Long-term outcomes in leadless Micra transcatheter pacemakers with elevated thresholds at implantation: Results from the Micra Transcatheter Pacing System Global Clinical Trial

Systematic review of leadless pacemaker

Conventional pacing systems consist of a pacemaker and one or more leads threaded from the device pocket through veins into the heart conducting the pacing therapy to the desired pacing site. Although these devices are effective, approximately one in eight patients treated with these traditional pacing systems experiences a complication attributed to the pacemaker pocket or leads. With the technological advances in electronics, leadless pacemakers that small enough to implant within the heart were introduced. Leadless pacemakers have been developed to overcome many of the challenges of transvenous pacing including complications related to leads or pacemaker pockets. This review aims to provide an overview of advantages of leadless pacemaker, complications and limitations of leadless pacemaker, leadless pacemaker candidate, and future directions of this promising technology.

Aveir VR real-world performance and chronic pacing threshold prediction using mapping and fixation electrical data

AIMS

Aveir VR performance and predictors for its pacing threshold (PCT) in a real-world cohort were investigated.

METHODS

Electrical measurements at various stages of an Aveir VR implant were prospectively collected. Predictors for 3-month PCT were studied. A retrospective cohort of consecutive 139 Micra implants was used to compare the PCT evolution. High PCT was defined as ≥1.5 V, using a pulse width of 0.4 ms for Aveir and 0.24 ms for Micra. Excellent PCT was defined as ≤0.5 V at the respective pulse width.

RESULTS

Among the 123 consecutive Aveir VR implant attempts, 122 (99.2%) were successful. The majority were of advanced age (mean 79.7) and small body size (mean BSA 1.60). Two patients (1.6%) experienced complications, including one pericardial effusion after device reposition and one intraoperative device dislodgement. Eighty-eight patients reached a 3-month follow-up. Aveir 3-month PCT was correlated with impedance at mapping (P = 0.015), tether mode (P < 0.001), end-of-procedure (P < 0.001), and mapping PCT (P = 0.035), but not with PCTs after fixation (P > 0.05). Tether mode impedance >470 ohms had 88% sensitivity and 71% specificity in predicting excellent 3-month PCT. Although it is more common for Aveir to have high PCT at end of procedure (11.5% for Aveir and 2.2% for Micra, P = 0.004), the rate at 3 months was similar (2.3% for Aveir and 3.1% for Micra, P = 1.000).

CONCLUSION

Aveir VR demonstrated satisfactory performance in this high-risk cohort. Pacing thresholds tend to improve to a greater extent than Micra after implantation. The PCT after fixation, even after a waiting period, has limited predictive value for the chronic threshold. Low-mapping PCT and high intraoperative impedance predict chronic low PCT.

Comparative assessment of safety with leadless pacemakers compared to transvenous pacemakers: a systemic review and meta-analysis

BACKGROUND

Leadless pacemakers (LP) and transvenous pacemakers (TVP) are two stable pacing platforms currently available in clinical practice. Observational data show mixed results with regards to their comparative safety. This meta-analysis was aimed to evaluate the comparative safety of LP over TVP.

METHODS

The study protocol was registered in PROSPERO registry (CRD42022325376). Six databases were searched for published literature from inception to April 12, 2022. RevMan 5.4.1 was used for statistical analysis. Odds ratio (OR) and mean difference were used to estimate the outcome with a 95% confidence interval (CI).

RESULTS

A total of 879 studies were imported from the databases. Among these, 41 papers were screened for full text and 17 meet the inclusion criteria. Among them, pooled results showed 42% lower odds of occurrence of complications in the LP group (OR 0.58, CI 0.42-0.80) compared to TVP group. Notably, 70% lower odds of device dislodgment (OR 0.30, CI 0.21-0.43), 46% lower odds of re-intervention (OR 0.54, CI 0.45-0.64), 87% lower odds of pneumothorax (OR 0.13, CI 0.03-0.57), albeit, 2.65 times higher odds of pericardial effusion (OR 2.65, CI 1.49-4.70) were observed in the LP group.

CONCLUSIONS

This meta-analysis showed LP to be a significantly safer modality compared to TVP, in terms of re-intervention, device dislodgment, pneumothoraxes, and overall complications. However, there were higher rates of pericardial effusion in the LP group. There was a diverse number of patients included, and all studies were observational. Randomized trials are needed to validate our findings.

Comparison of first- and second-generation leadless pacemakers in patients with sinus rhythm and complete atrioventricular block

INTRODUCTION

The efficacy and safety of leadless cardiac pacemakers (LPMs) as an alternative to conventional transvenous cardiac pacing have been largely reported. The first generation of the MicraTM transcatheter pacing system (VR; Medtronic) was able to provide single-chamber VVI(R) pacing mode only, with a potential risk of pacemaker syndrome in sinus rhythm patients. A second-generation system (AV) now provides atrioventricular synchrony through atrial mechanical (Am) sensing capability (VDD mode).

OBJECTIVE

We sought to compare VR and AV systems in sinus rhythm patients with chronic ventricular pacing (Vp) for complete atrioventricular block.

METHODS

All consecutive patients implanted with an LPM in our department for complete atrioventricular block were retrospectively screened. Patients with atrial fibrillation, sinus dysfunction, or Vp burden <20% at 1 month postimplantation were excluded. Patients were systematically followed with a visit at 1 month, and then at least once a year.

RESULTS

A total of 93 patients-45 VR (2015-2020) and 48 AV (2020-2021)-were included. VR and AV patients had similar baseline characteristics, except for VR patients being older (80 ± 8 vs. 77 ± 9 years, p = 0.049). The mean Vp burden was 77% in the VR and 82% in the AV group (p = 0.38). In AV patients, the median AV synchronous beats rate was 78%, with 65% having a >66% rate. An E/A ratio <1.2 as measured on echocardiography was the only independent predictor of accurate atrial mechanical tracking (p = 0.01). One-year survival rate was similar in both groups. Five patients in the VR and 0 in the AV group eventually developed pacemaker syndrome within 1 year post-implantation (p = 0.02).

CONCLUSION

In sinus rhythm patients with chronic Vp for complete atrioventricular block implanted with an LPM, the atrial mechanical sensing algorithm allowed significant atrioventricular synchrony in most patients and was associated with no occurrence of-otherwise rare-pacemaker syndrome.

Five-year safety and efficacy of leadless pacemakers in a Dutch cohort

BACKGROUND

Adequate real-world safety and efficacy of leadless pacemakers (LPs) has been demonstrated up to three years after implantation. Longer-term data is warranted to assess the net clinical benefit of leadless pacing.

OBJECTIVE

To evaluate the long-term safety and efficacy of LP therapy in a real-world cohort.

METHODS

In this retrospective cohort study, all consecutive patients were included with a first LP implantation from December 21, 2012 to December 13, 2016 in six Dutch high-volume centers. The primary safety endpoint was the rate of major procedure- or device-related complications (i.e., requiring surgery) at five-year follow-up. Analyses were performed with and without Nanostim battery advisory-related complications. The primary efficacy endpoint was the percentage of patients with a pacing capture threshold of ≤2.0V at implantation and without ≥1.5V increase at the last follow-up visit.

RESULTS

179 patients were included (mean age 79±9 years), 93 (52%) with a Nanostim and 86 (48%) with a Micra VR LP. Mean follow-up duration was 44±26 months. Forty-one major complications occurred, of which seven not advisory-related. The five-year major complication rate was 4% without advisory-related complications and 27% including advisory-related complications. Not advisory-related major complications occurred median 10 days (range 0-88 days) post-implantation. The pacing capture threshold was low in 163/167 (98%) and stable in 157/160 (98%).

CONCLUSION

The long-term major complication rate without advisory-related complications was low with LPs. No complications occurred after the acute phase and no infections occurred, which may be a specific benefit of LPs. The performance was adequate with a stable pacing capture threshold.

Leadless cardiac pacing: Results from a large single-centre experience

BACKGROUND

The efficacy and safety of leadless cardiac pacing as an alternative to conventional transvenous cardiac pacing in selected patients have been widely reported.

AIM

To report the experience of a high-volume implantation centre with older and new generations of leadless pacemakers.

METHODS

This retrospective observational study included the first consecutive 400 patients who underwent implantation of a leadless pacemaker in our centre. Complications and electrical parameters were evaluated during follow-up, comparing patients implanted with first-generation (Micra™ VR) and second-generation (Micra™ AV) leadless pacemakers (Medtronic, Minneapolis, MN, USA). Data were collected by a review of medical files.

RESULTS

Among 400 procedures, there were 328 Micra™ VR pacemakers and 72 Micra™ AV pacemakers implanted, followed for a median of 16 months (694 patient-years). The mean age was 77 years and both groups had a high burden of co-morbidities. Implantation success rate was 99.5%. A total of 87.5% of patients were discharged the day after the procedure. The pacing threshold remained stable and<2V in 96.5% of all patients. The perioperative complication rate at 30 days was 3.5%. Outcomes were similar between the two groups.

CONCLUSION

Leadless cardiac pacing is a safe and efficient alternative to conventional transvenous cardiac pacing.

Leadless Pacing: Therapy, Challenges and Novelties

Leadless pacing is a rapidly growing field. Initially designed to provide right ventricular pacing for those who were contraindicated for conventional devices, the technology is growing to explore the potential benefit of avoiding long-term transvenous leads in any patient who requires pacing. In this review, we first examine the safety and performance of leadless pacing devices. We then review the evidence for their use in special populations, such as patients with high risk of device infection, patients on haemodialysis, and patients with vasovagal syncope who represent a younger population who may wish to avoid transvenous pacing. We also summarise the evidence for leadless cardiac resynchronisation therapy and conduction system pacing and discuss the challenges of managing issues, such as system revisions, end of battery life and extractions. Finally, we discuss future directions in the field, such as completely leadless cardiac resynchronisation therapy-defibrillator devices and whether leadless pacing has the potential to become a first-line therapy in the near future.

Outcomes of leadless pacemaker implantation following transvenous lead extraction in high-volume referral centers: Real-world data from a large international registry

BACKGROUND

Limited data on the real-world safety and efficacy of leadless pacemakers (LPMs) post-transvenous lead extraction (TLE) are available.

OBJECTIVE

The purpose of this study was to assess the long-term safety and effectiveness of LPMs following TLE in comparison with LPMs de novo implantation.

METHODS

Consecutive patients who underwent LPM implantation in 12 European centers joining the International LEAdless PacemakEr Registry were enrolled. The primary end point was the comparison of LPM-related complication rate at implantation and during follow-up (FU) between groups. Differences in electrical performance were deemed secondary outcomes.

RESULTS

Of the 1179 patients enrolled, 15.6% underwent a previous TLE. During a median FU of 33 (interquartile range 24-47) months, LPM-related major complications and all-cause mortality did not differ between groups (TLE group: 1.6% and 5.4% vs de novo group: 2.2% and 7.8%; P = .785 and P = .288, respectively). Pacing threshold (PT) was higher in the TLE group at implantation and during FU, with very high PT (>2 V@0.24 ms) patients being more represented than in the de novo implantation group (5.4% vs 1.6 %; P = .004). When the LPM was deployed at a different right ventricular (RV) location than the one where the previous transvenous RV lead was extracted, a lower proportion of high PT (>1-2 V@0.24 ms) patients at implantation, 1-month FU, and 12-month FU (5.9% vs 18.2%, P = .012; 3.4% vs 12.9%, P = .026; and 4.3% vs 14.5%, P = .037, respectively) was found.

CONCLUSION

LPMs showed a satisfactory safety and efficacy profile after TLE. Better electrical parameters were obtained when LPMs were implanted at a different RV location than the one where the previous transvenous RV lead was extracted.

Peri-procedural and mid-term follow-up age-related differences in leadless pacemaker implantation: Insights from a multicenter European registry

BACKGROUND

Age-related differences on leadless pacemaker (LP) are poorly described. Aim of this study was to compare clinical indications, periprocedural and mid-term device-associated outcomes in a large real-world cohort of LP patients, stratified by age at implantation.

METHODS

Two cohorts of younger and older patients (≤50 and > 50 years old) were retrieved from the iLEAPER registry. The primary outcome was to compare the underlying indication why a LP was preferred over a transvenous PM across the two cohorts. Rates of peri-procedural and mid-term follow-up major complications as well as LP electrical performance were deemed secondary outcomes.

RESULTS

1154 patients were enrolled, with younger patients representing 6.2% of the entire cohort. Infective and vascular concerns were the most frequent characteristics that led to a LP implantation in the older cohort (45.8% vs 67.7%, p < 0.001; 4.2% vs 16.4%, p = 0.006), while patient preference was the leading cause to choose a LP in the younger (47.2% vs 5.6%, p < 0.001). Median overall procedural (52 [40-70] vs 50 [40-65] mins) and fluoroscopy time were similar in both groups. 4.3% of patients experienced periprocedural complications, without differences among groups. Threshold values were higher in the younger, both at discharge and at last follow-up (0.63 [0.5-0.9] vs 0.5 [0.38-0-7] V, p = 0.004).

CONCLUSION

When considering LP indications, patient preference was more common in younger, while infective and vascular concerns were more frequent in the older cohort. Rates of device-related complications did not differ significantly. Younger patients tended to have a slightly higher pacing threshold at mid-term follow-up.

Predictors of Pacing Capture Threshold Exacerbation After Leadless Pacemaker Implantation

The predictors of pacing capture threshold (PCT) exacerbation after leadless pacemaker implantation remain unknown. We analyzed the predictors of poor PCT by identifying risk factors using multivariate logistic regression analysis for 211 patients with leadless pacemaker implantation. Twenty patients met the criteria for elevated PCT levels and were categorized in the poor PCT group. Multivariate analyses revealed that PCT (P < 0.0001) and pacing impedance (P = 0.03) were independent predictors of PCT exacerbation. Elevated PCT levels and low pacing impedance during leadless pacemaker implantation were potential risk factors for the replacement of leadless pacemakers after the procedure.

Leadless Pacemaker Implantation in the Emergency Bradyarrhythmia Setting: Results from a Multicenter European Registry

Background. Data on leadless pacemaker (LPM) implantation in an emergency setting are currently lacking. Objective. We aimed to investigate the feasibility of LPM implantation for emergency bradyarrhythmia, in patients referred for urgent PM implantation, in a large, multicenter, real-world cohort of LPM recipients. Methods. Two cohorts of LPM patients, stratified according to the LPM implantation scenario (patients admitted from the emergency department (ED+) vs. elective patients (ED−)) were retrieved from the iLEAPER registry. The primary outcome of the study was a comparison of the peri-procedural complications between the groups. The rates of peri-procedural characteristics (overall procedural and fluoroscopic duration) were deemed secondary outcomes. Results. A total of 1154 patients were enrolled in this project, with patients implanted due to an urgent bradyarrhythmia (ED+) representing 6.2% of the entire cohort. Slow atrial fibrillation and complete + advanced atrioventricular blocks were more frequent in the ED+ cohort (76.3% for ED+ vs. 49.7% for ED−, p = 0.025; 37.5% vs. 27.3%, p = 0.027, respectively). The overall procedural times were longer in the ED+ cohort (60 (45−80) mins vs. 50 (40−65) mins, p < 0.001), showing higher rates of temporary pacing (94.4% for ED+ vs. 28.9% for ED−, p < 0.001). Emergency LPM implantation was not correlated with an increase in the rate of major complications compared to the control group (6.9% ED+ vs. 4.2% ED−, p = 0.244). Conclusion. LPM implantation is a feasible procedure for the treatment of severe bradyarrhythmia in an urgent setting. Urgent LPM implantation was not correlated with an increase in the rate of major complications compared to the control group, but it was associated with longer procedural times.

Fluoroscopic Predictors of Acceptable Capture threshold during the Implantation of the Micra Transcatheter Pacing System

Introduction

Few predictors of low capture threshold before the deployment of the Micra transcatheter pacing system (Micra TPS) have been determined. We aimed to identify fluoroscopic predictors of an acceptable capture threshold before Micra TPS deployment.

Methods

Sixty patients were successfully implanted with Micra TPS. Before deployment, gooseneck appearance of the catheter shaft was quantified using the angle between the tangent line of the shaft and the cup during diastole in the right anterior oblique (RAO) view. The direction of the device cup toward the ventricular septum was evaluated using the angle between the cup and the horizontal plane in the left anterior oblique (LAO) view.

Results

Of the 95 deployments we evaluated, 56 achieved an acceptable capture threshold of ≤2.0 V at 0.24 ms. In this acceptable threshold group, the deflection angle of the gooseneck shaft was significantly larger and the device cup was placed more horizontally with a lower elevation angle compared with those in the high threshold group. A deflection angle of ≥6° and an elevation angle of ≤30° were identified as the predictors of an acceptable capture threshold after deployment. An acceptable capture threshold was achieved in 24/31 (77.4%) patients in whom either angle criterion was satisfied at the first deployment.

Conclusions

Diastolic gooseneck appearance of the delivery catheter in the RAO view or near‐horizontal direction in the LAO view predicts an acceptable capture threshold after deployment. The shape of the delivery catheter before deployment should be evaluated using multiple fluoroscopic views to ensure successful implantation of Micra TPS.

Development and validation of a risk score for predicting pericardial effusion in patients undergoing leadless pacemaker implantation: experience with the Micra transcatheter pacemaker

AIMS

There is limited information on what clinical factors are associated with the development of pericardial effusion after leadless pacemaker implantation. We sought to determine predictors of and to develop a risk score for pericardial effusion in patients undergoing Micra leadless pacemaker implantation attempt.

METHODS AND RESULTS

Patients (n = 2817) undergoing implant attempt from the Micra global trials were analysed. Characteristics were compared between patients with and without pericardial effusion (including cardiac perforation and tamponade). A risk score for pericardial effusion was developed from 18 pre-procedural clinical variables using lasso logistic regression. Internal validation and future prediction performance were estimated using bootstrap resampling. The scoring system was also externally validated using data from the Micra Acute Performance European and Middle East (MAP EMEA) registry. There were 32 patients with a pericardial effusion [1.1%, 95% confidence interval (CI): 0.8-1.6%]. Following lasso logistic regression, 11 of 18 variables remained in the model from which point values were assigned. The C-index was 0.79 (95% CI: 0.71-0.88). Patient risk score profile ranged from -4 (lowest risk) to 5 (highest risk) with 71.8% patients considered low risk (risk score ≤0), 16.6% considered medium risk (risk score = 1), and 11.7% considered high risk (risk score ≥2) for effusion. The median C-index following bootstrap validation was 0.73 (interquartile range: 0.70-0.75). The C-index based on 9 pericardial effusions from the 928 patients in the MAP EMEA registry was 0.68 (95% CI: 0.52-0.83). The pericardial effusion rate increased significantly with additional Micra deployments in medium-risk (P = 0.034) and high-risk (P < 0.001) patients.

CONCLUSION

The overall rate of pericardial effusion following Micra implantation attempt is 1.1% and has decreased over time. The risk of pericardial effusion after Micra implant attempt can be predicted using pre-procedural clinical characteristics with reasonable discrimination.

CLINICAL TRIAL REGISTRATION

The Micra Post-Approval Registry (ClinicalTrials.gov identifier: NCT02536118), Micra Continued Access Study (ClinicalTrials.gov identifier: NCT02488681), and Micra Transcatheter Pacing Study (ClinicalTrials.gov identifier: NCT02004873).

Intraoperative sensing increase predicts long-term pacing threshold in leadless pacemakers

PURPOSE

High pacing threshold (HPT) and very high pacing threshold (VHPT) are known to have a negative impact on leadless pacemaker battery longevity, representing the most common reason for device repositioning. In this study, we evaluated if intraoperative electrical parameters recorded during Micra™ VR implant would be able to predict device performance during follow-up (FU).

METHODS

A total of 93 patients undergoing Micra™ VR implant were retrospectively considered. Patients were enrolled in the study if electrical assessment was performed at least twice at implant, at Micra™ final positioning and after removal of the delivery system. All patients received a FU visit at 1 and 12 month after discharge. R-wave sensing amplitude, pacing threshold (PT), and impedance were recorded at each visit.

RESULTS

When compared to the first assessment, R-wave sensing amplitude increased by 19.1% after 13 ± 4 min (+ 1.71 ± 0.2 mV, 95% CI 1.4 to 2.02; p < .001). Conversely, there was a significant PT decrease of 22.1% at 12-month FU (- 0.22 ± 0.03 V, 95% CI - 0.13 to - 0.31; p < .001). Among patients with HPT, acute increase of R-wave sensing of 1.5 mV after 14 ± 4 min predicted a significant reduction of PT below 1 V/0.24, at 12-month post-implant (R = 0.72, 95% CI 0.13 to 0.33, p < .001), with a sensitivity of 87.5% (95% CI 0.61-0.98) and a specificity of 88.8% (95% CI 0.51-0.99).

CONCLUSION

A 1.5-mV increase in R-wave amplitude at implant is predictive of PT normalization (< 1.0 V/0.24 ms) at 12-month FU. This finding may have practical implications for device repositioning in case of HPT recording at implant.

Leadless pacemaker implantation sites confirmed by computed tomography and their parameters and complication rates

BACKGROUND

Implantations of leadless pacemakers in the septum lower the risk of cardiac perforation. However, the relationship between the implantation site and the success rate, complication rate, and pacemaker parameters are not well-investigated.

METHODS

Patients who underwent leadless pacemaker implantation with postprocedural computed tomography (CT) between September 2017 and November 2020 were analyzed. Septum was targeted with fluoroscopic guidance with contrast injection. We divided patients into two groups based on the implantation site confirmed by CT: septal and non-septal, which included the anterior/posterior edge of the septum and free wall. We compared the complication rates and pacemaker parameters between the two groups.

RESULTS

A total of 67 patients underwent CT after the procedure; among them, 28 were included in the septal group and 39 were included in the non-septal group. The non-septal group had significantly higher R wave amplitudes (6.5 ± 3.3 vs. 9.7 ± 3.9 mV, p = .001), lower pacing threshold (1.0 ± 0.94 vs. 0.63 ± 0.45 V/0.24 ms, p = .02), and higher pacing impedance (615 ± 114.1 vs. 712.8 ± 181.3 ohms, p = .014) after the procedure compared to the septal group. Cardiac injuries were observed in four patients (one cardiac tamponade, one possible apical hematoma, two asymptomatic pericardial effusion), which were only observed in the non-septal group.

CONCLUSIONS

Leadless pacemaker implantation may be technically challenging with substantial number of patients with non-septal implantation when assessed by CT. Septal implantation may have a lower risk of cardiac injury but may lead to inferior pacemaker parameters than non-septal implantation.

The wireless pacemaker is on again; from electro-stimulation to synchronization

Leadless stimulation of the right ventricle is now a reality, especially in patients with very specific indications and clinical characteristics, even in the absence of randomized studies to support its use. The reduction of device costs and the refinement of atrioventricular synchronization algorithms will sanction its greater diffusion in the future. The possibility of using leadless technology also for resynchronization therapy, on the other hand, is currently a promising option but, pending randomized studies with robust case histories and adequate follow-ups, it should still be considered as a niche therapy, to be limited to centres highly specialized and in patients in whom conventional resynchronization has been impossible or ineffective.

Successful Leadless Pacemaker Implantation in an Elderly Patient With Dextrocardia and Situs Inversus

Leadless pacemaker is indicated in patients with symptomatic bradycardia as an alternative therapy when transvenous pacemaker implantation is considered difficult or at high risk. The experience of implanting leadless pacemaker in patients with dextrocardia and situs inversus is limited. A 94-year-old male was transferred to our hospital due to advanced atrio-ventricular block with episode of syncope. Chest radiograph and computed tomography revealed dextrocardia with situs inversus. Emergency cardiac catheterization was performed and a temporary pacemaker was inserted, but the patient removed it due to delirium. So, a leadless pacemaker was implanted to him. Shorter time of bed-rest after the implantation and shorter hospital stay would be beneficial of implanting a leadless pacemaker. Precise anatomical evaluation would be important to perform implantation efficiently and safely.

Tine-Based Leadless Pacemaker: Strategies for Safe Implantation in Unconventional Clinical Scenarios

Leadless pacemakers (LPs) have emerged as a meaningful alternative to transvenous pacemakers for single-ventricular pacing. LPs eliminate many of lead- and pocket-associated complications observed with transvenous pacemakers. Owing to the lack of atrioventricular synchronous pacing until recently, the use of LP was generally reserved for those patients who either required minimal ventricular pacing or had permanent atrial fibrillation. The only commercially available LP is the Micra transcatheter pacing system (Micra-TPS, Medtronic Inc. Fridley, Minnesota), which requires insertion of a 27-F (outer diameter) introducer sheath in the femoral vein. The LP is delivered to the right ventricle using a 23-F delivery catheter. Owing to the need for a large-bore sheath, the pivotal studies for the Micra transcatheter pacing system excluded patients with indwelling inferior vena cava filters and included only a few patients with bioprosthetic or repaired tricuspid valve. Subsequent real-world experience has demonstrated the overall safety and feasibility of LP placement, and use in various unconventional clinical settings has been validated, albeit with specific precautions. Additionally, incorporation of adjunctive techniques and strategies can improve the safety of the procedure in routine clinical settings as well. The objective of this state-of-the-art review is to highlight the key procedural elements to facilitate safe and efficient implantation of LP in routine as well as in unique clinical settings.

A Predictive Model for the Long-Term Electrical Performance of a Leadless Transcatheter Pacemaker

OBJECTIVES

This study sought to formulate a predictive model for describing the long-term electrical performance of Micra (Medtronic, Mounds View, Minnesota).

BACKGROUND

The Micra leadless pacemaker is an alternative ventricular pacing option that avoids the pitfalls of transvenous leads. However, well-defined metrics to predict the long-term electrical performance of the device are lacking.

METHODS

We identified all patients who underwent successful Micra implantation enrolled in the investigational device exemption study, continued access study, or post-approval registry with complete 1-year post-implantation data or system revision due to elevated thresholds (N = 1,843). The analysis endpoint was an elevated pacing capture threshold (PCT) at ≥12 months post-implantation, defined as ≥2.0 V at 0.24 ms or an increase of ≥1.5 V from implantation or need for system revision due to elevated thresholds at ≤12 months post-implantation. We evaluated for univariate and multivariate associations between patient and device characteristics at implantation and for elevated thresholds at 12 months.

RESULTS

Among the total cohort, 75 patients (4.1%) had elevated thresholds at 12 months; of these, 13 required system revisions. Predictors associated with elevated thresholds in univariate analysis included the total number of deployments (excluded from the multivariable model), impedance and PCT at implantation, male sex, history of diabetes, and ischemic cardiomyopathy. Multivariable regression modeling found that male sex, history of diabetes, implantation PCT of ≥2 V, and impedance of <800 Ω were independent predictors of elevated PCT at 12 months (all p < 0.05).

CONCLUSION

A history of diabetes, male sex, elevated PCT, and low impedance at implantation were independent predictors of elevated thresholds at 12 months. These metrics represent the foundation of a simple tool to aid in procedural decision making.

Accidental Snapping of Right Ventricular Pacing Lead with MICRA

Leadless Pacemaker implantation rates are increasing worldwide. These pacemakers have to be deployed, captured and redeployed in order to achieve optimal electric parameters. Various complications occur during this procedure. We herein report a unique case, where right ventricular (RV) pacing lead of the patient was accidently snapped with the tines during deployment of intracardiac pacemaker in an elderly male with pocket site infection.

Life cycle management of Micra transcatheter pacing system: Data from a high-volume center

BACKGROUND

Data on the management of Micra transcatheter pacing system (TPS) at the time of an upgrade or during battery depletion is limited.

OBJECTIVE

We sought to evaluate the management patterns of patients implanted with a Micra TPS during long-term follow-up.

METHODS

We retrospectively identified patients who underwent Micra implantation from April 2014 to November 2019. We identified patients who underwent extraction (n = 11) or had an abandoned Micra (n = 12).

RESULTS

We identified 302 patients who received a Micra during the period of the study. Mean age was 72.7 ± 15.4 years, 54.6% were men, and left ventricular ejection fraction was 51.9 ± 5.2%. Mean follow-up was 1105.5 ± 529.3 days. Procedural complications included pericardial tamponade (n = 1) treated with pericardiocentesis, significant rise in thresholds (n = 6) treated with reimplantation (n = 4), and major groin complications (n = 2). Indications for extraction included an upgrade to cardiac resynchronization therapy (CRT) device (n = 3), bridging after extraction of an infected transvenous system (n = 3), elevated thresholds (n = 3), and non-Micra-related bacteremia (n = 2). The median time from implantation to extraction was 78 days (interquartile range: 14-113 days), with the longest extraction occurring at 1442 days. All extractions were successful, with no procedural or long-term complications. Indications for abandonment included the need for CRT (n = 6), battery depletion (n = 2), increasing thresholds/failure to capture (n = 3), and pacemaker syndrome (n = 1). All procedures were successful, with no procedural or long-term complications.

CONCLUSION

In this large single-center study, 6% of patients implanted with a Micra required a system modification during long-term follow-up, most commonly due to the requirement for CRT pacing. These patients were managed successfully with extraction or abandonment.

Single-chamber leadless pacemaker for atrial synchronous or ventricular pacing

Leadless pacing is a major breakthrough in the management of bradyarrhythmia. Results of initial clinical trials that have demonstrated a significant reduction in acute and long-term pacing-related complications have been confirmed by real-world experience in a broader spectrum of patients. Nonetheless current use of a leadless pacemaker is hampered by its limited atrial sensing and pacing capability, as well as battery life-span and retrievability. We review the current clinical outcome data, indications and contraindications, implantation and retrieval techniques, synchronous ventricular pacing, and other clinical considerations. We also provide an overview of the latest advancements in leadless pacing technology including device-to-device communication and energy harvesting technology.

Predictors of increase in pacing threshold after transcatheter pacing system implantation due to micro-dislodgement

BACKGROUND

Achieving a favorable pacing threshold with a Micra transcatheter pacing system (Micra-TPS) is needed to reduce battery depletion. In some cases, the threshold increases shortly after the device is implanted, and a higher pacing threshold may be required. This study aims to identify the causes and predictors of the increase in pacing threshold observed shortly after Micra-TPS implantation.

METHODS

The study included 64 consecutive patients who underwent Micra-TPS implantation between 2017 and 2020. The patients were divided into two groups depending on their pacing threshold: the increased pacing threshold (IPT) group (threshold increased by ≥0.5 V/0.24 ms within 1 month of implantation) and the stable pacing threshold (SPT) group.

RESULTS

Excluding four patients who could not be followed up, of the 60 remaining patients, nine (15%) were in the IPT group and 51 (85%) were in the SPT group. The IPT group had significantly lower implant impedance values and higher implant thresholds than the SPT group (582 ± 59 vs 755 ± 167 Ω [P < .001] and 1.29 ± 0.87 vs 0.71 ± 0.40 V/0.24 ms [P = .014]). Implant impedance and threshold may serve as predictors of a threshold increase after implantation (area under the curve: 0.737-0.943 and 0.586-0.926, respectively).

CONCLUSIONS

An IPT was noted shortly after Micra-TPS implantation owing to micro-dislodgement because of insufficient anchoring of the device to the myocardium. Impedance >660 Ω and threshold <1.0 V/0.24 ms may predict an increase in pacing threshold.

Feasibility and long-term effectiveness of a non-apical Micra pacemaker implantation in a referral centre for lead extraction

Aims

To demonstrate the feasibility and long-term performances of a non-apical Micra pacemaker implantation.

Methods and results

Fifty-two consecutive patients underwent Micra implantation, targeting a non-apical site of delivery when feasible. Each patient received a regular follow-up (mean 13 ± 9 months). The first 17 patients were also enrolled in the Micra transcatheter pacing system trial (Group 1); the remaining ones presented broader indications and included post-extraction subjects (Group 2). In 19 of 52 patients (Group 1: 6%, Group 2: 51%; P = 0.002) Micra was implanted because of high-risk characteristics that discouraged the implantation of a traditional pacemaker. In 31 of 52 patients (60%) Micra was implanted in a non-apical location, with a lower rate of single delivery compared with apical sites (48% vs. 81%, P = 0.035), but without any impact on electrical performance. Pacing threshold remained optimal in the majority of patients (94%), regardless of the site of implantation (apical vs. non-apical location: 0.50 vs. 0.52 V/0.24 ms; P = 0.856) and group membership, with only 6% of the subjects showing elevated values (mean 1.92 ± 0.92 V/0.24 ms) at the last follow-up. No device-related adverse events were registered.

Conclusion

Micra pacemaker implant is a safe and effective procedure even in a real life cohort of high-risk patients. A non-apical site of implantation is feasible in the majority of patients allowing stable electrical performance at long-term follow-up.

Peak deflection index as a predictor of a free-wall implantation of contemporary leadless pacemakers

BACKGROUND

Leadless pacemakers are an effective treatment for bradycardia. However, some cases exhibit pericardial effusions, presumably associated with device implantations on the right ventricular free-wall. The present study was carried out to find the ECG features during ventricular pacing with a Micra, which enabled distinguishing free-wall implantations from septal implantations without using imaging modalities.

METHODS

Thirty-one consecutive patients who received Micra implantations in our facility were enrolled. The location of the device in the right ventricle was evaluated using echocardiography or computed tomography in order to determine whether the device was implanted on the septum (Sep group), apex (Apex group), or free-wall (FW group). The differences in the 12-lead ECG during ventricular pacing by the Micra were analyzed between the Sep and FW groups.

RESULTS

The body of the Micra was clearly identifiable in 22 patients. The location of the device was classified into Sep in 12 patients, Apex in 4, and FW in 6. The mean age was highest in the FW and lowest in the Sep group (82.7 ± 6.6 vs. 72.8 ± 8.7 years, p = 0.027). The peak deflection index (PDI) was significantly larger in the FW group than Sep/Apex group in lead V1 (Sep: 0.505 ± 0.010, Apex: 0.402 ± 0.052, FW: 0.617 ± 0.043, p = 0.004) and lead V2 (Sep: 0.450 ± 0.066, Apex: 0.409 ± 0.037, FW: 0.521 ± 0.030, p = 0.011), whereas there was no difference in the QRS duration, transitional zone, and QRS notching.

CONCLUSION

The PDI in V1 could be useful for predicting implantations of Micra devices on the free-wall and may potentially stratify the risk of postprocedural pericardial effusions.

Leadless Micra Pacemaker Use in the Pediatric Population: Device Implantation and Short-Term Outcomes

The development of Leadless cardiac pacemakers avoids the inherent complications that may occur secondary to lead insertion. A large number of devices have been inserted in adult patients although data in pediatric patients are lacking. We aimed to assess our experience with the Leadless device in the pediatric population. We performed a retrospective study on all pediatric patients who underwent insertion of a Leadless pacemaker in our center. Data were collected for demographic, procedural, and outcome variables. Nine patients with a median (IQR) age and weight of 13 (12-14) years and 37 (31-50) kg, respectively, were enrolled. The median (IQR) procedural time was 62 (60-65) min with insertion thresholds of 0.5 (0.35-1) Volts at 0.24 ms. All devices were successfully inserted without complication. One device was replaced with a single-lead endocardial pacemaker at 1 year for increased thresholds. Leadless pacemaker device insertion is feasible in pediatric patients. Further studies and long-term follow-up are needed to ascertain device longevity and complication rates.

The feasibility of leadless pacemaker implantation for superelderly patients

BACKGROUND

The safety and efficacy of the leadless pacemaker (LP) have been confirmed in previous reports, yet studies on LPs in superelderly patients are limited.

METHODS AND RESULTS

A total of 62 patients aged over 85 years old were implanted with single-chamber pacemakers due to symptomatic bradyarrhythmia at Sakakibara Heart Institute from May 2014 through July 2019. We divided them into two groups, a transvenous (TV) single-chamber pacemaker group (35 patients) and an LP group (27 patients), and compared the groups. Mean participant age was 90.3 ± 3.8 y.o., 41.9% were male, and mean participant body mass index (BMI) was 21.3 kg/m² . The LP group contained a significantly larger proportion of patients with dementia than the TV group did (63% vs. 37.1%, P = .04). The complication-free rate tended to be lower in the LP group in spite of the higher frequency of dementia (88.6% vs. 92.6%, P = .68). At implantation, the pacing threshold was significantly higher in the LP group than in the TV group (1.30 ± 0.91 V vs. 0.71 ± 0.23 V, P < .01), but over the first 3 months after the operation the pacing threshold in the LP group gradually improved (0.82 ± 0.2 V vs. 1.05 ± 1.02 V, P = .16). The procedure time and time from operation to discharge were also shorter in the LP group.

CONCLUSIONS

LP implantation appears to be safe and is accordingly becoming the cornerstone for Japanese superelderly patients indicated for single-chamber pacemakers, even for those with small bodies and dementia. However, careful procedures and long follow-ups are needed until a greater volume of data is reported.

The unstable pacing thresholds of the leadless transcatheter pacemaker affected by body positions in subacute phase after implant

Background

If the threshold at implant of leadless transcatheter pacemakers (LTPs) is less than 2.0 V, pacing thresholds reportedly decrease significantly by 1 month and maintain an optimal value of less than 1.0 V by 6 months.

Case summary

We report a case series of two patients with unstable pacing thresholds of the LTPs in the subacute phase after implant. The first patient (77-year-old man) was implanted an LTP for sick sinus syndrome. At that time of implant, the pacing threshold was 0.9 V at 0.24 ms. At 1 week and 1 month later, the threshold had increased to more than 2.0 V at 0.24 ms. We investigated the trend data for the week and found variations in the threshold. The second patient (81-year-old man) was implanted an LTP for bradycardia and atrial fibrillation. The pacing threshold at implantation was 0.63 V at 0.24 ms. One week later, the threshold had increased in supine position and decreased in sitting position. The trend data for the week were fluctuating greatly.

Discussion

The pacing threshold may increase to more than 2.0 V with significant fluctuation on assessment at 1 week and 1 month after implantation in association with changes in body position, even though we confirmed a stable threshold at implant. If an increased threshold is observed, it is necessary to check the trend data and threshold in each body position.

Leadless Pacemakers: State of the Art and Future Perspectives

Leadless pacemaker therapy is a new technology that aims at avoiding lead- and pocket-related complications of conventional transvenous and epicardial pacing. To date, 2 self-contained leadless pacemakers for right ventricular pacing have been clinically available: the Nanostim Leadless Pacemaker System and the Micra Transcatheter Pacing System. Additionally, a new multicomponent leadless pacemaker for endocardial left ventricular pacing has been proposed as an alternative choice for cardiac resynchronization therapy. In this review, we describe the state of the art of leadless pacing and compare the currently available devices with traditional transvenous leadless pacemakers.

Design and evaluation of the Micra Transcatheter Pacing System for bradyarrhythmia management

Permanent cardiac pacemakers have traditionally comprised a surgically implanted subcutaneous pulse generator affixed to at least one transvenous pacing lead. Despite technological advances, implant-related complications and transvenous-lead failure rates have remained high. The Micra Transcatheter Pacing System is a miniaturized single chamber pacemaker that is implanted directly into the right ventricle, eliminating the subcutaneous pocket and creating a leadless pacemaker system. Registry data show an extremely high implant success rate, significantly lower major complication rates than transvenous pacemakers, stable pacing parameters and reliable battery performance. In this review we summarize the available clinical literature and highlight the promising efficacy and safety of the Micra Transcatheter Pacing System.