A Needle in a Haystack
Hypertrophic Cardiomyopathy (HCM) is a rare but devastating diagnosis for an athlete. The abbreviation is also pronounced “hocum”. HCM is a huge deal in the sports world for one major reason; it can kill you. It is commonly reported that hypertrophic cardiomyopathy is the commonest case of exercise-related sudden cardiac death. Moreover, the most common initial sign is not chest pain or shortness of breath, it is sudden death! Every time we do sports physicals and listen to the heart this is THE major issue we are trying to uncover. The most difficult aspect of diagnosing this condition is that it like looking for a needle in haystack as it is believed that 0.06% of athletes have this condition.
Screening and Diagnosis
The debate regarding what type of screening tests are done is a challenging and contentious one. Some argue that all athletes should have an EKG done, as in the NCAA, which is believed to catch more than 95% of cases. However, others argue that the only way to truly be certain is to obtain an ultrasound (echocardiogram) of the heart and measure the thickness of the wall of the left ventricle. A third group argues that for non-professional athletes we do not have the resource to do this type of testing and the level of false positives is too high which could potential eliminate athletes from play who are perfectly healthy. For argument sake let’s assume that the NFL does both an EKG and an ultrasound of the heart. To understand more about hypertrophic cardiomyopathy you have to learn a little bit about how the heart works.
Basic Physiology
Of the four chambers of the heart, the largest is the left ventricle (LV). The left ventricle is responsible for pumping blood out to the entire body through the aorta. The blood leaves the left ventricle to supply the body through the aortic valve and out through the aorta. An important point in HCM is that there needs to be a wide enough space for the blood to be pushed out through the aortic valve when the left ventricle squeezes. A key step is that there are papillary muscles in place to help keep the other valves closed so the blood only flows in one direction.
Hypertrophic Cardiomyopathy
In hypertrophic cardiomyopathy the inner wall of the left ventricle (aka septum) is abnormally thickened and composed of irregular muscle cells. These factors are the primary cause of the down stream effects of this condition.
One issue is that the thickened wall decreases the amount of blood that can fill the ventricle and eventually go out to the body on each beat. Secondly, due to the irregular muscle and thicker wall, structures can physically block the blood from getting out of the left ventricle. This blocked outflow can cause turbulence and is what we can hear with stethoscope as a murmur! Lastly, the combination of these two features of this condition can predispose an athlete to develop an arrhythmia. The “lucky” athletes have some symptom such as shortness of breath, chest pain, or passing out with exercise, which prompts a workup and diagnosis. However, the most common presentation is simple for the athlete to collapse and die, with the diagnosis being made after the fact.
Millimeters Matter
If an individual has a wall width of 2.0 cm they would certainly fit the criteria for HCM. Typically ventricular wall measurements 1.3 cm or less would be classified as normal. However some athletes who are well trained with well developed hearts can have measurements of 1.3-1.5 cm, which is considered normal physiologic adaptation. On the other hand, some athletes with the 1.3 - 1.5 cm thickness could fall in to a grey area where we can't be sure of the diagnosis based only on the wall thickness measurements. One additional feature is to look at the size of the chamber of the ventricle and the ability to fill with blood. Athletes in the grey zone with a small filling area of the ventricle and impaired function during filling of the heart would be of high concern for HCM. As one might imagine, it is complex and highly variable. Although extremely rare, these measurement can be the difference of in an athlete's career or even their life.