Sudden cardiac death refers to a situation where the heart suddenly stops pumping effectively. It most commonly happens in older people who have pre-existing known heart problems. Unfortunately, rarely it may affect an outwardly healthy appearing young person. In many instances this happens in the setting of sports.
The incidence of sudden cardiac death in high school athletes is 1 in 200,000. So fortunately it’s very rare. However, given the large number of high school athletes in the United States (several million), there are many cases every year.
There are a number of potential causes of sudden cardiac death in athletes. The most common is hypertrophic cardiomyopathy (HCM). This is a genetic disorder that affects proteins in the heart muscle cell. It results in an excessively thick heart muscle, most commonly the interventricular septum or middle wall of the heart. Patients with HCM may be prone to ischemia (decreased oxygen delivery) during athletics. This may trigger an electrical malfunction in the heart resulting in sudden cardiac death.
Hypertrophic cardiomyopathy is thought to account for at least 40% of cases of sudden cardiac death in young athletes. Unfortunately it can be a difficult problem to detect. Up to half of patients with HCM won’t have any physical exam findings out of the ordinary. The best way to diagnose it is with an echocardiogram. In addition, over the past several years genetic testing has become available to confirm the diagnosis. Patients with HCM are usually restricted from strenuous activity and competitive athletics. Long-term prognosis is variable.
The second most common cause of sudden cardiac death in young athletes is a congenital coronary artery anomaly. The coronary arteries are blood vessels that feed the heart muscle with oxygen and nutrients. They originate off the first part of the aorta and travel back to the heart muscle. Most individuals have a right and a left coronary artery, each originating from one side of the aorta. The congenital coronary artery anomaly most commonly associated with sudden cardiac death is an anomalous origin of the left coronary artery from the right sinus of Valsalva. The anomalous left coronary artery travels between the aorta and pulmonary artery. A number of factors can contribute to decreased blood flow in the setting of athletics, resulting in ischemia and decreased oxygen delivery to the heart.
A congenital coronary artery anomaly is thought to account for 15-20% of cases of sudden cardiac death in young athletes. Unfortunately these patients will not have any abnormal findings on physical examination. An ECG is typically normal as well. Echocardiography can detect congenital coronary artery anomalies; however a detailed exam with close attention to the coronaries is necessary. Many screening protocols commonly used to detect hypertrophic cardiomyopathy don't include visualization of the coronary arteries.
Cardiac ion channelopathies account for a good portion of the remainder of cases of sudden cardiac death in young athletes. Cardiac ion channels are gates or pores in the cell wall that allow electrolytes to pass in and out of the cell. The movement of electrolytes creates the electrical current in the heart. Some individuals or born with genetic defects that cause these channels to form abnormally. This affects the passage of electrolytes and therefore can disturb the electrical current in the heart muscle. Potentially lethal heart rhythms can be the result. Examples of cardiac ion channelopathies include long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia (CPVT). Many of these abnormalities can now be screened for with genetic testing.
Controversy exists as to the best method of screening young athletes for these rare but potentially deadly disorders. A screening ECG may detect an electrical abnormality but may not detect hypertrophic cardiomyopathy. In addition, it is of no use in screening for congenital coronary artery abnormalities. A screening echocardiogram is excellent for HCM but may miss congenital coronary artery anomalies unless careful attention is paid. It does not provide any use in detecting electrical problems. A combination of the two tests increases the accuracy of screening, but increases the time and cost involved. Currently the American Heart Association does not endorse mass population screening with either an ECG or echocardiogram. Instead, it recommends a thorough history and physical examination with close attention to details that may suggest one of these disorders. If any concern is raised, then more involved testing in the form of an ECG, echocardiogram, and cardiology consultation is recommended.
Penn Laird II, M.D.
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