Cerebrovascular Directional Coupling assessed via Causal Squared Coherence in Patients Presenting Silent Stroke after Surgical Aortic Valve Replacement.

Patients undergoing surgical aortic valve replacement (SAVR) are at risk of developing stroke after the intervention, usually detected via diffusion-weighted magnetic resonance imaging (DW-MRI). Previous studies suggested the maintenance of cerebral autoregulation (CA) as derived from time series analysis of mean arterial pressure (MAP) and mean cerebral blood velocity (MCBv) after SAVR, but the association of CA markers with the presence of recent ischemic lesions was not assessed so far. This study investigates closed-loop cerebrovascular control via causal cross-spectral analysis in 23 subjects (19 males, age 57±16 years) who recently underwent SAVR. Analyses were performing at rest in supine position (REST) and during an active standing test (STAND). Traditional MAP-MCBv coherence (K2) was computed as well as causal coherence (K2) was assessed from MAP to MCBv, i.e. along the pressure-to-flow arm, and from MCBv to MAP, i.e. along the flow-to-pressure arm, in the frequency bands typically used to describe CA. As detected via DW-MRI, 9 patients exhibited recent ischemic lesions (classified as STROKE) and 15 did not (noSTROKE). Results showed that STROKE patients showed an increased variability of MCBv during STAND and an inability to decouple MAP and MCBv variability series during STAND compared to REST, suggesting possible CA impairment. Trends in the coupling strength were observed in the high frequency band (0.15-0.4 Hz) regardless of the direction of the MAP-MCBv interactions. The proposed techniques allowed the investigation of the closed loop relationship between MAP and MCBv in association with damages of the brain microcirculation after SAVRClinical Relevance- Cerebral autoregulation might be reduced in patients exhibiting recent ischemic brain lesions after surgical aortic valve replacement.