Abstract
Leadless pacemakers, specifically Micra (Medtronic), have recently become a preferred alternative to transvenous pacemakers for use in bradyarrhythmia. Problems with conventional transvenous pacemakers include wound infection, lead disconnection, and tricuspid valve dysfunction. While Micra has the advantage of not being associated with the aforementioned complications, there have been reports of cardiac injury during Micra implantation, which have raised safety concerns. Many reports have evaluated Micra safety, but its effect on cardiac function remains unclear. In an 85-year-old man with bradycardic atrial fibrillation, a heart rate of approximately 35 bpm, and symptoms of dizziness, we analyzed ventricular workload, ejection fraction of the left and right ventricles, and inter/intraventricular synchrony using cardiac blood pool scintigraphy and myocardial work. Micra was successfully implanted into the right ventricular septum via the left femoral vein. A follow-up, 2 days later, showed no major complications associated with Micra pacing threshold and impedance. At this time, there was no apparent worsening of heart failure. Micra implantation for bradycardic atrial fibrillation has the potential to improve left ventricular work efficiency without the loss of ventricular synchrony.
Keywords: Atrial fibrillation, Cardiac pool scintigraphy, Micra, Myocardial work, Ventricular synchrony
Background
Currently, lead pacemakers are used as a treatment modality for bradycardic atrial fibrillation. The pacemaker body is implanted in a pocket in the anterior chest, and the lead is implanted in the right ventricle via the subclavian vein. However, complications such as pocket infection, lead disconnection, and tricuspid valve dysfunction are frequently encountered [1]. A relatively new treatment modality using a leadless pacemaker, Micra (Medtronic, Tokyo), has recently been used to resolve such complications [2]. However, there are concerns regarding the safety of Micra and the associated procedural complications [3]. Furthermore, few reports have examined the changes in ventricular cardiac function following Micra implantation [4]. In this study, we evaluated inter/intraventricular synchrony using cardiac blood pool scintigraphy and changes in the left ventricular (LV) workload using preoperative and postoperative echocardiography and myocardial work in a patient with the Micra pacemaker implanted for bradycardic atrial fibrillation.
Case presentation
An 85-year-old man was admitted to our hospital for prostate cancer surgery. However, electrocardiography on admission showed bradycardic atrial fibrillation with a heart rate of approximately 35 bpm and symptoms of dizziness, indicating the need for implantation of a permanent pacemaker. The patient was concerned that the implantation of a conventional lead pacemaker would cause the implantation site to stand out. Therefore, a decision to implant the Micra pacemaker was made.
The patient was diagnosed with right bundle branch block and paroxysmal atrial fibrillation but was asymptomatic 3 years ago.
On examination, the patient's height and weight were 173 cm and 73 kg (body mass index 24.4 kg/m2), respectively; leg edema was not observed. However, chest radiography revealed mild pulmonary congestion. Preoperatively, the serum creatinine level was 1.32 mg/dL [reference range, 0.61-1.04 mg/dL] and B-type natriuretic peptide level was 222 pg/mL [reference, <18.4 pg/mL]. Electrocardiography (ECG) showed bradycardia, atrial fibrillation, and right bundle branch block. Echocardiography revealed preserved LV contractility with mild aortic, mitral, and moderate tricuspid regurgitation. Cardiac blood pool scintigraphy was performed before Micra implantation to confirm that there were no problems with the ejection fraction (EF), interventricular synchrony, or left intraventricular synchrony.
Micra was successfully implanted into the right ventricular (RV) septum via the left femoral vein (Fig. 1). Two days after implantation, a pacemaker check that included various parameters (VVI: 60 bpm, impedance: 650 ohms, sensing: 5.5 mV, threshold: 0.63 V/0.24 ms) was performed to confirm that there were no problems. ECG, cardiac pool scintigraphy, and echocardiography were performed.
Fig. 1.
Micra implantation; Micra was implanted into the right ventricular septum.
ECG showed ventricular pacing with a left bundle branch block waveform (QRS time, 146 ms). Biventricular contractility and inter/intraventricular synchrony were also evaluated using cardiac pool scintigraphy pre and postoperatively. The results showed a slight decrease in the contractility of both ventricles (left ventricular ejection fraction preoperatively, 59.4; postoperatively, 47.2% and right ventricular ejection fraction: preoperatively, 52.7; postoperatively, 40.7%). However, phase analysis results showed an increase in the RV standard deviation and bandwidth; there was no apparent change in the left intraventricular synchrony and interventricular synchrony (Fig. 2).
Fig. 2.
Evaluation of cardiac pool scintigraphy before (A) and after (B) Micra implantation. Phase analysis results showed no obvious changes in the inter or left intraventricular synchrony in both ventricles.
Additionally, the recorded echocardiograms were analyzed using myocardial work (Fig. 3).
Fig. 3.
Myocardial work analysis. Comparison before (A) and after (B) Micra implantation showed an improvement in work efficiency.
The results showed that global wasted work decreased from 372 to 91 mmHg%, and global work efficiency improved from 82% to 91%. Other results of the analysis were as follows: global longitudinal strain (GLS), -19% to -13%, and global work index (GWI), 842-947 mmHg%.
A 2-day follow-up revealed no major issues with Micra pacing threshold and impedance, as well as no obvious worsening of the heart failure.
Discussion and conclusions
In this study, cardiac pooled scintigraphy was performed to evaluate the EF of both the left and right ventricle before and after Micra implantation, as well as interventricular and intraventricular synchrony. In addition, we combined cardiac workload with myocardial work to examine the effect of Micra implantation on circulatory dynamics when Micra was used to improve bradycardia.
As reported for conventional RV pacing, a left bundle branch-block-like waveform of pacing may cause cardiac dyssynchrony [5]. Furthermore, the QRS duration may be even wider depending on the implantation site [6]. However, one explanation for the results of this study is that LV synchrony may be affected by the site of Micra implantation.
In contrast, the analysis using myocardial work showed a change in each index. While no significant difference was observed in the patient's systolic blood pressure before and after implantation, differences in the heart rate, ventricular rhythm, and change from the right to the left bundle branch block were detected. Positive results of the myocardial work analysis included an improvement in work efficiency due to a decrease in wasted work and increase in GWI [7,8], which is an index of the overall LV function. However, a negative aspect was the decrease in GLS and EF.
In this case, if these effects of Micra-VR/VVI on GLS and EF are explained by the fact that the left bundle branch-dependent stimulatory excitation was originally obtained, we speculated that Micra implantation for bradycardia may have resulted in a right bundle branch-dominant stimulation, which caused a decrease in strain and ultimately EF. In support of this hypothesis, strain analysis showed significant reduction in LV septal and anterior septal strains, reflecting a negative effect of RV pacing, which was not limited to Micra implantation. Evidently, asynchrony of the right ventricle is a possible factor in reduced RV contractility.
If the impact of Micra on cardiac function is to be more accurately evaluated, it would be desirable to compare it to the impact of a conventional lead pacemaker or conduct a long-term reevaluation. The impact may also vary greatly depending on the site of Micra implantation. It would be interesting to accumulate evidence regarding the relationship between fluoroscopic position and perform data analyses accordingly in the future.
A follow-up 2 days later showed no major problems with the Micra pacing threshold and impedance. At this time, there was no apparent worsening of heart failure.
In conclusion, Micra implantation for bradycardic atrial fibrillation demonstrated the potential to improve LV work efficiency without the loss of ventricular synchrony.
Authors’ contributions
NI, SI, and SM analyzed the data and wrote the manuscript. NI and SM collected all the relevant materials. All authors have reviewed and approved the final manuscript.
Ethics approval and consent to participate
The research related to human use has complied with all the relevant national regulations, institutional policies, and the tenets of the Declaration of Helsinki, and has been approved by the author's institutional review board or equivalent committee (KENI198).
Availability of data and materials
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Patient consent
Informed consent was obtained from the patient for the publication of this case report.
Acknowledgments
The authors thank physiologist Yuko Morishita for her assistance with echocardiography.
Footnotes
Funding: The authors received no financial support for the research, authorship, and/or publication of this article.
Competing Interests: The authors declare that they have no competing interests.
References
- 1.Dilsizian V, Budde RPJ, Chen W, Mankad SV, Lindner JR, Nieman K. Best practices for imaging cardiac device-related infections and endocarditis: a JACC: Cardiovascular Imaging Expert Panel Statement. JACC Cardiovasc Imaging. 2022;15:891–911. doi: 10.1016/j.jcmg.2021.09.029. [DOI] [PubMed] [Google Scholar]
- 2.El-Chami MF, Bonner M, Holbrook R, Stromberg K, Mayotte J, Molan A, et al. Leadless pacemakers reduce risk of device-related infection: review of the potential mechanisms. Heart Rhythm. 2020;17:1393–1397. doi: 10.1016/j.hrthm.2020.03.019. [DOI] [PubMed] [Google Scholar]
- 3.Okabe T, Afzal MR, Houmsse M, Makary MS, Elliot ED, Daoud EG, et al. Tine-based leadless pacemaker. JACC Clin Electrophysiol. 2020;6:1318–1331. doi: 10.1016/j.jacep.2020.08.021. [DOI] [PubMed] [Google Scholar]
- 4.Beurskens NEG, Tjong FVY, de Bruin-Bon RHA, Dasselaar KJ, Kuijt WJ, Wilde AAM, et al. Impact of leadless pacemaker therapy on cardiac and atrioventricular valve function through 12 months of follow-up. Circ Arrhythm Electrophysiol. 2019;12 doi: 10.1161/CIRCEP.118.007124. [DOI] [PubMed] [Google Scholar]
- 5.Zhang S, Zhou X, Gold MR. Left bundle branch pacing: JACC review topic of the week. J Am Coll Cardiol. 2019;74:3039–3049. doi: 10.1016/j.jacc.2019.10.039. [DOI] [PubMed] [Google Scholar]
- 6.Victor F, Mabo P, Mansour H, Pavin D, Kabalu G, de Place C, et al. A randomized comparison of permanent septal versus apical right ventricular pacing: short-term results. J Cardiovasc Electrophysiol. 2006;17:238–242. doi: 10.1111/j.1540-8167.2006.00358.x. [DOI] [PubMed] [Google Scholar]
- 7.Russell K, Eriksen M, Aaberge L, Wilhelmsen N, Skulstad H, Gjesdal O, et al. Assessment of wasted myocardial work: a novel method to quantify energy loss due to uncoordinated left ventricular contractions. Am J Physiol Heart Circ Physiol. 2013;305:H996–1003. doi: 10.1152/ajpheart.00191.2013. [DOI] [PubMed] [Google Scholar]
- 8.Vecera J, Penicka M, Eriksen M, Russell K, Bartunek J, Vanderheyden M, et al. Wasted septal work in left ventricular dyssynchrony: a novel principle to predict response to cardiac resynchronization therapy. Eur Heart J Cardiovasc Imaging. 2016;17:624–632. doi: 10.1093/ehjci/jew019. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
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Data Availability Statement
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.