Deep Vein Thrombosis (DVT)
The most common presentations of venous thrombosis are DVT of the leg(s) and pulmonary embolism, which is the end-result of DVT. Any thrombus in the venous circulation can separate from its thrombotic bed within the venous wall lining and migrate with the venous circulation to the right side of the heart where it is then propelled along with the deoxygenated blood to the lung vasculature, obstructing it and thereby preventing adequate ventilation. Because of these processes, DVT is a life-threatening condition and pulmonary embolism can be a life-ending condition.
DVT risk is increased, according to the theory of its genesis, with a triad of conditions:
- Alterations in blood flow (“stasis”)
- Endothelial injury (damage to the innermost wall layer)
- Inherited (congenital) or acquired (estrogen or pregnancy, trauma, surgery, malignancy) hypercoagulable states
Although superficial thrombosis is considered a less severe disorder than DVT, there is evidence that those with varicose veins have a fivefold increase in DVT risk and twice the pulmonary embolism risk than those without them.
Confirmation of chronic venous disease can be made by ultrasound to identify venous reflux (reversed flow). This is the first condition in the triad of conditions cited above.
The Doppler technology in the combined ultrasound procedure (combined with B mode ultrasound as “duplex ultrasound”) reflects sound waves off of red blood cells and thereby renders an image that indicates motion or the lack thereof. The B (brightness) mode of ultrasound, the other component, renders an image based on differences in tissue densities. As such, thrombi can be easily identified in accessible areas like the legs or arms.
Although duplex ultrasound has largely replaced more invasive investigations via CT and MRI venography (invasive due to contrast media used), these procedures are still important adjuncts when diagnosis needs further confirmation or a suspected thrombosis is in an ultrasound-inaccessible area.
How Can Deep Venous Thrombosis Be Diagnosed?
Thrombus formation involves a failure of natural anticoagulation, either congenital or acquired systemically, or due to injury locally.
Testing for Congenital Risk of DVT
Congenital risk can be assessed by family history and blood testing. A history of a close relative with pulmonary emboli, deep vein thrombosis (DVT), or sudden death for reasons that were never identified can prompt physicians to test for risks of DVT.
Blood tests for inherited clotting disorders include mutations in Factor V Leiden and prothrombin and congenital deficiencies of antithrombin, protein C, and protein S.
Testing for Acquired Risk of DVT
The following contribute to risk for DVT:
- Trauma or surgical manipulations
- Pregnancy and estrogen replacement
- Renal or liver disease
- Inflammatory bowel disease
Testing for these includes a variety of diagnostic methods, from blood work and imaging (ultrasound, CT, and MRI) to invasive venography.
Tests After Diagnosis of DVT Is Established
Identification of actual thrombus formation mandates that mere diagnostics progress to prevention (pulmonary emboli or thrombus extension) and treatment (anticoagulation or clot removal). Once anticoagulation is begun, the progress of the clot dissolution can be followed by duplex ultrasound testing. The anticoagulation can be monitored via blood tests that measure the amount of anticoagulation and adjustments in dosing can be made accordingly. If interventional (invasive) therapy is necessary, these same blood tests can be used to assure that the coagulation is back to normal to prevent hemorrhagic complications before performing these procedures.
Tests After DVT Is Treated
Post-thrombotic syndrome is a condition that is a combination of reflux due to valvular incompetence and the resulting venous hypertension seen after a prior thrombotic episode. Venous insufficiency with associated pain, vein dilation, edema, skin pigmentation, and venous ulcers are common after treatment and require follow-up via ultrasound surveillance.
Management of Deep Venous Thrombosis
Since deep vein thrombosis (DVT) and its subsequent pulmonary emboli have such a high morbidity and mortality rate, management is aggressive. Treatment includes anticoagulation (first and foremost) and when indicated, invasive intervention. The risk of recurrent thrombosis and pulmonary emboli are greatest immediately after diagnosis of DVT, so treatment should be immediate.
Whether the risk of thrombosis is congenital or acquired, anticoagulation is indicated for the presence of any deep vein thrombi that are identified. This involves the use of systemic anticoagulation for up to 10 days, which is accomplished via
- Subcutaneous low molecular weight heparin or fondaparinux (once-daily Arixtra)
- Direct oral anticoagulants: rivaroxaban (Xarelto) or apixaban (Eliquis). These are direct clotting cascade factor Xa and thrombin inhibitors. They have similar efficacy to injected heparin and have the convenience of avoiding injections, but they are more expensive and should there be a delay in acquiring them, anticoagulation can begin immediately with subcutaneous heparin until they are available.
After the initial treatment, anticoagulation should be continued long-term. If the agent used for long-term maintenance is different than that used for the immediate initial therapy, a transition is required that assures continued effective anticoagulation. First choice long-term anticoagulants are the factor Xa and thrombin inhibitors unless there is pregnancy, renal insufficiency, or cancer. These fixed-dose agents do not require routine laboratory monitoring for dose changes like warfarin does. Management of DVT also requires close surveillance using duplex ultrasound imaging, as the presence of a DVT is a risk in itself for recurrent DVT and pulmonary emboli. If there is frequent showering of the lung vasculature with emboli from DVT, a filter can be placed in the vena cava to act as a filter.
Prevention of Deep Venous Thrombosis
There may be no way to prevent DVT, except by recognizing its risk factors and acting on them with limb elevation, compression stockings, and mobility. In patients with a strong family history of DVT, pulmonary embolism, or sudden unexplained death, tests for inherited defects in the clotting cascade should be done and if there were to be findings indicating the prudence of anticoagulation, such a preventative measure should be implemented.
Prevention via DVT Ultrasound
Any previous DVT, family history of DVT or pulmonary embolism, malignancy, or other risk factors, make occurrence and recurrence more likely. Duplex ultrasound, the dual ultrasonographic techniques of B mode and Doppler ultrasonography, are very accurate and cost-effective in surveillance of the deep veins of the lower extremities and pelvis in those who carry these risks.
Prevention of Complications After an Established Diagnosis of DVT
In considering prevention in regards to an established diagnosis of deep vein thrombosis (DVT), preventing its complication, pulmonary embolism, is the true goal, since this is what causes the unacceptable morbidity and mortality associated with DVT. Once DVT is diagnosed, the efforts of prevention center on avoiding the migration of thrombi to the pulmonary circulation.
The best way to prevent pulmonary embolism is to reduce the thrombosis with anticoagulation. The ultimate goal is to prevent death, so if pulmonary embolism is suspected, hemodynamic stability should be determined by the presence or absence of hypotension (shock). Supplemental oxygen and hemodynamic support with intravenous fluids are used, along with initiating anticoagulation in those not already being anticoagulated. If a patient is not already in a hospital, rapid transport is necessary to offer the best chances of preventing serious morbidity or mortality.