Response to: Critical Analysis of the TYRX Absorbable Antibacterial Envelope's Impact on Device Pocket Healing

While we agree to more studies on the topic, as acknowledged in our manuscript: “Larger, controlled studies are needed to confirm these findings and ensure their generalizability to a broader patient population,” their conclusions merit some additional precision. Our study is the first to describe the histology in patients with a previous TYRX implant, building on our previous animal studies [1]. Our conclusions are not that a thinner pocket is preferable, but that reducing the inflammatory response, calcification, and fibrosis around the leads may help prevent complications during generator replacement. The difference in capsule thickness—our biopsies were only performed on the anterior capsule, not the posterior capsule, as Massaro et al. also did, alongside the anterior biopsies—is significant histopathologically but not clinically in terms of erosion risk. Their analysis of the Massaro paper does not align with the conclusion of their manuscript, which describes the opposite. Reducing the inflammatory response and fibrosis through additional methods (including the TYRX pocket) may be beneficial for future replacements, as well as lowering infection risk. They do not address Twiddler syndrome in their manuscript. Regarding the calcification process, we described the histology using standard methods and acknowledged the differences with the Massoro series. The comment about standardized histopathologic definitions seems difficult to understand, given that our histopathology scoring was based on Annex E of the International Standards Organization (ISO) 10993-6:2016, with the study pathologist blinded to the patient data. Pathologists from both our group and theirs collaborated to ensure the most accurate comparison possible, taking into account the differences in methodologies. In reference to the Yang et al. paper, this comparison is not suitable, as their study involved prosthetic heart valves exposed to rheology with blood flow. In contrast, the TYRX pocket is a fully resorbable implant with a limited timeframe for a foreign body reaction. Most responses to biodegradable polymers are an M2 response that is associated with healing. They promote angiogenesis, accelerate skin cell proliferation and re-epithelialization, and regulate collagen remodeling that inhibits scar hyperplasia [2]. Furthermore, the immunomodulatory response to the TYRX pocket will be temporary due to the fully absorbable nature of the material. Adding Rifampicin to the mesh has also been proposed to reduce the immune response. Finally, Twiddler syndrome is well described in cases involving de novo implants. In our series, all patients had undergone previous surgeries, and no systematic pocket enlargement was performed; therefore, the risk of Twiddler syndrome would be minimal. Additionally, some studies have reported a possible benefit of the TYRX pocket in managing this syndrome, in addition to securing the device within the pocket [3-5]. The risk of Twiddler in de novo implants with a TYRX pocket is not known; in higher-risk patients, fixation of the device with nonabsorbable sutures remains a valuable option. A recent animal study also looked at migration and rotation of the device with a third-generation TYRX pocket and found no significant mobility [6]. Regarding their reference to the Yatomi et al. manuscript, this group described the natural pocket thickness measured from the surface echo, noting a thinner skin over the device in patients with a small BMI, as well as in those with other comorbidities, such as low hemoglobin, heart failure, and renal dysfunction. This aims to suggest pocket inspection during follow-up; however, it is essential to remember that no TYRX or other pocket device will completely prevent erosion. Good surgical technique, deep implantation over the pectoralis major fascia, or considering a subpectoral implant in high-risk patients to avoid erosion, remain the best preventive strategies. We thank the authors for their comments on our manuscript. Francois Philippon, MD, FRCPC, FHRS, FCCS, FCHRS Renu Virmani, MD Aloke V, Finn, MD

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