About Hypertophic Cardiomyopathy
Hypertrophic Cardiomyopathy (HCM) is an inherited heart disease that causes thickening of the heart muscle of the left ventricle which is the main pumping chamber of the heart.
Four diagrams show different types of sub-basal HCM, variants distinct from the usual HCM that involves the proximal septum.
(A) Pure apical HCM.
(B) Apical HCM with extension to the mid-LV.
(C) Apical and mid-HCM with severe encroachment of the the LV cavity resulting in a small slit-like LV cavity in diastole, but no apical akinetic chamber.
(D) Mid-LV HCM with mid-LV obstruction and an apical akinetic chamber. Severe Symptoms in Mid- and Apical HCM. Shah et al. Echocardiography 2009.
HCM occurs in men and women of all ages. The muscular walls of the adult left ventricle are normally 11 mm or less in thickness. In HCM the left ventricular walls are greater than 14 mm thick, and may rarely be as thick as 50 mm. Occurring in 1 of every 500 people, recent studies have shown that HCM is more common than previously thought. Indeed, though Hypertrophic Cardiomyopathy is a scientific and probably unfamiliar name, it is a serious health problem, as families affected by the condition know very well.
Our hearts are composed of four chambers. The right atrium and right ventricle pump the blood to the lungs where it receives oxygen. The left ventricle, particularly the left ventricle, pumps oxygenated blood to the body. HCM most commonly thickens the left ventricular walls called the septum and anterior walls, though thickening of any of the walls is possible. The septum is the wall between the left and right ventricle.
Marked concentric thinkening with resulting small left ventricular chamber.
As the heart becomes muscle-bound and thickened the left ventricle fills poorly This reduces the amount of blood the heart can hold, especially during exercise. As a result, HCM patients may suffer from shortness of breath and exercise intolerance. Patients may also experience chest pain, which is caused by narrowed small coronary arteries inside the heart muscle. In addition to the overgrowth of muscle, there is an overgrowth of fibrous tissue, or scarring. These scars and the poor blood supply cause cardiac electrical irritability and may lead to sudden cardiac death, which occurs in 1.0% of HCM patients each year. The cause of death is a chaotic rapid heart rhythm called ventricular fibrillation. However, identifiable risk factors may increase this risk to as high as 4%. It is the young age of HCM patients, and thus the long duration of risk, that makes HCM an important health issue for those affected by the disease.
Some people with HCM have no idea that they are sick. In uncommon cases, adolescents and young adults with no prior symptoms at all can die suddenly without knowing they have the disease. HCM is the most common cause of sudden cardiac death in young people less than 30 years old, and it is the most common cause of sudden death on the athletic field. These tragic deaths occur in otherwise healthy school age youths, affecting individuals who may be premier athletes and considered paragons in their communities. Their deaths emotionally devastate their families, schools and communities.
Flow out of the left ventricle catches the mitral valve leaflet and will push it into the septum.
SAM Begins at Low LV Outflow Tract Velocity in obsructive HCM. Sherrid et al. JACC, 2000.
Obstructive HCM is an important variant of HCM. In obstructive HCM, muscular thickening and an abnormal mitral valve result in obstruction inside the left ventricle. This impedes the ejection of blood to the body.
Here you can see the cause of SAM (systolic anterior motion of the mitral valve). The mitral valve is caught by the flow out the left ventrical and is pushed into the septum. This obstruction forces the heart to work harder.
Obstructive patients have more symptoms and a loud murmur which often brings them to their physician’s attention.
In contrast, non-obstructive HCM, may be more difficult to detect. These patients may go undiagnosed and yet can still have significant cumulative risk for sudden cardiac death over time.
A. Massive asymmetric left ventricular hypertrophy compared to a normal heart. B. Muscle cell disarray and fibrous tissue compared with normal. Hypertrophic Cardiomyopathy: From Gene Defect to Clinical Disease. Chung MW, Tsoutsman T, Semsarian C. Cell Research 2003
HCM is caused by mutations of the molecular motors of the heart—the sarcomeric proteins that cause the heart to contract or squeeze. The normal alignment of muscle cells, reminiscent of a grid of city street blocks, is absent and disorganization reigns. This chaotic abnormality in HCM is called "myocardial fiber disarray".
Abnormalities in >11 genes have been shown to cause HCM, with over 1000 different mutations on these genes potentially causing HCM. The disease is transmitted from one generation to the next, and each child of an affected person has a 50:50 chance of inheriting the condition. Because HCM is inherited, family members may carry a gene for the disease even if they have no symptoms. All parents, children, brothers and sisters of patients with HCM should be periodically screened with echocardiogram and electrocardiogram (EKG). This is particularly important in teenagers and young adults because, even if they have no symptoms, those who have thick hearts should not compete in sports.
An alternative strategy has recently emerged. Here, blood from the patient is tested- genotyped - looking for the mutations that cause HCM. Testing finds a gene known to be associated with HCM in 50% of patients. If it is, the patient's relatives can have their blood tested as well, but for that specific mutation found in the index patient. This is a more definitive approach and in many cases is more cost-effective.
After thorough evaluation, treatment for HCM may include medications to relieve symptoms. For some patients, those deemed to be a high risk for sudden death, an implantable defibrillator is recommended. Patients with drug-refractory obstruction may be candidates for surgical septal myectomy to relieve obstruction, or alcohol septal ablation.
Though HCM can, infrequently, cause sudden cardiac death, and disabling symptoms in other patients, most patients survive until old age, and many symptoms can be relieved by medical, surgical, or interventional management.