Myocardial remodelling phenotypes after cardiac stereotactic body radiotherapy assessed by serial late-gadolinium enhanced cardiac MRI

Background

Cardiac stereotactic body radiotherapy (SBRT) has emerged as a non-invasive option for refractory ventricular tachycardia (VT), yet the structural myocardial response to irradiation remains poorly defined. Late gadolinium enhancement cardiac MRI (LGE-CMR) enables quantitative assessment of scar and ablation effects, but its application after SBRT is limited. Published studies report both increases and decreases in scar volume, leaving uncertain whether these reflect distinct reactions or sequential stages of a unified remodelling process.

Objective

To characterize early (±3-month) myocardial remodelling after SBRT using serial LGE-CMR, and to identify common architectural patterns of structural response.

Methods

Five patients treated with SBRT for drug- and ablation-refractory VT underwent baseline and follow-up LGE-CMR (median interval 3.2 months [range 2.5–3.5]).

Co-registered images were analysed for total LV mass, border-zone (BZ) and scar core, and conduction corridor geometry (number, length, and protectedness). Segmentation was standardized by signal-intensity thresholds and visually verified for wall-thickness and contrast-to-noise consistency between timepoints.

Results

Pre- and 3-month post-SBRT LGE-CMR from five representative cases are shown in Figure 1, arranged from maximal decrease (left) to maximal increase (right) in indexed substrate volume (BZ + scar). Serial analysis revealed heterogeneous volumetric trajectories (−58 % to +56 %), yet a consistent architectural transformation across all cases. Regardless of direction, irradiated regions exhibited clear homogenization of myocardial texture, with loss of patchiness and smoother transitions between viable (blue) and scar/BZ (red/yellow) tissue. These qualitative changes occurred without systematic variation in total LV mass or in the number of conduction corridors, although corridor geometry and protectedness differed between timepoints. Quantitative co-registration confirmed that signal-intensity distributions within treated regions became more compact and spatially contiguous, reflecting a reproducible pattern of early structural reorganization within the first three months post-SBRT.

Conclusion

Serial LGE-CMR after cardiac SBRT reveals a previously unrecognized homogenizing myocardial remodelling, a structural simplification of the arrhythmogenic substrate that occurs regardless of whether scar volume expands or contracts. Rather than inducing de novo fibrosis alone, SBRT reorganizes existing myocardial architecture through region-specific inflammatory and contractile kinetics, producing a more uniform and electrically stable substrate. This concept provides a mechanistic bridge between radiation biology and electrophysiologic remodelling, positioning quantitative CMR as a promising early biomarker of SBRT efficacy and substrate transformation.Myocardial Remodelling Phenotypes