The world didn't end on Dec. 21, 2012 — doomsday, according to some predictions — but Blake Brunner wondered for a moment if it had. His vision went black, then returned and then he collapsed.

"I was freaking out," the Forest Lake teenager recalled.

A mechanical pump in his chest was failing, he would later learn, and was no longer pushing blood through his body to assist his weakened heart.

So while Brunner credits his young life to this pump, called a left ventricular assist device, or LVAD, one could understand his excitement when doctors recently suggested they might be able to remove it.

Turns out, his heart might be strong enough to resume full-time duty — a possibility that once seemed far-fetched in medicine.

"We've been praying for this," said his mother, Shannon Brunner.

LVADs are implanted when patients' hearts lose their efficiency — often due to disease or a heart attack — and can't keep pace with the body's need for blood.

LVAD implants used to end in one of two ways: Either patients died with them after living lives extended by the devices, or they survived long enough to receive a heart transplant.

Over the past decade, door No. 3 emerged, when cardiologists noticed that certain LVAD patients had hearts that appeared stronger and healthier after months or years of rest.

Brunner is one of the first patients to be evaluated for an "explant" at the Minneapolis Heart Institute at Abbott Northwestern Hospital in Minneapolis. A final decision might come this week. And two other patients are lined up behind him.

"Pretty much any heart should show some signs of recovery" when given the opportunity to rest, said Dr. Benjamin Sun, a cardiothoracic surgeon at Abbott. "In retrospect, it probably shouldn't surprise us."

The critical question is which patients to consider for explants. Doctors find the evidence preliminary, though research does support explants for patients who are younger, whose problems weren't caused by heart attacks, and who can tolerate heavy doses of beta blocker medications that lower blood pressure and improve blood flow.

Explant surgery remains in its infancy, with the University of Minnesota Medical Center, Fairview, having completed only about a dozen. None have taken place at Mayo Clinic.

Cardiologists nonetheless have high hopes that more and more patients can give up the devices. Complication rates with LVADs are somewhat high — including risk of stroke, infection and internal bleeding — and successful explants also mean patients are less likely to need heart transplants, which conserves the limited supply of donor hearts.

Brunner collapsed at home nearly three years ago, and doctors discovered he had an enlarged heart that wasn't contracting properly. It quickly became clear an LVAD would be necessary, and that a transplant would follow if his heart didn't recover over time.

Overnight, the teenager had to adapt to a new life. The LVAD tubing in his chest was tethered through his skin to a 6-pound battery pack and control device on his beltline. He could no longer run hard or swim because he risked disconnecting or damaging the device.

Complications always seemed to disrupt special occasions in Brunner's life — like the fluid buildup in his lungs that he tried to hide from his parents until he could go to his junior prom in 2013. Instead, he spent the night at Abbott. At least his date visited in her dress.

"The true friends came out after [the implant], you know," Brunner said.

Brunner graduated from Forest Lake High School on schedule this spring, despite the medical mishaps, but he delayed plans to earn a degree in cooking. For now, he makes and delivers pizzas — taking care to keep sauce and mozzarella out of his battery pack.

He walks on a treadmill and tries to stick to heart-healthy foods, though that's not easy for a teenager with access to free pizza.

"I make sure I only get the 8-inch," he said.

'Marathon muscle'

The most successful clinical trial of explanting LVADs occurred in England in the early 2000s, with an experimental protocol that included gradually turning down the cardiac devices and giving the patients clenbuterol, a powerful but controversial medication that promotes breathing and muscle growth. The approach at Abbott is similar, but with at least one key exception — clenbuterol isn't a legal medication for use in humans in the United States.

Sun said doctors still disagree on how to prepare patients for explants, including whether to test them by turning down their pumps to see if their hearts are ready to function on their own. Part of the problem is that doctors don't yet understand just how the heart recovers from injury, though Sun said there is general agreement that it does recover.

"The heart's a marathon muscle," he said. "You can leave it on the couch for a little while, but it needs to run."

Patients are better off if they can avoid transplants, which require potent medications to prevent the immune system from attacking the donor heart, and they often need follow-up transplants. Addressing the shortage of donor hearts is also important, as 57 people died awaiting transplants in Minnesota from 2011 to 2013, according to data from the U.S. Organ Procurement and Transplantation Network.

Some patients need defibrillators (devices that shock the heart back into a regular rhythm) after an explant because the procedure can leave scar tissue that can result in abnormal heartbeats. But it's still a good trade, because defibrillators are safety-net devices and offer fewer complications than LVADs, said Dr. Peter Eckman, medical director of the LVAD program at the University of Minnesota Medical Center.

"You're still bionic," he said, "but the risk profile of a defibrillator is far, far less."

While researchers work on building a better LVAD, scientists at the U are trying to see if injecting stem cells in LVAD patients could promote faster healing and increase the chances of a successful explant later on.

A pivotal test

The final step in evaluating Brunner came last Tuesday, when an Abbott cardiologist threaded a catheter into his heart and watched as the LVAD was turned to its lowest setting while Brunner pedaled a stationary bike while lying on his back.

Casual chatter about the Vikings and quarterback controversies quickly faded as Brunner pedaled for 15 minutes, the pedal tension increasing every three minutes.

"Nobody gets out of this one without getting completely pooped," said John Hyatt, pulmonary function technologist, as he tried to reassure Brunner. "Not even D1 athletes."

Brunner's breath grew more labored, and the control room monitors showed he was working harder.

Doctors at Abbott will meet this week to discuss Brunner's results and decide whether to OK him for an explant.

Brunner knows it isn't a sure thing. But the teenager still can dream. He misses swimming and wave pools, and has a road trip in mind if he is no longer tethered to an LVAD.

"At spring break," he said, "I'm going to go to the Dells."

Jeremy Olson • 612-673-7744