Cardiovascular magnetic resonance findings in His-bundle pacing: Insights to pacing threshold rise

BACKGROUND: The mechanisms underlying pacing threshold elevation in His bundle pacing (HBP) despite an electrically intact lead remain poorly understood. This can compromise long-term battery life and increase the need for generator replacement or lead revision, adding procedural risk for patients and costs for healthcare systems. Using multiparametric cardiac magnetic resonance imaging (CMR), this proof-of-concept study examined whether the myocardium at the lead tip can be visualised with conventional CMR sequences, whether imaging remains safe despite elevated pacing thresholds, and whether fibrosis at the implantation site can be identified. METHODS: We prospectively enrolled 16 patients with HBP systems, of whom 9 had an increased pacing threshold. A significant increase was defined as a rise of ≥1.0V/1.0 ms. All scans were performed on a 1.5T scanner using standard bSSFP cine imaging and IR TFE late gadolinium enhancement (LGE) imaging in atrial-focused short-axis, long-axis, and modified aortic valve (AV) views to optimally visualise the HBP insertion site. LGE was assessed visually in different views. RESULTS: All MRI images were evaluable and showed no visual artefacts. The tip of the HBP lead was best visible on short-axis and AV planes. No periprocedural safety issues occurred, in particular pacing thresholds remained unaffected, demonstrating that CMR is feasible even in patients with elevated pacing thresholds, a scenario often considered a relative contraindication. In the case-control comparison, the presence of LGE at the His lead implantation site was associated with increased pacing thresholds, although our small cohort showed no association with clinical markers. Given the limited sample size, these findings are exploratory and hypothesis-generating. CONCLUSIONS: This proof-of-concept study shows that the HBP lead implantation site can be visualized with conventional CMR sequences, and that MRI can be performed safely even in patients with elevated pacing thresholds. Pacing threshold rises were associated with LGE at the implant site, suggesting a mechanistic link and traction-related micro-injury. These findings highlight that local tissue remodeling should be considered when selecting and optimizing His-bundle implantation techniques.