Obstructive hypertrophic cardiomyopathy (NORD)

Obstructive hypertrophic cardiomyopathy is a genetic disorder where the walls of the heart become thicker, or hypertrophied. While it might seem a thicker heart is a good thing, the larger muscles prevent the ventricles—the two lower chambers of heart—from fully relaxing between contractions. In addition, the walls of the heart are stiffer and less compliant, so they can’t stretch out as much.  This reduces the amount of blood that gets into the heart, lowering the cardiac output, or the amount of blood pumped out of the heart per minute.  

Usually, the left ventricle is more affected, and in most cases, muscle growth is asymmetrical, meaning that the wall between the two ventricles, called the septum, grows larger relative to the free wall. In some people, the thickened septum can obstruct the outflow of blood from the left ventricle, which is why hypertrophic cardiomyopathy is sometimes called obstructive hypertrophic cardiomyopathy. In these cases, the blood that comes out of the left ventricle is forced through a smaller opening, which creates a “pulling” effect on the nearby mitral valve that further obstructs the outflow of blood.  

Most cases of obstructive hypertrophic cardiomyopathy are familial. This means the condition is inherited from a parent. Inheritance is autosomal dominant, meaning only a single copy of a disease-causing gene variant is needed to cause the disease. Variants in many different genes that code for proteins found in heart muscle, such as myosin and troponin T. can cause obstructive hypertrophic cardiomyopathy.

Symptoms of obstructive hypertrophic cardiomyopathy can begin at any age, but they most often start in early adulthood. Over time, the heart becomes unable to do its job effectively, leading to signs of heart failure such as excessive tiredness and shortness of breath, especially during exercise.   

Because there is less blood coming out of the heart, the amount of blood transported to the brain can decrease. This may cause fainting. Individuals are also more prone to developing arrythmias, or irregular heart rhythms, which can sometimes be life-threatening. Of note, obstructive hypertrophic cardiomyopathy is the most common cause of sudden cardiac death in young individuals, especially young athletes.