Microvascular dysfunction in COVID-19: the MYSTIC study

Abstract

Rationale: Pre-clinical and autopsy studies have fueled the hypothesis that a dysregulated vascular endothelium might play a central role in the pathogenesis of ARDS and multi-organ failure in COVID-19.

Objectives: To comprehensively characterize and quantify microvascular alterations in patients with COVID-19.

Methods: Hospitalized adult patients with moderate-to-severe or critical COVID-19 (n = 23) were enrolled non-consecutively in this prospective, observational, cross-sectional, multi-center study. Fifteen healthy volunteers served as controls. All participants underwent intravital microscopy by sidestream dark field imaging to quantify vascular density, red blood cell velocity (V_RBC), and glycocalyx dimensions (perfused boundary region, PBR) in sublingual microvessels. Circulating levels of endothelial and glycocalyx-associated markers were measured by multiplex proximity extension assay and enzyme-linked immunosorbent assay.

Measurements and main results: COVID-19 patients showed an up to 90% reduction in vascular density, almost exclusively limited to small capillaries (diameter 4-6 µm), and also significant reductions of V_RBC. Especially, patients on mechanical ventilation showed severe glycocalyx damage as indicated by higher PBR values (i.e., thinner glycocalyx) and increased blood levels of shed glycocalyx constituents. Several markers of endothelial dysfunction were increased and correlated with disease severity in COVID-19. PBR (AUC 0.75, p = 0.01), ADAMTS13 (von Willebrand factor-cleaving protease; AUC 0.74, p = 0.02), and vascular endothelial growth factor A (VEGF-A; AUC 0.73, p = 0.04) showed the best discriminatory ability to predict 60-day in-hospital mortality.

Conclusions: Our data clearly show severe alterations of the microcirculation and the endothelial glycocalyx in patients with COVID-19. Future therapeutic approaches should consider the importance of systemic vascular involvement in COVID-19.

Keywords: COVID-19; Endothelial glycocalyx; Endotheliopathy; Microcirculation; Sublingual microscopy.

Fig. 1

Endothelial glycocalyx dimensions in vivo and in vitro and capillary density in COVID-19 patients with (w/) and without (w/o) mechanical ventilation (MV) and healthy controls. a Median and IQR values of vascular density of healthy controls and COVID-19 patients based on the diameter class from 4 to 25 µm. b Bar charts showing the percentage of loss of vascular density in COVID-19 patients with (red) and without (orange) mechanical ventilation compared to healthy controls (diameter class from 4 to 10 µm). *q < 0.05, **q < 0.01, ***q < 0.001 Boxplots of c of capillary V_RBC, d PBR values, and endothelial glycocalyx constituents e syndecan-1 and f hyaluronic acid of healthy controls (green) and COVID-19 patients with (red) or without (orange) mechanical ventilation (MV) *p < 0.05, **p < 0.01, ***p < 0.001

Fig. 2

Comparisons of a priori selected markers of endothelial dysfunction in COVID-19 patients with and without mechanical ventilation and healthy controls. Boxplots of a angiopoietin-1, b angiopoietin-2, c soluble TIE2, d VEGF-A, e sFLT-1, f VEGF-D, g ADAMTS13, h soluble thrombomodulin, and i ACE2 between healthy controls and COVID-19 patients with (red) and without (orange) mechanical ventilation (MV)

Fig. 3

Survival probability of COVID-19 patients according to different endothelial markers. Kaplan–Meier curves with 95% CIs showing survival probability of COVID-19 patients with a low/high PBR, b low/high ADAMTS13, and c low/high VEGF-A. ^#ADAMTS13 of one patient could not be measured due to technical reasons

Fig. 4

Endothelial, glycocalyx, and microcirculation damage in COVID-19. The image illustrates a simplified overview summarizing the findings of this study