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]

SAQ 2 — Integrated management plan (10 marks, 30 minutes)

Prompt: Outline your integrated management plan, justifying your anticoagulation choice given her renal impairment, the rationale for monitoring versus reperfusion, and your approach to duration. [1]

Model answer

Immediate management (2 marks): [1]

Continuous cardiac monitoring, high-flow oxygen to keep saturations 94 to 98 percent, IV access, and analgesia (paracetamol first; avoid NSAIDs once anticoagulated). She is already on therapeutic anticoagulation. I would prepare a rescue-thrombolysis plan (alteplase 100 mg over 2 hours) to activate immediately if she becomes hypotensive or shocked. [1]

Anticoagulation choice — navigating the renal impairment (4 marks): [1]

Her eGFR of 32 complicates the DOAC choice. Apixaban remains the best-evidenced DOAC in moderate-to-severe renal impairment and does not require a dose adjustment at 5 mg twice daily in this range, though I would monitor renal function closely. The AMPLIFY regimen (Agnelli et al., NEJM 2013) is apixaban 10 mg twice daily for 7 days then 5 mg twice daily. Rivaroxaban and dabigatran are largely avoided when eGFR is below 30 (dabigatran is predominantly renally cleared and contraindicated; rivaroxaban needs caution). An equally valid alternative in severe renal impairment is a weight-adjusted unfractionated heparin infusion (rapidly reversible and dialysis-filterable), which would be my choice if she were to receive thrombolysis or if renal function deteriorated further. Warfarin is a longer-term option and is unaffected by renal function, but requires an LMWH/heparin bridge of at least 5 days until the INR is at least 2.0 for 24 hours. [1]

My decision: Apixaban 10 mg twice daily for 7 days then 5 mg twice daily, with daily renal function monitoring. I would not reduce her to apixaban 2.5 mg twice daily — that dose reduction requires ANY TWO of age at least 80, weight at most 60 kg, or creatinine at least 133 micromol/L, none of which she meets. [1]

Monitoring versus reperfusion (2 marks): [1]

She is intermediate-high risk. Standard care is anticoagulation plus close monitoring with a rescue thrombolysis plan. Catheter-directed thrombolysis (delivering a low-dose lytic directly into the clot, reducing systemic bleeding) is an option in a centre with interventional capability for selected intermediate-high-risk patients, but is not mandatory. I would not give prophylactic systemic thrombolysis given the PEITHO bleeding signal. [1]

Duration — this is a provoked PE (1 mark): [1]

Her PE was provoked by recent major orthopaedic surgery (total knee replacement 5 weeks ago), a strong transient risk factor. The recommended duration is 3 months. Beyond 3 months, with the surgical trigger removed, the recurrence risk falls to baseline and extended anticoagulation adds bleeding risk without commensurate benefit. I would therefore plan a defined 3-month course. [1]

Communication and follow-up (1 mark): [1]

I would explain the diagnosis and the rationale for anticoagulation, counsel her on bleeding signs (black stools, prolonged nosebleeds, neurological symptoms), and arrange thrombosis clinic follow-up at 2 to 4 weeks to review tolerance and renal function, and at 3 months to confirm cessation. I would advise against long-haul flights for at least 2 weeks and recommend graduated compression stockings for the postoperative period. If she develops persistent dyspnoea at 3 to 6 months, she should return for CTEPH screening with a V/Q scan. [1]