Thrombin Generation to Predict the Risk of Venous Thromboembolism Recurrence, Major Bleeding and Death in the Elderly: A Prospective Multicenter Cohort Study
Authors: Vrotniakaite-Bajerciene Kristina , Rütsche Sereina , Calzavarini Sara , Quarroz Claudia , Stalder Odile , Mean Marie , Righini Marc , Beer Jürg Hans , Frauchiger Beat , Osterwalder Joseph , Kucher Nils , Matter Christian , Husmann Marc , Banyai Martin , Aschwanden Markus , Mazzolai Lucia , Hugli Olivier , Rodondi Nicolas , Aujesky Drahomir , Angelillo-Scherrer Anne 
Published: November 2021

Abstract
Introduction: Venous thromboembolism (VTE), comprising deep vein thrombosis (DVT) and pulmonary embolism (PE), constitutes a worldwide major health issue, and a leading cause of death. VTE incidence increases exponentially with age mainly due to the accumulation of risk factors and comorbidities predisposing to thrombosis. This leads to greater morbidity impact of VTE on elderly patients, who are also at higher risk of bleeding. Consequently, identification of older patients who might benefit from indefinite anticoagulation treatment is paramount. In order to facilitate the identification of these patients, the benefit/risk ratio should be carefully evaluated by considering clinical and laboratory information. Thrombin activity can be recorded by continuously measuring cleavage of a fluorescent substrate, resulting in a thrombin generation (TG) curve. Recent association studies show promising data of thrombin generation parameters predicting first VTE in elderly (Wang H et. al. RPTH 2021, 5:e12536). However, the predictive ability of thrombin generation for recurrent VTE, major bleeding and mortality in the elderly is unknown. The goal of this study was to prospectively investigate the performance of the TG assay one year after index VTE in predicting the risk of VTE, recurrence, major bleeding and mortality up to 2 years in elderly population.
Methods: The study was conducted as part of the Swiss Cohort of Elderly Patients with VTE (SWITCO65+), a prospective multicenter cohort study to assess medical outcomes and quality of life in elderly patients with acute VTE in Switzerland. For the present study, the clinical outcomes were VTE recurrence, major bleeding and mortality, which were assessed parallel to clinical data of thrombosis and other general laboratory parameters including thrombophilia testing in over a 3-year period. Blood samples for assessment of TG parameters were drawn 12 month after the index VTE. Venous blood was drawn after minimal venostasis and processed by double centrifugation according to the recommendation of the subcommittee of the Scientific and Standardization Committee of ISTH. TG measurements were performed with the calibrated automated thrombogramm assay (Stago, Asnières-sur-Seine, France) in two experimental settings: 1pM tissue factor (TF) with/without thrombomodulin (TM) and 13.6 pM TF with/without activated protein C (APC). In addition, reference plasma (Cryocheck Reference Control Normal, PrecisionBiologic, Dartmouth, Canada) was tested in all experiments in order to correct day-to-day variations. Lag time, velocity index, time to peak, peak height, endogenous thrombin potential (ETP) were measured and peak and ETP ratio obtained in presence/absence of TM or APC were calculated. Results from the reference plasma were used to calculate the normalized ETP and peak ratio in 1 pM setting and peak ratio in 13.6 pM TF setting.
Results: TG was assessed in 565 patients 12 months after the index VTE. At this time, 59% of patients were still anticoagulated. Eleven percent of them had cancer-related VTE, 20% provoked VTE and 68% unprovoked VTE. The prevalence of inherited risk factors for VTE was in line with previous reports on European patients with VTE.
Patients still anticoagulated 12 months after the index VTE were less likely to develop recurrent VTE in the next 24 months than patients without anticoagulation. However, the incidence of major bleeding and mortality was comparable in anticoagulated and non-anticoagulated patients.
TG was faster and lower in anticoagulated than in non-anticoagulated patients.
Some thrombin generation parameters measured 12 months after the index VTE (Figure 1) were discriminatory for VTE recurrence, major bleeding and mortality (Table 1). In addition, several thrombin generation parameters measured in patients not under anticoagulation 12 months after the index VTE were associated with an increased risk of VTE recurrence, major bleeding and mortality up to 24 months. These associations remained after adjustment for potential confounding factors for the risk of VTE recurrence, major bleeding and mortality (Table 2).
Conclusion: In elderly patients, several parameters of thrombin generation were associated with VTE recurrence, major bleeding and/or mortality. These findings may serve as the basis for validation in a prospective interventional outcome trial.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.