The first lecture I ever gave to medical students was in my first year of a pulmonary disease fellowship and the topic was DVT and PE. The ventilation perfusion scan had recently become available and the two anticoagulants, heparin and coumadin, were used and remained unchallenged in that category until relatively recently.Duration of therapy was not part of my lecture as I probably did not know what to say.
Much effort and research has been devoted to venous thromboembolic disease since then and through the efforts of the American College of Chest Physicians guidelines on virtually every aspect of DVT and PE appear with some regularity and are widely quoted. Here is a link to a brief review of some of the highlights of the latest (8 th) version by the ACCP.
Information continues to accumulate and a recent paper concerning the issue of duration of therapy has been published from Canada (as much the literature on this topic has been) and this editorial from the CMAJ discusses their findings.
While the authors could discern no pattern of risk factors that predicted likelihood of recurrence in men their data suggested that could be the case in women. Younger, thin women with no elevation of d-dimer and no clinical signs of post phlebitis syndrome were thought to at a low enough risk to possibly justify stopping earlier rather than later the anticoagulant.They generated a so-called clinical decision rule which the authors emphasize is not ready for prime time.It is a post hoc rule and the age and body weight risk factors they identified have not been usually implicated.
How long to treat a patient with a unprovoked DVT or PE continues to be a perplexing clinical problem. The longer you treat the greater the likelihood of a serious bleeding complication, the shorter the period of anticoagulation, the greater the risk of thrombotic events. Six months for an unprovoked DVT seems like the usual recommendation and shorter for a provoked event.
The September 2, 2008 issue of the Annals of Internal Medicine has a useful section regarding DVTs (their "In the Clinic" section entitled "Deep Venus thrombosis" and if you want a single reference to read on the topic that looks like a good place to start.
To my way of thinking, if the D-dimer remains elevated it may be too soon to stop the coumadin.