The Medical Examiner's Office said yesterday that the cause of death was a rare congenital heart defect known as anomalous coronary artery, or ACA. The condition restricts blood flow to the heart and can often result in a sudden heart attack.
A medical expert said the school would have needed a defibrillator to shock Sebastian's heart to have any chance of saving him, although the chances still may have been remote.
"CPR is very important, but what saves people on site is getting shocked," said Dr. Peter Kowey, head of cardiology at Main Line Health Systems. "The problem with this anomaly is you can do so much damage to your heart muscle very, very quickly that the chances of saving this [kid] aren't that great even if somebody had been there with a defibrillator."
Jackson does not have a defibrillator, Ciarianca-Kaplan said.
According to experts, ACA is found in about 1 percent to 2 percent of the general population. It is present at birth and often not diagnosed until late adolescence or adulthood because of the lack of symptoms. One of the most well-known cases of ACA was Hall of Fame basketball player Peter Press "Pistol Pete" Maravich, who collapsed and died during a pickup basketball game following his illustrious career.
It is unclear what triggered Sebastian's cardiac arrest. Kowey said it often happens as a result of physical exertion, but that is not always the case.
"It's a tough situation all the way around," he said. "All of us would like to see kids get found before this happens. The problem is that this is so unusual, so rare, that it's really hard to put into place any kind of system to prevent it."
In the wake of Sebastian's death, parents and school activists have decried the lack of resources in Philadelphia schools - many of which don't have full-time nurses, counselors and librarians due to severe budget cuts.
Education labor leaders and even Superintendent William Hite pointed to the tragic death as an example of the need for increased funding.
The Passyunk Square Civic Association is collecting donations for memorial and funeral costs for Sebastian's family. Checks may be sent to the association at: PO Box 18052, Philadelphia, Pa., 19147. They should be made payable to Passyunk Square Civic Association, which will write a check to the funeral home. All donations should say "Family of Jackson student" on the memo line.
On Twitter: @ChroniclesofSol