There are conditions that can cause sudden cardiac death even in young healthy athletes, typically by causing a lethal arrhythmia. Sudden cardiac death affects fewer than 10 per million young athletes per year. More than 80 percent of these are actually due to an undiagnosed underlying heart problem.

Q: Can getting hit by a baseball cause a heart attack in a young, healthy, athletic teenager?


A: The heart attack we normally think of is from a blockage of the arteries that bring blood (carrying oxygen and nutrition) to the muscles of the heart, typically from atherosclerotic disease. This can impair the heart's ability to pump blood, as well as cause the electrical system that synchronizes the heartbeat to malfunction (arrhythmia). These can lead to sudden cardiac death.


People younger than 35 rarely have severe atherosclerotic disease, so this kind of a heart attack is unusual in this age group. However, there are conditions that can cause sudden cardiac death even in young healthy athletes, typically by causing a lethal arrhythmia.


Sudden cardiac death affects fewer than 10 per million young athletes per year. More than 80 percent of these are actually due to an undiagnosed underlying heart problem. For example, in young athletes, hypertrophic cardiomyopathy (where the heart muscle is abnormally thick) accounts for 20 percent to 50 percent of sudden cardiac death events, abnormal development of the coronary arteries for 10 percent to 20 percent, myocarditis (inflammation of the heart muscles, usually due to infections including certain viral infections) for 5 percent to 25 percent, and other conditions (including inherited conditions which affect the heart's electrical system) for the rest.


A physical blow to the chest can cause sudden cardiac death by causing an arrhythmia even when there is no underlying heart disease; this is called commotio cordis (meaning "commotion of the heart"). The ancient martial art technique of Dim Mak (touch of death) may have been based on commotio cordis.


The commotio cordis registry established in 1995 has recorded about 225 cases, so commotio cordis is rare (although underreporting is likely). Despite this, studies of commotio cordis in animals have helped gain understanding of this condition.


The heart's electrical system carefully regulates the heartbeat. There is a limited part of this electrical cycle (about 1 percent to 3 percent) where a blunt blow to the chest may induce a haphazard and ineffective heart rhythm (ventricular fibrillation or Vfib). Not only must this blow hit during this small susceptible window, but it must hit a precise location over the heart and have sufficient energy to cause Vfib.


Studies have shown that for harder projectiles (for example, a ball or puck), lower velocities are required to deliver this potentially lethal strike. Studies have also shown that commercially available chest protectors are not effective at protecting against commotio cordis.


The typical commotio cordis scenario is a young athlete getting hit in the chest by a speeding ball/puck (although a blow from another person or a stationary object can do it as well), and then either immediately collapsing (most common) or collapsing within a few seconds (less common, although cases where someone is hit when batting then collapses at first base have been reported). At this point the person's heartbeat has stopped from disruption of its electrical system.


Commotio cordis is most common in boys around 16 (most cases occur between ages 7 and 25) and during competitive sporting events (more than half of cases), although recreational sports account for a quarter of cases and other situations (such as fights, accidents or falls) for the rest.


Once commotio cordis induces Vfib, treatment with prompt CPR (too often delayed since people think the victim has just passed out), and early defibrillation (using an automatic external defibrillator or AED) are indicated. The odds of "restarting" the victim's heart drop very rapidly -- to less than 5 percent if treatment is delayed even 5 minutes -- so waiting for an ambulance to arrive is not optimal. Data from the commotio cordis registry show that fewer than 1 in 4 victims survive.


As noted above, commercially available chest protectors don't help much (if at all), so:


- Younger children should use a softer ball.


- Coaches should teach kids how to avoid chest blows, such as turning away from an errant pitch and not blocking a hockey/lacrosse shot with their chests.


- Playing fields should be clean and flat in order to minimize "bad hops."


Coaches and others responsible for sporting activities should learn CPR and how to use an AED (I think everyone should learn these potentially life-saving techniques). AEDs should be available at all sporting events and mass gathering.


Massachusetts-based Dr. Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.