Theo fainted three times in two years. The fourth time, something was watching.

The first time Theo fainted, he was fourteen and standing in line for a school bus. The second time, he was sitting on a bench between periods of a hockey game. The third time, he was brushing his teeth, and he hit his chin on the sink on the way down.

Each time, he came round within a minute. Each time, he felt fine afterwards. Each time, the tests came back normal: an ECG in the emergency department, a two-week monitor, an echocardiogram, a treadmill test, blood work. The phrase his mother, Dana, heard most often in those two years was "probably nothing."

"Probably nothing is a terrible thing to hear about your kid," she says. "Because it means probably something, and nobody knows what."

The problem with rare

Fainting in teenagers is common, and most of it really is nothing: a drop in blood pressure from standing too fast, or from being too hot, or too hungry. A small fraction is something else. A heart rhythm problem that lasts a few seconds and comes once every six months will not show up on a two-week monitor, because it does not happen during those two weeks.

"You need the recording from the moment it happens," says Dr. Samuel Okafor, the pediatric electrophysiologist who took over Theo's care when the third episode was referred. "Not a description of it afterwards. Not a normal test on a normal day. The moment."

In March of last year, Dr. Okafor recommended a Corta monitor: a device about the size of a paper clip, placed just under the skin of the chest in a ten-minute procedure with local anesthetic. It records Theo's heart rhythm continuously and keeps any episode it detects. A bedside reader on Theo's nightstand collects the data while he sleeps and sends it on.

"I was worried it would stop him playing," Dana says. "It didn't stop anything. He had a sore spot for a week and a story to tell the team."

A Tuesday in February

For eleven months, the monitor recorded nothing of interest. Theo played a full season in goal. The reader sent its nightly report and the reports were boring.

Then, on a Tuesday evening in February, Theo stood up from the kitchen table, felt the world go gray at the edges, and sat back down. He did not quite faint. He told his mother he felt weird, and she told him to press the button on his key fob, which marks the moment for the care team.

He did not need to. The monitor had already caught it.

The reader sent the recording that night. When the device clinic opened at 7:30 the next morning, it was at the top of the triage queue: forty seconds of a very fast, regular rhythm that started and stopped abruptly. Dr. Okafor called Dana before Theo's first class.

Something with a name

The rhythm was a supraventricular tachycardia, caused by an extra electrical pathway in Theo's heart that he had been born with. It is treatable. In April, Theo had a catheter ablation, a procedure that finds and disables the extra pathway. He went home the same day.

Back in goal

Theo is sixteen now. The monitor stays in for another few months, to make sure the ablation did its job, and then it will come out. So far it has recorded nothing, which is what everyone wants it to keep doing.

He was back in goal by the start of this season. His mother says she still watches him stand up from the kitchen table. "I don't think that goes away," she says. "But it's different now. It has a name, and it's been fixed, and I have a strip I can look at."

Theo has a shorter version. "It's a paper clip that called my doctor," he says. "That's pretty much it."

Nexaform Labs is a fictional company. The people, places and figures in this story are invented for demonstration.