Prognosis

Whether a DVT is due to major transient risk factors (e.g., trauma, surgery), minor transient risk factors (prolonged hospitalization or medical illness), major persisting risk factors (e.g., cancer), or no identified risk factors (unprovoked) is a significant determinant of recurrence. The extent and location of the initial clot influence the risk of post-thrombotic syndrome, which is the major sequela of DVT. DVT seldom alters the overall prognosis of the patient; the presence or absence of an underlying malignancy, and the presence or absence of underlying medical comorbidity, such as liver disease or chronic kidney disease, remain the major prognostic determinants among DVT patients. People with cancer have reduced survival rates compared with people without cancer, and cancer patients who sustain DVT have a shorter life expectancy than cancer patients without venous thromboembolism (VTE), though this appears to be related to an association with more severe malignancy and VTE, rather than to the DVT itself. When a patient dies from DVT, it is usually from pulmonary embolus (PE) or from a major hemorrhage as a complication of the anticoagulation therapy.

In one systematic review, during the initial 3 months of anticoagulation, the rate of recurrent fatal VTE was 0.4% with a case-fatality rate of 11.3%. The rate of fatal major bleeding events was 0.2% with a case-fatality rate of 11.3%. After anticoagulation, the rate of fatal recurrent VTE was 0.3 per 100 patient-years with a case-fatality rate of 3.6%.[239]

In community cohort studies, the incidence of acute recurrent DVT within 60 days is as high as 25% to 30%. The reasons for this acute recurrence are not known, but subtherapeutic anticoagulant therapy or patient nonadherence to therapy may contribute.[240][241]

In patients with acute DVT or PE enrolled in prospective cohort studies, only 5% of patients develop recurrent VTE during the initial 6 months of anticoagulation; however 30% of patients develop recurrent VTE between 6 months and 5 years after the initial event, if off anticoagulation.[242][243]

Compared with patients with no thrombophilic defects, the rate of recurrence during warfarin therapy is not increased in the presence of one or more defects.[244]

The incidence of major life-threatening hemorrhage owing to anticoagulant treatment is low, with the precise risk varying by anticoagulant agent and patient characteristics.

Recurrence

Consensus guidelines recommend 3 months of oral anticoagulant therapy, unless contraindicated by bleeding, in all patients with VTE, with reassessment for possible extended therapy after the initial 3 months of treatment.[245] Patients with DVT occurring in the setting of a major or minor transient provocation will usually stop anticoagulants after completion of at least 3 months of therapy. Consideration should be given to indefinite treatment among patients who have idiopathic or unprovoked DVT.[246] Patients with cancer continue anticoagulants, as long as they are tolerated, while the cancer is active, and if the risk of bleeding remains low to moderate without any recent major bleeding episodes.[18]​ Regular reassessment is necessary in patients with cancer as the risks of VTE and bleeding regularly change given modifications in pharmacotherapeutic, surgical, and radiation therapies.[19][42]​​​

Many studies have attempted to identify subgroups of patients with unprovoked VTE who do not need to be treated indefinitely with oral anticoagulation. There is strong evidence that the risk of recurrent VTE is higher in the following patients: male sex; those with a diagnosis of a proximal DVT (versus isolated calf DVT); those with ultrasound evidence of residual clot; those who have an elevated D-dimer 1 month after stopping a 3- to 6-month course of oral anticoagulation; and those who had an unprovoked DVT.[18]​​[41]​​ Several risk assessment models have been developed for this purpose, including the DASH score, the Vienna Prediction Model, and the "Men Continue and HER-DOO2" model.[191] The latter model identifies a subset of women with low risk for recurrent VTE after an initial unprovoked event, and a prospective validation study of this model was published.[192]

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