No Guidance for Calf Clots from CACTUS

Treatment evidence regarding venous thromboembolism is not particularly sparse – except what to do about calf VTE. The most robust evidence is three decades old, and of little use for generalizing to modern diagnostic methods and direct oral anticoagulants.

This, then, is the CACTUS trial – a randomized, double-blind, placebo-controlled trial examining the need for treatment of isolated calf DVT with subcutaneous nadroparin. The primary outcome was a composite measure of extension of calf DVT to proximal veins, contralateral DVT, or symptomatic pulmonary embolism. Safety endpoints were bleeding, death, and treatment-related adverse events.

Sadly, this evidence is mostly bereft of guidance. Over the six-year course of this trial, they screened 746 patients and only enrolled 259 – 50% of their goal sample. There were four (3.3%) VTE in the nadroparin group compared with seven (5.4%) in the placebo cohort, and these differences failed to reach statistical significance. Furthermore, clinically significant bleeding occurred in one patient in the nadroparin group, along with one clinically significant adverse medication reaction (heparin-induced thrombocytopenia). Thus, the authors conclude: “Nadroparin was not superior to placebo in reducing the risk of proximal extension or venous thromboembolic events in low-risk outpatients with symptomatic calf DVT, but did increase the risk of bleeding.”

However, half the patients enrolled had deep muscular DVT, further reducing the risk profile of their already grossly underpowered cohort. Thus, the question remains open – and probably the most relevant evidence would come from an adequately powered trial comparing the natural course of disease to both oral antiplatelet agents and direct oral anticoagulants.
“Anticoagulant therapy for symptomatic calf deep vein thrombosis (CACTUS): a randomised, double-blind, placebo-controlled trial”

https://www.ncbi.nlm.nih.gov/pubmed/27836513

Thanks to Tom Deloughery (@bloodman) for his insights!