Your personal risk for pulmonary embolism
Posted on 2 May 2017
A pulmonary embolism occurs when a blood clot forms in the body, becomes dislodged, travels though the body’s venous system, and then becomes lodged in one of the blood vessels in the lungs. A Mediclinic haematologist explains the combination of risk factors, including genetics, and how they screen for these.
Despite it not sounding like a run-of-the-mill condition, pulmonary embolism (PE) is one of the most common cardiovascular diseases. Current statistics are not available for South Africa, but in the US up to 1-2 people out of every 1 000 is affected, and estimates suggest between 60 000 and 100 000 patients die every year as a result of either a pulmonary embolism or a deep vein thrombosis (DVT).*
What exactly is a pulmonary embolism?
Dr Jacques Janse van Rensburg, a haematologist at Mediclinic Vergelegen, says there are different types of embolism, which is an obstruction of a vein or artery. It could be a piece of fat, an air bubble, or more commonly a blood clot.
‘Nine times out of 10 when we’re talking about a pulmonary embolism, we mean a blood clot that has formed in the body and has moved into the lungs through the blood stream,’ says Dr Janse van Rensburg.
The circulatory system in the body comprises of the arterial system, that carries blood away from the heart and is responsible for delivering oxygen rich blood to the body, and the venous system which returns blood to the heart and lungs. Strokes can be a result of an embolism on the arterial side, where an embolus in the blood flows away from the heart to the brain. Embolisms are however not the only cause of a stroke.
‘In a pulmonary embolism, we’re referring to the venous circulation,’ Dr Janse van Rensburg explains. ‘That means all the blood that has to come back to the heart, which pumps it to the lungs. The lungs then add oxygen to the blood that goes to the left side of the heart, which pumps it into the rest of the body. In the process the lungs act as a filter for the clot.’
A PE is a blood clot that forms anywhere in the parts of the body where blood has to flow back to the right side of the heart – it could be in the legs, abdomen, close to the heart or even inside the lung.
*Deep vein thrombosis (DVT) is where the blood clot usually develops in the deep leg vein. DVT and PE together are known as venous thromboembolism (VTE).
What causes a pulmonary embolism?
Virchow’s Triad is named after the German physician who listed the three physiological factors that can contribute to a pulmonary embolism:
- Stasis, or low blood flow: ‘When blood doesn’t flow it clots – it’s programmed to do that,’ says Dr Janse van Rensburg.
- Hyper-coaguability: This is an abnormality in the clotting of the blood that can be inherited or acquired (for example hormonal manipulation through the use of the contraceptive pill).
- Endothelial injury: This is damage to the inner lining of blood vessels. ‘There are a number of factors that cause inflammation on the inside of blood vessels that can also lead to a clot,’ Dr Janse van Rensburg explains.
Dr Janse van Rensburg refers to the normal flow of blood in the body as a balance that needs to be maintained. When a patient presents with a PE, he would first rule out stasis or endothelial injury, which could have provoked an imbalance that led to a clot. Once those two contributing factors have been ruled out, Dr Janse van Rensburg would then look at hyper-coaguability.
He says the risk of getting a clot increases as you age, but you have to get past a threshold for your balance to be tilted enough to form a clot.
‘I get patients referred to me who are 20 years old and they’ve had a clot. Firstly they were in a cast, and they were also on hormonal manipulation. So their scale is tilted, but the question is this: Many patients on hormonal manipulation are in casts and don’t get a clot, so what causes some patients’ risk to be increased, in other words, what pushes them over the threshold?’
Where hyper-coaguability is in question, there are two risk categories: family history or unknown.
If a patient’s direct family member has had an unprovoked clot, regardless of whether tests show anything is wrong, that patient has inherited something that will put them at double the risk of developing a clot in a high-risk situation.
High-risk situations include:
- Long flights
- Taking certain medication
- During and after pregnancy – when oestrogen levels are higher
- Any acute illness (e.g. pneumonia) or chronic inflammatory conditions (e.g. HIV, lupus, etc.)
Who should get tested?
According to Dr Janse Van Rensburg, genetic testing is limited. ‘Even if we test everything we know of, there are a number of factors we don’t know about.’
If a patient presents with an unprovoked clot in the area of the leg below the knee, they will undergo a consultation examining family, lifestyle and medical history. Such patients will not necessarily be labeled hyper-coagulable, or require genetic testing.
‘But if it’s an unprovoked clot from the knee up, to the lungs, or in an abnormal area (such as arm or bowel), they need to be investigated. And as part of the investigation, we do genetic testing,’ Dr Janse Van Rensburg adds.
There are a number of known thrombophilias (embolisms) that can be tested. These will also determine any other associated risks and inform whether (and which) family members should possibly also be tested. Whether or not those tests come back positive, the patient will have to be on blood thinners indefinitely.
Patients who present with a provoked clot, for example after having been on bed rest, in a cast, and who were not given blood thinners, will not necessarily require testing. Above all, each case must be individualised.