with HCM are at increased risk for sudden cardiac death. Age is also relevant to this process of risk stratification, as stable patients under 60 years old are (by age) at generally lower sudden death risk and may not require ICDs.
The prophylactically placed ICD is arguably the most significant treatment advance in HCM in 50 years. Cardiologists now at Lahey are responsible for the introduction and development of ICDs in HCM.
A highly visible but counter-intuitive phenomenon in HCM is sudden deaths in competitive athletes. It should be emphasized that such individuals are undiagnosed prior to their event. About one-third of all athlete sudden deaths are due to HCM with the remainder associated with a variety of other genetic/congenital conditions.
The answer is yes, based on 2 decades of study. Many patients affected by HCM can live long lives without experiencing major symptoms or complications and do not require major therapeutic interventions to achieve normal or extended longevity, usually without significant HCM-related disability. Nevertheless, because chronic diseases like HCM can be unpredictable, we regard routine annual clinical surveillance at Lahey and/or with your referring cardiologist as highly beneficial.