Increased task-relevant fMRI responsiveness in comatose cardiac arrest patients is associated with improved neurologic outcomes

Early prediction of the recovery of consciousness in comatose cardiac arrest patients remains challenging. We prospectively studied task-relevant fMRI responses in 19 comatose cardiac arrest patients and five healthy controls to assess the fMRI's utility for neuroprognostication. Tasks involved instrumental music listening, forward and backward language listening, and motor imagery. Task-specific reference images were created from group-level fMRI responses from the healthy controls. Dice scores measured the overlap of individual subject-level fMRI responses with the reference images. Task-relevant responsiveness index (Rindex) was calculated as the maximum Dice score across the four tasks. Correlation analyses showed that increased Dice scores were significantly associated with arousal recovery (P < 0.05) and emergence from the minimally conscious state (EMCS) by one year (P < 0.001) for all tasks except motor imagery. Greater Rindex was significantly correlated with improved arousal recovery (P = 0.002) and consciousness (P = 0.001). For patients who survived to discharge (n = 6), the Rindex's sensitivity was 75% for predicting EMCS (n = 4). Task-based fMRI holds promise for detecting covert consciousness in comatose cardiac arrest patients, but further studies are needed to confirm these findings. Caution is necessary when interpreting the absence of task-relevant fMRI responses as a surrogate for inevitable poor neurological prognosis.

Abstract WMP16: Elevated Cerebral Neurite Orientation Dispersion and Density Imaging and Diffusion Kurtosis Values Are Associated With Poor Neurologic Outcome in Comatose Cardiac Arrest Patients

Background: For cardiac arrest survivors initially comatose after restoration of spontaneous circulation (ROSC), the extent of brain injury and expected neurologic outcome are crucial for patient management decisions. Advanced diffusion imaging approaches such as neurite orientation dispersion and density imaging (NODDI) or diffusion kurtosis imaging may provide additional insight into tissue integrity and potential for recovery of consciousness complementary to standard diffusion tensor imaging (DTI).

Methods: Multi-shell diffusion imaging was acquired in a prospective study of comatose cardiac arrest patients and in 5 controls. Neurite orientation dispersion (OD), intracellular volume fraction (ICVF), mean kurtosis (MK), axial kurtosis (AK), radial kurtosis (RK), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD) and fractional anisotropy (FA) were calculated. Median whole-brain values in patients with poor outcomes (no arousal recovery [AR] by discharge) were compared with those with AR and to controls (1-way ANOVA, post-hoc 1-sided Wilcoxon exact test).

Results: 18 patients (mean ±SD 48±23 y, 39% men) and 5 controls (37±19 y, 40% men) were analyzed. Median (range) Glasgow Coma Scale was 3 [3-5]. 10 patients exhibited AR, 8 did not. Median [IQR] time-to-MRI was 5 [4-8] days. FA (P=0.009), MK (P=0.017), AK (P=0.026), RK (P=0.014), OD (P=0.018) and ICVF (P=0.0038) were significantly different (see Figure). FA control values were greater than AR and no AR (P<0.05). MK, AK, RK, OD and ICVF values in the no AR group were greater than in the AR and control groups (P<0.05).

Discussion: This is the first report investigating early NODDI and diffusional heterogeneity changes in post-cardiac arrest comatose patients. Patients who failed to recover arousal demonstrated greater values for all kurtosis and NODDI metrics compared to controls. Potential bias from early withdrawal of life sustaining treatment and small cohorts are limitations.