Any organ of your body can shut down for a while and you can recover—with one exception, your heart. Cardiac arrest lasting only minutes can result in death. But why should the heart of a healthy, physically fit, top-performing athlete stop? Just as physical conditioning results in making skeletal muscles bigger and stronger, it does the same for the heart. The heart responds to increased demand by getting bigger and stronger. However, if an individual has a large number of mutations in genes responsible for proteins involved in contractions of cardiac muscle, that muscle will be less efficient. To compensate for that inefficiency, the heart gets even bigger than a normal heart would when repeatedly challenged by excessive exercise. Especially in the walls of the left ventricle, hypertrophy can have two serious consequences: (1) The opening of the aorta is at the top of the heart next to the septum that divides the two ventricles. Enlargement of that septum can block the entrance to the aorta, so the cardiac output falls. (2) The bundle of His and the left and right bundle branches that convey the pacemaker potential to the ventricular muscle course down through the septum. Hypertrophy of the septum can interfere with conduction of these critical signals. If advanced conditions of HCM are discovered, there are surgical procedures that remove some of the heart muscle.
The mutations responsible for the development of HCM are not rare, but most people who carry them live their entire lives without even knowing they are at risk for HCM. Why? Most people do not place the excessive demands on their hearts that athletes do. So what can be done to reduce the risk of death by HCM? Preventative measures such as genetic screening could allow carriers of the mutations to make decisions about whether or not to pursue extreme physical activity. Physical examinations including ECGs, sonograms, and even magnetic resonance imaging (MRI) would enable diagnosis and recommendations to decrease levels of physical exertion. The work presented in Investigating Life: Silencing Mutant Myosin Genes suggests a potential future treatment through gene therapy. If safe reagents could be developed to silence the mutant genes, and those reagents were applied before severe HCM developed, they could have a protective benefit.