ABSTRACT
Background: Vaccine-induced immune thrombosis and thrombocytopenia (VITT) has been recognized as a rare thrombotic complication of adenovirus-based vaccines against COVID-19. While VITT presents some common features with heparin-induced thrombocytopenia (HIT), VITT antibodies differ from typical HIT antibodies by their ability to induce spontaneous platelet aggregation in the absence of heparin. In this context, reliable functional tests are of crucial importance to confirm VITT diagnosis. Aim(s): To compare the performances of Heparin-Induced Multiple Aggregometry (HIMEA) and Heparin-Induced Platelet Activation assay (HIPA) for VITT diagnosis. Method(s): From April to October 2021, 7 patients meeting the 5 following criteriae of definite VITT were included: Onset of symptoms 5-42 days after vaccination, thrombosis, thrombocytopenia, D-dimers >4000 ng/mL and positive anti-PF4 IgG (Zymutest HIA IgG and/or Lifecodes PF4 IgG). HIMEA was performed on whole blood from healthy donors in the hematology laboratory of Alexandra General Hospital. HIPA was performed on washed platelets from healthy donors in the hematology laboratory of Bichat Hospital. Result(s): 4 patients showed a characteristic pattern that was concordant between the two methods. HIMEA showed a sigmoid curve with elevated area under the curve (mean AUC 189+/-78 AU) in saline, that was lower (mean 148+/-51 AU) in the presence of heparin 1 IU/mL and further decreased (mean 34+/-28 AU) in the presence of heparin 100 IU/mL. HIPA showed positive aggregation in the presence of saline and heparin 0,2 IU/mL but no aggregation with heparin 50 IU/mL. 2 patients who showed lower AUC in HIMEA saline (109 and 60 AU) had weakly positive or negative results with HIPA. In these 2 cases, blood was drawn after intravenous immunogloblulin (IVIG) initiation. 1 patient showed discrepant results with typical positive HIMEA but negative HIPA patterns. Conclusion(s): VITT antibodies show heterogenous reactivity patterns that can be highlighted only by using different functional assays such as HIMEA and HIPA. IVIG treatment can be reponsible for lower antibody reactivity.
ABSTRACT
Background : Coronavirus disease 2019 (COVID-19) is associated with a significant risk of thrombosis. A resistance to fibrinolysis has been highlighted in COVID-19 patients but its clinical relevance has not been established yet. In experimental stroke models, Nacetylcysteine (NAC) promoted lysis of tPA-resistant thrombi by reducing large von Willebrand factor (vWF) multimers. Aims : To better characterize the clinical relevance of fibrinolysis resistance in COVID-19 patients and to evaluate the capacity of NAC to restore fibrinolysis in vitro . Methods : 28 critically ill patients with COVID-19 and 28 healthy controls were included in this single-center observational study. A modified thromboelastography assay (ROTEM ® Delta) using EXTEM ® reagent and 150 ng mL -1 t-PA (Actilyse ® ) was performed in the presence of 10 mM NAC or buffer. Residual percentage of clot firmness 30 min after coagulation (LI30) and time required to complete lysis (LT) assessed the efficiency of t-PA-triggered fibrinolysis. Results : Blood clots from COVID-19 patients were resistant to fibrinolysis as indicated by increased LI30 (median 94% [35-100] versus 1% [0-45], P = 0.0007) and prolonged LT (2609 s [1855-3043] versus 1560 s [1376-1994], P = 0.0003) compared to healthy controls. LI30 and LT were positively correlated with vWF levels ( r = 0.6, P = 0.009 and r = 0.5, P = 0.04, respectively), suggesting a role for vWF in fibrinolysis resistance. Resistance to tPA-induced fibrinolysis was delayed in patients with thrombosis ( n = 10) compared to patients without thrombosis, as indicated by higher LI30 (100% [97-100] versus 82.5% [0.5-97];P = 0.002) and prolonged LT (3189 s [2706-3772] versus 2217 s [1583 2840];P = 0.008). Both LI30 and LT were correlated with SOFA ( r = 0.7, P = 0.0003 and r = 0.5, P = 0.01, respectively) and Simplified Acute Physiology Score (SAPS) II scores ( r = 0.7, P = 0.0004 and r = 0.7, P = 0.0009, respectively). In vitro, NAC efficiently restored fibrinolysis in COVID-19 patient blood. Conclusions : Resistance to fibrinolysis in critically ill COVID-19 patients is associated with thrombosis and clinical severity. NAC could represent a new adjunct therapy to promote endogenous fibrinolysis in severe COVID-19 patients.