The U.S. Food and Drug Administration’s approval of an expanded indication for a leadless pacemaker for patients “who may benefit from maintenance of atrioventricular synchrony” will make this technology potentially available to nearly half of the Americans who need a pacemaker, roughly triple the number of patients who have been candidates for a leadless pacemaker up to now.
“Thiswas huge. The complication rate with leadless pacemakers has been 63% less than the rate using pacemakers with transvenous leads,” said , a cardiac electrophysiologist and a coinvestigator on some of the studies that led to the new indication. By expanding the types of patients suitable for leadless pacing “we’ll achieve AV [atrioventricular] synchrony in more patients with fewer complications,” said Dr. Chinitz, professor of medicine and director of the Cardiac Electrophysiology and Heart Rhythm Center at NYU Langone Health in New York.
Because the device is both leadless and requires no pocket owing to its small size and placement in a patient’s right ventricle, it has implications for potentially broadening the population that could benefit from the device, he said in an interview. “When we started with this pacemaker, it was limited to elderly patients with persistent atrial fibrillation who needed only ventricular pacing, a very small group,” just under 15% of the universe of patients who need pacemakers. The broadened indication, for patients with high-grade AV block who also have atrial function, makes it possible to think of using this safer and easier-to-place device in patients who need infrequent pacing, and in patients with multiple comorbidities that give them an increased complication risk, he said. The new indication means “you’re treating a much broader patient population, doing it more safely, and creating the foundation for expanding this technology.”
The Micra AV pacemaker uses the same basic design as the previouslyMicra Transcatheter Pacing System, which came onto the U.S. market in 2016 and provides single-chamber pacing. An accelerometer on the device allows it to detect atrial motion and thereby synchronize ventricular and atrial contractions, which led to the new indication. Although the Micra AV device looks similar to the original single-chamber model, it has an entirely new circuitry that prolongs battery life during dual-chamber pacing as well as new software that incorporates the accelerometer data, explained , a cardiac electrophysiologist, and vice president of medical affairs and chief medical officer of cardiac rhythm and heart failure at Medtronic in Minneapolis. The battery of the Micra AV is designed to last about 15 years, Dr. Chinitz noted.
Results from two studies that Dr. Chinitz helped run established the safety and efficacy of the device for dual-chamber pacing. The(Micra Atrial Tracking Using a Ventricular Accelerometer) study included 64 patients who completed the study at 12 worldwide centers, which produced an average 80% AV synchrony in 33 patients with high-degree AV block (The other patients in the study had predominantly intrinsic AV conduction; ). The study included 75 patients with either second- or third-degree AV block at 12 worldwide centers and showed that AV synchrony increased from an average of 27% without two-chamber pacing to 89% with the dual-chamber function turned on, and with 95% of patients achieving at least 70% AV synchrony ( ).
The 2016 indication for single-chamber pacing included patients with “high-grade” AV bloc with or without atrial fibrillation, typically patients for whom dual-chamber pacemaker was not a great option because of the risks for complication but with the downside of limited AV synchrony, a limitation now mitigated by the option of mechanical synchronization, Dr. Kowal said. The AV device remains intended for patients with high-grade AV node block, which means patients with second- or third-degree block, he added in an interview. The estimatedof third-degree AV block among U.S. adults is about 0.02%, which translates into about 50,000 people; the estimated of second-degree AV block is much less, about 10% of the third-degree prevalence.
Despite the substantial cut in complications by a leadless and pocketless pacemaker, “some patients may still benefit from a traditional dual-chamber pacemaker,” specifically active patients who might sometimes get their heart rates up with exercise to levels of about 150 beats/min or higher, Dr. Kowal said. That’s because currently the programing algorithms used to synchronize the ventricle and atrium become less reliable at heart rates above 105 beats/min, he explained. However, the ability for mechanical synchronization to keep up at higher heart rates should improve as additional data are collected that can refine the algorithms. It’s also unusual for most patients who are pacemaker candidates to reach heart rates this high, he said.
The MARVEL and MARVEL 2 studies were sponsored by Medtronic, the company that markets Micra pacemakers. Dr. Chinitz has received fees and fellowship support from Medtronic, and has also received fees from Abbott, Biosense Webster, Biotronik, and Pfizer, and he has also received fellowship support from Biotronik and Boston Scientific. Dr. Kowal is a Medtronic employee.