Pulmonary Embolism (PE) is a life-threatening medical condition in which a substance in the bloodstream (a clot or a fatty embolism) creates a blockage of an artery in the lung or in one of the blood vessels leading to it. This blockage may lower levels of oxygen in the blood and cause damage to other organs in the body – some of which may be irreversible. In severe cases, the embolism may lead to a sudden overload on the heart and cause death.
One of the key risk factors for PE is the existence of a large blood clot or several small ones in the deeper veins which are situated in the lower extremities. This type of clotting is called Deep Vein Thrombosis, or DVT. Even when DVT does not lead to a PE, it may affect the lower limbs and cause damage while presenting swelling, pain and infection.
Upon diagnosing DVT, it is necessary to compress the afflicted area and make lifestyle changes to prevent development of a PE, such as use of blood thinners, nutritional changes, and increasing mobility – as one of the key risk factors for DVT is prolonged immobility and lack sufficient blood flow (e.g. as a result of long flights, bed rest). Other factors that increase the risk of DVT are surgery (especially lengthy procedures), family history of DVT, and obesity, among others.
Despite the high risk and the fact that there are symptoms associated with PE, many cases of PE are diagnosed at a very late stage, sometimes even after presenting with symptoms at the hospital. A study conducted among PE patients in Spain several years ago estimated that one third of the 436 patients in the study received a delayed diagnosis of PE. Another study conducted in France in 2018 found that at least one in six patients diagnosed with a PE was diagnosed after a delay of seven days or more. According to an estimate by the American CDC, 60,000 – 100,000 Americans die every year as a result of pulmonary embolism.
What causes misdiagnosis or delayed diagnosis?
Pulmonary embolism has a number of symptoms, including: coughing up blood, shortness of breath, chest pain and fainting. But some of these symptoms are not exclusive to PE and may present in patients with chronic lung disease such as asthma or COPD (Chronic Obstructive Pulmonary Disease). This duality may mislead the diagnosing physician and lead to misdiagnosis of PE as an exacerbation of an existing medical condition or even pneumonia.
The absence of symptoms associated with PE may also cause a delay in diagnosis. Patients who do not report shortness of breath or faintness may be sent home without physicians suspecting they may develop a PE. Patients from lower socio-economic backgrounds may refrain from seeking medical attention, whether due to ignorance of the relationship between symptoms and risks, because they are smokers (so shortness of breath or coughing are not perceived as extraordinary), or lack of financial resources.
In addition, medical imaging that reveal PE indicators may also be misinterpreted as lung infiltrates (an area of the lung filled with inflammatory liquid, seeming lighter than the dark area of the lung) and may mislead physicians, causing them to diagnose an infection without ruling out PE.
Although the diagnosis of PE focuses on blood clots close to the lungs, tests should be expanded to look into the bloodstream and the limbs in order to identify clots that may cause DVT in the future. Physicians should be aware of the two phenomena and the connection between them in order to get a clinical picture that is accurate and allows for a quick reaction. In both cases, the treatment would involve anticoagulant medication such as warfarin, heparin, and others.
How is DVT diagnosed?
The leading clinical model for diagnosing DVT is called the Wells Model which predicts the likelihood of a DVT to occur in the future. As part of this test, the blood vessels in the limbs are examined, and a relevant medical history is taken. The physician fills out a questionnaire that weights the clinical examination with the information received and calculates whether there is a high or low risk of DVT.
After receiving the result of the Wells Test, a blood test called D-Dimer is taken. This is an auxiliary diagnostic test and is not used for determining a diagnosis on its own. Even after confirming or ruling out the diagnosis, there is need for further supporting tests to reach the final diagnosis.
Another diagnostic measure at the physician's disposal is imaging (lung and limb x-rays, CT) to help identify blood clots. However, even these do not allow for a full diagnosis of a PE. Studies have shown that among patients who were sent home after being underdiagnosed (i.e. they were discharged and later developed a PE), CT tests showed distal clots (far from the heart) and not central clots (close to the heart), which are more associated with PEs. This means that even distal clots could serve as warning signals. In addition, conventional imaging tests cannot distinguish between old clots, which do not pose an immediate risk of PE, and new and dangerous clots. A clinical study held in 2019 offers a potential solution to this issue: a tracer called 18F-GP1, injected into patients undergoing PET-CT scans, is attracted to "living" blood platelets and can indicate whether the blood clot is relatively new or has been there for a while. The tracer managed to identify, characterise, and detect new clots with a high risk of PE and other complications.
An initial study of 20 patients suffering from acute DVT or PE showed that the tracer managed to identify clotting foci in all patients. Additionally, it recognised new clotting activity in the legs of 12 patients – activity that was not recognised using traditional imaging devices.
Prompt diagnosis of DVT or PE may prevent harm to the limbs, damage to the lungs, and can save lives. To this end, physicians and caretakers must be informed and aware of all symptoms and risk factors of the condition. Shortness of breath or chest pain that appear after a long flight or childbirth – require immediate attention. Patients have to make sure that doctors have performed thorough checks to rule out all symptoms to ensure they do not join the dangerous statistics of those who are diagnosed too late.