Figure 1.

Harlequin syndrome. ECMO circuit induces hypercoagulable state due to a low-flow state and non-pulsatile blood flow. This leads to endothelial injury, microcirculation disruption, and differential hypoxemia. Over time, as the left ventricle regains its function, deoxygenated blood is pumped by the heart to the cerebral blood vessels leading to cerebral autoregulation impairment and global hypoxia. This clinically presents as HIBI. This figure is created with the BioRender software, with the assistance of Soorin Chung in finalizing the graphic design.