Welcome to the Minneapolis Heart Institute Foundation® Hypertrophic Cardiomyopathy (HCM) Center.
The HCM Center at the Minneapolis Heart Institute Foundation (MHIF) is world-renowned for its expertise in Hypertrophic Cardiomyopathy. The center conducts research and offers advice to individuals diagnosed with HCM. The following information provides more information on the condition, diagnostic tests and potential treatments.
Below are excerpts from “A Guide to Hypertrophic Cardiomyopathy: For Patients, Their Families and Interested Physicians” by Dr. Barry J. Maron and Lisa Salberg. The full book is available for sale on the publisher’s website.
What is HCM?
Cardiomyopathy is a general term describing any condition in which the heart muscle is structurally and functionally abnormal. There are many types of cardiomyopathy (e.g., dilated, restrictive and right ventricular), but here we are focusing only on hypertrophic cardiomyopathy (HCM).
HCM is a genetic disease affecting the heart muscle. The most consistent feature of HCM is excessive thickening (hypertrophy) of the left ventricle. Hypertrophy is usually defined as a wall thickness of 15mm or more, but any wall thickness (including normal) is consistent with the presence of a gene causing HCM. The consequences of HCM to patients are related, in part or solely, to the abnormally thickened left ventricular heart muscle, which in turn is a consequence of the basic genetic defect.
Hypertrophy may be widespread throughout the left ventricle, but may also be more limited in distribution, involving only very small portions of the wall; there is no single pattern of muscle thickening which is “typical” for HCM. The region of the left ventricle which is usually the site of the most prominent thickening is the ventricular septum, the portion of muscle which separates the left and right ventricular cavities. These patterns of hypertrophy do not represent separate disease states, but are all part of the HCM spectrum.
What is the cause of HCM?
As emphasized earlier, HCM is a genetically transmitted and usually familial condition. The pattern of inheritance of HCM is known as autosomal-dominant, which means that the disease (and the mutant gene) occurs in about 50 percent of the relatives in each consecutive generation. Therefore, the likelihood of an affected parent transmitting the abnormal gene to their child is statistically about one in two. However, autosomal-dominant inheritance does not necessarily mean that in each family if there are four offspring, two must be affected – only that this is the statistical probability. In reality, it could be zero of four or even four of four offspring who will carry the mutant gene.
In addition, some individuals with this disease appear to be “sporadic” cases – that is, there are no other relatives in the family known to have evidence of HCM. There is always the possibility of a de novo (new) mutation – that is, the first member of the family with the mutant gene and expressed disease.
What are the symptoms of HCM?
Symptoms are generally similar to that of other forms of heart disease. Most commonly, patients report shortness of breath or chest pain. Patients often relate “good and bad days,” during which symptoms may be perceived as quite different in degree. The precise basis for this variability is uncertain. However, when relating symptoms to your cardiologist, it is important not to limit your history to either extreme (i.e., the best or worst), but rather provide the complete spectrum of complaints which you experience on a daily basis. It is particularly important to advise your cardiologist of any new or consistently increased symptoms.
- Shortness of breath: Exercise capacity may be limited by shortness of breath (also called exercise dyspnea) and fatigue. Most HCM patients experience only mild exercise limitation but occasionally it becomes severe.
- Chest pain: Chest pain or pressure (sometimes called angina) is a common symptom. It is usually brought on by exertion and relieved by rest, but may also occur at rest. In HCM, chest discomfort may take different forms. The cause of the pain is thought to be insufficient oxygen supply to the heart muscle (ischemia).
- Fatigue: This is a complaint distinctive from shortness of breath with exertion; many patients complain of excessive tiredness, either related or unrelated to exertion.
- Palpitations: Patients may occasionally feel an extra or skipped beat, which may be normal and unrelated to HCM. Sometimes, however, such an awareness of the beating heart may be prolonged and indicative of an irregular heart rhythm. Palpitations begin suddenly, and may be associated with symptoms such as sweating or lightheadedness. Such episodes should be reported to your cardiologist and investigated.
- Lightheadedness, near-fainting, and fainting: Patients with HCM may experience lightheadedness, dizziness or loss of consciousness, fainting, or the perception that loss of consciousness is imminent, but then does not, in fact, occur. Such episodes may occur in association with exercise, or without apparent provocation, and the reason for these events is not always clear even after testing. Unfortunately, such episodes represent the most difficult HCM symptom to evaluate because they occur without warning and are over long before your physician can investigate their origin.
How is HCM diagnosed and what tests are used?
- Physical examination: In many patients with HCM, the physical examination is unremarkable. Only a soft heart murmur or no murmur at all may be heard. However, most HCM patients (particularly young people) have a prominent heart impulse that can be felt or even seen on the left side of the chest, which reflects the thickened and forcibly contracting heart.
When present, the most obvious finding on physical examination that raises suspicion of HCM is a loud systolic heart murmur. Such murmurs usually indicate partial obstruction to blood flow out of the left side of the heart, and may be transient, changing spontaneously throughout the day and with activity.
While HCM may be suspected by findings on physical examination, this is not usually the way a definitive diagnosis is made.
- Echocardiogram: The standard primary test for the clinical diagnosis of HCM is an ultrasound scan of the heart called a two-dimensional echocardiogram. This is a safe, non-invasive test which produces two-dimensional images of the heart that are viewed in real time and recorded along with one-dimensional views. The excessive thickness of the left ventricular wall in HCM is easily measured from the echocardiographic images. An additional ultrasound mode called Doppler includes a color-coded image of blood flow within the heart.
- Electrocardiogram (ECG): The standard ECG is performed by placing electrodes on the chest, wrists and ankles and recording the electrical signals from the heart. In HCM, the ECG usually shows a wide variety of abnormal electrical signals, usually due to the muscle thickening. Alternatively, in a minority of patients, the ECG may be normal or show only very minor alterations. The ECG abnormalities seen are not specific to HCM and may also be found in many other heart conditions.
- Cardiovascular magnetic resonance imaging (MRI or CMR): While two-dimensional echocardiography is the most common clinical test used to diagnose HCM, MRI has rapidly penetrated into clinical cardiology providing high-resolution images of the heart, with three-dimensional reconstruction often superior to echocardiography. MRI may allow more precise measurement of left ventricular wall thickness, including when the echocardiogram is ambiguous, or of insufficient technical quality. In select patients, MRI may image thick areas of the wall that are inaccessible to conventional echocardiography.
Therefore, MRI may be the only imaging test capable of making the diagnosis of HCM in some patients and may also play a role in judging the level of risk for sudden death in two ways: 1) identifying areas of extreme thickening of the left ventricle which itself can be a risk factor, and 2) recognizing scarring.
- Genetic testing: Commercial genetic testing (for genotyping HCM patients) is now widely available in the United States and several other countries. Laboratory DNA analysis is the most definitive method for diagnosing HCM by identification of the gene mutation responsible for the disease. This procedure tests the known and most common genes causing HCM, as well as those conditions that mimic HCM (also known as phenocopies).
Interpretation of this test can be complex, but here is how the use of genetic testing play out. First, knowing your mutation has no role in predicting prognosis, the clinical course of your disease, or risk of sudden death. Second, the principal value of genetic testing is in family screening – that is, in identifying family members who may be genetically affected by have a normal echocardiogram (or MRI), and may be at risk for developing the disease. Clinical screening is usually recommended first.
General outlook for patients with HCM
The severity of symptoms and risk of complications vary greatly between HCM patients, and it should be emphasized that many individuals never experience serious problems related to their disease. Indeed, HCM may not reduce life expectancy. It is not unusual for patients to be in their 70s and 80s without significant disability, impaired quality of life, or the requirement for major treatment interventions to achieve these goals.
The most accurate mortality rate characterizing the overall disease is about 0.5 percent per year, with appropriate major treatments including implanted (or external) defibrillators, myectomy surgery and occasionally heart transplant. This is the same expectation as for the general population of the same age.
Treatments for HCM
There are several treatment options available directed toward improving heart function, relieving symptoms, and preventing the complications of HCM such as sudden death. Patients with no symptoms may not require treatment, unless they are judged to be at increased risk for sudden death. For patients who require therapy for their disease, one or more of the following strategies may be considered.
- Medical management: Medications are usually the first line of treatment for HCM patients experiencing heart failure symptoms, and many patients benefit from the administration of such medications with a reduction in those symptoms. A relatively small number of drugs are currently used in treating HCM, and the choice of which one to use first is often made on an individual patient basis. The drugs most commonly used in HCM (but for different reasons) are as follows:
- Calcium channel blockers
- Disopyramide (Norpace®)
- Amiodarone (Cordarone®; Pacerone®)
- Implantable defibrillators: HCM patients at high risk for sudden death may be candidates for an ICD, a sophisticated device which is permanently implanted internally and is capable of sensing potentially lethal arrhythmias and then automatically introducing a shock to terminate these arrhythmias and restore normal heart rhythm for preservation of life. At the same time, an ECG recording is stored in the device to permit documentation of the event.
ICDs have become smaller and much easier to implant in unobtrusive positions on the chest, requiring in most instances only an overnight hospital stay without major surgery.
Patients must also be aware of the possible complications associated with ICDs such as false-shocks due to fast but benign heart rates. Furthermore, there is a small chance of infection, and problems with the leads, including breakage, are not uncommon and may require removal. There have recently been industry-based recalls of defective leads and generators that have affected ICD patients. Although frustrating and unsettling, these developments should not discourage HCM patients from decisions for potentially life-saving ICD treatment.
- Surgery: Surgery (the ventricular septal myectomy operation) is reserved for those patients with marked outflow obstruction who have severe symptoms uncontrolled by treatment with medications. The purpose of a myectomy is to relieve symptoms of shortness of breath. Surgery is not performed for the purpose of reducing sudden death risk.
- Alcohol septal ablation (nonsurgical myectomy): More recently, an alternative procedure has been devised to reduce the thickening of the upper septum (and thereby relieve outflow obstruction) without the need for open-heart surgery. Indeed, alcohol septal ablation appears to reduce obstruction and symptoms almost to the same degree as surgery.
However, there are some important issues concerning alcohol ablation worth considering. At present, the extent to which alcohol septal ablation should be performed in HCM patients remains a somewhat controversial and largely unresolved issue.
- Pacemakers: Pacemakers are used in HCM for several reasons. Occasionally, when the normal electrical signal fails to traverse the ventricles, either because of sinus node failure or heart block, implanting a pacemaker is appropriate and necessary.
- Heart transplantation and end-stage HCM: For a very small minority of HCM patients, heart transplantation may be recommended when there is severe, progressive disability and uncontrolled symptoms of shortness of breath with exertion usually associated with impaired heart contraction. This part of HCM is labeled as the “end stage.” The only predictor of “end stage” is a family history of the end stage. It represents an instance in the natural history of HCM characterized by a dramatic change in the structure and function of the left ventricle.
When end stage is identified, patients are advised to contact a transplantation program in their state of residence and obtain their perspective on the requirements of being “listed” for heart transplant. The primary reason for this is that sometimes, after being stable for many years, a patient’s symptoms in the end stage phase can progress rapidly and unpredictably. Fortunately, the “end stage” is uncommon.