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| ORIGINAL ARTICLE |
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| Year : 2021 | Volume
: 6
| Issue : 1 | Page : 47-53 |
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A prospective, multicenter, single-arm study of performance of the micra transcatheter pacemaker in chinese patients: A comparison to the global experience
Keping Chen1, Shu Zhang1, Liqun Wu2, Xingbin Liu3, Yangang Su4, Yujie Zhou5, Jiangang Zou6, Jian-An Wang7, Meixiang Xiang7, Chengjun Guo5, Xuejun Ren5, Xiaofeng Hou6, Shufeng Liu8, Ming Zhang9, Dedra H Fagan8, Kejiang Cao6
1 Arrhythmia Center, State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
2 Department of Cardiology, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
3 Department of Cardiology, West China Hospital, Sichuan University, Chengdu, Sichuan Province, China
4 Department of Cardiology, Shanghai Zhongshan Hospital, Shanghai, China
5 Beijing Anzhen Hospital, Capital Medical University, Beijing, China
6 Department of Cardiology, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province, China
7 Department of Cardiology, The Second Affiliated Hospital of Zhejiang University School of Medicine, Hangzhou, Zhejiang Province, China
8 Medtronic, Inc., Minneapolis, MN, USA
9 Medtronic (Shanghai) Management Co., Ltd., Shanghai, China
| Date of Submission | 16-Feb-2021 |
| Date of Decision | 30-Mar-2021 |
| Date of Acceptance | 25-Apr-2021 |
| Date of Web Publication | 30-Jun-2021 |
Correspondence Address:
Dr. Shu Zhang
Fuwai Hospital CAMS and PUMC, No. 167, Belishi Road, Xicheng District, Beijing
China
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/ijhr.ijhr_4_21
Background: We have compared the patient characteristics and safety and efficacy results of the Micra transcatheter pacemaker from the China Micra Transcatheter Pacing Study with those from the global trials. Subjects and Methods: In this prospective, multicenter, single-arm study, patients with a class I or II guideline recommendation for single-chamber pacemaker therapy were enrolled from seven centers in China between July 30, 2018, and December 12, 2018. The primary outcome measure of this study was freedom from system- or procedure-related major complications through 6 months postimplantation (prespecified performance goal 83%). Patient baseline characteristics and major complications were compared with data from the global trials. Performance after medically indicated magnetic resonance imaging (MRI) scans was characterized. The study was approved by the ethics committee at each participating center and registered with ClinicalTrials.gov (Identifier: NCT03624504). Results: Implantation was successful in 81 of 82 (98.8%) patients with a mean follow-up of 8.7 ± 1.5 months. Chinese patients who had lower body mass index were more often female, and less frequently had a pacing indication associated with atrial fibrillation (AF) compared with global patients. Through 6 months postimplantation, two major complications occurred, with a major complication-free rate of 97.6% (95% confidence interval: 90.6–99.4%), exceeding the primary endpoint performance goal (P = 0.002). The major complication rate was in line with rates from the Micra investigational trial and Post-Approval Registry (2.4% vs. 3.7% and 2.9%, respectively, P = 0.50). Among 14 patients who underwent 3T MRI scans, electrical performance was stable with mean pre- and post-MRI pacing thresholds of <0.5 V. No MRI-related device performance issues were observed. Conclusion: In the hands of new operators in China, the Micra pacemaker was implanted successfully with a very low complication rate. Although Chinese Micra patients were on average of smaller stature and the majority had a pacing indication not associated with AF, Micra performance was excellent and in line with the global trial experience.
Keywords: Bradycardia, device-related complications, leadless pacemaker, magnetic resonance imaging, Micra
How to cite this article:
Chen K, Zhang S, Wu L, Liu X, Su Y, Zhou Y, Zou J, Wang JA, Xiang M, Guo C, Ren X, Hou X, Liu S, Zhang M, Fagan DH, Cao K. A prospective, multicenter, single-arm study of performance of the micra transcatheter pacemaker in chinese patients: A comparison to the global experience. Int J Heart Rhythm 2021;6:47-53 |
How to cite this URL:
Chen K, Zhang S, Wu L, Liu X, Su Y, Zhou Y, Zou J, Wang JA, Xiang M, Guo C, Ren X, Hou X, Liu S, Zhang M, Fagan DH, Cao K. A prospective, multicenter, single-arm study of performance of the micra transcatheter pacemaker in chinese patients: A comparison to the global experience. Int J Heart Rhythm [serial online] 2021 [cited 2023 Jun 3];6:47-53. Available from: https://www.ijhronline.org/text.asp?2021/6/1/47/319971 |
| Introduction | |  |
Permanent cardiac pacing has been the mainstay treatment for patients with permanent symptomatic bradycardia since the 1950s; however, complications with traditional transvenous pacemakers occur in up to 1 in 8 patients and can be attributed to transvenous pacing leads and subcutaneous pockets.[1],[2],[3],[4] Given these complications and impact on patient quality of life, development of alternative pacing devices has grown and led to the advent of leadless pacemakers.[5],[6]
The leadless Micra™ Transcatheter Pacing System (TPS) was designed to minimize and circumvent complications associated with transvenous pacing systems.[6] Results from both the Micra Investigational Device Exemption (IDE) study and the Micra Post-Approval Registry (PAR) demonstrated the safety and efficacy of the device. In both trials, which primarily included patients from the United States and Western Europe, the device was successfully implanted in >99% of patients, with a low major complication rate and up to a 63% reduction in major complications compared with transvenous pacemakers.[6],[7],[8]
With the consistent safety and efficacy results seen with the Micra investigational study and postmarket analysis, understanding how leadless pacemaker implantation impacts various and specific patient populations is of growing interest. Although there has been consistent performance with each investigation, whether this performance is consistent in the Chinese population is currently unknown. To address this, we compared the patient characteristics and performance results of the China Micra Transcatheter Pacing Study with the results of existing global trials.
| Subjects and Methods | | |
Study design
The China Micra Transcatheter Pacing Study was a prospective, multicenter, single-arm clinical trial (registered with ClinicalTrials.gov, NCT03624504 on 10 August 2018). The aim of the study was to confirm the safety and efficacy profile of Micra in Chinese patients for regulatory approval in China. The study was done in accordance with the Good Clinical Practice guidelines and the Declaration of Helsinki. The protocol was approved by the ethics committee at each of the seven participating centers [Table 1]. Adverse events were reviewed by a clinical events committee comprised of three independent physicians. All patients provided written informed consent before study inclusion.
Patients and procedures
Patients who were at least 18 years of age, willing to undergo study-specific required procedures for the follow-up time period, and met class I or II guideline recommendations for single-chamber ventricular pacing guidelines were eligible for inclusion in the study.[9],[10] Patients with an existing or prior pacemaker, implantable cardioverter-defibrillator, or cardiac resynchronization therapy device, unstable angina pectoris, or with an acute myocardial infarction within the prior 30 days were excluded from this study.
Micra (Medtronic, Inc., Minneapolis, MN, USA) is a single-chamber ventricular pacemaker which is 90% smaller than a transvenous system and is self-contained in a hermetically enclosed capsule. Features and functionality of the device are similar to capabilities provided by existing single-chamber pacemakers including rate-adaptive pacing, remote monitoring capabilities, and automated pacing capture threshold management. In addition, Micra is magnetic resonance imaging (MRI) conditionally safe for full-body scans due to its small size and low amount of ferrous material.[11],[12]
The device is implanted via catheter through the femoral vein and is implanted directly inside the right ventricle of the heart. The device is fixated into the myocardium, and following fixation and adequate electrical measurements, a tether is cut, and the delivery system is removed.
All patients enrolled in the study and successfully implanted with Micra were followed at predischarge, 1, 3, and 6 months postimplantation. During evaluations, adverse events were documented and device status, including electrical performance, was assessed.
Endpoints
The primary objective of this study was to demonstrate the safety of Micra by estimating the Micra implant procedure- and/or system-related major complication-free survival probability through 6 months postimplantation. To that end, the primary study endpoint was defined as a patient's first occurrence of a major complication related to the Micra system and/or Micra procedure as determined by the clinical events committee that occurs on or prior to 6 months postimplantation. Events classified as major complications are as follows: death, permanent loss of device function due to mechanical or electrical dysfunction of the device, system revision, hospitalization, or prolonged hospitalization by at least 48 h.
A secondary objective of the study evaluated the effectiveness of Micra, characterized by pacing capture thresholds, impedance, and sensing amplitude at implant and follow-up visits.
In addition, to demonstrate the safety of Micra in the MRI environment, data were collected on patients undergoing medically indicated 3T MRI scans during the study period. There were no restraints on the number of patients included in this evaluation.
Statistical analysis
The study sample size of 82 patients successfully implanted with the Micra system provided 80% power to test the study's primary safety objective against an objective performance criterion of 83%. The 6-month Kaplan–Meier estimate of the freedom from major complications was evaluated against the performance goal of 83% using a one-sample Wald test implying that the primary safety objective would be met if the lower two-sided 95% confidence limit of the Kaplan–Meier estimate exceeded 83%.
Electrical parameters were summarized using means, standard deviations, and standard errors at scheduled study visits as well as pre- and postclinically indicated MRI scans.
Patient and procedure characteristics were compared between the China Micra study and the global IDE and PAR trials,[6],[7] using the F-test for continuous variables and the Chi-square test for categorical variables. The percentage of ventricular pacing obtained from the device memory at each patient's last follow-up visit was compared between pacing indications (atrial fibrillation [AF] vs. no AF) using the Wilcoxon rank-sum test. Major complication rate through 6 months was compared among the three studies using the log-rank test. All analyses were conducted with the SAS software version 9.4 (SAS Institute, Cary, NC, USA).
| Results | | |
Patient characteristics
A total of 82 patients were enrolled and underwent implant attempt by 9 certified implanters at 7 centers in China from July 30, 2018, to December 12, 2018. The device was successfully implanted in 81 patients (98.8%). One patient had an unsuccessful implant attempt due to unacceptable electrical parameters; this patient did not experience any adverse events and subsequently exited from the study [Figure 1]. Patients were on average 68.6 ± 11.8 years of age, were mostly (50.6%) female, and had multiple comorbidities, including chronic obstructive pulmonary disease and diabetes [Table 2]. However, China Micra patients were significantly younger, with a lower body mass index (BMI), and had a lower rate of comorbidities compared with global Micra patients from the IDE and PAR. Fewer China Micra patients had a condition the implanting physician felt precluded the patient from receiving a transvenous pacemaker. Although the most common indication for pacing was bradyarrhythmia with AF for both China Micra and global patients, a larger proportion of China Micra patients had a primary pacing indication not associated with AF (55.6% vs. 36.1% [IDE] and 37.8% [PAR]). The reason (not mutually exclusive) for selecting VVI pacing in non-AF patients was predominately an expectation for infrequent pacing (84%); other reasons included value of new technology (31%), advanced age (16%), high risk with dual chamber (9%), and sedentary lifestyle (4%). | Figure 1: Patient flow diagram. Patient disposition for China Micra study
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The majority of China Micra patients (92.5%) had the device placed in the right ventricular (RV) septum, with a mean of 2.3 ± 1.4 deployments. Contrast was used during implant in all patients, whereas intraprocedural anticoagulation was used in 63.0% of patients, both of which differed significantly from the global patient population [Table 3]. The mean fluoroscopy and implant times (9.7 ± 7.2 and 36.9 ± 19.8 min, respectively) did not differ significantly from the global patient experience. All 81 successfully implanted China Micra patients completed the protocol required 6 months of follow-up, with a mean follow-up duration of 8.7 ± 1.5 months (range: 6.2–10.6 months).
Safety
A total of 2 major complications were reported in China Micra patients, for a 6-month major complication-free rate of 97.6% (95% confidence interval: 90.6%–99.4%), meeting the primary safety objective (P = 0.002). The first event was an arteriovenous fistula which occurred during implant in a 70-year-old female with a BMI of 17.2. Approximately 2 months postimplantation, the patient was hospitalized and had a femoral artery stent implanted to repair the AV fistula. The second event was pyrexia that occurred 1 day postimplantation in an 82-year-old female patient. The patient's hospitalization was prolonged for observation and the event resolved after 3 days.
Through 6 months postimplantation, the major complication rate was 2.4% in China Micra patients. The major complication rate was in line with the rates from the Micra IDE trial (3.7%) and Micra PAR [2.9%, P = 0.50; [Figure 2]]. | Figure 2: Major complication rate through 6 months by study. Major complication rates through 6 months postimplantation for Micra China, Micra IDE, and Micra PAR studies. IDE = Investigational Device Exemption; PAR = Post-Approval Registry
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Electrical performance
Mean pacing capture thresholds were 0.52 ± 0.26 V at implant and remained stable through 6 months postimplantation [0.50 ± 0.32 V, [Figure 3]a. The threshold was <2 V for 98.8% of all patients at 6 months postimplantation. Impedance was 874 ± 228 Ω at implant and 632 ± 125 Ω at 6 months [Figure 3]b. R-wave amplitude was 9.4 ± 3.9 mV at implant and 13.9 ± 4.2 at 6 months postimplantation [Figure 3]c. Median ventricular pacing percentage was significantly higher among patients with a pacing indication associated with AF (59.4% vs. 42.3% for non-AF indication, P = 0.0019). The cumulative average ventricular pacing percentages classified by different indications are summarized in [Table 4]. | Figure 3: Electrical parameters at each visit from implant through 6 months. (a) Pacing capture thresholds. (b) Impedance. (c) Sensing. The dots represent the means, and the vertical lines represent the standard errors of the means. n = 81 patients implanted with Micra. PHD = Prehospital discharge
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 | Table 4: Average ventricular pacing percentages at end of study follow-up
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Magnetic resonance imaging experience
A total of 14 patients underwent clinically indicated 3T MRI scans at 83.3 ± 37.4 days postimplantation. Of the 14 MRI scans, 9 were of the thoracic cavity, 4 were cerebral scans, and 1 was a spinal scan. Reasons for the scans are shown in [Table 5]. The mean pacing capture thresholds were not significantly different from pre-MRI to 1 month post-MRI [0.45 ± 0.12 V and 0.47 ± 0.14 V, respectively, [Figure 4]a. The mean impedance pre-MRI scan was 710 ± 167 Ω and remained unchanged at 1 month post-MRI [707 ± 173 Ω, [Figure 4]b. R-wave amplitude did not differ from pre-MRI to 1 month post-MRI [15.2 ± 4.3 and 15.2 ± 4.1 mV, [Figure 4]c. | Figure 4: Electrical parameters pre- and 1-month post-MRI scanning. (a) Pacing capture thresholds. (b) Impedance. (c) Sensing. Blue line represents mean value from 14 patients undergoing MRI scan. Gray lines are individual patient data. The dots represent the means, and the vertical lines represent the standard errors of the means. n = 14 patients with MRI scan. MRI = Magnetic resonance imaging
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| Discussion | | |
The prospective, multisite, single-arm pre-market China Micra study had several important findings. First, 98.8% of patients were successfully implanted with the device in the hands of new operators, with a 2.4% rate of major complications through 6 months, meeting the study's primary safety objective. Importantly, there were no device- or procedure-related infections, dislodgements, or pericardial effusion major complications reported, and safety results were in line with that of the global IDE and PAR studies. In addition, pacing thresholds were low and stable through 6 months. Finally, among patients undergoing clinically indicated 3T MRI scans, no device performance issues were noted, and thresholds remained unchanged pre- and 1 month post-MRI.
There were several differences in patient characteristics between Chinese patients and global patients. One of the most prominent differences observed among Chinese patients enrolled in this study was a lower BMI compared to the patients in the global studies, likely largely due to racial differences. Interestingly, while patients with lower BMIs have previously been shown to be at a higher risk for perforations during device implant procedures,[6],[7],[13],[14],[15] there were no perforations reported in the Chinese patient cohort. One potential explanation for this is that most devices in this study were placed in the RV septum, a location that has been shown to have a lower risk of perforation associated with it compared to other locations.[16] In addition, intravenous contrast was used in 100% of patients during the implant procedure, which combined with orthogonal radiographic views aids in confirming the position of the delivery system and mitigates risk for perforation. Since most implanters in the China Micra TPS study were new to implanting Micra, standard procedural steps were specified and recommended for each implanter in the study, including contrast use and implantation in the RV septum. As BMI also correlates with femoral vein size, there is also concern on the feasibility of implant and vascular complications due to the large-bore catheter used for implantation of Micra. Although China Micra patients had a lower BMI, only major complications were only reported in one venous access site. These findings are corroborated by prior reports demonstrating the safety of Micra in patients from Asian countries with low BMI.[17],[18]
Although Micra is inherently MRI safe, there are limited published reports on patients implanted with a Micra device undergoing MRI scanning.[19],[20],[21] Fourteen patients in the present study underwent 3.0T MRI scanning for clinically indicated reasons. Of these, nine were of the thoracic cavity. Electrical parameters were unchanged from prior to MRI scanning and 1 month post-MRI scanning, suggesting that there were no adverse device electrical effects following the MRI. These results align with findings from a prior single-center report, which found no change in Micra device parameters through 3 months post-MRI and no reported clinical events during or after MRI scans.[19]
Limitations
Although the alignment of results from the present study with the global Micra safety and efficacy evidence is reassuring, there are several limitations to consider. The China Micra TPS study had a small sample size with only 82 patients and a relatively short follow-up time of 6 months. Given the unique characteristics and medical practice environments within China, additional data will be needed to evaluate the interregional differences. Further, additional evidence is needed to optimize patient selection when considering comorbidities such as AF, heart failure, chronic obstructive pulmonary disease, and other conditions that are considered high risk for complication. The promising results from the global trials suggest that Micra is safe even in patients with these comorbidities.
| Conclusion | | |
In the hands of new operators in China, the Micra leadless pacemaker was implanted successfully with a very low complication rate. Although Micra China patients were on average of smaller stature and the majority had a pacing indication not associated with atrial fibrillation, performance was excellent and in line with the global trial experience. These findings suggest that Micra can be extended to Chinese patients despite China-specific medical practices and environments.
Financial support and sponsorship
This China Micra study was financially supported by Medtronic, Inc., USA. The content is solely the responsibility of the authors and does not represent the official views of the funding agency.
Conflicts of interest
DF, SL, and MZ are employees and shareholders of Medtronic, Inc. The other authors declare that there are no conflicts of interest. No conflicts of interest exist between Medtronic, Inc. (USA), Medtronic (Shanghai) Management Co., Ltd. (China), and publication of this paper.
Editor note: KC, SZ, KC, and XL are Editorial Board members of International Journal of Heart Rhythm. The article was subject to the journal's standard procedures, with peer review handled independently of these Editorial Board members and their research groups.
Institutional review board statement
The study was approved by the ethics committee at each participating center and registered with ClinicalTrials.gov (Identifier: NCT03624504).
Declaration of patient consent
The authors certify that they have obtained all appropriate consent from patients. In the forms, the patients have given their consent for their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity forms.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]
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