Zach Conrad set out on a bike ride he figured would take about two hours. He left his Philadelphia rowhome, snaked along the edge of the Schuylkill River, then in and around the trails of Wissahickon Valley Park. A regular competitor in triathlons, the distance wasn't outside of his normal training regimen.

He has no memory of what happened next.

"I was biking along, and must have realized that something wasn't quite right, and stopped, got off my bike, sat down next to a wall and took my helmet off," says Conrad, a tall, wiry, unfailingly polite guy who was 36 years old when this occurred in 2012.

"And then [I] proceeded to slump over."

That's when a passerby, a woman named Charity, spots him on the trail.

"She looked at me and realized that it didn't look good, so she came over and called 911. And then sat down and she said she tried to talk to me while we waited for help."

Soon, two other women come cycling along the trail, Sally Poliwoda and her friend Kristin. Charity, frantic, waives them over and asks if they can somehow help.

"He was on his side," says Poliwoda, who happens to be an emergency room nurse. "I remember flipping him over, and he was blue. Not moving, not breathing, not reacting, he was out. I thought he was already deceased."

Might as well try

Sally knew that attempting CPR, even when the outcome looks grim, couldn't hurt. She gets her friend Kristin into position.

"So I quickly told her, I'm gonna breathe, you are gonna push on his chest, and we are gonna count together," remembers Poliwoda.

And they start. They're doing CPR on Conrad while a crowd begins to form on the bike path. It takes a bit of time for the ambulance to arrive, or at least, it seems to.

"I don't think it was that long," says Poliwoda. "I think those things feel that way in the moment. And I kept thinking, where's help, where's help?" 

A bit of color returns to Conrad's face, but he turns blue again as the minutes tick away.

"Even if this is a lost cause, we can't stop," Sally says. "I know if we stop, he will definitely not survive. So that never crossed my mind, stopping, until we got relieved by rescue."

Eventually the ambulance pulls up, and the EMS workers come running down the path. They affix an automated external defibrillator, an AED, to his chest. It detects a rhythm and delivers three shocks. The medics load Conrad into the ambulance and rush him off to a nearby hospital. 

Sally Poliwoda is left standing there, trying to make sense of what just happened.

"He had a brand new shiny wedding band on, and that was really sad, cause I thought, oh my gosh, this young guy is married to somebody. I thought they are going to take him to the hospital, they are probably going to pronounce him."

The big chill

Poliwoda was right. Zach was newly married, to a pediatric gastroenterologist named Máire, who had worked a 24-hour shift the day before his bike ride.

"So I was asleep and my phone was on vibrate, totally dead to the world, blissful sleep," she says. "And I woke up to someone banging on the door...and I found my best friend. She just told me that something had happened to Zach and people were trying to get in touch with me."

Máire races to the hospital, where she is joined by friends and family. It quickly became clear that Zach, unconscious, but with a stabilized heart rate, would need more advanced care than this smaller facility could provide. That afternoon, he is transferred to the Hospital of the University of Pennsylvania, where he is first seen by Dr. Benjamin Abella.

"And I do remember that he was like many cardiac arrest patients, completely unresponsive," says Abella. "He would not open his eyes, would not move."

Zach was diagnosed with ventricular fibrillation, a disturbance in his heart's electrical rhythm. It caused his heart to start misfiring, and stop pumping blood. When the paramedics shocked him, the organ started beating again, but it wasn't clear how much damage had been done.

"We always worry that patients in this state are having ongoing brain injury, which is a very big problem for patients after cardiac arrest," explains Abella.

While it was his heart that started the problem, Abella and his team were worried the lack of blood flow would put Zach's brain in jeopardy. Abella says the hours after a cardiac arrest are really a race against the clock.

"And so one of the ways we can affect that injury is to lower core body temperature," he says. "We call that therapeutic hypothermia."

The concept is simple: a lower temperature slows down the body's systems, potentially limiting inflammation that could cause complications. At least, that's how it works, in theory.

"It is still actually a mystery how hypothermia works to improve survival after cardiac arrest," he says. "We know some of the partial mechanisms, reduction of brain swelling, decreased cellular metabolisms. So there are definitely ways that we understand it, but it is probably far more complex than that."

This isn't exactly an experimental treatment, though. There is clear scientific evidence that it can benefit patients. And while doctors and researchers are still working to refine therapeutic hypothermia, it has a long history in medicine. 

"Although its modern iteration dates from the 1950s, there are actually documented examples of understanding the role of hypothermia as early as Napoleon's invasion of Russia," says Abella.

We're talking about the year 1812.

"There was a surgeon who worked with Napoleon's army who observed that soldiers who were mortally injured but kept cold sometimes made it. As opposed to soldiers who were injured severely but warmed up and brought near the campfire and given warm cognac. They often died."

Okay, so cognac is out.

The methods for cooling are vastly improved, too. For many patients, it's now done through an infusion of chilled saline.

"It is not as easy as it sounds. There is technology involved and medications we have to give," explains Abella. "We lower the core body temperature from normal, 98.6-degrees Fahrenheit, to around 91-to-92-degrees Fahrenheit. Which doesn't sound like a lot, but as far as brain processes and body physiology, it is a huge temperature difference."

Waiting game

Máire remembers watching as Zach's body temperature was slowly reduced.

"He's completely asleep, eyes closed," she says. "He had a breathing tube, so he had all the work done for him. He had several different IVs, and then he had these cool water blankets that were underneath his legs and arms."

Zach stayed like this, comatose, his body temperature held down around 91-degrees, for 30 hours, just about the maximum amount of time for therapeutic hypothermia.

And those are some long hours when you don't know if he's even going to wake up.

"Or if he was going to have full movements in his body, was he going to be able to write again?" says Máire. "Was he going to be able to have a normal conversation? Was he able to work his job that he had before? Was he going to be able to work any job? All those sorts of questions that were floating around. Yes, I wanted him to be safe, and wanted him alive, but what was his quality of life gonna be?"

Máire, as a doctor, knew that the outcomes in these situations are usually poor. Only about 10 percent of people who have cardiac arrest survive. CPR, like Sally and Kristin performed on Zach, increases the chances to around 40 percent, but even then, many people experience long term cognitive and memory problems.

It turned into, really, just a waiting game to see what would happen to Zach.

"The first day or two are really frightening," says Abella. "There are a lot of ups and downs, a lot of instability, and Zach had some features of this. And we always counsel patients' families that watching a patient go through this is really a marathon, not a sprint."

When the time comes, Dr. Abella slowly begins to warm Zach's body back up.

"So I think at that moment he actually opened his eyes, I had walked out of the room, of course, just like when everything good happens," says Máire. "And my parents were there and so they came running to say, he moved. He's fluttering his eyes and he moved."

Soon, Zach is thrashing his arms and legs, pulling at all the cords, sort of in a delirious state. Then he settles down.

"And he looked at me, and I knew he knew it was me," says Máire. "But he didn't quite have the words yet to say very much. I knew he knew that I was someone he loved, and that he wanted me close, and he squeezed my hand. But it took, I think, several hours before he could come up with all the words to sort of fill in those pieces."

By the next night, Zach was fully conscious, alert and conversing. It was clear everyone's worst fears weren't going to be realized. Máire left briefly to get some food.

"And before I knew it, I looked down at my phone, and I looked at Facebook, and Zach had posted on Facebook," she laughs. "And he's like, 'Hey everybody, I'm okay. Just wanted to let you know, thanks.' And I'm like, oh my god! He's posting on Facebook, we have to go back, what is going on?"

A gray area

Zach spent another week in the hospital, during which time he had a defibrillator implanted in his body. It monitors his heart rhythm and can deliver a jolt if he goes into cardiac arrest again. And, it's really not clear if he will. Doctors still aren't sure why it happened in the first place.

"There are no obvious indicators, I don't have any structural abnormalities in my heart. There are no genetic markers that they can find that indicate that this should have happened," he says. "It just did."

That randomness may seem terrifying, but it's something Dr. Benjamin Abella sees time and again. For him, cardiac arrest is more like a problem to solve. And with therapeutic hypothermia, he's got a promising treatment to refine.

He acknowledges it also makes for great cocktail party conversation.

"When you are in the business of treating arrest patients, some of the language and conversations you have are pretty bizarre. And many of us in resuscitation science throw around terms like 'he was dead,' 'now he's not.' We talk in a way that seems bizarre."

"But it really is a strange and awkward thing because in every sense of the word, Zach was dead. And now he's not. And that is amazing, and we are realizing that yes, death in the first minutes to hours may be a gray area. Historically, it was a very precise line, you were alive, or then you were dead. Not as much so anymore, and we are pushing the boundary further and further, and it makes it very exciting, but it does make for some strange conversations."