St. Jude Medical Inc. has launched the U.S. clinical trial of its leadless pacemaker, the Nanostim, as it aims to win regulatory approval.

The device is less than 10 percent the size of a conventional pacemaker. Unlike other pacemakers, it does not have wires — called leads — that snake into the heart. Instead, the tiny pacemaker is implanted directly into the heart itself.

Nanostim is for patients who need “single-chamber pacing” — that is, only a single ventricle needs its rhythm sped up. But Dr. Mark Carlson, chief medical officer for St. Jude, said the goal is to expand the capabilities of such a tiny technology.

“We are certainly interested in bringing leadless technology to the full spectrum of pacing for patients,” he said in an interview. “This is the initial endeavor. This is the logical and good place to start.”

St. Jude’s Leadless II trial is designed to evaluate the Nanostim for U.S. Food and Drug Administration approval. Its first use in the United States was at Mount Sinai Hospital in New York by Dr. Vivek Reddy.

St. Jude has had its share of issues with leads. In 2010, it pulled its Riata defibrillator lead from the U.S. market because of problems with inner wires coming through outer insulation. Its QuickSite and QuickFlex pacemaker leads also were pulled for the same reasons.

Besides avoiding design flaws with leads, St. Jude said the new device will reduce complications and improve patient comfort. Cardiologists must create a “pocket” just beneath the skin of the patient’s chest to hold a traditional pacemaker generator. Doctors can implant Nanostim without such surgery, inserting it into the heart with a catheter that is steered up through a vein in the leg.

St. Jude said the Nanostim is fully retrievable, meaning that it can be repositioned during the implant procedure and later removed from the heart if necessary.

“I believe this pioneering, compact device, which is placed directly inside the heart, may be a true game-changing technology in cardiovascular medicine and may help revolutionize care for patients with arrhythmias,” said Reddy, the study’s co-investigator and director of electrophysiology services at Mount Sinai. “My guess is that, ultimately, this will replace traditional devices. It is hard to understand why anyone would use a traditional pacemaker.”

The Nanostim also eliminates the visible lump and scar that come with a conventional pacemaker. St. Jude said that could mean an improved quality of life for patients by allowing them to live more-active, uninhibited lifestyles.

Medtronic’s competitor

St. Jude is not alone in developing tiny leadless pacemakers. St. Jude acquired Nanostim in October of last year, instantly giving the Little Canada-based medical technology company the world’s first commercially available leadless pacemaker, with plans to start sales in Europe.

Then, in December, Med­tronic announced the Micra Transcatheter Pacing System in Europe. The Medtronic device is about the size of a large vitamin and, like Nano­stim, is implanted directly into the heart.

St. Jude’s Nanostim is the first to proceed to clinical ­trials in the United States.

Cardiac pacemakers treat bradycardia, which is a heart rate that is too slow. More than 4 million people worldwide have an implanted pacemaker or other cardiac rhythm management device, and an additional 700,000 patients receive the devices each year.

‘I want to live’

Three days ago, Gregory Dobin, 83, became the first patient in the United States to receive a leadless pacemaker when Reddy implanted the Nanostim into his heart. Dobin’s daughter, Lucy, said the procedure took 10 minutes. Her father was out of the hospital the next day.

Nanostim is his first pacemaker.

Dobin, whose heart rate was dropping as low as 28 beats per minute, said doctors told him the device would be less invasive than a conventional pacemaker, yet perform just as well.

“I was close to death. I want to live,” said the man who emigrated to the United States from Ukraine 37 years ago. “Now you can check your watch to my heartbeat.”

Said his daughter: “It took them a lot longer to prep him before the surgery than it did to do the procedure itself.”

The Leadless II pivotal trial will evaluate the safety and effectiveness of the Nanostim and will enroll approximately 670 patients at 50 centers in the United States, Canada and Europe. In preliminary trials, the device performed about the same as conventional pacemakers, St. Jude said. Implanting the pacemaker took an average of 28 minutes.

Even with a smaller battery, the device is expected to have a battery life span of more than nine years at 100 percent pacing and more than 13 years at 50 percent pacing.

Nanostim was approved for sale in Europe and other markets in 2013. It is not yet available for sale in the U.S.