Calf DVT: treat or follow?

W. Kent Williamson, M.D.
Medical director, Providence Noninvasive Vascular Labs
Chairman, Providence Vascular Quality Council-Oregon
Pacific Vascular Specialists

David A. Ellis, M.S.
Clinical vascular research associate
Providence St. Vincent Medical Center

Published October 2011

Management of calf deep vein thrombosis, or CVT, has been a longstanding challenge for physicians. Controversy over best-practice guidelines coupled with a lack of knowledge regarding the relative risks for propagation and embolization can make deciding treatment difficult.

Is it wiser to anticoagulate or follow the DVT? With ongoing review of best available data, we can better understand the continuing debate surrounding this pathology and render more informed choices for patients with calf DVT.

Conflicting natural history

In managing CVT, the goal is to avoid propagation and subsequent embolism while reducing unnecessary anticoagulant therapy. This requires accurate data on propagation and embolization rates. Unfortunately, studies on the natural history of CVT have presented conflicting data, with the incidence of propagation from symptomatic distal calf vein thrombosis to proximal deep veins reported at anywhere from 3 to 30 percent.

The reported variability may be due in part to older diagnostic techniques that lacked the ability to accurately differentiate between muscular and axial thrombi. Although advances in duplex ultrasonography have improved our ability to identify isolated muscular versus axial venous thrombosis, the fact that few studies have compared muscular and axial DVT also contributes to general uncertainty.

With so much uncertainty regarding CVT risk, physicians often are left wondering which way to turn. Although more high-quality randomized trials are needed, the American College of Chest Physicians has established some basic, evidence-based guidelines that can aid physicians in the decision-making process.

Guidelines for treatment

In 2008, the ACCP convened a group of experts to update the latest graded clinical guidelines regarding antithrombotic and thrombolytic therapy to simplify decision-making.

According to the ACCP: “The strength of any recommendation depends on two factors: the tradeoff between benefits, risks, burden and cost, and the level of confidence in estimates of those benefits and risks.

“If benefits do or do not outweigh risks, burden and costs, a strong recommendation is designated as Grade 1. If there is less certainty about the magnitude of the benefits and risks, burden and costs, a weaker Grade 2 recommendation is made. Support for these recommendations may come from high-quality, moderate-quality or low-quality evidence, labeled, respectively, A, B and C.”

The following suggestions represent ACCP Grade 1A recommendations regarding treatment of calf DVT:

  • For patients with objectively confirmed CVT, it is recommended that they receive initial, short-term treatment with IV unfractionated heparin, subcutaneous low molecular weight heparin (LMWH), monitored or fixed-dose subcutaneous unfractionated heparin or subcutaneous fondaparinux.
  • For patients with a CVT secondary to a reversible risk factor or unprovoked CVT, it is recommended to treat with a vitamin K antagonist (VKA) for three months, with evaluation of the risk-benefit ratio for long-term therapy after this period.
  • For patients with CVT and cancer, recommended treatment is low molecular weight heparin for the first three to six months of long-term therapy. Subsequent anticoagulant therapy with VKA or LMWH is recommended indefinitely or until the cancer is resolved (Grade 1C).
  • Dosage of VKAs should be adjusted to maintain an INR range between 2.0 and 3.0, with a goal of 2.5. High-intensity VKA therapy with an INR range of 3.1-4.0 is not recommended.
  • When feasible, early ambulation is preferential to bed rest for patients with acute CVT.

For patients where anticoagulation is not elected, consider serial duplex examinations to ensure thrombus stability, or perhaps a vena cava filter.

Some practitioners may be hesitant to implement anticoagulation therapy in otherwise healthy, low-risk patients. Yet this hesitation places the patient at an unknown and largely preventable risk for propagation and life-threatening embolization.

Until more consistent data on incidence of propagation for calf deep vein thrombosis are reported, this is simply a risk not worth taking.

Clinical articles by W. Kent Williamson, M.D.