Hypertrophic cardiomyopathy screening
Hypertrophic cardiomyopathy, or HCM, is the leading cause of sudden cardiac death (SCD) in young athletes. HCM is frequently asymptomatic until SCD, and thus its prevention requires screening. Screening by medical history and physical exam are ineffective, indicating heart abnormalities in only 3% of patients who subsequently suffered SCD. However, HCM can be detected with 80%+ accuracy by echocardiograms, which may be combined with pre-screening by electrocardiograms (ECGs). Routine cardiac screening of athletes has been implemented in Italy since the 1970s, and has resulted in an 89% drop in cases of SCD among screened athletes. In the United States, the American Heart Association has "consistently opposed" such routine screening. (See (Sanghavi 2009) for a popular summary of literature and discussion). However certain chapters of the American College of Cardiology are backing screening models provided by private entities and nonprofit organizations.
HCM is a genetic disorder that causes the muscle of the heart (the myocardium) to thicken (or hypertrophy) without any apparent reason. When the heart thickens and becomes enlarged, particularly at the septum and left ventricle, it can cause dangerous arrhythmias (abnormal heart rhythms). The thickening of the heart makes it harder for blood to leave, forcing the heart to work more vigorously to pump blood.
HCM occurs in up to two per 1000 people in the general population, being a primary and familial malformation. While younger individuals are likely to have a more severe form of hypertrophic cardiomyopathy, the condition is seen in people of all ages. Studies have shown that HCM is generally regarded as the most common cause of sudden cardiac death in athletes, accounting for 36% of deaths. Almost half of deaths in HCM happen during or just after the patient has done some type of physical activity. Sudden death is frequently the first indication of the presence of HCM, where 90% of deaths in athletes occur in males. This is potentially due to the higher frequency of participation at a higher intensity in male athletics. 60% of athletes are of high school age at the time of death.
The first symptom of HCM among very young patients tends to be sudden collapse and possible death. However, other symptoms include exertional dyspnea (most common), chest pain, dizziness, fainting, high blood pressure (hypertension), heart palpitations, fatigue and shortness of breath. However, some patients have no symptoms and may not realize they have the condition until it is found during a routine medical exam.
Athlete's Heart vs. HCM
Quite often, HCM can be mistaken for a condition known as athlete’s heart. Both involve growth of the myocardium, however the latter generally is not correlated with incidences of SCD. While HCM can be linked to family history, athlete’s heart arises purely as a function of intense exercise (usually at least an hour a day, everyday. Since the body is operating at high training levels, the heart adapts and grows in order to pump blood more efficiently. Stoppage of exercise for three months generally leads to a decrease in wall/septum thickness in those with athlete’s heart, whereas those with HCM exhibit no decline.
People with athlete’s heart do not exhibit an abnormally enlarged septum, and the growth of heart muscle at the septum and free ventricular wall is symmetrical. The asymmetrical growth seen in HCM results in a less-dilated left ventricle. This in turn leads to a smaller volume of blood leaving the heart with each beat.
|Septum thickness||<15 mm||>15 mm|
|Symmetry||Yes (for septum and LV wall)||No (septum much thicker|
|Deconditioning||Reduction within 3 months||None|
Screening and Diagnosis
Screening young athletes to detect HCM is an essential process in preventing a possible sudden cardiac death as most at victims do not show prior symptoms. Rarely HCM can induce symptoms like dyspnea (difficulty breathing) or chest pain that are related to the aforementioned heart defect. However the subsequent abnormalities of HCM like myocarditis, an inflammation of the heart muscle, will likely be asymptomatic and those at risk will likely never know unless screened and diagnosed by a medical doctor.
Most medical professions and researchers agree that there are three methods of screening for HCM and sudden cardiac death, each with their own benefits and weaknesses:
- Physical examination and medical history is ineffective, catching only 3% of cases;
- ECGs detect heart abnormalities and detect 70% of asymptomatic HCM, but cannot specify that the abnormality is specifically HCM;
- Echocardiograms detect 80%+ of HCM, and are used to diagnose HCM specifically – the correct diagnosis of HCM is always made by using an echocardiogram.
1) Physical Examination and Medical History
Defined: Refers to a thorough but general physical examination that most patients / athletes would receive at any check-up with their doctor. This method of screening looks for some of the symptoms mentioned above as well as heart palpitations or unusual chest X-rays. In addition, the existence of diseased family members that may have suffered from sudden cardiac death is important because of the genetic transfer of the disease. This is the method used in most United States school sports and youth organizations.
While cheap and easily performed by trained medical staff, it is impossible for a physical examination and medical history screening to detect the disease HCM and is therefore unreliable.
2) 12 Lead Electrocardiogram (ECG)
Defined: Is a test performed by a doctor or trained health professional to measure the electrical signals produced by the heart. The ECG cannot be used to directly detect HCM but is useful in detecting general heart abnormalities to subsequently recommend further testing. Even an asymptomatic patient will demonstrate an abnormal ECG in 70% of cases. Although extra costs are associated with the equipment and professional assistance, it is an effective method of screening when used as a referral for echocardiography screening.
3) Echocardiography (ECHO)
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Defined: A Transthoracic Echocardiogram provides a 2-D image to a doctor from standard ultrasound that is directly and reliably able to detect HCM in athletes. This procedure is expensive but is considered to be optimally used when implemented after an abnormal ECG and is the only test of choice to confirm a diagnosis. Studies indicate that doctors are able to detect HCM from an ECHO anywhere from 80% to 100% of the time.
Successful models of intervention using ECG
As previously discussed, ECG screening appears to be the most feasible and effective method for screening for HCM. There are contrasting policies with regards to national standards on screening young athletes for cardiovascular abnormalities. Below are a few successful interventions, followed by the United States’ approach.
By law, all competitive athletes are required to undergo physiological testing prior to competing. This consists of a history, physical examination, urinalysis, resting and exercise ECG, and pulmonary functioning test. All of these are conducted by a sports physician. If there are abnormalities, further screening of ECHO (echocardiography) is required.
- A study of 4050 Italian national team athletes revealed high levels of efficiency of their 12-lead ECG in detecting HCM in young athletes. This led to the disqualification of athletes with HCM from their respective sports.
- Over a period of 25 years, there have been monitored trends in cases of sudden death in screened and unscreened athletes. Sudden cardiovascular death accounted for 55 deaths in screened athletes and 265 in unscreened athletes. Overall, there has been an 89% decrease in incidence of athlete death due to cardiovascular abnormalities.
European Association for Cardiovascular Prevention in Sports Cardiology
This is supported by the International Olympic Committee, and follows the Italian strategy consisting of personal and family history, physical exam, and 12-lead resting ECG. FIFA also performed preparticipation screening in all soccer players in the world championships in Germany in 2006.
To date, there is no national policy for the screening of CVD or sudden cardiac death in young athletes. Though many screening programs are currently being run by private entities as well as various non profit organizations. Most state laws require competitive athletes to undergo a physician-mediated physical examination and history. ECG or echocardiograms are rarely used. A medical history and physical exam have shown to have little sensitivity or power to detect HCM or other risk conditions. The theory behind this lack of national standard is that screening is viewed as an aspiration to identify a rare cardiovascular disease with low incidence in a large population (approximately 2 in 1000 individuals).
- Following Their Hearts, David Hill, Training & Conditioning, 16.2, March 2006
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- Sanghavi, Darshak (February 3, 2009), "Dying To Play: Why don't we prevent more sudden deaths in athletes?", Slate.com