The heart muscle thickens greatly (often asymmetrically) and the muscle cells may become disorganised (which can interfere with the passage of electrical signals through the muscle), without any obvious trigger. In most cases the disease is hereditary, resulting from a gene abnormality. The disease is thought to affect at least 125,000 people in the UK.
In one form of hypertrophic cardiomyopathy (hypertrophic obstructive cardiomyopathy or HOCM) the muscle mass of the left ventricle and the wall that divides it from the right side of the heart (the septum) becomes larger than it should be. This leads to narrowing of the passage through the heart and obstruction of the blood flow out of the heart.
In addition the muscle is stiff and has difficulty relaxing, increasing the amount of pressure required to expand the heart while blood flows in. This reduces the blood holding capacity of the heart.
The altered structure may distort the mitral valve between the chambers of the heart (the left atrium and left ventricle) which may then leak. It’s also known as asymmetric septal hypertrophy (ASH) or idiopathic hypertrophic subaortic stenosis (IHSS).
The condition can be present in the foetus and cause stillbirth, or may develop in infancy. But, more usually, it develops during childhood or early adulthood.
In another form of the disease, non-obstructive hypertrophic cardiomyopathy, the enlarged muscle doesn’t obstruct the blood flow.
The symptoms of hypertrophic cardiomyopathy include shortness of breath on exertion, dizziness, fainting and angina pectoris (angina is chest pain or discomfort caused by reduced blood supply to the heart muscle.) The obstruction to blood flow from the left ventricle increases the ventricle’s work, and a heart murmur may be heard. Some people have cardiac arrhythmias. These are abnormal heart rhythms that in some cases can lead to sudden collapse and death.
Treatment, which includes anti-arrhythmia drugs, aims to control symptoms and prevent complications such as sudden collapse. Surgery may be necessary to remove some of the muscle or repair the mitral valve. A special device called an implanted cardioverter defibrillator (ICD) may need to be put into the heart to deliver and electric shock which will get the heart back into a normal heart rhythm whenever arrhythmias occur, in order to prevent sudden death.
Because there may be a genetic cause, other members of the family should be screened to check for the faulty gene.