What is Deep Vein Thrombosis (DVT)?
Deep vein thrombosis is an abnormal clotting of blood in the deep veins, resulting in partial or complete blockage of the deep vein lumen. It occurs in the lower extremities and can cause a range of symptoms such as pain and swelling in the lower extremities.
What are the factors of deep vein thrombosis?
The three major recognized causative factors of venous thrombosis are blood stasis, venous wall damage and hypercoagulability, with “blood stasis” playing a key role in the formation of venous thrombosis.
Why do deep vein thrombosis occur in the lower extremities?
The human blood starts from the heart, is transported to the lower extremities through the arterial system, and is then returned to the heart through the venous system, which is the longest journey. And due to the effect of gravity, the blood tends to slow down in the lower limbs and stagnate in the veins. If the calf muscles, which are known as the “second heart”, are at rest at this time, the veins of the lower extremities are relatively easy to form thrombosis in the same state as all parts of the body.
Among the bilateral lower limbs, the left lower limb is more likely to form deep vein thrombosis than the right, which is related to its anatomical position. The left common iliac vein is sandwiched between the right common iliac artery and the sacral isthmus, which makes it easy for the left common iliac vein to be in contact with the front and back walls for a long time, which not only obstructs the reflux of the left common iliac vein, but also forms intraventricular adhesions.
Who is prone to lower extremity DVT?
People with a high risk of DVT are: bedridden or inactive for a long time after surgery; trauma, obesity, hyperlipidemia or age over 40; patients with myocardial infarction, heart failure, stroke, nephrotic syndrome; patients with malignant tumor; patients with oral contraceptives, pregnancy, varicose veins or previous history of thrombosis, etc.
Patients with surgery and trauma are especially prone to lower extremity DVT. Patients with acute thoracic and abdominal surgery, hip or knee replacement surgery, hip fracture, severe trauma and acute spinal injury are at very high risk for thromboembolism.
Why does pregnancy increase the incidence of lower extremity deep vein thrombosis?
During pregnancy, the enlarged uterus compresses the blood vessels in the abdominal cavity, obstructing the blood flow back to the lower extremities and aggravating the blood stagnation in the lower extremities. At the same time, the blood in the body is secondary to hypercoagulation during pregnancy. The incidence of DVT in the lower extremities is greatly increased by the synergistic effect of the two factors.
What is economy class syndrome?
Economy class syndrome refers to a prolonged airplane ride in which the left side is immobile in a confined space, slowing down the venous blood flow in the lower extremities, causing stasis and forming DVT in the lower extremities. After getting off the plane, the thrombus is dislodged when moving around, and then the blood flows back to the right heart, and then enters the pulmonary artery to cause embolism, making the lungs ischemic and hypoxic, causing symptoms such as chest pain, shortness of breath and blood clotting, which can lead to sudden death in serious cases. Broadly speaking, “economy class syndrome” also includes prolonged travel in trains and automobiles, which may cause deep vein thrombosis in lower limbs or further lead to pulmonary embolism.
What is the risk of deep vein thrombosis?
The incidence of asymptomatic DVT is 5-7% and is mostly confined to the distal veins of the lower extremities. In some patients, the first and only symptom is sudden death, and the cause is “pulmonary embolism”: DVT is detected in 70-90% of patients with pulmonary embolism. In the United States, the mortality rate of pulmonary embolism is the third highest after cancer and coronary heart disease. Therefore, deep vein thrombosis is called the “silent killer”.
In China, with the change of people’s dietary structure and living habits, the incidence of lower limb deep vein thrombosis is increasing every year. However, the medical community is still far from understanding this disease, about 70% of the patients with pulmonary embolism are missed or misdiagnosed as myocardial infarction, coronary heart disease and pulmonary disease, and about 30% of the patients die due to untimely diagnosis and treatment.
What are the symptoms of lower extremity deep vein thrombosis?
Lower limb swelling, pain and superficial varicose veins are the three main symptoms of DVT of lower limbs. Pain is mostly cramping or dull pain, and superficial varicose veins are mostly the manifestation of the establishment of collateral circulation in the chronic stage.
What types of DVT can be classified?
Generally, there are three types: peripheral, central and mixed. There are also two special types: femoral cyanosis and femoral leukomalacia, both of which are emergency cases of DVT in the lower extremity and require emergency surgery to remove the embolus in order to save the affected limb.
How to determine the upper boundary of lower extremity DVT easily?
It can be determined by the level of edema in the lower extremity. Generally, edema below the middle of the calf is in the N vein; edema below the knee is in the superficial femoral vein; edema below the middle of the thigh is in the femoral vein; edema below the buttock is in the common iliac vein; edema in bilateral lower limbs is in the inferior vena cava.
It is important to note that bilateral lower extremity edema in inferior vena cava thrombosis is often symmetrical and can easily be overlooked and misdiagnosed.
What tests can be performed to help diagnose deep vein thrombosis of the lower extremities?
In addition to the physician’s careful physical examination, the following ancillary tests are useful in diagnosing and identifying lower extremity deep vein thrombosis: lower extremity deep vein ultrasound imaging, lower extremity venography, spiral CTA or MRI, and radionuclide examination.
What is the value of lower extremity venous ultrasonography in diagnosing lower extremity DVT?
Because of the high specificity and sensitivity of venous ultrasonography for thrombus detection, and its non-invasive, reproducible, easy operation and obvious price advantages, venous ultrasonography has become the main preferred method for diagnosing DVT of lower extremities. Combining the information provided by B-mode ultrasonography, Doppler spectrum analysis and color Doppler flow imaging, experienced ultrasonographers can diagnose central DVT with a sensitivity and specificity of 97% and peripheral DVT with a sensitivity of 75%.
Moreover, in patients with DVT of the lower extremities on standard anticoagulation therapy, regular deep vein ultrasound follow-up and normal deep vein findings are safe for guiding clinical discontinuation of anticoagulants.
How are lower extremity venograms evaluated?
Lower extremity venography has been considered the “gold standard” for the diagnosis of lower extremity DVT. It can not only effectively determine the presence of thrombus, but also provide detailed information on the location, extent, and shape of the thrombus and the collateral circulation, as well as further information on the thrombosis of the pelvic and intra-abdominal venous system. Because of its accuracy and comprehensiveness in the diagnosis of DVT, phlebography can be used to identify the diagnostic value of other testing methods.
However, venography is an invasive test, which can cause infection and even induce venous thrombosis in case of improper operation; moreover, the applied contrast agent can lead to allergic reaction, vascular damage, and in severe cases, renal failure. Therefore, the application of venography is somewhat limited, and caution should be exercised when considering this method for the diagnosis of DVT.
What is the treatment for DVT?
Current treatment modalities include anticoagulation, thrombolytic therapy and surgery.
What is anticoagulant therapy?
In the human physiological condition, thrombosis and dissolution are in balance with each other. Once venous thrombosis occurs, the body’s coagulation process dominates. The targeted application of drugs to block the activation of coagulation factors in the process of thrombosis is anticoagulation therapy.
What are the commonly used anticoagulant drugs? What should I pay attention to in the anticoagulation process?
The commonly used anticoagulant drugs include two major categories: heparin and coumarin derivatives. The former are injectable drugs, short-acting anticoagulants, generally used for anticoagulation during surgery or for the treatment of acute thrombotic diseases. Low-molecular heparin is a small molecular weight heparin fragment purified by cleavage of common heparin, which is simple to use, has a long half-life and few bleeding complications, and is gradually being widely used. The latter is represented by warfarin, an oral class of drugs, which is a long-acting anticoagulant, mostly used to prevent recurrence after thrombosis treatment or to prevent vascular occlusion after various revascularization procedures.
Regardless of which type of anticoagulant is applied, there is a risk that a small dose will not achieve the anticoagulant effect and a large dose will greatly increase bleeding complications. Therefore, it is important to monitor the changes of blood coagulation function during the application process to adjust the drug dose.
How to decide the thrombolytic treatment for lower extremity DVT?
Currently, there is still controversy in the vascular surgery medical community at home and abroad as to whether thrombolytic therapy is used for DVT of the lower extremity. The immediate recanalization rate of lower extremity thrombosis with thrombolysis is relatively high, but the occurrence of pulmonary embolism and the recurrence rate of DVT are uncertain. It is generally accepted that the earlier thrombolysis is performed after thrombosis, the better the outcome if there are no contraindications, while it is less effective beyond 7 days.
What are the modalities of thrombolytic therapy?
Thrombolytic therapy includes systemic application of thrombolytic drugs, arterial application of thrombolytic drugs in the affected limb, and deep vein application of thrombolytic drugs in the affected limb.
What are the advantages and disadvantages of each thrombolytic treatment method?
Systemic thrombolysis is performed by puncturing a superficial vein, which is easy to operate, reproducible and easy to care for, but the drug dose is larger, so bleeding complications are more likely to occur. Arterial thrombolysis of the affected limb requires femoral artery puncture, which is difficult to operate and more painful for the patient, and is prone to hematoma if operated improperly, but the drug concentration in the affected limb is large and the drug dose is smaller than that of systemic thrombolysis, so the bleeding complications are smaller. In deep vein thrombolysis of the affected limb, the drug enters the target vein directly, the drug is in full contact with the thrombus, and the drug dose is small, but the thrombus must be partially recanalized.
Indications for surgery of deep vein thrombosis of lower extremity?
The indications for surgery are mainly for acute DVT of lower extremity: primary iliofemoral vein thrombosis with disease duration not exceeding 72 hours, or within 7-10 days after the onset of the disease if there is a condition for DVT. In addition, femoral cyanosis and femoral leukomalacia require emergency surgery.
Can DVT recur in the lower extremity after surgery or thrombolytic therapy?
DVT of the lower extremity is very likely to recur! After thrombolytic therapy or surgery, standardized anticoagulation therapy must be administered.
Why should I have a vena cava filter placement?
Because the greatest risk of DVT in the lower extremity is that the dislodged embolus leads to pulmonary embolism, which can lead to sudden death, and the inferior vena cava filter acts as an umbrella to capture some of the dislodged embolus. Especially for patients who have already had a pulmonary embolism or who need thrombolytic therapy, the risk of embolus dislodgement is higher and inferior vena cava filter placement is feasible. Placement of an inferior vena cava filter can significantly reduce the incidence of pulmonary embolism.
Venous filters can be divided into permanent and temporary types. They are carefully selected according to the different clinical characteristics of the patient.
Anticoagulation therapy is still required after the placement of vena cava filters. In addition, the cost-benefit ratio of vena cava filter placement needs to be further investigated.
In addition to the above treatment, what else should be taken into account during the treatment process?
Patients with DVT of the lower extremities are treated with bed rest, elevation of the affected extremity, and local moist hot compresses. The duration of bed rest is usually 10 days, and light activities can be performed when the general symptoms and local pressure pain are relieved. When they get up and move around, they need to wear gradient decompression elastic stockings or use elastic bandage.
What is post-deep vein thrombosis syndrome of the lower extremity?
Post-thrombosis syndrome of lower limb DVT refers to the swelling and edema of the lower limbs after treatment of DVT, but after standing or moving around, it gradually causes varicose veins in the lower limbs, skin pigmentation and sclerosis of the lower legs, and even ulcer formation.
What is the typology of post-deep vein thrombosis syndrome of lower limbs?
According to the different types of original lesions, post DVT syndrome of lower limbs is divided into peripheral type, central type and mixed type accordingly.
How is the treatment of post DVT syndrome different from acute DVT of the lower extremity?
The treatment of post-DVT syndrome of the lower extremity is mainly non-surgical, including elastic bandages or elastic stockings. For central and mixed types, venous bypass or venous diversion may be considered if there is a limited stenosis or occlusion of the deep veins; venous stenting may also be considered.