Pulmonary Embolism

Key points

• Thromboembolic disease, including pulmonary embolism (PE) is the leading cause of direct maternal mortality in the UK.
• The investigations used to diagnose PE carry risks of radiation exposure, reaction to contrast media and false positive diagnosis, are inconvenient for patients and incur costs for the health services.
• This study forms a part of a larger study (DiPEP) aiming to estimate the diagnostic accuracy, effectiveness and cost-effectiveness of strategies for selecting pregnant or postpartum women with suspected PE for imaging.

Surveillance Period

March 2015 – September 2016

Background

Thromboembolic disease, including pulmonary embolism (PE) has been identified as the most important cause of direct maternal mortality in the UK^[1], but can be difficult to diagnose. Pregnant and postpartum women with appropriately diagnosed and treated PE have a low risk of adverse outcomes, so accurate diagnosis can result in substantial benefits. However, the investigations used to diagnose PE (diagnostic imaging with VQ scanning or CT pulmonary angiography) carry risks of radiation exposure, reaction to contrast media and false positive diagnosis, are inconvenient for patients and incur costs for the health services. Clinicians therefore face a difficult choice when deciding how to investigate suspected PE in pregnant and postpartum women, between risking the potentially catastrophic consequences of missed diagnosis if imaging is withheld and risking iatrogenic harm to women without PE if imaging is over-used.

Current practice

Guidelines from the RCOG^[2] recommend that pregnant or postpartum women with suspected PE should all receive diagnostic imaging. Current data suggest that use of this unselective approach is resulting in a low prevalence of PE among those investigated. The most recent studies of suspected PE in pregnancy report prevalence of between 1.4 and 4.2%, while audit data from Sheffield Teaching Hospitals NHS Foundation Trust show a prevalence of 2% among those undergoing imaging. We therefore appear to be exposing 50 women (and fetuses in pregnant women) to the risks of diagnostic imaging for everyone who actually has PE.

These recommendations for pregnant and postpartum women contrast with National Institute for Health and Care Excellence (NICE) guidelines for the general (non-pregnant) population with suspected PE, for whom diagnostic imaging is selectively used based upon structured clinical assessment and D-dimer measurement^[3].

D-dimer: current guidance

Studies of D-dimer in pregnant and postpartum women suggest that high levels of positivity at conventional test thresholds limit the diagnostic value of this test. However, indirect evidence from studies of D-dimer for suspected DVT in pregnancy suggests it may have potential diagnostic value with use of a higher threshold^[4].

The current RCOG guidance states that D-dimer testing should not be performed to diagnose acute venous thromboembolism (VTE) in pregnancy, but does note that a low level of D-dimer in pregnancy is likely, as in the non-pregnant woman, to suggest that there is no VTE (2). Guidelines from the European Society for Cardiology state that in pregnancy D-dimer measurement may be performed in order to avoid unnecessary irradiation, as a negative result has a similar clinical significance as in non-pregnant patients, i.e. indicates that PE is very unlikely^[5].

This study is therefore specifically seeking information about D-dimer levels in women in whom PE is diagnosed, in order that we can further evaluate its diagnostic value and reporters are asked to ensure that this information is obtained where available.

Objective

To use the UK Obstetric Surveillance System to identify all women with diagnosed pulmonary embolism (PE) in pregnancy and postpartum in the UK, and describe their characteristics and diagnostic investigations, and use this information in the wider (DiPEP) study estimating the diagnostic accuracy, effectiveness and cost-effectiveness of strategies for selecting pregnant or postpartum women with suspected PE for imaging.

Case definition

EITHER PE is confirmed using suitable imaging (angiography, computed tomography, echocardiography, magnetic resonance imaging or ventilation-perfusion scan) showing a high probability of PE

OR PE is confirmed at surgery or postmortem

OR a clinician has made a diagnosis of PE with signs and symptoms consistent with PE present, and the patient has received a course of anticoagulation therapy (>1 week)

Funding

NIHR HTA.

Ethics approval

The study has been approved by the Brent REC (study ref 14/LO/1695).

References

1. Knight M, Kenyon S, Brocklehurst P, Neilson J, Shakespeare J, Kurinczuk JJ (Eds), on behalf of MBRRACE-UK. Saving Lives, Improving Mothers' Care - Lessons learned to inform future maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2009-12. Oxford: National Perinatal Epidemiology Unit, University of Oxford, 2014.

2. Greer I, Thomson A. The acute management of thrombosis and embolism during pregnancy and the puerperium (RCOG Green-top guideline no. 37b). London: RCOG, 2010.

3. National Institute for Health and Care Excellence. NICE clinical guideline 144: Venous thromboembolic diseases: the management of venous thromboembolic diseases and the role of thrombophilia testing. 2012. Available from: http://guidance.nice.org.uk/CG144

4. Chan WS, Lee A, Spencer FA, Chunilal S, Crowther M, Wu W, et al. D-dimer testing in pregnant patients: towards determining the next 'level' in the diagnosis of deep vein thrombosis. Journal of thrombosis and haemostasis : JTH. 2010;8(5):1004-11.

5. Konstantinides SV, Torbicki A, Agnelli G, Danchin N, Fitzmaurice D, Galie N, et al. 2014 ESC guidelines on the diagnosis and management of acute pulmonary embolism. European heart journal. 2014;35(43):3033-69, 69a-69k.

Download the Data Collection Form (DCF)

UKOSS Pulmonary Embolism Form