Pulmonary Embolism — Written Clinical Reasoning

SAQ 1 — Diagnostic reasoning and risk stratification (10 marks, 30 minutes)

Prompt: Walk through the diagnostic algorithm you applied, the role of the D-dimer in this patient, and the risk stratification that determines your level of monitoring. ^[1]

Model answer

Pre-test probability and imaging pathway (4 marks): ^[1]

This woman has a Wells score of 7.5, which places her in the PE-likely category (greater than 4). In a PE-likely patient, the correct next step is CT pulmonary angiography directly — a D-dimer has no role here, because even a negative high-sensitivity D-dimer does not have a sufficiently low likelihood ratio to exclude PE at high pre-test probability, and a positive result would simply prompt the CTPA anyway. The CTPA confirmed a large central pulmonary embolus with right ventricular strain, consistent with her presentation. ^[1]

Examiner point: The two-tier Wells score (PE likely greater than 4, PE unlikely 4 or less) was established by Wells et al. (Ann Intern Med 2001). Committing to a structured pre-test probability before testing is mandatory — every subsequent test interpretation depends on it. ^[1]

Why D-dimer was bypassed (2 marks): ^[1]

D-dimer is a rule-OUT test only. It is highly sensitive and poorly specific. Its role is to safely exclude PE in a PE-unlikely patient. In a PE-likely patient, the post-test probability after a negative D-dimer remains above the treatment threshold, so imaging is required regardless. In older patients where a D-dimer IS being used, the age-adjusted cutoff (age multiplied by 10 micrograms/L for age over 50) safely increases the exclusion rate, as shown by ADJUST-PE (Righini et al., JAMA 2014). ^[1]

Risk stratification — she is intermediate-high risk (4 marks): ^[1]

Although she was briefly hypotensive (96 systolic) on arrival, she is now normotensive, which moves her out of the high-risk category. She is, however, intermediate-HIGH risk by the ESC framework: she has right ventricular dysfunction on echo (dilation with septal flattening) AND a positive biomarker (troponin 0.06). Her sPESI is at least 1 (pulse 114, saturation under 95 percent, recent surgery), confirming she is not low-risk and requires inpatient admission. ^[1]

The implication: she needs continuous cardiac monitoring, serial troput measurements, and a low threshold for rescue thrombolysis if she decompensates. She should NOT receive prophylactic (upfront) systemic thrombolysis — the PEITHO trial (Meyer et al., NEJM 2014) showed that tenecteplase in intermediate-risk PE reduced the composite of death or decompensation but at the cost of significantly increased major bleeding and an intracranial haemorrhage rate of around 2 percent. Prophylactic lysis is reserved for high-risk (massive) PE. ^[1]