Hypertrophic cardiomyopathy: Description.
Hypertrophic cardiomyopathy is a condition that affects the performance of the heart in several ways.
What happens in hypertrophic cardiomyopathy?
As with other heart muscle diseases, hypertrophic cardiomyopathy (HCM) changes the structure of the heart muscle (myocardium). The individual muscle cells enlarge, increasing the thickness of the heart walls.
Such an increase in size of tissues or organs due to cell growth is commonly called hypertrophy in medicine. Hypertrophy in HCM is asymmetric, so the heart muscle thickens unevenly.
On the one hand, a heart wall that is too thick becomes stiffer; on the other hand, this worsens the blood supply to its own muscle cells. Especially when the heart beats faster, not enough blood reaches the individual cells via the coronary vessels.
In hypertrophic cardiomyopathy, not only do the muscle cells grow, but more connective tissue is incorporated into the heart muscle (fibrosis). As a result, the left ventricle is less expandable and the phase of blood filling (diastole) is disturbed.
It is thought that fibrosis and cellular misarrangement occurs first. The muscle thickening is then a reaction to this, so that the heart can pump more forcefully again.
Hypertrophic cardiomyopathy is most noticeable in the muscles of the left ventricle. However, it can also affect the right ventricle. The weaker pumping action causes typical symptoms.
What are the different forms of hypertrophic cardiomyopathy?
Hypertrophic cardiomyopathy is divided into two types: Hypertrophic obstructive cardiomyopathy (HOCM) and hypertrophic non-obstructive cardiomyopathy (HNCM). HNCM is the milder of the two variants because, unlike HOCM, blood flow is not further disrupted.
Hypertrophic obstructive cardiomyopathy (HOCM).
In HOCM, the thickened heart muscle constricts the ejection pathway within the left ventricle. The muscle thus obstructs itself in its work: It cannot pump blood unimpeded from the ventricle through the aortic valve into the aorta. The narrowing (obstruction) usually results from asymmetric hypertrophy of the cardiac septum (also made of muscle) just before the aortic valve.
It is estimated that about 70 percent of all hypertrophic cardiomyopathies are associated with narrowing of the ejection tract (obstruction). As a result, the symptoms of HOCM are usually more pronounced than those of the non-obstructive type. How severe the narrowing is can vary from individual to individual.
Cardiac workload and some medications (e.g., digitalis, nitrates, or ACE inhibitors) also influence the degree of obstruction. If it occurs only under exertion, some physicians refer to it as hypertrophic cardiomyopathy with dynamic obstruction.
Who does hypertrophic cardiomyopathy affect?
Hypertrophic cardiomyopathy affects about two out of every 1000 people in Germany. Frequently, several cases of the disease occur in one family. The age of onset can vary, depending on the cause. Many forms of HCM occur in childhood or adolescence, others only in later life. The gender distribution also depends on how HCM develops. There are both variants that are found primarily in women and again those that occur primarily in men. Along with myocarditis, hypertrophic cardiomyopathy is one of the most common causes of sudden cardiac death in adolescents and athletes.
Hypertrophic cardiomyopathy: symptoms
Many symptoms are typical complaints of chronic heart failure. Because the heart fails to supply the body with sufficient blood and thus oxygen, patients may then suffer from:
- Fatigue and reduced performance
- shortness of breath (dyspnea), which occurs or increases during physical exertion
- fluid retention (edema) in the lungs and in the periphery of the body (especially in the legs), caused by the backlog of blood.
The thickened heart walls in HCM require more oxygen than a healthy heart. At the same time, however, the performance of the heart is reduced and so is the oxygen supply to the heart muscle. The imbalance can manifest itself in a feeling of tightness and pressure in the chest (angina pectoris) during exertion or even at rest.
Frequently, cardiac arrhythmias also occur in hypertrophic cardiomyopathy. Sufferers sometimes experience these as heart palpitations. If the heart is briefly completely out of rhythm, this can also lead to dizziness and fainting spells (syncope) in conjunction with the general heart weakness (due to reduced blood flow to the brain).
In rare cases, the rhythm disturbances in the context of HCM are so severe that the heart stops beating abruptly. Such a so-called sudden cardiac death occurs predominantly during or after strong physical exertion.
Hypertrophic cardiomyopathy: causes and risk factors
A large proportion of hypertrophic cardiomyopathies are caused by defects in the genetic material. These genetic mutations interfere with the formation of specific proteins involved in building the smallest muscle unit (sarcomere). Because affected individuals can pass on such genetic defects directly to their offspring, they often occur in familial clusters.
Inheritance is predominantly autosomal dominant. However, the disease manifests itself differently in each offspring. Hypertrophic cardiomyopathy is the most common hereditary heart disease.
In addition, there are other triggers of HCM that do not directly affect the heart muscle, but in the course of which the heart is damaged. These include diseases such as Friedrich ataxia, amyloidoses, and malformation syndromes such as Noonan syndrome. Some of these are also hereditary.
Hypertrophic cardiomyopathies also do not include enlargement of the heart muscle caused by valvular defects or high blood pressure.
Hypertrophic cardiomyopathy: examinations and diagnosis
If hypertrophic cardiomyopathy is suspected, then in addition to an examination, the history of the patient’s disease and in his or her family is important. If relatives already have HCM, other family members are more likely to have it as well. The closer the degree of kinship, the greater the risk.
After the doctor has questioned the patient extensively about his or her symptoms, he or she examines the patient physically. He pays particular attention to signs of cardiac arrhythmia and cardiac insufficiency. The examiner can also gain important insights by listening to the patient’s heart. This is because hypertrophic obstructive cardiomyopathy is often conspicuous by a flow murmur that is usually absent in non-obstructive forms. It usually intensifies under physical exertion.
In order to establish the diagnosis of HCM and to exclude other diseases with similar symptoms, the physician uses special examination methods. The most important of these are:
- Cardiac ultrasound (echocardiography, UKG): In HCM, the examiner can detect a thickening of the heart walls and measure it.
- Electrocardiogram (ECG): HCM often shows specific rhythm disturbances on the ECG, such as atrial fibrillation or a permanently elevated heart rate. Hypertrophy also shows up on the ECG in typical jagged shapes. Under certain circumstances, doctors may see a left bundle branch block.
- Cardiac catheterization: This can be used to assess the coronary arteries (coronary angiography) and to take tissue samples from the heart muscle (myocardial biopsy). Subsequent examination of the tissue under a microscope allows an accurate diagnosis.
Hypertrophic cardiomyopathy is present when the wall of the left ventricle is thicker than 15 millimeters at any point (normal: about 6-12 mm). However, if the patient has a genetic predisposition, i.e. a close family member has already suffered from HCM, or if corresponding genetic changes have even been discovered in the patient himself (genetic testing), then this limit is no longer decisive.
If the results of an ultrasound examination are not conclusive, magnetic resonance imaging (MRI) is another option. With this examination, the condition of the heart muscle can be precisely assessed and, for example, possible fibrosis can also be detected.
Hypertrophic cardiomyopathy: treatment
It is not possible to cure hypertrophic cardiomyopathy. However, many cases are mild forms that should be monitored medically, but do not initially require further treatment.
As a general rule, those affected should take it easy on themselves physically and not put the heart under intense strain. If symptoms occur that restrict patients in their daily lives, various therapeutic options are available to alleviate the symptoms.
Drugs such as beta blockers, certain calcium antagonists and so-called antiarrhythmics are available to counteract cardiac arrhythmias and symptoms of heart failure. The formation of blood clots is prevented with blood-thinning agents (anticoagulants).
Surgical or interventional procedures may also be used. In the case of pronounced cardiac arrhythmias – and an associated high risk of sudden cardiac death – there is the option of inserting a defibrillator (ICD implantation). Other risk factors also speak in favor of implantation, such as:
- Sudden cardiac death in the family
- Frequent fainting spells
- Blood pressure drop under exertion
- Ventricular wall thickness over 30 millimeters
Hypertrophic cardiomyopathy: disease course and prognosis.
Hypertrophic cardiomyopathy has a better prognosis than many other forms of heart muscle disease. It may even remain completely without symptoms, especially if it does not interfere with blood flow through the aortic valve.
However, life-threatening cardiac arrhythmias are possible. Undetected HCM is one of the most common causes of sudden cardiac death. Without therapy, it kills about one percent of adults (especially athletes) and about six percent of children and adolescents each year.
However, as long as the disease is detected in time and is not too advanced, many symptoms and risks of hypertrophic cardiomyopathy can be well managed with the right treatment.
