Anticoagulation of Isolated Calf DVTs

Journal Club Podcast #32: August 2016

Oprah anticoagulate.jpg

A quick review of the literature on anticoagulation in isolated below the knee DVTs, and why we still don't have an answer...

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Articles:
Vignette:

Mr. M is a 53-year-old patient with a history of high blood pressure and high cholesterol who flew back to St. Louis from Shanghai five days ago. Two days after getting back he noted pain and swelling in his left calf, which he thought was due to a muscle strain while getting off of the airplane. Since then, the swelling has remained constant while the pain has worsened slightly. He reports a dull ache that is worse with ambulation and improves with rest. He denies shortness of breath or chest pain.

On physical exam his vitals are normal, his lungs are clear, and he has a normal S1 and S2 without a cardiac murmur or gallop. He has mild swelling noted to the left calf with focal calf tenderness. There is no erythema, warmth, or induration, and his pulses are symmetric bilaterally.

Concerned for a possible DVT given his recent long flight, you obtain lower extremity dopplers which reveal echogenic material in the peroneal and soleal veins consistent with acute DVT, but no signs of DVT proximal to the calf.

You call the patients PMD to discuss management, and she recommends sending the patient home with no therapy because, "It's just a calf DVT. You don't treat those." While you understand that has been the classic teaching, you also remember listening to an ERCAST Podcast in the last couple of years that spoke about the controversy surrounding this dogma. You send Mr. P home and recommend repeat dopplers in 5-7 days, but later decide to search the literature in order to make your own evidence-based decision...

PICO Question:

Population: Adult patients with isolated calf DVT distal to the popliteal veins

Intervention: Therapeutic anticoagulation (heparin, low molecular weight heparin, factor Xa inhibitor, direct thrombin inhibitor, or vitamin K antagonist)

Comparison: No anticoagulation.

Outcome: Propagation of clot to the popliteal veins or beyond, PE, bleeding, death, cost, patient satisfaction, quality of life.

Search Strategy:

An advanced PubMed search was conducted using the strategy “calf AND (thrombosis OR DVT) AND anticoagulation” (http://tinyurl.com/hx4onng) with 180 articles resulting. From these, the four most relevant articles were chosen.

Bottom Line:

The management of DVTs isolated to the calf veins has remained a controversial topic for many years. The 2008 guidelines produced by the American College of Chest Physicians (ACCP) recommended long-term (3 month) anticoagulation for all patients with DVT, regardless of proximal extension. Updated ACCP guidelines produced this year, on the other hand, make no specific recommendation, offering options of either treating or not treating isolated calf DVTs, as long as surveillance ultrasounds are performed. This lack of a firm recommendation seems based less on actual evidence, as it is on the low quality of evidence, which we will review.

This clinical conundrum has persisted for decades, with research extending at least into the 1980s. In 1985, Lancet published a randomized, controlled trial from Sweden (Lagerstedt 1985), in which patients with DVT isolated to the calf vein (as detected by phlebography) received either warfarin or no further anticoagulation (following a 5-day course of IV heparin in both groups). With 52 patients randomized, the authors found that the risk of recurrent clot was significantly lower in the warfarin group, with a NNT of 3.5 (95% CI 2.2 to 8.5). Unfortunately, this does not seem to be a very patient-centered outcome, and no patient in either group developed a PE.

In 2010, an article published in the Journal of Vascular Surgery (Schwarz 2010) randomized patients with isolated calf muscle vein (soleal or gastrocnemius) DVT to naroparin or compression therapy alone. They found no difference in progression of clot into either deep calf veins (peroneal or posterior tibial) or proximal veins, with a RR of 0.98 (95% CI 0.14 to 6.7). Unfortunately, this small study was poorly reported and failed to adhere to CONSORT guidelines, making assessment of internal validity nearly impossible. Additionally, the inclusion of calf muscle veins only, which may be less likely to propagate or result in PE, would not detect benefit in patients with deep calf vein clot.

A recent pilot randomized, controlled trial conducted in the UK (Horner 2014) randomized patients with any isolated calf DVT to either warfarin or anti-inflammatory medication. Seventy patients were analyzed, and for the composite outcome of proximal propagation, symptomatic PE, VTE-related sudden death, or major bleeding, they found a statistically nonsignificant trend towards benefit with anticoagulation (absolute risk reduction 11.4%, 95% CI -1.5% to 26.7%). Although the study was small, it was designed to demonstrate the feasibility of a much larger study, which is currently underway. Such a study will provide the best evidence to date regarding this treatment.

The most recent evidence on this subject was a retrospective observational study conducted at UC Davis. Outcomes of patients with isolated calf DVT were assessed based on whether or not there was an intention for them to receive any form of anticoagulation. The composite outcome of proximal DVT or PE was less likely in those treated with anticoagulation (RR 0.36, 95% CI 0.15 to 0.84). This benefit persisted after adjustment was made for several confounders. Unfortunately, observational studies are never able to control for the unknown confounders, and such evidence does little to inform us of whether anticoagulation provides any actual benefit. Also, less than half the patients in the study underwent repeat testing to assess for propagation of DVT, and such testing was more likely to occur in the control group, biasing the results in favor of the treatment group. The study also included primarily inpatients, and less than 4% were from the ED.

The evidence reviewed here is notably lacking in large, randomized controlled trials of good methodology, making it difficult to make firm recommendations. The current Chest guidelines make sense given this lack of evidence, and the decision to treat or not treat isolated calf DVTs should be based on several factors, including location (muscle vs. deep veins), need for ongoing immobilization, and bleeding risk. Emergency physicians will have to work closely with primary care physicians and admitting teams when making such decisions, given the controversy surrounding this topic.

Posted on October 2, 2016 .