This blog will discuss the use of computed tomography pulmonary angiography (CTPA) in patients suspected of having pulmonary embolism (PE) with evidence from relevant literature. It is an area of imaging that is of interest to me because I find the heart a fascinating organ to study.
PE is a blood clot in the blood vessels that carry blood from the heart into the lungs which can be deadly if not caught in time. The clot in the legs is known as deep vein thrombosis (DVT) (Morley et al, 2015). Symptoms include chest pain, shortness of breath and coughing up mucus or blood which can be caused by conditions such as cancer, heart failure, pregnancy and weakness in the wall of a blood vessel (NHS Choices, 2015). Other than CTPA, there are other diagnostic imaging procedures undertaken in order to diagnose PE in secondary care. These include chest x-ray, ventilation-perfusion scan, electrocardiography and lower limb compression venous ultrasound (National Institute of Health and Care Excellence, 2015a).
The National Institute for Health and Care Excellence (NICE, 2015b) guidelines say that patients suspected of having PE have CTPA immediately or are given anticoagulant therapy if it is not available immediately. In the case of pregnancy, contrast allergy or severe renal dysfunction the recommended pathway is ventilation-perfusion scan. This follows the review undertaken by Condliffe (2016), where first line investigation method after clinical examination was CTPA.
According to Walen et al. (2016) the specificity value of CTPA ranges between 81% and 98%, which makes it very valuable in excluding PE. However, the sensitivity values range from 60% to 100% which is a significant difference. The literature they have used as evidence is quite old, dating back to 1993. However, this is not discussed further as the aim of this study was to examine the diagnostic value of CTPA by influencing the behaviour of referrers. They explained that documenting Wells scores and D-dimer test scores on the request form increased the diagnostic yield from 23 % to 29.6 %. This is an important factor to consider. Research into diagnostic protocols of PE in the UK could be useful as this study was conducted in the Netherlands.
According to Mortensen and Gutte (2014) the sensitivity of CTPA was recorded to be 94 % and specificity value as 93 % using various sources as evidence. However, the authors have used sources that are over 10 years old. Considering this was published in 2014, it raises the question of whether they failed to include more up to date research to confirm these values. Furthermore, the diagnostic accuracy of CTPA is confirmed by Laugharne et al. (2013) using sources from 2005. This reveals a trend that would suggest more recent research has not been undertaken. They also mention that no CTPA examination was undiagnostic suggesting that the use is valid. While this study was conducted in the UK, it may not be applicable to the wider population as the sample included only elderly patients with the majority being female. They also justify the use of CT due to its availability in hospitals.
There was some debate on the topic of overdiagnosis and the impact on patients and healthcare providers. According to Wiener et al. (2013) small blood clots do not pose a significant risk and therefore do not need treatment. However this is challenged by Quantrill (2013), as he cites Wiener as acknowledging the drop in mortality by 3% after the introduction CTPA in diagnostic protocols. It is important to mention that Wiener used data on the trends in the US and this may not be generalisable to the UK or the rest of the world. Quantrill (2013) also points out that untreated PE can lead to severe health complications and death, highlighting the importance of offering treatment. The basis of Wiener’s (2013) argument is that the emboli are reabsorbed into the body without any clinical manifestations. Quantrill (2013) counters this by saying the effects of anticoagulation therapy is low enough to justify the benefit of giving it.
PE is treated with anticoagulant medicines and the amount of the medicine is measured regularly to check the dose is correct to prevent blood clots from reforming (NHS Choices, 2015).
Condliffe, R. (2016) Pathways for outpatient management of venous thromboembolism in a UK centre. Thrombosis Journal [online] 14 (1) [Accessed 14 November 2017].
Laugharne, M.J., Paravasthu, M., Preston, A., Hill, K.O. (2013) CT pulmonary angiography in elderly patients: Outcomes in patients aged > 85 years. Clinical Radiology [online] 68 (5) pp. 449-454 [Accessed 14 November 2017].
Mortensen, J., Gutte, H. (2014) SPECT/CT and pulmonary embolism. European Journal of Nuclear Medicine and Molecular Imaging [online] 41 (sup1) pp. 81-90 [Accessed 14 November 2017].
National Institute for Health and Care Excellence (2015a) Pulmonary embolism – Scenario: Managing suspected pulmonary embolism. Available at: https://cks.nice.org.uk/pulmonary-embolism#!scenario [Accessed 14 November 2017].
National Institute for Health and Care Excellence (2015b) Venous thromboembolic diseases: diagnosis, management and thrombophilia testing. Available at: https://www.nice.org.uk/guidance/cg144/chapter/Key-priorities-for-implementation [Accessed 14 November 2017].
Quantrill, S.J. (2013) Risk-benefit ratio favours all pulmonary emboli, no matter how small. The British Medical Journal [online] 347 (5121) [Accessed 14 November 2017].
Walen, S., de Boer, E., Edens, M.A., van der Worp, C.A.J, Boomsma, M.F., van den Berg, J.W.K. (2016) Mandatory adherence to diagnostic protocol increases the yield of CTPA for pulmonary embolism. Insights into Imaging [online] 7 (5) pp. 727-734 [Accessed 14 November 2017].
Wiener, R.S., Schwartz, L.M., Woloshin, S. (2013) When a test is too good: how CT pulmonary angiograms find pulmonary emboli that do not need to be found. The British Medical Journal [online] 347 (7915) [Accessed 14 November 2017].