For decades, pacemakers have successfully treated abnormal heart rhythms in millions of Americans here and across the country, delivering electrical impulses that keep the heart beating.

Implanting the devices could take hours and leave patients with telltale scars or huge bumps below the collarbone. It could take weeks just to feel normal again.

But just hours after Bill McHutchison got the new Micra Transcatheter Pacing System earlier this year, he felt like his old self. That was on a Tuesday in July. The next day, he was back home in Stone Mountain.

“Thursday I was out walking, ” said the 85-year-old great-grandfather. “I went shopping on Friday. I went back to my normal routine and I can sleep at night without worrying my heart is going to stop.”

McHutchison is among a dozen metro Atlantans who’ve been implanted with the pacemaker at Emory Hospital, one of about 50 centers participating in an international clinical trial to assess Micra’s effectiveness and safety. Researchers are hoping to enroll as many as 780 patients at the center.

“The truly different thing about this pacemaker is that it’s about one-tenth the size of a traditional pacemaker and has no wires, ” said Dr. Michael S. Lloyd, a cardiac electrophysiologist and associate professor of medicine at the Emory University School of Medicine. “It’s placed directly into the patient’s heart through an IV tube that is inserted into a thigh vein. The bottom line is it doesn’t require skin surgery and it takes substantially less time to do —- on average just 15 minutes.”

Lloyd said Emory has had the largest number of participants in the trial. Anyone who has an extremely slow heart rate and is experiencing dizziness or fainting would be eligible to participate.

Lloyd said that there are an estimated 3 million people living with pacemakers, and about 600,000 pacemakers are implanted in the world every year.

“So you can understand that this will be a pretty important technology, ” he said. “I think it’s exciting and I am happy that Emory is involved. I think this is going to be the way pacemakers are implanted in the future.”

Unlike conventional pacemakers, the Micra TPS does not require the use of wires or “leads” that must be threaded through blood vessels to connect to the heart and are sometimes the source of medical complications such as infection and vein injury. Lloyd said he’s hoping this might be a safer alternative for people needing certain types of pacemakers.

McHutchison enrolled in the trial in June after a stroke landed him in the hospital. Tests showed the stroke was the least of his problems, that not only did McHutchison have atrial fibrillation, a quivering or irregular heartbeat that can lead to blood clots, stroke, heart failure and other heart-related complications, but his heart rate was severely low.

He needed a pacemaker.

“I had reservations, but in searching it over and talking to my daughters who are nurses, one of them told me to go for it, ” McHutchison said.

Although he still felt good, McHutchison said that in addition to his low heart rate, his ankles were swelling.

Almost immediately after the surgery, however, he said he was back to normal, doing water aerobics three times a week, walking and biking.

“I feel good, ” he said the other day. “In fact, I just came back from the pool. The one thing about this pacemaker is I don’t have to worry if I’m going to wake up the next day. I’m set at 60 beats a minute, and if it goes below that, it will adjust.”

Go to MyAJC.com/living to see video that demonstrates how the Micra Transcatheter Pacing System works.