A histological and mechanical analysis of the cardiac lead-tissue interface: implications for lead extraction

Attenuating Chronic Fibrosis: Decreasing Foreign Body Response with Acellular Dermal Matrix

Surgical implants are increasingly used across multiple medical disciplines, with applications ranging from tissue reconstruction to improving compromised organ and limb function. Despite their significant potential for improving health and quality of life, biomaterial implant function is severely limited by the body's immune response to its presence: this is known as the foreign body response (FBR) and is characterized by chronic inflammation and fibrotic capsule formation. This response can result in life-threatening sequelae such as implant malfunction, superimposed infection, and associated vessel thrombosis, in addition to soft tissue disfigurement. Patients may require frequent medical visits, as well as repeated invasive procedures, increasing the burden on an already strained health care system. Currently, the FBR and the cells and molecular mechanisms that mediate it are poorly understood. With applications across a wide array of surgical specialties, acellular dermal matrix (ADM) has emerged as a potential solution to the fibrotic reaction seen with FBR. Although the mechanisms by which ADM decreases chronic fibrosis remain to be clearly characterized, animal studies across diverse surgical models point to its biomimetic properties that facilitate decreased periprosthetic inflammation and improved host cell incorporation. Impact Statement Foreign body response (FBR) is a significant limitation to the use of implantable biomaterials. Acellular dermal matrix (ADM) has been observed to decrease the fibrotic reaction seen with FBR, although its mechanistic details are poorly understood. This review is dedicated to summarizing the primary literature on the biology of FBR in the context of ADM use, using surgical models in breast reconstruction, abdominal and chest wall repair, and pelvic reconstruction. This article will provide readers with an overarching review of shared mechanisms for ADM across multiple surgical models and diverse anatomical applications.

Allometrically scaling tissue forces drive pathological foreign-body responses to implants via Rac2-activated myeloid cells

Small animals do not replicate the severity of the human foreign-body response (FBR) to implants. Here we show that the FBR can be driven by forces generated at the implant surface that, owing to allometric scaling, increase exponentially with body size. We found that the human FBR is mediated by immune-cell-specific RAC2 mechanotransduction signalling, independently of the chemistry and mechanical properties of the implant, and that a pathological FBR that is human-like at the molecular, cellular and tissue levels can be induced in mice via the application of human-tissue-scale forces through a vibrating silicone implant. FBRs to such elevated extrinsic forces in the mice were also mediated by the activation of Rac2 signalling in a subpopulation of mechanoresponsive myeloid cells, which could be substantially reduced via the pharmacological or genetic inhibition of Rac2. Our findings provide an explanation for the stark differences in FBRs observed in small animals and humans, and have implications for the design and safety of implantable devices.

Electrical stimulation of cochlear implant promotes activation of macrophages and fibroblasts under inflammation

Objectives

The implanted electrodes deliver electric signals to spiral ganglion neurons, conferring restored hearing of cochlear implantation (CI) recipients. Postimplantation intracochlear fibrosis, which is observed in most CI recipients, disturbs the electrical signals and impairs the long-term outcome of CI. The macrophages and fibroblasts activation is critical for the development of intracochlear fibrosis. However, the effect of electric stimulation of cochlear implant (ESCI) on the activity of macrophages and fibroblasts was unclear. In the present study, a human cochlear implant was modified to stimulate cultured macrophages and fibroblasts.

Methods

By measuring cellular marker and the expression level of cytokine production, the polarization and activity of macrophages and fibroblasts were examined with or without ESCI.

Results

Our data showed that ESCI had little effects on the morphology, density, and distribution of culturing macrophages and fibroblasts. Furthermore, ESCI alone did not affect the polarization of macrophages or the function of fibroblasts without the treatment of inflammatory factors. However, in the presence of LPS or IL-4, ESCI further promoted the polarization of macrophages, and increased the expression of pro-inflammatory or anti-inflammatory factors, respectively. For fibroblasts, ESCI further increased the collagen I synthesis induced by TGF-β1 treatment. Nifedipine inhibited ESCI induced calcium influx, and hereby abolished the promoted polarization and activation of macrophages and fibroblasts.

Conclusion

Our results suggest that acute inflammation should be well inhibited before the activation of cochlear implants to control the postoperative intracochlear fibrosis. The voltage-gated calcium channels could be considered as the targets for reducing postimplantation inflammation and fibrosis.

Level of Evidence

NA.

Two Independent Capsules Surrounding a Single Textured Implant in Ehlers-Danlos Syndrome

Textured breast implants are associated with prolonged inflammation leading to increased risk for complications such as the development of anaplastic large cell lymphoma. The underlying molecular mechanisms that drive increased inflammation toward textured implants (compared with smooth implants) remain poorly understood. Here, we present the first known case of a patient with Ehlers-Danlos syndrome (EDS) who developed two independent fibrotic capsules around a single textured silicone implant. The patient was found to have one internal capsule tightly adherent to the implant and a second external capsule that was attached to the surrounding tissue. We observed that the internal implant-adherent capsule was composed of a highly aligned and dense collagen network, completely atypical for EDS and indicative of a high mechanical stress environment. In contrast, the external nonadherent capsule, which primarily interacted with the smooth surface of the internal capsule, displayed disorganized collagen fibers with no discernible alignment, classic for EDS. Remarkably, we found that the internal capsule displayed high activation of monocyte chemoattractant protein-1, a mechanoresponsive inflammatory mediator that was not elevated in the disorganized external capsule. Taken together, these findings demonstrate that the tight adhesion between the textured implant surface and the internal capsule creates a high mechanical stress environment, which is responsible for the increased local inflammation observed in the internal capsule. This unique case demonstrates that mechanical stress is able to override genetic defects locally in collagen organization and directly connects the textured surface of implants to prolonged inflammation.

Injectable conductive hydrogel can reduce pacing threshold and enhance efficacy of cardiac pacemaker

Background: Pacemaker implantation is currently used in patients with symptomatic bradycardia. Since a pacemaker is a lifetime therapeutic device, its energy consumption contributes to battery exhaustion, along with its voltage stimulation resulting in local fibrosis and greater resistance, which are all detrimental to patients. The possible resolution for those clinical issues is an injection of a conductive hydrogel, poly-3-amino-4-methoxybenzoic acid-gelatin (PAMB-G), to reduce the myocardial threshold voltage for pacemaker stimulation. Methods: PAMB-G is synthesized by covalently linking PAMB to gelatin, and its conductivity is measured using two-point resistivity. Rat hearts are injected with gelatin or PAMB-G, and pacing threshold is evaluated using electrocardiogram and cardiac optical mapping. Results: PAMB-G conductivity is 13 times greater than in gelatin. The ex vivo model shows that PAMB-G significantly enhances cardiac tissue stimulation. Injection of PAMB-G into the stimulating electrode location at the myocardium has a 4 times greater reduction of pacing threshold voltage, compared with electrode-only or gelatin-injected tissues. Multi-electrode array mapping reveals that the cardiac conduction velocity of PAMB-G group is significantly faster than the non- or gelatin-injection groups. PAMB-G also reduces pacing threshold voltage in an adenosine-induced atrial-ventricular block rat model. Conclusion: PAMB-G hydrogel reduces cardiac pacing threshold voltage, which is able to enhance pacemaker efficacy.

Controlling Experimental Parameters to Improve Characterization of Biomaterial Fouling

Uncontrolled protein adsorption and cell binding to biomaterial surfaces may lead to degradation, implant failure, infection, and deleterious inflammatory and immune responses. The accurate characterization of biofouling is therefore crucial for the optimization of biomaterials and devices that interface with complex biological environments composed of macromolecules, fluids, and cells. Currently, a diverse array of experimental conditions and characterization techniques are utilized, making it difficult to compare reported fouling values between similar or different biomaterials. This review aims to help scientists and engineers appreciate current limitations and conduct fouling experiments to facilitate the comparison of reported values and expedite the development of low-fouling materials. Recent advancements in the understanding of protein-interface interactions and fouling variability due to experiment conditions will be highlighted to discuss protein adsorption and cell adhesion and activation on biomaterial surfaces.

Quantitative and Qualitative Assessment of Adhesive Thrombo-Fibrotic Lead Encapsulations (TFLE) of Pacemaker and ICD Leads in Arrhythmia Patients-A Post Mortem Study

The demand for cardiac implantable electronic devices for arrhythmia therapy is still unabated and rising. Despite onward optimizations, lead-related problems such as infections or fractures often necessitate lead extraction. Due to adhesive thrombo-fibrotic lead encapsulations (TFLE) transvenous lead extraction is challenging and risky. However, knowledge on TFLEs and possible correlations with technical lead parameters and dwelling time (DT) were hitherto insufficiently studied. Therefore, we analyzed TFLEs of 62 lead from 35 body donor corpses to gain information for a potential lead design optimization. We examined both TFLE topography on the basis on anatomical landmarks and histo-morphological TFLE characteristics by means of histological paraffin sections and scanning electron microscopy of decellularized samples. The macroscopic analysis revealed that all leads were affected by TFLEs, mainly in the lead bearing veins. Half (47.2%) of the right-ventricular leads possessed adhesions to the tricuspid valve. On average, 49.9 ± 21.8% of the intravascular lead length was covered by TFLE of which 82.8 ± 16.2% were adhesive wall bindings (WB). The discrete TFLEs with at least one WB portion had a mean length of 95.0 ± 64.3 mm and a maximum of 200 mm. Neither sex, DT nor certain technical lead parameters showed distinct tendencies to promote or prevent TFLE. TFLE formation seems to start early in the first 1-2 weeks after implantation. The degree of fibrotization of the TFLE, starting with a thrombus, was reflected by the amount of compacted collagenous fibers and likewise largely independent from DT. TFLE thickness often reached several hundred micrometers. Calcifications were occasionally seen and appeared irregularly along the TFLE sheath. Leadless pacemaker systems have the advantage to overcome the problem with TFLEs but hold their own specific risks and limitations which are not fully known yet.

High-voltage impedance rise; mechanism and management in patients with transvenous implantable cardioverter-defibrillators: a case series

Background

We describe a case series of patients for a gradual rise in daily, low-voltage sub-threshold measurement (LVSM) of shock (high-voltage, HV) impedance in a group of patients with Boston Scientific implantable cardioverter-defibrillators (ICDs) and investigate the cause of the abnormality.

Case summary

Six patients presented with a gradual rise in HV impedance above normal range (132.5 ± 20.8 Ω). Patients were young with a mean age of 29 ± 11 years, four patients had hypertrophic cardiomyopathy, one left ventricular non-compaction, and one long QT. All lead designs were silicon body with GORE polytetrafluoroethylene (ePTFE) coated coils, and a lower true shock impedance (TSI) was seen in all cases with full output synchronized shock. We compared the rate of HV impedance rise with our historical cohort of Boston ICDs using an unpaired t-test. The change in impedance per month was significantly higher amongst our six patients when compared with our cohort of Boston Scientific ICDs (3.2 ± 1.9 Ω/month vs. 0.0008 ± 0.005 Ω/month, P < 0.001). Patients were individually investigated and management discussed in a dedicated device multi-disciplinary team meeting (MDT).

Discussion

There are distinct differences between TSI and LVSM. The TSI is derived from a full output shock, whilst LVSM is calculated from a small current output. These cases highlight the inaccuracies of the LVSM measurement. The gradual rise in LVSM is significantly higher than the value for TSI in these patients we propose the most likely mechanism is encapsulation fibrosis surrounding the right ventricular shock coil. Management for these patients requires vigorous testing to rule out electrical failure, and replacement maybe necessary.

In Vivo Models for the Study of Fibrosis

Significance: Fibrosis and scar formation pose a substantial physiological and psychological burden on patients and a significant public health burden on the economy, estimated to be up to $12 billion a year. Fibrosis research is heavily reliant on in vivo models, but variations in animal models and differences between animal and human fibrosis necessitates careful selection of animal models to study fibrosis. There is also an increased need for improved animal models that recapitulate human pathophysiology. Recent Advances: Several murine and porcine models, including xenograft, drug-induced fibrosis, and mechanical load-induced fibrosis, for different types of fibrotic disease have been described in the literature. Recent findings have underscored the importance of mechanical forces in the pathophysiology of scarring. Critical Issues: Differences in skin, properties of subcutaneous tissue, and modes of fibrotic healing in animal models and humans provide challenges toward investigating fibrosis with in vivo models. While porcine models are typically better suited to study cutaneous fibrosis, murine models are preferred because of the ease of handling and availability of transgenic strains. Future Directions: There is a critical need to develop novel murine models that recapitulate the mechanical cues influencing fibrosis in humans, significantly increasing the translational value of fibrosis research. We advocate a translational pipeline that begins in mouse models with modified biomechanical environments for foundational molecular and cellular research before validation in porcine models that closely mimic the human condition.

Transfemoral extraction of pacemaker and implantable cardioverter defibrillator leads using Needle's Eye Snare: a single-center experience of more than 900 leads

The femoral approach with the Needle's Eye Snare (NES) is often used for bailout after failure of the superior approach for transvenous lead extraction (TLE). The safety and efficacy of the NES as a first-line tool for TLE remain unclear. The medical records of patients who underwent TLE via the femoral approach utilizing the NES from May 2014 to June 2019 in Peking University People's Hospital were retrospectively reviewed. Nine hundred and eighty-five leads were extracted in 492 patients (369 men; mean age 72.8 ± 29.0 years). The median (range) number of leads extracted per patient was 2 (1-6). The mean indwelling time of all extracted leads was 112.6 ± 52.0 months. The complete procedure success rate, clinical success rate, and failure rate were 94.1% (463/492), 97.8% (481/492), and 1.1% (11/492), respectively. Major complications including death occurred in nine patients (1.9%), of whom eight developed cardiac tamponade. Among these eight patients, emergency pericardiocentesis followed by rescue surgical repair if necessary was successful in 6 (75.0%) and failed in 2 (25.0%). No significant differences were found in the clinical success rate or major complications rate between patients with pacemakers and implantable cardioverter defibrillators, or between patients with infected and uninfected leads. A femoral approach with the NES is safe and effective for TLE of both pacing and defibrillator leads and could be considered a first-line approach. Cardiac tamponade was the most frequent cardiovascular complication. A strategy of emergency pericardiocentesis followed by a rescue surgical approach seems to be reasonable technique to treat a cardiac tamponade.

Evaluating platelet activation related to the degradation of biomaterials using molecular markers

The effective assessment of platelet activation is an important component of the evaluation of cardiovascular implants. Currently, most evaluation is performed based on the ISO 10993-4 international standard. However, the methods specified in this standard were originally designed for non-degradable materials, and the applicability of these methods to evaluate degradable materials has not been carefully assessed. Here, the platelet activation response was evaluated (using blood from health rabbits) for three typical degradable materials (collagen, polylactic acid, and hydroxyapatite) by measuring the widely used molecular markers CD62 P, CD63, and CD40 L and the three molecular markers PF4, β-TG, and TXB2 that are referenced in the ISO 10993-4 standard. The variations of these six markers were compared in the simulated degradation of the three test materials. The results showed differences in platelet activation with degradation that were strongly related to the surface physicochemical properties. Changes in the surface roughness and contact angle of the materials correlated with changes in the degree of platelet activation. The six tested platelet activation molecular markers show promise for assessment of platelet function in degradable medical devices, providing guidance for quality control strategies and the design and improvement of safe medical devices.

Biocompatibility studies on cerium oxide nanoparticles - combined study for local effects, systemic toxicity and genotoxicity via implantation route

An implantation study of cerium oxide nanoparticles (CeO2-NP) combined with 28-day systemic toxicity and genotoxicity studies aligned to current regulatory standards was conducted. The results suggested that local tissue reactions caused by CeO2-NP was minimal (implantation irritation index of less than 3) and was better tolerated than most other implant materials tested in our laboratory. Furthermore, CeO2-NP showed virtually no systemic toxicity or in vivo micronucleus induction in bone marrow via implantation route. Chemical analysis showed that CeO2-NP migrated from the implant sites (250 mg per site) in low levels and was deposited predominantly in liver (191.8 ± 35.1 ng g-1 of tissue; P < 0.01), lungs (263.4 ± 30.9 ng g-1 of tissue; P < 0.001), spleen (211.2 ± 6.5 ng g-1 of tissue; P < 0.001) and kidneys (272.8 ± 20.4 ng g-1 of tissue; P < 0.001). These observations provide a base line biocompatibility and toxicity data on CeO2-NP. The current findings will also be useful in defining standards for nanoparticle containing biomaterials and devices.

Neointimal fibrotic lead encapsulation - Clinical challenges and demands for implantable cardiac electronic devices

Every tenth patient with a cardiac pacemaker or implantable cardioverter-defibrillator implanted is expected to have at least one lead problem in his lifetime. However, transvenous leads are often difficult to remove due to thrombotic obstruction or extensive neointimal fibrotic ingrowth. Despite its clinical significance, knowledge on lead-induced vascular fibrosis and neointimal lead encapsulation is sparse. Although leadless pacemakers are already available, their clinical operating range is limited. Therefore, lead/tissue interactions must be further improved in order to improve lead removals in particular. The published data on the coherences and issues related to lead associated vascular fibrosis and neointimal lead encapsulation are reviewed and discussed in this paper.

Lead Extraction Considerations for the Referring Cardiologist

The population of patients with cardiac implantable electronic devices (CIEDs) continues to grow due to increasing indications in an aging population and breakthroughs in both the medical and the surgical care of patients with heart disease. As a result, there has been a growing need for device and lead extractions due to the growing population of patients with CIEDs and the subsequent need for system upgrades or revisions because of complications, infections, and lead advisory alerts.

Electromagnetic interference caused by common surgical energy-based devices on an implanted cardiac defibrillator

BACKGROUND

Surgical energy-based devices emit energy, which can interfere with other electronic devices (eg, implanted cardiac pacemakers and/or defibrillators). The purpose of this study was to quantify the amount of unintentional energy (electromagnetic interference [EMI]) transferred to an implanted cardiac defibrillator by common surgical energy-based devices.

METHODS

A transvenous cardiac defibrillator was implanted in an anesthetized pig. The primary outcome measure was the average maximum EMI occurring on the implanted cardiac device during activations of multiple different surgical energy-based devices.

RESULTS

The EMI transferred to the implanted cardiac device is as follows: traditional bipolar 30 W .01 ± .004 mV, advanced bipolar .004 ± .003 mV, ultrasonic shears .01 ± .004 mV, monopolar Bovie 30 W coagulation .50 ± .20 mV, monopolar Bovie 30 W blend .92 ± .63 mV, monopolar instrument without dispersive electrode .21 ± .07 mV, plasma energy 3.48 ± .78 mV, and argon beam coagulator 2.58 ± .34 mV.

CONCLUSION

Surgeons can minimize EMI on implanted cardiac defibrillators by preferentially utilizing bipolar and ultrasonic devices.