The human heart rate is under the influence of various hormonal and neural control mechanisms. Normally, conduction of an electrical impulse through the heart begins at the sinoatrial (SA) node and spreads throughout the heart muscle. The SA node is also known as the heart’s natural “pacemaker,” and there are multiple ways in which the natural pacing ability of the heart can be permanently damaged. The heart rate can slow when this occurs, compromising the normal hemodynamics and blood flow necessary to sustain life. These conditions, called bradyarrhythmias, can be treated by a technology known as artificial cardiac pacemakers. This implantable technology delivers an impulse to the heart tissue, restoring normal heart rate and cardiac output. Traditional cardiac pacing systems use transvenous leads that are implanted percutaneously. Although highly effective, there are many complications associated with transvenous pacing, such as infection, blood clots, and valvular injury. Leadless pacemakers can significantly reduce certain risks. Although the idea of a leadless pacemaker first emerged in the 1970s, it was not until 2016 that the first leadless pacemaker was approved for clinical use in the United States.
In 2021, a systematic review and meta-analysis was published examining the safety and efficacy of two common leadless pacemakers; Nanostim and Micra. The primary safety endpoint was significant complications, and efficacy was measured by reviewing acceptable pacing capture threshold data. Both Nanostim and Micra leadless systems were associated with good pacing capture thresholds at one year more than 90% of the time. Micra was found to have a 51% lower risk of complications than traditional transvenous pacing. The Nanostim system also had a favorable safety profile with a reported complication incidence of less than 7% at one year.
The Micra Coverage with Evidence Development Study is an ongoing observational cohort study of the US Medicare population comparing outcomes of leadless pacing against traditional pacing. In March 2022, results of over 6,000 leadless pacer patients and 10,000 traditional pacer patients were published. The study found that the Micra leadless pacing system was associated with a 38% lower rate of required reintervention and a 31% lower risk of chronic complications than traditional pacing. However, interestingly there was no difference in adjusted all-cause mortality between the two groups at two years.
Although results of leadless pacemaker systems are promising, significant limitations of available literature include the short length of follow-up and the observational nature of studies. Extended data and well-conducted randomized controlled trials evaluating essential outcomes such as battery longevity, efficacy, and safety will be required to confidently support the pervasive adoption of leadless pacing technology in clinical practice.