L.A. Marathon heart attack victim doing better

Running a marathon is usually considered solid proof of cardiovascular fitness. Not so for Jay Yim, a runner in the recent Los Angeles Marathon.

Yim, 21, suffered a heart attack around mile 18 and was taken to the Ronald Reagan UCLA Medical Center. He’s expected to make a full recovery.

Here’s what happened:

After Yim collapsed in West L.A., LAPD motorcycle officer Joshua Sewell was one of the first people to come to Yim’s aid. When he got no response and found no pulse, Sewell yelled for someone to call an ambulance and recruited an LAPD bicycle officer to help administer CPR. Together, they performed chest compressions and mouth-to-mouth resuscitation. Bystander Dr. Charles Chandler of UCLA joined in, and he eventually got a pulse.

At the hospital, Yim was found to have suffered some seizures as well, possibly caused by the cardiac arrest, said Dr. Paul Vespa, director of neurocritical care at UCLA, who treated Yim. An MRI showed some brain swelling, and doctors decided to induce hypothermia.

In that process, the patient is put into a coma and his or her body is cooled to 89.6 degrees. The process, still somewhat controversial, basically brings on hibernation, Vespa said, causing a metabolism shutdown. “When you have a brain injury,” he said, “a whole number of bad pathways get activated, and that can lead to cell death and damage. Hypothermia blocks those pathways.”

Yim’s body was warmed after about 48 to 72 hours, and he is now awake and talking. He’s undergoing physical therapy, and his overall prognosis is excellent. What caused his cardiac arrest still isn’t known, and although it’s unusual for someone of his age and good health to suffer a heart attack, dehydration or inadequate nutrition during a marathon or other physical activity can trigger such catastrophic events.

Undiagnosed congenital cardiovascular conditions can fell young athletes, too, which is why some physicians advocate electrocardiogram screenings for high school and college athletes.

But Yim, a USC pre-med student originally from Phoenix, has some incentive to run again. Sewell, who ran the marathon in 2006, said he promised he’ll finish the last 8.2 miles with Yim when he’s able. “I told him that, and he got a big old smile on his face,” Sewell said.

“Everything was in Jay’s favor,” said Yim’s older brother Roy, a law student from Florida. “It’s weird how it all turned out.”

jeannine.stein@latimes.com