What is hypertrophic cardiomyopathy?
Hypertrophic cardiomyopathy (HCM) is a disease (inherited as autosomal dominant pattern or sporadic) in which our heart muscle (also known as myocardium) becomes abnormally thick or hypertrophied. As a result, there is development of left ventricular outflow tract obstruction which makes it harder for the heart to pump blood. Before going any further, it is important to have a discussion on normal blood circulation pattern through the heart.
Here is a simple diagram to show our circulatory system:
Hypertrophic cardiomyopathy (HCM) is the leading cause of sudden cardiac death in the young. It may also cause devastating imbalance in the heart's electrical system.
How common is this condition?
The overall prevalence of HCM in general population is 0.2%.
What are the patterns of inheritance of HCM?
In 50% cases it is sporadic. Sometimes it may be inherited as autosomal dominant pattern.
Which genes are responsible for HCM?
Hypertrophic cardiomyopathy is usually caused by gene mutations. As a result of these mutations the heart muscle grows abnormally thick. There is also abnormal arrangement of heart muscle fibers known as myofiber disarray.
70% patients suffering from HCM have mutations in genes encoding beta myosin, alpha tropomyosin and troponin T. In fact over 200 distinct mutations have been identified in genes encoding for sarcomeric proteins. These include:
Troponin T (chromosome 1)
Troponin I (chromosome 19)
Myosin binding protein C (chromosome 11)
Myosin light chain (chromosome 2 and 12)
Beta myosin heavy chain (chromosome 14)
Alpha tropomyosin (chromosome 15)
Why is it so dangerous?
Hypertrophic cardiomyopathy is like a silent killer. In most of the cases it goes unnoticed, because many of the patients with hypertrophic cardiomyopathy have few, if any, symptoms. Thus sudden cardiac death may be the initial manifestation in a healthy young person! Sometimes the thickened heart muscle can cause vogue symptoms like shortness of breath or irregular heart beats which are not essentially taken care of by the patients at all.
What are the most common symptoms shared by patients with HOCM?
Patients with hypertrophic cardiomyopathy may not have any symptoms at all. Those who have, the most common symptoms are:
Chest pain, especially during exercise or exertion
Shortness of breath, especially during exercise or exertion
Fainting, especially during exercise or exertion (may be the cause of fainting in an adult athlete)
Palpitations (subjective sensation of rapid, fluttering or pounding heartbeats)
Dizziness or vertigo
'Hypertrophic cardiomyopathy' (HCM) is the widely used term for the disorder. Some patients with this disorder have evidence of left ventricular outflow tract gradient-only then is the term 'hypertrophic obstructive cardiomyopathy' (HOCM) appropriate. That means 'hypertrophic cardiomyopathy' is predominantly a non-obstructive disease. In fact, 75% of patients do not have a significant resting outflow tract gradient and may lead a normal healthy life.
How severe is the condition?
The severity of hypertrophic cardiomyopathy is variable. Most people with hypertrophic cardiomyopathy have a form of the disease in which the wall (septum) between the two ventricles becomes enlarged and obstructs adequate blood flow (hypertrophic cardiomyopathy with obstruction or hypertrophic obstructive cardiomyopathy). This one is the dangerous variety.
Sometimes hypertrophic cardiomyopathy occurs without significant obstruction of blood flow. But the ventricles may become stiff, which reduces the volume of blood the ventricle can hold and gets pumped out to the body with each beat. This variety is referred to as hypertrophic cardiomyopathy without obstruction or nonobstructive hypertrophic cardiomyopathy. Patient often has mild symptoms in this variety.
Hypertrophic cardiomyopathy usually affects men and women equally.
The condition is predominantly inherited. There's a 50 percent chance that the children of those with hypertrophic cardiomyopathy will inherit the genetic mutation for the disorder. Siblings of those with hypertrophic cardiomyopathy need screening echocardiography and other investigations to rule out this condition.
Fortunately, hypertrophic cardiomyopathy doesn't cause significant symptoms in many patients. However, in some people, hypertrophic cardiomyopathy can cause severe signs and symptoms mostly shortness of breath, chest pain or fainting on exertion.
But the worse problem is sudden unexplained rhythm disturbance. People with hypertrophic cardiomyopathy are at risk of dangerous abnormal heart rhythms (also called arrhythmias). Most common ones are ventricular tachycardia or ventricular fibrillation. Most ventricular fibrillations are amenable to an implantable defibrillator. These abnormal heart rhythms can cause sudden unexplained cardiac death in a healthy adult. In fact, hypertrophic cardiomyopathy is the leading cause of heart-related sudden death in people under 30.
Possible complications of hypertrophic cardiomyopathy include:
Mitral and other valve disorder
Blood flow obstruction from heart