In the context of endothelial injury^1,2 and a prothrombic milieu,^1,3 venous and arterial microthrombosis and macrothrombosis are common manifestations of COVID-19.⁴ Venous thromboembolism (VTE) is the most commonly reported thrombotic complication, with higher incidence rates among critically ill patients.⁵ A 2020 systematic review estimated that 28% of critically ill patients with COVID-19 had VTE.⁶

Coronavirus disease 2019 (COVID-19), currently a worldwide pandemic, is a viral illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The suspected contribution of thrombotic events to morbidity and mortality in COVID-19 patients has prompted a search for novel potential options for preventing COVID-19-associated thrombotic disease. In this article by the Global COVID-19 Thrombosis Collaborative Group, we describe novel dosing approaches for commonly used antithrombotic agents (especially heparin-based regimens) and the potential use of less widely used antithrombotic drugs in the absence of confirmed thrombosis. Although these therapies may have direct antithrombotic effects, other mechanisms of action, including anti-inflammatory or antiviral effects, have been postulated. Based on survey results from this group of authors, we suggest research priorities for specific agents and subgroups of patients with COVID-19. Further, we review other agents, including immunomodulators, that may have antithrombotic properties. It is our hope that the present document will encourage and stimulate future prospective studies and randomized trials to study the safety, efficacy, and optimal use of these agents for prevention or management of thrombosis in COVID-19. ^* Drs. Bikdeli and Madhavan contributed equally to this manuscript.

Importance: The optimal treatment of intermediate-high–risk pulmonary embolism (PE) remains unknown.Objective: To assess the effect of conventional catheter-directed thrombolysis (cCDT) plus anticoagulation vs anticoagulation monotherapy in improving echocardiographic measures of right ventricle (RV) to left ventricle (LV) ratio in acute intermediate-high–risk PE.Design, Setting, and Participants: The Catheter-Directed Thrombolysis vs Anticoagulation in Patients with Acute Intermediate-High–Risk Pulmonary Embolism (CANARY) trial was an open-label, randomized clinical trial of patients with intermediate-high–risk PE, conducted in 2 large cardiovascular centers in Tehran, Iran, between December 22, 2018, through February 2, 2020.Interventions: Patients were randomly assigned to cCDT (alteplase, 0.5 mg/catheter/h for 24 hours) plus heparin vs anticoagulation monotherapy.Main Outcomes and Measures: The proportion of patients with a 3-month echocardiographic RV/LV ratio greater than 0.9, assessed by a core laboratory, was the primary outcome. The proportion of patients with an RV/LV ratio greater than 0.9 at 72 hours after randomization and the 3-month all-cause mortality were among secondary outcomes. Major bleeding (Bleeding Academic Research Consortium type 3 or 5) was the main safety outcome. A clinical events committee, masked to the treatment assignment, adjudicated clinical outcomes.Results: The study was prematurely stopped due to the COVID-19 pandemic after recruiting 94 patients (mean [SD] age, 58.4 [2.5] years; 27 women [29%]), of whom 85 patients completed the 3-month echocardiographic follow-up. Overall, 2 of 46 patients (4.3%) in the cCDT group and 5 of 39 patients (12.8%) in the anticoagulation monotherapy group met the primary outcome (odds ratio [OR], 0.31; 95% CI, 0.06-1.69; P = .24). The median (IQR) 3-month RV/LV ratio was significantly lower with cCDT (0.7 [0.6-0.7]) than with anticoagulation (0.8 [0.7-0.9); P = .01). An RV/LV ratio greater than 0.9 at 72 hours after randomization was observed in fewer patients treated with cCDT (13 of 48 [27.0%]) than anticoagulation (24 of 46 [52.1%]; OR, 0.34; 95% CI, 0.14-0.80; P = .01). Fewer patients assigned to cCDT experienced a 3-month composite of death or RV/LV greater than 0.9 (2 of 48 [4.3%] vs 8 of 46 [17.3%]; OR, 0.20; 95% CI, 0.04-1.03; P = .048). One case of nonfatal major gastrointestinal bleeding occurred in the cCDT group.Conclusions and Relevance: This prematurely terminated randomized clinical trial of patients with intermediate-high–risk PE was hypothesis-generating for improvement in some efficacy outcomes and acceptable rate of major bleeding for cCDT compared with anticoagulation monotherapy and provided support for a definitive clinical outcomes trial.Trial Registration: ClinicalTrials.gov Identifier: NCT05172115