Pulmonary Embolism (PE)

When to Order CTPA or D-dimer

• D-dimer

  • Use as a screening tool in patients with low or intermediate pre-test probability (e.g. Wells score ≤4)

  • Negative D-dimer in a low-risk setting reliably excludes PE

  • High-risk patients require imaging regardless of D-dimer due to its low specificity

  • Age-adjusted D-dimer cut-off is often used for patients >50 years to reduce false positives

• CTPA (CT Pulmonary Angiogram)

  • First-line imaging for moderate to high pre-test probability or if D-dimer is positive

  • Avoid if known contrast allergy or significant renal impairment (consider V/Q scan instead)

  • Can diagnose other pathologies (e.g. pneumonia, pleural effusions) that mimic PE

Expected ECG Changes in PE

• Normal ECG in ~20% of cases

• Sinus tachycardia is most common (~45%)

• T-wave inversion in V1–V3

• S1Q3T3 pattern (~20%)

• RBBB or right axis deviation (up to 20%)

• Non-specific ST-segment and T-wave changes

• ECG findings are neither sensitive nor specific but may prompt further investigation

Notes:

• Consider validated scoring tools (Wells score, Geneva score) to stratify pre-test probability

• PERC (Pulmonary Embolism Rule-out Criteria) can help exclude PE in very low-risk patients

• If clinical suspicion remains high despite negative investigations, consult with a specialist or arrange further imaging

• In pregnant or contrast-allergic patients, a ventilation-perfusion (V/Q) scan is preferred to avoid risks of CTPA

• PE should be managed urgently with anticoagulation if confirmed or strongly suspected

• Persistent tachycardia or unexplained dyspnoea post-PE may require evaluation for chronic thromboembolic pulmonary hypertension

Approach to investigation of pulmonary embolism