Title : White matter disease as a modifier of recovery potential after cardiac arrest
Abstract:
Survival after cardiac arrest has improved substantially with advances in resuscitation techniques and post–cardiac arrest care. However, hypoxic–ischemic brain injury (HIBI) remains a major cause of mortality and long-term neurological disability among survivors. Consequently, predicting recovery of consciousness or functional outcome remains a major challenge in neurocritical care. Neuroprognostication after cardiac arrest is often more reliable at the physiological extremes. Patients with findings, such as preserved EEG background continuity and the absence of significant gray matter injury on diffusion-weighted MRI, frequently achieve favorable neurological recovery. In contrast, patients with established markers of severe brain injury, including extensive cortical or deep gray matter diffusion restriction on diffusion-weighted MRI, typically experience poor neurological outcomes. However, a substantial intermediate group exists in whom conventional prognostic markers are inconclusive or discordant, limiting the ability of standard clinical examination and neuroimaging to accurately predict recovery in this group.
Although white matter disease (WMD) following HIBI has been studied thoroughly in the literature, its involvement in predicting outcomes remains incompletely understood. Wallerian-like degeneration and diaschisis have been proposed as contributors to impaired consciousness after HIBI by disrupting distributed brain network activity.
We hypothesize that WMD exerts a nonlinear, reserve-based effect on neurological recovery after HIBI, rather than acting as a binary predictor of outcome. When WMD is minimal or absent, a floor effect occurs in which recovery is largely determined by the severity of the arrest itself and the extent of gray matter injury. Conversely, when WMD is severe, a ceiling effect emerges in which loss of network reserve limits the range of possible recovery despite a similar degree of HIBI. We propose that WMD is most informative in the intermediate range, where measures of white matter microstructure and connectivity are most likely to reveal relevant variation in recovery potential. We further propose a conceptual framework in which network reserve, defined as the capacity of large-scale brain networks to maintain effective information integration and flexible reconfiguration under structural and vascular constraints, mediates neurological resilience following HIBI. In this model, network reserve serves as the bridge between vascular reserve and structural reserve, ultimately influencing cognitive recovery. We will discuss the contributions of diffusion tensor imaging, blood-oxygen-level–dependent cerebrovascular reactivity, functional magnetic resonance imaging and high-density electroencephalography to the evaluation of network reserve, reflecting the functional integrity and adaptability of large-scale brain networks. We believe that the integration of these modalities into a unified framework that combines structural, vascular, and network reserve may provide a more comprehensive model for predicting neurological recovery following HIBI.
