When Kyle Chase Johnson set off to run the half marathon Sunday morning, there was no sign anything was wrong.
But a rare defect had been lingering in the background since Mr. Johnson was born and, about 2 miles from the finish line, it killed him.
Mr. Johnson, 23, had an abnormality in his coronary artery system, Allegheny County medical examiner Karl Williams said Monday, a defect that is present in less than 1 percent of the population and kills even fewer.
The coronary arteries supply oxygenated blood to the heart, so when they are pinched or have a "slit-like opening," the heart can suddenly stop, especially when exerted during heightened physical activity, according to doctors.
Such defects can be especially traumatic because most people don't exhibit any symptoms, making the condition extremely difficult to detect.
Dozens of types of congenital heart defects can cause health problems, but the one that killed Mr. Johnson is known as an anomalous coronary artery -- a defect that can cause sudden death in athletes.
About 1 in 200,000 athletes in the U.S. suffers sudden cardiac death, according to Vivek Allada, chief of pediatric cardiology at Children's Hospital of Pittsburgh of UPMC and an expert on sudden cardiac death in athletes.
Mr. Johnson's coronary artery had an "abnormal pathway around the aorta," according to Dr. Williams, meaning the oxygen-rich blood supply to Mr. Johnson's heart was likely insufficient.
Friends and family said Mr. Johnson never complained of chest pain, shortness of breath or fainting -- all signs of the defect.
He ran a half marathon -- 13.1 miles -- in New York City a couple months ago.
"He looked healthy. He always looked healthy," said Alex Calder, Mr. Johnson's longtime friend and new roommate in a Downtown apartment.
"There's no family history at all," Mr. Johnson's stepfather, Bryan Deal, said when asked whether other family members had any related medical problems.
"He played four years of high school football at North Allegheny that involved extensive training, running and lifting," said Mr. Deal, of Franklin Park, noting that his stepson "never had any complaints" and comes from an athletic family.
Mr. Johnson graduated from Penn State a year ago and had an accounting job at Deloitte & Touche.
Dr. Williams said Mr. Johnson's case is not unlike that of Pete Maravich, the Beaver County native and NBA player who died suddenly of a congenital heart defect during a pickup basketball game in 1988, several years after injury ended his professional career.
Those who have this condition often are diagnosed incidentally, said cardiologist Timothy Wong, a co-director of UPMC's hypertrophic cardiomyopathy center.
"It's easy to second-guess this," Dr. Wong said. "But this is a rare condition and isn't easy to diagnose in the absence of symptoms."
An electrocardiogram, echocardiogram, cardiac MRI or cardiac CT could all point to abnormal coronary arteries, but athletes in the U.S. are not universally screened.
"Like with anything else in life, there's risk in everything that we do," Dr. Wong said. "A lot of policy-makers have given a lot of thought to how much testing people should have before people participate in sports. Anytime you do a screening, you might find incidental things that never would have been a problem to begin with."
In the U.S., there isn't universal screening of athletes for conditions that can cause sudden cardiac arrest, and that may not be a bad thing, according to Dr. Allada.
He points to countries that have experimented with universally screening athletes to explain why it may not make medical or economic sense to give every athlete an electrocardiogram.
"The screening EKG is not foolproof," Dr. Allada said, noting that both false negatives and false positives are possible.
Italy and Israel experimented with universal EKGs for athletes.
Sudden deaths among athletes diminished, but they ended up falling to about the rate that already exists in the U.S. -- 1 per 100,000 athletes, Dr. Allada said.
And in Italy, the testing led to increases in suicide among people who tested positive and were told to avoid physical activity, he said.
Another consideration is the economic cost of widespread screening.
It would cost about $60 billion to screen all 20 to 25 million U.S. athletes, which means each life saved could cost millions of dollars and might not guarantee better overall health outcomes, according to Dr. Allada.
Even if Mr. Johnson had been screened, it isn't obvious that anything could have been done to save him.
Surgery can repair congenital heart defects in some circumstances, doctors say, but in Mr. Johnson's case, there was no reason for doctors to look for a defect and it is not clear that tests necessarily would have revealed it.
"If he had fainted with exercise two months ago, that would have been a red flag," Dr. Allada said. "In the absence of that, it would be very hard to imagine that screening would have prevented this."
Alex Zimmerman: email@example.com or 412-263-3909. First Published May 5, 2013 7:30 PM