Young people aren’t immune from sudden cardiac arrest—and in some cases, they’re actually more vulnerable than adults. Here’s a look at the most common causes.

Hereditary heart conditions

Hypertrophic Cardiomyopathy

According to Stuart Berger, MD, associate professor of pediatrics and cardiology at Children’s Hospital of Wisconsin, and SCA Foundation Adviser, hereditary heart conditions account for about two-thirds of all sudden cardiac arrest cases in young people. These include hypertrophic cardiomyopathy (HCM), which thickens the walls of the left ventricle, obstructing the flow of blood from the heart. HCM affects about 1 in 500 young people and is rarely diagnosed in advance of a cardiac event, so it remains the most common cause of heart-related sudden death in athletes and young people under 30.

Long QT Syndrome

Long QT Syndrome is another hereditary heart condition that can cause sudden cardiac arrest. Affecting 1 in 7,000 young people, long Qt syndrome predisposes a person to an abnormality in the heart’s electrical system. Simply put, the stage during which the heart is recharging for the next heartbeat is prolonged, making the electrical recovery phase inefficient. It’s during this lengthened period that the heart is most vulnerable to electrical irregularities and sudden cardiac arrest. In certain forms of long Qt syndrome, physical and emotional stress can trigger sudden cardiac arrest.

An unknown number of people are born with coronary artery abnormalities that affect the flow of blood from the aorta to the heart muscle. If the blood supply to the heart is diminished, the heart becomes starved of oxygen and is vulnerable to arrhythmias and sudden cardiac arrest.


Causing fewer than 20 percent of all cases of sudden cardiac arrest, myocarditis is an inflammatory disease of the middle layers of the heart. The disease may begin with a viral illness, but it’s not the virus that leads to cardiac arrest. “It’s the response to the virus that attacks the heart,” Berger says. Viral myocarditis can be acute—meaning the person still has viral symptoms such as those associated with the flu or walking pneumonia—or it can be chronic, meaning that the disease persists in a person who has otherwise recuperated.

Commotio Cordis

Commotio cordis is an electrical disturbance caused by a blow to the chest that occurs at precisely the wrong time in the cardiac cycle, resulting in ventricular fibrillation and sudden collapse. Young athletes, who have pliable chest walls, are at risk even when wearing chest protectors and have died while playing baseball, softball, lacrosse and hockey. Since 1995, 182 cases of commotio cordis have been reported to the national Commotio Cordis registry. The average age of a commotio cordis victim is 15, and the current survival rate is just 18 percent.

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-Laura McNeal