Leadless pacemaker Medtronic’s Micra is one of a handful of tiny pacemakers that could hit the market once given approval from the FDA. (The Minnesota Star Tribune)

A panel of doctors convened by the Food and Drug Administration on Thursday recommended extensive monitoring of a new class of tiny pacemakers following a frank assessment of the unknown risks and benefits of the game-changing technology.

"I think this is a very disruptive technology and it is at the beginning of a long career that we can't predict," New York cardiologist and FDA panel member Dr. David Slotwiner said at Thursday's daylong meeting of the FDA's Circulatory System Devices Panel in Gaithersburg, Md.

All three of the major heart-device companies that operate in Minnesota — Boston Scientific Corp., Medtronic PLC, and St. Jude Medical Inc. — plan to sell miniaturized pacemakers that fit entirely within the heart's right ventricle. Analysts at Leerink Partners have projected annual sales of at least $700 million for the devices in coming years, following commercial approval.

Medtronic and St. Jude anticipate FDA approval before the end of this year. Boston Scientific plans to present initial clinical data on its device next month but has not yet applied for FDA approval. German heart-device maker Biotronik SE & Co. has also confirmed it is developing a similar device.

Thursday's panel meeting was one of the last steps before the FDA decides whether to approve Medtronic's Micra and St. Jude's Nanostim pacemakers, though the agency still has yet to rule on whether the clinical data gathered so far prove the tiny new pacemakers are as safe and effective as the older models.

The new devices are known as "leadless" pacemakers because they touch the heart tissue directly, rather than using long thin wires called leads to deliver electric pulses to the heart.

Among the conditions of approval the panel recommended Thursday is extensive long-term surveillance of the devices because of several unanswered questions, including whether the devices are more prone to damaging heart tissue than traditional pacemakers. Another key question is whether they can be removed from the heart after the batteries wear out.

Medtronic Vice President Dr. David Steinhaus said it wasn't surprising that attention focused on lingering questions about the new devices.

"The old pacemakers are very tried and true," Steinhaus said. "Now you've got a new technology, and the FDA is looking for guidance in terms of what will we tolerate."

Much of the concern Thursday centered on whether the new pacemakers are associated with higher rates of a serious complication called perforation, which is when part of the device penetrates deeper into the heart tissue than intended.

"Cardiac perforation is a big deal to me, because it is potentially lethal," panel member and New York cardiologist Dr. Jeffrey Borer said. "It looks as if there are about 50 percent more perforations with the leadless pacemaker."

Steinhaus argued that the company's data suggest the rate is within the limits of previous trials.

Officials with St. Jude noted complications declined after they revised their training and implantation guidelines in European trials. Medtronic said it did not see any such "learning curve" among its early clinical trial sites.

Nevertheless, the panel recommended the FDA require the companies to run a robust training program for any doctors certified to implant leadless pacemakers.

Early data on perforation exist because the complication is typically seen within 30 days of implant. Real-world data on long-term issues like battery life don't exist yet — no patient has had the device long enough to deplete the battery and face the decision of whether to remove it or implant a second one right next to it.

St. Jude's device is designed to be removed if desired after the battery runs out; Medtronic's recommendation is to leave the device in place.

The panel members on Thursday recommended the FDA require the companies to study the devices for as long as it will take to determine what will happen when leadless pacemaker batteries start dying eight to 12 years from implantation.

Joe Carlson • 612-673-4779

Twitter: @_JoeCarlson