Anticoagulants
Heparin augments the activity of antithrombin III and prevents the conversion of fibrinogen to fibrin. Full-dose LMWH or full-dose unfractionated IV heparin should be initiated at the first suspicion of DVT or PE.
With proper dosing, several LMWH products have been found safer and more effective than unfractionated heparin both for prophylaxis and for treatment of DVT and PE. Monitoring the aPTT is neither necessary nor useful when giving LMWH, because the drug is most active in a tissue phase and does not exert most of its effects on coagulation factor IIa.
Many different LMWH products are available around the world. Because of pharmacokinetic differences, dosing is highly product specific. Several LMWH products are approved for use in the United States: enoxaparin (Lovenox), dalteparin (Fragmin), and tinzaparin (Innohep). Enoxaparin and tinzaparin are currently approved by the FDA for treatment of DVT. Dalteparin is FDA approved for prophylaxis and has approval for cancer patients. Each of the other agents has been approved by the FDA at a lower dose for prophylaxis, but all appear to be safe and effective at some therapeutic dose in patients with active DVT or PE.
Fractionated LMWH administered subcutaneously is now the preferred choice for initial anticoagulation therapy. Unfractionated IV heparin can be nearly as effective but is more difficult to titrate for therapeutic effect. Warfarin maintenance therapy may be initiated after 1-3 days of effective heparinization.
The weight-adjusted heparin dosing regimens that are appropriate for prophylaxis and treatment of coronary artery thrombosis are too low to be used unmodified in the treatment of active DVT and PE. Coronary artery thrombosis does not result from hypercoagulability but rather from platelet adhesion to ruptured plaque. In contrast, patients with DVT and PE are in the midst of a hypercoagulable crisis, and aggressive countermeasures are essential to reduce mortality and morbidity rates.
Enoxaparin (Lovenox)
Exonaparin was the first low-molecular-weight heparin (LMWH) released in the United States. It was approved by the FDA for both treatment and prophylaxis of DVT and PE. Enoxaparin enhances the inhibition of factor Xa and thrombin by increasing antithrombin III activity. In addition, it preferentially increases the inhibition of factor Xa. LMWH has been used widely in pregnancy, although clinical trials are not yet available to demonstrate that it is as safe as unfractionated heparin. Except in overdoses, checking PT or aPTT has no utility, as aPTT does not correlate with anticoagulant effect of fractionated LMWH. Factor Xa levels can be monitored if concern arises about whether the dose is adequate.
Dalteparin (Fragmin)
Dalteparin is an LMWH with many similarities to enoxaparin but with a different dosing schedule. It is approved for DVT prophylaxis in patients undergoing abdominal surgery. Except in overdoses, checking PT or aPTT has no utility, as aPTT does not correlate with anticoagulant effect of fractionated LMWH. LMWH. Factor Xa levels can be monitored if concern arises about whether the dose is adequate.
Tinzaparin (Innohep)
Tinzaparin is approved for treatment of DVT in hospitalized patients. Enhances inhibition of factor Xa and thrombin by increasing antithrombin III activity. In addition, preferentially increases inhibition of factor Xa.
Heparin (Hep-Lock U/P, Hep-Lock, Hep-Flush-10)
Heparin augments the activity of antithrombin III and prevents conversion of fibrinogen to fibrin. It does not actively lyse but is able to inhibit further thrombogenesis. Heparin prevents the reaccumulation of a clot after spontaneous fibrinolysis. When UFH is used, the aPTT should not be checked until 6 hours after the initial heparin bolus, because an extremely high or low value during this time should not provoke any action
Warfarin (Coumadin, Jantoven)
Warfarin (Coumadin) interferes with the hepatic synthesis of vitamin K–dependent coagulation factors. It is used for the prophylaxis and treatment of venous thrombosis, pulmonary embolism, and thromboembolic disorders. Never administer warfarin to patients with thrombosis until after they have been fully anticoagulated with heparin (the first few days of warfarin therapy produce a hypercoagulable state). Failing to anticoagulate with heparin before starting warfarin causes clot extension and recurrent thromboembolism in approximately 40% of patients, compared with 8% of those who receive full-dose heparin before starting warfarin. Heparin should be continued for the first 5-7 days of oral warfarin therapy, regardless of the PT time, to allow time for depletion of procoagulant vitamin K–dependent proteins.
Tailor the warfarin dose to maintain an INR in the range of 2.5-3.5. The risk of serious bleeding (including hemorrhagic stroke) is approximately constant when the INR is 2.5-4.5 but rises dramatically when the INR is over 5. In the United Kingdom, a higher INR target of 3-4 often is recommended.
Evidence suggests that 6 months of anticoagulation reduces the rate of recurrence to half of the recurrence rate observed when only 6 weeks of anticoagulation is given. Long-term anticoagulation is indicated for patients with an irreversible underlying risk factor and recurrent DVT or recurrent pulmonary embolism.
Procoagulant vitamin K–dependent proteins are responsible for a transient hypercoagulable state when warfarin is first started and stopped. This is the phenomenon that occasionally causes warfarin-induced necrosis of large areas of skin or of distal appendages. Heparin is always used to protect against this hypercoagulability when warfarin is started; when warfarin is stopped, however, the problem resurfaces, causing an abrupt, temporary rise in the rate of recurrent venous thromboembolism.
At least 186 different foods and drugs reportedly interact with warfarin. Clinically significant interactions have been verified for a total of 26 common drugs and foods, including 6 antibiotics and 5 cardiac drugs. Every effort should be made to keep the patient adequately anticoagulated at all times, because procoagulant factors recover first when warfarin therapy is inadequate.
Patients who have difficulty maintaining adequate anticoagulation while taking warfarin may be asked to limit their intake of foods that contain vitamin K.
Foods that have moderate to high amounts of vitamin K include Brussels sprouts, kale, green tea, asparagus, avocado, broccoli, cabbage, cauliflower, collard greens, liver, soybean oil, soybeans, certain beans, mustard greens, peas (black-eyed peas, split peas, chick peas), turnip greens, parsley, green onions, spinach, and lettuce.
Fondaparinux sodium (Arixtra)
Fondaparinux sodium is a synthetic anticoagulant that works by inhibiting factor Xa, a key component involved in blood clotting. It provides a highly predictable response and has a bioavailability of 100%. The drug has a rapid onset of action and a half-life of 14-16 hours, allowing for sustained antithrombotic activity over a 24-hour period. Fondaparinux sodium does not affect prothrombin time or activated partial thromboplastin time, nor does it affect platelet function or aggregation.
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A large pulmonary artery thrombus in a hospitalized patient who died suddenly.
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Pulmonary embolism was identified as the cause of death in a patient who developed shortness of breath while hospitalized for hip joint surgery. This is a close-up view.
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Lung infarction secondary to pulmonary embolism occurs rarely.
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Posteroanterior and lateral chest radiograph findings are normal, which is the usual finding in patients with pulmonary embolism.
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High-probability perfusion lung scan shows segmental perfusion defects in the right upper lobe and subsegmental perfusion defects in right lower lobe, left upper lobe, and left lower lobe.
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A normal ventilation scan will make the noted defects in the previous image a mismatch and, hence, a high-probability ventilation-perfusion scan.
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Anterior views of perfusion and ventilation scans are shown here. A perfusion defect is present in the left lower lobe, but perfusion to this lobe is intact, making this a high-probability scan.
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A segmental ventilation perfusion mismatch is evident in a left anterior oblique projection.
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A pulmonary angiogram shows the abrupt termination of the ascending branch of the right upper-lobe artery, confirming the diagnosis of pulmonary embolism.
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A chest radiograph with normal findings in a 64-year-old woman who presented with worsening breathlessness.
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This perfusion scan shows bilateral perfusion defects. The ventilation scan findings were normal; therefore, these are mismatches, and this is a high-probability scan.
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This ultrasonogram shows a thrombus in the distal superficial saphenous vein, which is under the artery.
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A posteroanterior chest radiograph showing a peripheral wedge-shaped infiltrate caused by pulmonary infarction secondary to pulmonary embolism. Hampton hump is a rare and nonspecific finding. Courtesy of Justin Wong, MD.
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Computed tomography angiogram in a 53-year-old man with acute pulmonary embolism. This image shows an intraluminal filling defect that occludes the anterior basal segmental artery of the right lower lobe. Also present is an infarction of the corresponding lung, which is indicated by a triangular, pleura-based consolidation (Hampton hump).
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Computed tomography angiography in a young man who experienced acute chest pain and shortness of breath after a transcontinental flight. This image demonstrates a clot in the anterior segmental artery in the left upper lung (LA2) and a clot in the anterior segmental artery in the right upper lung (RA2).
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Computed tomography angiogram in a 55-year-old man with possible pulmonary embolism. This image was obtained at the level of the lower lobes and shows perivascular segmental enlarged lymph nodes as well as prominent extraluminal soft tissue interposed between the artery and the bronchus.
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Computed tomography venograms in a 65-year-old man with possible pulmonary embolism. This image shows acute deep venous thrombosis with intraluminal filling defects in the bilateral superficial femoral veins.
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The pathophysiology of pulmonary embolism. Although pulmonary embolism can arise from anywhere in the body, most commonly it arises from the calf veins. The venous thrombi predominately originate in venous valve pockets (inset) and at other sites of presumed venous stasis. To reach the lungs, thromboemboli travel through the right side of the heart. RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle.
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A spiral CT scan shows thrombus in bilateral main pulmonary arteries.
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CT scan of the same chest depicted in Image 18. Courtesy of Justin Wong, MD.
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Longitudinal ultrasound image of partially recanalized thrombus in the femoral vein at mid thigh.
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Sequential images demonstrate treatment of iliofemoral deep venous thrombosis due to May-Thurner (Cockett) syndrome. Far left, view of the entire pelvis demonstrates iliac occlusion. Middle left, after 12 hours of catheter-directed thrombolysis, an obstruction at the left common iliac vein is evident. Middle right, after 24 hours of thrombolysis, a bandlike obstruction is seen; this is the impression made by the overlying right common iliac artery. Far left, after stent placement, image shows wide patency and rapid flow through the previously obstructed region. Note that the patient is in the prone position in all views. (Right and left are reversed.)
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Lower-extremity venogram shows outlining of an acute deep venous thrombosis in the popliteal vein with contrast enhancement.
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Lower-extremity venogram shows a nonocclusive chronic thrombus. The superficial femoral vein (lateral vein) has the appearance of 2 parallel veins, when in fact, it is 1 lumen containing a chronic linear thrombus. Although the chronic clot is not obstructive after it recanalizes, it effectively causes the venous valves to adhere in an open position, predisposing the patient to reflux in the involved segment.
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Pulmonary embolus.
