This document discusses the patient pathway for suspected non-massive pulmonary embolism (PE) at the authors' trust. It utilizes a pre-test probability assessment and D-dimer testing before imaging. If the pre-test probability is low, a negative D-dimer can exclude PE without imaging. For higher probability or positive D-dimer, CT pulmonary angiogram is the preferred imaging test. The pathway can safely exclude PE in around a quarter of patients without unnecessary imaging. The document also discusses considerations for different imaging options and the need to investigate patients with unprovoked PE for underlying malignancy.

1. Illustration and Evaluation of the Patient Pathway for Suspected Non-Massive Pulmonary Embolism
Introduction
National guidelines for suspected non-massive pulmonary embolism (PE) recommend pre-
test probability (PTP) assessment and D-dimer assays before imaging (Bayes et al, 2011).
This poster illustrates and evaluates the patient pathway for presentations of suspected
non-massive PE at the authors Trust, which employs the algorithm from NICE clinical
guidance 144 (fig. 6). The value of following the various steps of the pathway will be
discussed, and their applications justified alongside alternative techniques.
Discussion
Common risk factors for a PE include malignancy, previous emboli, and immobilisation or
surgery, and presenting symptoms are non-specific (Shujaat, Shapiro, and Eden, 2013).
Clinical assessment alone is not sufficient, yet performing imaging on all suspected cases
is not justifiable (Bayes et al, 2011). Being that as few as 10% of suspected PEs are
positive, and since they can be excluded by other means, utilising the guidance can save a
quarter of patients from imaging studies (Shujaat, Shapiro, and Eden, 2013).
CT pulmonary angiogram (CTPA) has replaced other techniques as the gold standard
(Shujaat, Shapiro, and Eden, 2013). With specificity and sensitivity at 100% (Subramaniam
et al, 2006), the rapid acquisition of high contrast images, the availability, and non-
invasive nature, CT is safe to exclude a PE as a sole imaging test. Experts agree that it has
fulfilled conditions to replace conventional angiography as the reference standard, and
has demonstrated low numbers of inadequate studies varying from 0.9-3% in large
cohorts (Huisman and Klok, 2009). Fig.1 and fig.2: positive PE visualised on CTPA
3. Multi detector CT (MDCT) advances have dramatically
increased PE diagnoses (Remy-Jardin et al, 2007), and the
PTP Score
D-Dimer
CTPA
1. The two level simplified and dichotomised Wells score
(Wells et al, 2000) utilised at the authors Trust (fig. 5)
categorises a PE as being ‘likely’ or ‘unlikely’, based on
clinical features and risk factors (Huisman and Klok,
2009). With a result of 4 points or greater proving that a
PE is likely, immediate imaging should be offered. Those
with an unlikely result should first have a D-dimer assay
performed (Yin et al, 2012).
Other PTP scoring tools: see appendix 1.
2. D-dimer is a fibrin degradation product detected by
blood test. It is elevated in pregnancy, infection, liver
complications, malignancy, advanced age, thromboembolic
disease and post-surgery or trauma (Yin et al, 2012). Due to
being detected in multiple instances, its specificity is
reported to be 34%, however, with sensitivity of 90%, a
negative D-dimer and low PTP excludes a PE (Shujaat,
Shapiro, and Eden, 2013). The cut off for serum D-dimer is
500mg/l, below which a PE can be excluded (Vossen et al,
2012). In cases with a raised D-dimer, imaging should be
performed, as evidence shows a clear correlation between
elevated D-dimer, and PEs confirmed radiologically (Shah
et al, 2013).
Adjusting D-dimer assay for age: see appendix 2.
The Diagnostic Pathway Imaging Considerations
7. Availability of Imaging: In the case of a likely PTP or raised D-dimer when CT or
VQ scanning is not immediately available, parenteral anticoagulant therapy should
be given, followed by imaging, once it becomes available. (NICE, 2012).
9. Overuse of Imaging: Finding clinically insignificant emboli or incidental diagnoses
demonstrate that imaging is being adopted without consideration of the risks (Costa
et al, 2014). An increase in the number of deaths due to contrast induced
nephropathy, radiation-induced cancers, and anticoagulation of false-positive results
is well reported, with such aggressive testing shifting the risk for a few patients with
PE to many without (Shah et al, 2013).
8. Alternative Diagnoses: While an alternative or incidental diagnosis may be found
on a CTPA, it is not its intended application, and VQ scans are not useful for this
purpose (Costa et al, 2014). A limited CTPA which just images the main pulmonary
arteries, and a simple report stating ‘PE present’, ‘PE absent’ or ‘Non-diagnostic’, is
employed at the authors Trust for all CTPAs. This acts as a deterrent for requests for
alternative diagnoses, and to encourage the correct use of the algorithm, ultimately
saving healthy patients from irradiation (Chandra et al, 2013).
10. Dose Concerns: Radiosensitive organs such as the thyroid, breasts, and lungs are
irradiated during a CTPA. A 20 year old woman is at a 68% greater risk of breast
cancer manifestation by 35 years following a CTPA, than a 20 year old woman who is
not scanned, with a dose of 20mGy being delivered to each breast. However, at the
authors Trust, CTPA is preferred over VQ scans in pregnancy which give a dose of
0.29mGy, as while the mother receives a greater dose from the CTPA than the VQ,
the opposite is true for the foetus. (Huisman and Klok, 2009).
4. Ventilation/Perfusion (VQ) Scan: The VQ scan is used as an alternative for patients
with contraindications to contrast media (Shujaat, Shapiro, and Eden, 2013) and due it
its overall lower dose, it may be favourable in pregnancy (Bayes et al, 2011). It has a
positive predictive value of 85-90%, but has non diagnostic readings of 28-46%
(Huisman and Klok, 2009). Guidance recommends VQ for patients not suited for CTPA
due to compromised renal function (estimated glomerular filtration rate at the
authors trust must be >45), or for limiting radiation dose. (NICE, 2012). Fig.3 ‘V’ scan
and fig. 4 ‘Q’ scan demonstrating a PE.
5. Compression Ultrasound (CUS) of lower limbs: CUS is performed if the VQ scan is
non-diagnostic or a CTPA was performed on single slice scanner. A normal CUS with an
unlikely PTP rules out a PE, and with a normal CUS and a likely PTP, a D-dimer assay
should be performed. If this is normal, then PE is ruled out. A raised D-dimer should
have repeat CUS in 7 days (Huisman and Klok, 2009).
Other imaging techniques: see appendix 3.
6. Investigations for Malignancy: At the authors Trust, patients who have an
unprovoked PE are recommended to have further investigations for malignancy, which
involves physical examination, a chest radiograph, various blood tests and urinalysis. In
patients over 40, a venous abdomen pelvis CT scan (with an arterial chest added if the
apices and bases were omitted in the CTPA) is offered, and a mammogram in females.
This recommendation is supported in the NICE guidance 144 (NICE, 2012)
Clinical Feature Points
Clinical symptoms/signs of DVT
(leg swelling and pain on palpation of
deep veins)
3
Alternative diagnosis less likely than
PE
3
HR > 100bpm 1.5 1.5
Immobilisation (>3 days) or surgery in
past 4 wks
1.5
Previous DVT/PE 1.5
Haemoptysis 1
Malignancy (on treatment, treated in
last 6m or palliative)
1
Conclusion
This poster illustrated and evaluated the patient pathway for presentations of suspected
non-massive PE at the authors Trust, which utilises clinical guidance from NICE. It has
been discovered that while imaging is invaluable for PE exclusion or diagnosis when
necessary, it is being overused when non-imaging tests can be conclusive. Evidence has
shown that following the guidance on PTP and D-dimer algorithms can safely exclude the
diagnoses, saving a quarter of patients from unnecessary imaging. It has been discussed
that patients with unprovoked PE should be followed up with investigations for
malignancy, utilising recommendations from NICE.
Fig. 1 Fig. 2
Fig. 3 Fig. 4
Fig. 5 Wells PTP Score
(Wells et al, 2000)
Axial and coronal CTPA slices from the authors Trust showing left and right sided PEs (yellow circles)
Images courtesy of the authors Trust
Ventilation (V) scan and Perfusion (Q) scan showing images of a PE
Images courtesy of the authors Trust
Fig. 6 PE Diagnostic Algorithm
Courtesy of the authors Trust
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2. References
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thromboembolism assessment?” Journal of postgraduate medicine, vol. 57, no. 2, pp. 109-114.
Chandra, S., Sarkar, P.K., Chandra, D., Ginsberg, N.E. & Cohen, R.I. 2013, "Finding an alternative diagnosis does not justify increased use
of CT-pulmonary angiography", BMC Pulmonary Medicine, vol. 13, pp. 9-9.
Costa, A., Basseri, H., Sheikh, A., Stiell, I. & Dennie, C. 2014, "The yield of CT pulmonary angiograms to exclude acute pulmonary
embolism", Emergency Radiology, vol. 21, no. 2, pp. 133-141.
Huisman, M.V. & Klok, F.A. 2009, "Diagnostic management of clinically suspected acute pulmonary embolism", Journal of Thrombosis &
Haemostasis, vol. 7, pp. 312-317.
National Clinical Guideline Centre 2012, "Venous thromboembolic diseases: the management of venous thromboembolic diseases and
the role of thrombophilia testing.
Clinical Guideline Methods, evidence and recommendations", National Institute for Health and Clinical Excellence.
Remy-Jardin, M., Pistolesi, M., Goodman, L.R., Gefter, W.B., Gottschalk, A., Mayo, J.R. & Sostman, H.D. 2007, "Management of suspected
acute pulmonary embolism in the era of CT angiography: a statement from the Fleischner Society", Radiology, vol. 245, no. 2, pp.
315-329.
Shah, K., Quaas, J., Rolston, D., Bansal, S., Bania, T., Newman, D., Wiener, D. & Lee, J. 2013, "Magnitude of D-dimer matters for
diagnosing pulmonary embolus", The American Journal of Emergency Medicine, vol. 31, no. 6, pp. 942-945.
Shujaat, A., Shapiro, J.M. & Eden, E. 2013, "Utilization of CT pulmonary angiography in suspected pulmonary embolism in a major urban
emergency department", Pulmonary Medicine, , pp. 1-6.
Subramaniam, R.M., Chou, T., Swarbrick, M. & Karalus, N. 2006, "Pulmonary embolism: accuracy and safety of a negative CT pulmonary
angiogram and value of a negative D-dimer assay to exclude CT pulmonary angiogram-detectable pulmonary embolism",
Australasian Radiology, vol. 50, no. 5, pp. 424-428.
Vossen, J.A., Albrektson, J., Sensarma, A. & Williams, S.C. 2012, "Clinical usefulness of adjusted D-dimer cut-off values to exclude
pulmonary embolism in a community hospital emergency department patient population", Acta radiologica, vol. 53, no. 7, pp. 765-
768.
Wells PS, Anderson DR, Rodger M, Ginsberg JS, Kearon C, Gent M et al. Derivation of a simple clinical model to categorize patients
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83(3):416-420.
Yin, F., Wilson, T., Della Fave, A., Larsen, M., Yoon, J., Nugusie, B., Freeland, H. & Chow, R.D. 2012, "Inappropriate use of D-dimer assay
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Bounameaux, H. 2010, "Contemporary management of pulmonary embolism: the answers to ten questions", Journal of internal
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3. Appendices:
Appendix 2: Adjusting D-dimer for age
Typically, the cut off value for serum D-dimer is 500 mg/L, below which the diagnosis of PE can be ruled out. However one study concluded that this could be increased
to 1000 mg/L without affecting its sensitivity, safely eliminating the diagnosis in more patients, and further reducing the use of imaging (Bowman, Johns and Karstaedt,
2011). A PE is more likely to occur in the elderly, and multiple comorbidities associated with aging can mimic a PE clinically. Hence, the argument exists regarding the
usefulness of this value for the elderly, with evidence showing that a PE may be excluded in as few as 5% of patients over 80, compared with 60% in those under 40,
using this D-dimer value (Bounameaux, 2010).
Appendix 1: Other PTP scoring tools
“Geneva score (original and revised) - The original Geneva score is based on seven clinical factors and required interpretation of the findings on chest X-ray and arterial
blood gases. The revised Geneva score covers eight parameters in 3 clinical areas: risk factors, symptoms and clinical signs. Each of these is given 1 to 5 points
accordingly. This gives a possible score range of 0 to 25. A score of 11 or higher is classified as ‘high risk’ of PE; a score of 4 to 10 as ‘intermediate risk’ and a score of 0
to 3 as ‘low risk’.
Charlotte rule - Patients with suspected PE (based on empiric clinical assessment) are stratified into low-risk and high-risk (pre-test probability groups). Patients are
classified as high risk if they have at least two of the following:
• Age greater than 50
• Heart rate greater than systolic blood pressure
• Surgery in the past month
• Unilateral leg swelling
• Haemoptysis
• Unexplained oxygen saturation less than 95% on room air.”
(National Clinical Guideline Centre 2012, p 69.)
Appendix 3: Other imaging techniques
Pulmonary Angiogram (PA)
The PA was the traditional gold standard (Yin et al, 2012) reference imaging method (Huisman and Klok, 2009). However it is Invasive and resource demanding and no
longer routinely performed (Bounameaux, 2010).
Magnetic Resonance Angiography (MRA)
MRA has potential as an alternative for those unsuited to iodinated CM (Huisman and Klok, 2009), due to shortened acquisition times and improved spatial resolution.
Combined perfusion and non-contrast/contrast scans have a specificity of 93% (Remy-Jardin et al, 2007), however, 25% of scans are inadequate (Bounameaux, 2010).