What is hypertrophic heart disease?

Hypertrophic cardiomyopathy (HCM) is a condition in which a portion of the heart becomes thickened without an obvious cause. This results in the heart being less able to pump blood effectively.

Hypertrophic cardiomyopathy usually is inherited. It's caused by a mutation or change in some of the genes in heart muscle proteins. Hypertrophic cardiomyopathy also can develop over time because of high blood pressure, aging, or other diseases, such as diabetes or thyroid disease.

Although cardiomyopathy is asymptomatic in the early stages, symptoms are the same as those characteristically seen in any type of heart failure and may include shortness of breath, fatigue, cough, orthopnea, paroxysmal nocturnal dyspnea, and edema.

At present, there is no cure for Hypertrophic Cardiomyopathy. ... While we remain very hopeful that new treatments will continue to improve our understanding and the management of HCM, it is not likely that there will be an outright cure within the next 20 years.

How does hypertrophic cardiomyopathy thicken the muscle walls of the heart?

Researchers have learned a lot about Hypertrophic Cardiomyopathy (HoCM) since they developed tools to sequence the human genome in the early 2000's. It used to be the case that people had a narrow definition of HoCM, but that has changed recently.

There are several different genes that may be responsible for HoCM. All cause overgrowth of the heart muscle in one way or another. The most common (classic) form of the disease is an overgrowth of the interventricular septum (the muscular wall between the right ventricle and left ventricle) that intrudes into the chamber of the left ventricle.

To understand why this is important, you should know the job of the left ventricle. The function of the left ventricle is to contract, pressurize, and send oxygen-rich blood through the aortic valve into the aorta. From the aorta, the oxygenated blood travels to every part of the body. The most important places the blood travels are the heart (coronary arteries), lungs (bronchial arteries), and brain (carotid arteries). When someone has HoCM, the aortic valve can be blocked by the overgrown muscle. The effect is worsened by things that decrease blood pressure (eg, dehydration, extreme activity, or standing up quickly) because that means there is less pressure within in the left ventricle to pushes back against the overgrown muscle and keep the aortic valve accessible.

So, what happens when someone has HoCM? For some time, their heart can perform like everyone else's. They may go years without ever knowing it is an issue. All the while, the heart muscle is becoming unusually thick. Then, once the thickness has become critical (usually occurs in the mid- to late-teens), they are at a risk of sudden cardiac death. If that person does something heavily strenuous on a hot day, the heart/lungs are demanding lots and lots of blood from a heart that is physically losing its capability to pressurize the blood and send it to them. Suddenly, the person can have a heart attack (not enough blood to heart muscle through coronary arteries) and lose consciousness (not enough blood to the brain). A heart without enough blood is subject to abnormal heart rhythms that can be fatal. This is why an AED is absolutely necessary at high school sports settings. And it is why coaches are trained in AED use and CPR.

HoCM is treatable to some extent. It is not a death sentence if it is caught early. Children should have a sports physical that includes questions about HoCM and dynamic murmur testing every single year.

What are the different forms of hypertrophic cardiomyopathy, and how are they treated?

Obstructive HOCM: The hypertrophy is confined mainly to the septum (the muscle area between the the Lt. and Rt. ventricles). This area bulges into the blood-occupying chamber of the Lt ventricle and as the muscle contracts the bulge gets larger which the space gets smaller. This results in the blood from the lower part of the chamber getting trapped and not ejected. This can subsequently result in the apex (end of the heart) bulging outward under the high pressure. And overall, the result is similar to aortic stenosis (where the outflow heart valve is narrowed—a more common problem.) In addition, this narrowed area is about at the same level as the mitral valve and the Bernoulli effect (or venturi effect) will create s ‘suction that pulls the anterior leaflet of the mitral valve open. This in turn creates mitral regurgitation. The obstruction to outflow and the leaking of the mitral value leads to congestive heart failure, while the increased force of contraction that is needed by the heart puts a big strain on the muscle. This can lead to heart pain (angina). And, finally, since the entire pattern is worse when the body ‘exercises’ and makes the heart work even harder, it can cause a person to pass out (syncope).

Treatment of HOCM: If the condition is mild, then medications to ‘weaken the heart’—beta blockers, or verapamil—may be sufficient. If the main problem is the effect on the mitral valve leaflets, surgically replacing the mitral valve usually works. Or the bulging area of muscle can be removed surgically—a nonsurgical technique that accomplishes the same result has also been used (absolute—95%—ethanol will kill tissue. We inject it into the coronary artery branch to that area (first septal perforator) and turn it into scar tissue, which does not ‘bulge’. This may end requiring a pacemaker to correct electrical damage. Finally, pacemakers are often also used for other purposes: A biventricular pacemaker can be set to make the septum contract in the direction of the Rt. ventricle and away from the Lt., so that the bulging muscle moves out of the way. And this may be combined with a defibrillator/pacermaker because these patients have an increased risk of sudden death—so they get a “Bi-V AICD”.
*Note: when you see that many different possible treatments, it means none of them are ‘great’.

Nonobstructive HCM (also known as Concentric Hypertrophic Cardiomyopathy: Here the muscle of the Lt. Ventricle is generally thickened and does not obstruct the outflow of blood or cause mitral regurgitation. But the wall gets ‘stiff’ because it takes biochemical energy for the muscle to relax. When the wall is stiff, the pressure of the inflowing blood has to be high to fill the heart. (This is called diastolic heart failure) This high pressure will cause blood to ‘back up’ while trying to enter the heart, and the first place this happens is the lungs. They fill up with fluid and the patient is short of breath—called ‘congestive heart failure’.
Treatment of CHCM: Unfortunately we currently don’t have a way to fix this. Giving diuretics (‘water pills’) to reduce the fluid is standard. Sometimes if the hypertrophy is severe, surgery is done to remove the entire inner portion of the muscle, like coring an apple—this takes a very good surgeon…

Apical Hypertrophic Cardiomyopathy: More of the same except the thickening is confined to the lower end of the Lt. ventricle (apex). Now the bottom half of the chamber is essentially gone, and the diastolic heart failure is severe and hard to manage.