Conduction system disturbances necessitating permanent pacemaker implantation are common following cardiac surgery and transcatheter valve interventions. Conventional pacemakers in such patients have been associated with infectious complications, including endocarditis and pocket infections, as well as with the onset or worsening of tricuspid regurgitation. Leadless pacemakers have emerged in recent years as an alternative to conventional pacemakers to mitigate these complications. However, despite their proven safety and efficacy, leadless pacemakers also present certain limitations. There are two generations of these devices: the first generation (Micra-VR) and the second (Micra-AV), both of which provide pacing solely in the right ventricle, resulting in loss of interventricular synchrony. Neither Micra-VR nor Micra-AV can stimulate the atrium. However, the Micra-AV is capable of maintaining atrioventricular synchrony in patients with normal sinus node function due to its ability to sense atrial activity. Therefore, patients with sinus node dysfunction, which is common following these types of interventions, would not be suitable candidates for leadless pacemaker therapy. Additionally, leadless pacemakers may increase the prevalence of pacemaker-induced cardiomyopathy due to their inability to provide physiological pacing. 

This study conducted a single-center retrospective analysis involving 78 patients, 50 of whom underwent cardiac surgery and 28 transcatheter valve interventions. Forty of these patients received the Micra-VR and 38 the Micra-AV. Patients included had cardiovascular risk factors and comorbidities such as renal disease, coronary artery disease, atrial fibrillation, and heart failure. The average age was 65.9 years, with 52% male. Follow-up was conducted over 1.3 years in the Micra-VR group and 0.8 years in the Micra-AV group. There was only one implant-related complication: a femoral access site hematoma requiring evacuation. During follow-up, there was an increase in the pacing threshold and a decrease in impedance, both clinically insignificant. Sensing parameters remained stable. Pacing burden varied among patients, though overall pacing burden decreased. There was a significant reduction in left ventricular ejection fraction (LVEF), primarily among patients with reduced baseline LVEF. In subgroup analysis, this decline was observed in the Micra-VR group, with no significant change in the Micra-AV group. Six patients required conventional pacemaker implantation during follow-up—four due to LVEF decline and two due to sinus node dysfunction. 

The authors conclude that leadless pacemakers may serve as a viable alternative to conventional pacemakers in carefully selected patients following these interventions, provided the limitations of these devices are considered, and close follow-up is conducted to monitor the potential need for an upgrade. 

COMMENTARY: 

Leadless pacemakers represent a significant advancement in cardiac pacing. These devices operate similarly to traditional pacemakers but eliminate the need for leads connecting the device to the heart, potentially reducing some associated complications and risks. Generally, leadless pacemakers offer several potential advantages, such as reduced infection risk, decreased need for surgical reintervention for replacements, and lower tricuspid regurgitation rates. However, as with any medical innovation, leadless pacemakers also pose certain challenges and limitations. They may not be suitable for all patients, as they are only capable of pacing the right ventricle, resulting in loss of interventricular synchrony and making them unsuitable for specific pathologies like sinus node dysfunction. In fact, lead systems capable of stimulating the left bundle branch of the His bundle are currently being implanted, allowing narrow QRS ventricular pacing and intraventricular synchrony, counteracting the effects of left bundle branch block induced by pacing, particularly significant in patients with reduced LVEF and avoiding the need for an “upgrade” to resynchronization therapy. Another limitation is the inability to replace the battery at the end of its lifespan, necessitating the implantation of a new system (leadless or with leads) while leaving the old device in the ventricular cavity. In young patients, repeated replacements could theoretically limit right ventricular cavity space. Furthermore, as a relatively new technology, continued research and long-term data collection on their safety and efficacy are essential. 

The MICRA CED (Micra Clinical Evaluation) study is an observational study designed to evaluate the safety and efficacy of leadless pacemakers compared to conventional single-chamber VVI pacemakers. This study reported a higher rate of perforation and pericardial effusion in the leadless pacemaker group, though this rate was less than 1% and remained higher than in the conventional pacemaker group. Additionally, device-related complications and six-month complication rates were higher in the conventional pacemaker group. 

The present study assessed the safety and efficacy of leadless pacemakers after cardiac surgery or transcatheter valve interventions. In my opinion, the study has some limitations. It is a retrospective study with a small sample size and short follow-up period, potentially limiting its ability to capture long-term events and adequately compare outcomes across groups. Furthermore, there was no control group. A direct comparison between leadless and conventional pacemakers would have provided a more comprehensive assessment of the effectiveness and safety of leadless pacemakers in this specific clinical context. 

In conclusion, leadless pacemakers represent a safe and effective alternative for treating highly selected patients requiring cardiac pacing after cardiac surgery or structural valve interventions by catheterization. Their ability to prevent complications associated with conventional pacemakers makes them attractive in specific clinical scenarios. However, given the limited long-term evidence, ongoing evaluation of outcomes and complications as more clinical experience with these devices accumulates is essential. Careful patient selection and continuous monitoring are crucial to ensuring the long-term safety and efficacy of leadless pacemakers in clinical practice. 

REFERENCE: 

Huang J, Bhatia NK, Lloyd MS, Westerman S, Shah A, et al. Outcomes of leadless pacemaker implantation after cardiac surgery and transcatheter structural valve interventions. J Cardiovasc Electrophysiol. 2023 Nov;34(11):2216-2222. doi: 10.1111/jce.16074.