What is Hypertrophic Cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy is a genetic heart condition that causes the heart muscle to grow abnormally thick, without any obvious cause.  HCM affects 1 in 500 young adults (0.2%), which is equivalent to 600,000 people affected in the United States. (1)  In comparison, according to the ALS Association, it is estimated that as many as 30,000 Americans.

The main feature of hypertrophic cardiomyopathy is an excessive thickening of the heart muscle (hypertrophy literally means to thicken). Thickening is seen in the ventricular septal measurement (normal range .08-1.2cm), and in weight. In HCM, septal or wall measurements may be in the range of 1.3cm to 6.0+cm anywhere in the left ventricle. (2)

The severity of hypertrophic Cardiomyopathy varies widely. Most people with hypertrophic Cardiomyopathy have a form of the disease in which the wall (septum) between the two bottom chambers of the heart (ventricles) becomes enlarged and impedes blood flow out of the heart. This condition is sometimes called obstructive hypertrophic Cardiomyopathy.

HCM is genetic, but not everyone who carries the gene, will develop HCM.  Furthermore, HCM is usually diagnosed in young adults or adults, as it tends to develop in adolescence.   As a result, many people who are carriers or who have the disease are unaware of the condition.   Some patients are highly symptomatic while others have very minor symptoms.  Fortunately many have a normal life expectancy.

Sudden Cardiac Death (SCD) in relation to HCM

HCM annual mortality rates have recently been estimated at approximately 1%, with about half of these deaths, due to sudden cardiac death; however, HCM is the most common cause of SCD in young athletes. (4)

There are five risk factors for SCD to consider with HCM patients.  Studies have shown that individual risk factors have a low positive predictive accuracy, and that it is more important to consider all of the five risk factors together.

These risk factors include the following:

  • Ventricular tachycardia – an abnormally fast resting heart rate
  • Severe thickening of the heart (left ventricle wall thickening >30mm)
  • Abnormal blood pressure response during exercise
  • History of fainting
  • Family history of SCD in someone under the age of 45

The annual SCD rate is around 1% or less in patients with zero or one risk factor. Dustin had only one risk factor present.  His left ventricle was just about 28mm, close to the 30mm.

In patients with two or more risk factors, are at a higher risk of SCD and should consider the implementation of an implantable cardioverter-defibrillator, ICDs.

Symptoms and Detection of HCM

Sudden death due to HCM most commonly occurs in adolescents, who often are not aware of their condition. Genetic testing can identify whether a person has the genetic defect that can lead to HCM. HCM is usually diagnosed by an echocardiogram.

Symptoms of HCM include the following:

  • History of Fainting
  • Fatigue
  • Chest Pain or pressure during exercise
  • Shortness of Breath during Exercise
  • Heart Palpitations
  • Some patients may have a heart murmur