HYPERTROPHIC CARDIOMYOPATHY (HCM); Medical point of view
Hypertrophic cardiomyopathy (HCM), known in earlier times as "ox heart disease", refers to a massive hypertrophy of the left ventricle of the heart. The thickening of the heart muscle is not secondary to any other existing disease.
The cardiac cycle
The human heart is made up of 4 chambers: 2 atria and 2 ventricles.
The right atrium receives the venous blood return from the surrounding limbs and organs: arms, legs, brain, intestines, etc. The oxygen-depleted blood is then pushed to the right ventricle from where it is pumped into the lungs to be oxygenated. The left atrium receives the oxygen-rich blood from the lungs and sends it to the left ventricle. Then, the left ventricle propels this blood to the organs throughout the entire body.
In order to support the body's needs, the heart must contract and relax dozens of times every minute. The alternating contraction and relaxation of the myocardium is referred to as the cardiac cycle.
The contraction phase of the cardiac cycle is called systole. It causes blood to flow out of the left ventricle through the aortic valve into the aorta, which is the largest artery in the human body.
The heart muscle
The walls of the heart chambers are composed of a muscular tunic, the myocardium. Under normal conditions, the walls of the left ventricle are approximately 10 mm thick in adults. In children, the thickness will be compared to normal values determined on a body surface area basis.
Like any other muscle in the human body when subjected to a greater effort, the myocardium thickens as it contracts or, in medical terms, hypertrophies. This process is similar in many ways to the bodybuilder who lifts heavy weights to hypertrophy his muscles.
Abnormal stress on the heart muscle can be secondary to a variety of causes. The most common is high blood pressure, which overloads the heart with each beat. Stenosis of the aortic valve has a similar impact on the walls of the left ventricle.
In the absence of the aforementioned conditions, one would expect to see a heart muscle of normal thickness.
If hypertrophy of disproportionate severity is present, hypertrophic cardiomyopathy may be suspected.
As the heart muscle of the vast majority of people does not have such a thickness, and since symptoms rarely occur, thickness of the left ventricle has been established at 1.5 cm (15 mm) in adults. It is based on that criterion that a diagnosis of hypertrophic cardiomyopathy on cardiac ultrasound or magnetic resonance can be made.
In children, it is rather the deviation from normal values that is used.
A significant hypertrophy may cause an obstacle in the flow of blood to the aorta, making it even more difficult for the heart to work. In addition, the marked thickening of the left ventricle leads to abnormal stiffness that can interfere with the proper filling of the heart during relaxation.
Symptoms related to hypertrophic cardiomyopathy are due to a partial blockage during contraction, impaired filling of the left ventricle during relaxation, the muscle itself lacking oxygen due to an increased workload, and to the small arteries functioning poorly in the thickened heart muscle.
- Shortness of breath
People with the disease may experience shortness of breath, typically with exertion, and sometimes when lying down or suddenly in the middle of the night.
- Chest Pains
Chest pains similar to those in angina pectoris are also possible, as well as palpitations or loss of consciousness.
This pathology of the cardiac muscle may cause arrhythmia and palpitations may be perceived. Atrial fibrillation or ventricular arrhytthmia may be symptoms that will lead to diagnosis.
A near or total loss of consciousness during unusual exertion may happen in cases of asymmetric obstructive cardiomypathy.
Apart from a genetic predisposition or certain metabolic diseases, there are no risk factors for developing this condition.
It affects people of both sexes, and various ethnic and races equally.
It is estimated that about 1 in 500 people has hypertrophic cardiomyopathy and that approximately 1 in 200 people carries a gene that makes the person susceptible to developing it.
When the father or mother has hypertrophic cardiomyopathy or carries a gene that makes their offspring prone to having the disease, the child is at risk, 1 time out of 2, of carrying this same gene.
It is important to know that being a carrier of this gene does not necessarily mean that hypertrophy will develop, but screening should be done.
Unless specific risk factors exist, it is recommended that children of parents with this inherited genetic disorder have electrocardiogram and cardiac ultrasound tests performed every 2 years before adolescence, and each year after age 12.
When all test results are normal, screening can be repeated every 5 years, starting at age 21.
If the family gene is known, genetic testing of other family members may be done and the results discussed with a cardiologist or geneticist.
The medical follow-up of a person with hypertrophic cardiomyopathy is normally done by a cardiologist.
Follow-up usually consists of an annual appointment for an electrocardiogram (ECG), a cardiac ultrasound, an exercise test (usually on a treadmill) and the installation of a Holter for a 24-hour home recording of the patient's heartbeat.
The reason for these visits
The main purpose of these appointments and tests is to check for symptoms and to predict the risk of arrhythmia. This risk is assessed on the basis of several criteria. The presence of sudden death at an early age in the family is a relevant factor.
Life-threatening arrhythmia risk assessment
If the risk of severe arrhythmia is considered, the possibility of installing a defibrillator should be discussed.
A defibrillator is a small device implanted under the skin in the pectoral muscle. It monitors the heart rhythm and, when a dangerous arrhythmia occurs, the defibrillator restores the heart rhythm to normal.
Medication is available
As far as symptoms are concerned, various medications are available and have proven to be effective in alleviating them.
Clinical research is well underway to make available a medication specific to the impact of hypertrophy.
Clinical data indicate that the quality of life of patients studied has improved.
What about intervention
In very rare cases, surgery may be required to remove part of the hypertrophied muscle. It is also possible, according to clearly defined parameters, to reduce the thickness of the muscle by a selective injection of alcohol into an artery of the heart; the procedure takes place in a hemodynamics room. (This subject will be developed at a later date.)
Since medical follow-ups are now part of the treatment routine and that defibrillators are used for this condition, the life expectancy of people with hypertrophic cardiomyopathy is excellent and compares favourably with those without it.