Reply to the Editor‐Ventricular Pacing Morphology and Its Implications for S‐ICD Eligibility

We thank the authors for their insightful comments and the opportunity to further clarify the clinical context and scope of our study. We fully agree that, according to current Instructions for Use, patients with a clear indication for permanent pacing are generally considered ineligible for S-ICD therapy. Our study was not intended to advocate the routine combination of S-ICD and permanent pacing, nor to expand S-ICD indications in pacing-dependent patients [1]. As stated in the Background and Clinical Implications sections, our investigation was designed to address specific clinical scenarios in which S-ICD and pacemaker may coexist unintentionally or unavoidably, such as patients with a pre-existing pacemaker who subsequently develop an ICD indication but are at high risk for transvenous lead implantation, or patients with an S-ICD who later require pacing during follow-up. In patients with an existing pacemaker, where lead position is fixed, the clinical relevance of our findings lies not in altering the pacing site, but in risk stratification, and informed decision-making regarding the feasibility and expectations of S-ICD screening. In patients requiring pacing after S-ICD implantation, these insights may also help guide pacing site selection toward morphologies less likely to compromise sensing. Kataoka et al. correctly note that the prior study reported acceptable S-ICD sensing during ventricular pacing in combined leadless pacemaker–S-ICD systems. However, this study was conducted in a fundamentally different technical context, within modular cardiac rhythm management systems that rely on dedicated intrabody device–device communication [2]. Such systems presuppose coordinated device architecture, predefined communication vectors, and specific signal protocols that are not present in conventional, non-communicating device combinations. Moreover, the evidence was largely derived from animal studies. In contrast, our study specifically evaluated standard automated S-ICD pre-implantation screening without assuming any form of device–device communication. Our findings should therefore be viewed as complementary to, rather than contradictory with, prior reports. We agree that in patients with impaired left ventricular systolic function and a high anticipated pacing burden, cardiac resynchronization therapy represents an important. However, mimicking biventricular pacing was not feasible using single-site bipolar pacing with ablation catheters. Nonetheless, future studies comparing biventricular pacing and conduction system pacing with respect to S-ICD sensing performance would be of significant clinical interest. In summary, our study does not seek to redefine S-ICD indications or promote combined device strategies, but rather to clarify how paced ventricular activation influences S-ICD screening outcomes under current clinical practice. We believe these findings provide clinically meaningful insights for patient selection, expectation management, and future device planning in complex scenarios where pacing and defibrillation therapies intersect.