Development
A thrombus is a blood clot. Deep vein thrombosis (DVT) usually commences in deep veins in the calf below knee. If left untreated, clot can progressively extend into major veins above the knee or into the pelvis.
There are several potential conditions that predispose to DVT including:
- The contraceptive pill and hormone replacement therapy
- Abnormal blood clotting factors - thrombophilia.
- Varicose veins and their treatment
- Surgical operations particularly lower limb orthopedic procedures,
- Other medical conditions - heart or lung disease, malignancies, etc.
- Injuries to the legs.
- Any reason for prolonged immobilization of the legs.
- Pregnancy
Complications
Pulmonary embolism (PE) is a potentially life-threatening complication. It occurs when part or all of a thrombus breaks away from the deep vein to be carried through the right heart to the lungs. If the clot is small then it may cause no symptoms, but if it is large it can result in chest pain and shortness of breath, cardiac collapse or even sudden death.
Recurrent DVT. Most recurrent clots develop within two years following discontinuation of oral anticoagulation treatment. A blood test called D-dimer can help to determine when to stop taking anticoagulants with least risk of recurrence. If the test has returned to normal then the risk from stopping treatment is less than 10% whereas if it remains elevated then the risk is more than 30%.
Post-thrombotic syndrome. A thrombosed deep vein can reopen restoring normal function, reopen but with destruction of valves causing deep venous reflux, or stay occluded permanently causing deep venous obstruction, Deep venous reflux or obstruction frequently lead to late complications in the leg referred to as the post-thrombotic syndrome:
- Eczema
- Lipodermatosclerosis - damage to skin and fat
- Ulceration
However, most venous leg ulcers are caused by superficial venous reflux.
Diagnosis
A DVT frequently causes no symptoms and is only detected by investigations. If it is more severe then it can cause pain in the calf or thigh and swelling of the leg. The best method to show thrombus in deep veins is by ultrasound. The vein becomes partly or completely incompressible and in time the clotted blood starts to become gray rather than black allowing an approximate idea of how long it has been there. Ultrasound is also the best way to diagnose other conditions that can cause leg pain such as ruptured cysts or muscles.
Prevention
DVT prevention is particularly important for patients about to have an operation. Selected patients are given regular heparin injections for several days. Patients at low risk - those who are undergoing minor surgery and have no clinical risk factors for DVT - require no specific treatment. We have found that heparin is not required in most patients having ultrasound-guided sclerotherapy or endovenous laser ablation. Patients at higher risk of DVT - those undergoing minor surgery if they have clinical risk factors for DVT; those undergoing major surgery, especially orthopedic surgery, even without risk factors; bedbound patients with major medical illnesses - require preventive treatment including heparin injections and leg compression.
Treatment
Treatment is with anticoagulant drugs. Its primary aim is to reduce the risk of PE and recurrent DVT. These drugs do not dissolve clot although the body has a considerable capacity to open up the clotted veins while the patient is having treatment. Occasionally, a severe DVT is treated with other drugs that do dissolve clot or even by surgery, but only if the problem is recognized early.
- In the early stages, the most powerful anticoagulant is heparin which is given by regular injections.
- The limb must be firmly bandaged and it is now recognized that the patient can remain mobile walking, treated as an out-patient in most cases.
- At the same time, a longer acting anticoagulant called coumadin taken by mouth is prescribed. The dosage is regulated by regular blood tests called INR.
Anticoagulant drugs are stopped as soon as is reasonable because of the small risk that they can cause major bleeding. The drug is stopped when it is considered that the risk of PE or recurrent DVT has fallen to an acceptable level. This is usually no earlier than three months after diagnosis and treatment may be continued for longer or even indefinitely in patients with thrombophilia or ongoing medical diseases.
DVT and the Contraceptive Pill or Hormone Replacement
The combined oral contraceptive pill is widely used to prevent pregnancy and reduce gynaecological symptoms. The pill contains a mixture of the hormones oestrogen and progestogen. The original pill first introduced in the 1960s contained high levels of the hormones and had a considerable risk of causing thrombosis. Second and third generation pills now prescribed have less oestrogen and different progestogens. These still have an increased risk of causing DVT but the absolute risk is very low in most circumstances. However, the danger increases when combined with other risk factors such as having an operation or travelling long distances. For every 100,000 women who are not taking the pill, approximately 5-10 will develop a nonfatal blood clot in a year. Taking a second-generation pill increases this number to 15, and taking a third-generation pill increases it to 30. This increase is generally highest when starting the pill for the first time and disappears soon after stopping the pill. The risk of DVT is higher during pregnancy than while taking the second or third generation pill. Women who have had a DVT in the past or who are known to have a clotting disorder should use an alternative form of contraception.
There is no agreement as to whether the pill should be stopped before having an operation. There is a small increased risk of DVT but also a risk of unplanned pregnancy. Women undergoing minor procedures do not need to stop. However, women at increased risk of DVT should discuss the risks and consider stopping the pill 3-4 weeks before the procedure or continuing the pill and having DVT prophylaxis with heparin.
DVT and Thrombophilia
There are a number of abnormal clotting factors that predispose to DVT that are not uncommon in Caucasian and Middle Eastern people. They are collectively known as thrombophilia. They can be detected by blood tests which are indicated if there is a family history of DVT, past history of multiple miscarriages or apparently spontaneous DVT. The tests are too complex, time-consuming and expensive to recommend for all patients.
DVT and Treatment of Varicose Veins
DVT can occur after any form of treatment. Studies have shown that it occurs in 5% after surgical stripping, about 3% after ultrasound-guided sclerotherapy and rarely after endovenous laser ablation. However, most of these are confined to veins below knee, are not associated with symptoms and cause no apparent later harm. This potentially serious complication is very uncommon if the protocol of compression and regular daily walking is followed.
There are conflicting views as to whether or not to continue or stop the oral contraceptive pill prior to treatment. Hormones or treatment for varicose veins each slightly increase the risk of DVT and it is possible that the combination of the two further increases the risk although this has not been proven. However, injecting a sclerosant in the early stages of unrecognised pregnancy due to stopping contraception might harm the foetus leading to discussion for the need for termination. Accordingly, no advice can be given as to the best course of action that is appropriate for every patient. If oral contraception is ceased, it is imperative to ensure adequate alternative methods of contraception until treatment is completed. If oral contraception is continued, then the theoretical risk of thrombosis must be accepted. Similar considerations apply to hormone replacement therapy. Female patients are asked to sign a disclaimer as to whether to cease or continue oral contraceptives or hormone replacement therapy prior to treatment. Hormones can be recommenced at about one week after treatment is completed.
In a small number of patients at increased risk for DVT, we give heparin injections to limit the risk, continued daily for 7-10 days after treatment. If so, the patient will be supplied with a kit to store used syringes and a video to explain how to give the injections.
DVT and Orthopaedic Operations
Without measures to prevent thrombosis, there is a high incidence of DVT (45-50%) and PE (3-5%) after hip or knee joint replacement or surgery for fractured hip. This can be markedly reduced by prophylaxis although the risk is still present. It is known that the risk extends well beyond the time of discharge from hospital and there is evidence that prophylactic heparin should be continued for up to 4 weeks.
