Deep Vein Thrombosis (DVT)
Deep Vein Thrombosis (DVT) usually provokes an element of fear in most because it is known to carry the risk of blocking the blood vessels to the heart and causing death. This is known as Pulmonary Embolus (PE) and is the main reason for treating DVT as an emergency. Importantly, this is not the only risk, but it may lead to lifelong problems in the leg if not treated timeously and adequately. These problems include swelling, pain, skin changes and wound formation known as the “Post Thrombotic Syndrome’.
Thus, early treatment of deep vein thrombosis is absolutely essential.
DVT is typically thought to occur in bedridden, immobile, overweight patients, or in patients with cancer or post-surgery. However, we are seeing DVT more frequently in healthy, younger patients including athletes.
We need to ask ourselves why?
What is Deep Vein ThrombosisVeins are the blood vessels that take deoxygenated blood back to the heart to get more oxygen. If there is a change in flow the blood may clot causing a thrombosis. This then prevents blood from leaving the leg, with resultant swelling of the leg. The clot may then propagate causing more extensive symptoms with the risk of a piece breaking off and going to the lung. Veins have valves within them as they carry blood against gravity. Thus, the clot may sit on these valves with the risk of damaging them permanently.
There is an uncommon risk of stopping the arterial inflow to the leg with resultant massive swelling and the risk of gangrene and limb loss in extreme cases, although this is quite rare.
What are the symptoms of a DVT?
Symptoms will depend on which veins are affected in the leg.
If the thrombus involves one of the calf veins only, one may experience some mild or intermittent pain, or may not be aware of it at all.
If the vein behind the knee or in the thigh is blocked this will cause swelling of the calf which will be painful.
If the pelvic veins are affected, then the thigh may be swollen as well. This is important to note, as these patients require surgery to remove some of the thrombus load.
What causes DVT?
Virchows triad has been explained for centuries reviewing the cause of DVT. To prevent thrombosis, one needs good blood flow, in an adequate conduit (i.e. the blood vessel), and correct blood consistency. If any of these are altered there is a risk of thrombus.
Stasis refers to a change in the blood flow.
Traditionally, this occurs in patients with prolonged bed rest, stroke patients or prolonged travel. Some patients have congenital anomalies which become obvious during pregnancy, after spinal surgery or later in life when the vessel wall structure changes. This can result obstruction of blood flow out of the leg.
Vessel wall injury or vascular damage traditionally refers to injury to the vein wall by means of external trauma or placement of intravenous lines or some sort of inflammation. In athletes, this refers to physical trauma, strain or injury as well as repetitive microtrauma.
Hypercoagulability which may lead to thrombus. This refers to any cause which leads to an increased tendency to clot from ‘thickened blood’. There are, again congenital clotting defects which may predispose one to clotting. However, often they do only predispose one and another insult is necessary to actually cause the clot. Pregnancy, cancer, infection, trauma and some autoimmune diseases may cause a hypercoagulable state predisposing one to clotting.
Why do we treat DVT?
- Medical Treatment
- Surgical Treatment
How do we diagnose DVT?
The best investigation we have is to duplex Doppler ultrasound. This is like an ultrasound scan (such as done in pregnancy). It is non-invasive and safe. This can look at the blood vessels and confirm if there is thrombosis within them.
A blood test, called a D-dimer, may also be done (especially if there is no duplex Doppler ultrasound available).This is more a test of exclusion – i.e. if it is normal one will not have a DVT. However, if it is raised it may indicate that a thrombosis is present, but it can be raised for other reasons as well.
How is DVT treated?
The medical treatment of DVT involves certain blood thinners.
Typically we start with an injectable form of heparin and overlap this with the well known warfarin. Warfarin has been a difficult drug to manage as people metabolise it differently and it interacts with some food and other medications and needs continuous monitoring.
Newer oral tablets are now on the market that can be taken without the intense monitoring except in certain circumstances such as renal failure, pregnancy and obesity.
How long must treatment be continued
Treatment is individualised. However, in general:
- A known cause of DVT will be treated for 3 months.
- An unknown cause will be treated for at least 6 months, often longer.
- A pulmonary embolus will be treated for at least 1 year, depending on the cause.
- A risk factor that cannot be altered, such as cancer, will be treated lifelong.
Surgical intervention is reserved for ileofemoral DVT - that is DVT starting in the pelvis causing thigh and calf swelling.
The reason for this is that reducing the thrombus load will decrease the risk of future leg problems, most importantly the Post-Thrombotic Syndrome. The surgery typically involves instilling a thrombolytic agent – drug that dissolves clot, and then actually sucking the clot out.
Often, especially if on the left side, the cause of the DVT from the pelvis is a narrowing of the vein. If this is detected, then a stent may be placed at the same time.
Should the patient present with thrombus, emergent pharmacomechanical thrombolysis can be performed to remove the clot. This involves placing a catheter into the iliac vein and instilling a drug that breaks down the clot. Thereafter, a catheter can manually suck the clot out. This helps reduce the risk of developing post thrombotic syndrome.