A thrown baseball can cause sudden death from heart failure, even at modest, Little League speeds of 30 mph, according to a study published Thursday in the New England Journal of Medicine.
If the ball hits the chest at precisely the wrong moment in the heartbeat cycle the results can be fatal, said researchers who studied the effects of throwing balls at anesthetized young pigs. The study was intended to explain rare instances in which youngsters with no heart problems dropped dead on the playing field.The phenomenon is known as commotio cordis, or concussion of the heart. But until now, doctors could only speculate on exactly why a relatively mild blow to the chest can kill.
The answer, based on the study: The blow scrambles the heart's electrical signals at a particularly vulnerable moment.
"Not every blow to the chest is going to result in a death like this," said one of the researchers, Dr. Barry Maron of the Minnesota Heart Institute Foundation. "Timing, force and location have to conspire to produce this rare but tragic thing."
Commotio cordis usually results from being struck by a baseball, but reported cases have also involved softball, karate, football, hockey, even slam dancing. Children are most vulnerable, perhaps because their chest walls are thinner.
Two weeks ago, a 6-year-old boy in central Illinois died after a foul ball hit him in the chest as he waited to bat. The coroner called it a "freak accident" and said the force of the ball was probably enough to cause the boy's heart to fibrillate.
Maron theorized that sudden death can occur when the chest wall is struck during a vulnerable interval - just over 1/100th of a second - during which the heart repolarizes electrically in preparation for the next contraction, or heartbeat.
The study confirmed his theory: A moderate blow during repolarization can cause ventricular defibrillation, in which heart muscle fibers contract randomly instead of beating together and the heart cannot pump blood.
In the first part of the study, pigs 4 weeks to 8 weeks old and weighing 18 to 26 pounds were struck in the chest with a wooden ball at various points during the heartbeat cycle. The ball was thrown at 30 mph, the average speed of the balls that caused the death of at least 19 children in an earlier study by Maron. By comparison, a major-league fastball is generally around 90 mph.
All the pigs were under general anesthesia. Nine of 10 animals struck during the 15-millisecond interval of repolarization went immediately into ventricular defibrillation.
Four of nine pigs struck at a different point in the cycle - a brief interval after contraction - experienced complete heart stoppage for a few beats, then recovered.
In the second part of the study, baseballs of four different hardnesses were thrown at pigs when their hearts were repolarizing.
Thirty-five percent of the blows with a regulation baseball resulted in commotio cordis, compared with 8 percent of blows with the softest baseball, marketed for use by children ages 5 to 7.
The two moderately hard baseballs were not significantly safer than the regulation ball.
The results show that parents and coaches should use the softest safety balls with young children playing catch or T-ball, said Dr. Mark Link, the New England Medical Center researcher who led the study.