Microvascular remodeling and endothelial dysfunction across the post-COVID-19 spectrum: a prospective observational case-control study

<title>Abstract</title> Background Post-viral diseases, including post-COVID-19 syndrome (PCS) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), cause substantial long-term morbidity. Persistent cardiovascular risk after acute infection highlights the need for accessible tools to quantify microvascular health. Methods All Eyes on PCS is a prospective, observational study investigating the retinal microcirculation using retinal vessel analysis (RVA). We compared RVA parameters in 102 PCS patients with 204 age- and sex-matched healthy controls (matched from n = 303). Secondary matched analyses included never infected controls (n = 96), recovered individuals (n = 102), PCS patients, and PCS patients fulfilling ME/CFS criteria (n = 62). Laboratory variables, circulating markers of endothelial dysfunction and inflammation were compared between cohorts and their associations with RVA parameters were examined. Results Compared with healthy controls, PCS patients showed reduced venular flicker-induced dilation (3.7 ± 2.2% vs. 4.5 ± 2.7%, p = 0.005, Cohen´s d: 0.32), narrow retinal arterioles (CRAE, 178.3 ± 15.5 µm vs. 183.3 ± 15.9 µm, p = 0.009, d: 0.32), and lower arteriolar-to-venular ratio (0.83 ± 0.06 vs. 0.86 ± 0.07, p = 0.004, d: 0.35). Findings persisted after adjustment for cardiovascular risk factors and remained evident in an extended secondary matched analysis across never infected, recovered, and PCS patients. ME/CFS patients showed the most pronounced alterations. PCS severity correlated with lower AVR (r = -0.21, p = 0.037) and reduced arteriolar flicker-induced dilation (r = -0.21, p = 0.039), particularly for neurocognitive symptoms. IL-6, ICAM-1 and VCAM-1 were elevated in PCS and ME/CFS and lower AVR correlated with inflammatory and iron-related markers (all adjusted p &lt; 0.01). A combined model discriminated ME/CFS patients with good accuracy (AUC = 0.80). Conclusions PCS is associated with persistent endothelial dysfunction, most pronounced in ME/CFS patients and linked to symptom severity and ongoing inflammation. These findings support the potential use of RVA as a non-invasive tool for assessing and monitoring endothelial health in post-viral syndromes, with implications for cardiovascular risk stratification. Trial Registration The All Eyes on PCS Study has previously been registered at ClinicalTrials.gov (NCT05635552).