Bleeding and thrombotic events and intensity of heparin therapy in the two first waves of COVID-19.

A systemic inflammatory response occurs during SARS-CoV2 infection and is associated with hypercoagulability and thrombotic events. From March 2020 in our hospital different dosages of low-molecular weight heparin (LMWH) were introduced according to the level of patient care intensity. Because bleeding episodes occurred in hospitalized COVID-19 patients on heparin, the dosage of LMWH at the end of first wave was tailored on the severity of COVID-19. The aim of this study is to describe bleeding and thrombotic events in patients hospitalized with SARS-CoV2 infection on LMWH therapy in the two waves of COVID-19 and analyze the factors associated with these events. Among 1143 patients enrolled in the COVID-19 Network registry, 912 were included in the analysis, 537 of them admitted during the first wave and 375 during the second. Bleeding events were 30 (3.3%): 22 (2.4%) major and 8 (0.9%) non-major. Arterial and venous thrombotic events were 6 (0.7%) and 24 (2.6%). The incidence of venous thrombotic events was higher in the first than in the second wave (0.29% [95% CI 0.20-0.45] events/day vs. 0.05% [95% CI 0.02-0.16]), with a 71% risk reduction (95% CI 22%-94%). The incidence of bleeding was 0.33% (95% CI 0.22-0.50) vs 0.14% events/day (95% CI 0.07-0.28), with no statistical between-wave difference (HR 0.41 95% CI 0.16-1.08). After adjusting for the competing risks of death and comorbidities, patients in the second wave had lower odds to have thrombotic events than in the first wave (0.24 HR [95% C.I. 0.07-0.89]). In this retrospective study on COVID-19 we found a low rate of hemorrhagic and thrombotic events, that may be explained by the absence in the case material of patients admitted to intensive care unit.