What is the most appropriate investigation for a post-colostomy patient 6 days after surgery, presenting with palpitations, severe shortness of breath, atelectasis in the lower lobe, and right bundle branch block (RBBB) on electrocardiogram (ECG), with no signs of deep vein thrombosis (DVT) or leg edema?

CT Pulmonary Angiography (CTA) is the Most Appropriate Investigation

In a post-operative patient 6 days after colostomy presenting with palpitations, severe shortness of breath, lower lobe atelectasis, and new RBBB on ECG, CT pulmonary angiography (CTA) is the definitive investigation of choice to diagnose pulmonary embolism. 1, 2

Clinical Context and Risk Assessment

This patient presents with a high-risk scenario for pulmonary embolism (PE):

• Recent major abdominal surgery (colostomy 6 days prior) is a well-established risk factor for venous thromboembolism 1, 3
• Cardiopulmonary symptoms (palpitations and severe dyspnea) combined with new RBBB on ECG strongly suggest acute right ventricular strain from PE 1
• Post-operative day 6 falls within the highest-risk period for PE, as most fatal emboli occur within 30 days of surgery 3
• The absence of leg edema or tenderness does not exclude PE, as the majority of PE patients lack clinical DVT signs 1, 2

Why CTA is Superior to Doppler Ultrasound

CTA is the recommended initial lung imaging modality for non-massive PE and provides multiple diagnostic advantages over Doppler ultrasound in this clinical scenario: 1, 2

Direct Visualization of Pulmonary Vasculature

• CTA demonstrates sensitivity and specificity of 96-99% for PE, detecting emboli down to 2-3 mm in subsegmental arteries 2
• CTA provides 100% sensitivity and 100% specificity at the main/lobar level and 100% sensitivity with 99% specificity at the segmental level 1
• Patients with good quality negative CTA do not require further investigation or treatment for PE 1, 4

Assessment of Right Ventricular Strain

• CTA reveals critical prognostic information including RV/LV ratio, pulmonary artery diameter, and septal deviation that predict short-term mortality and need for ICU-level care 2
• This information directly impacts management decisions regarding escalation of therapy or alternative interventions 2

Detection of Alternative Diagnoses

• CTA frequently reveals other causes of respiratory deterioration such as pulmonary edema, pneumonia, or pleural effusion that would change management entirely 2, 4
• The lower lobe atelectasis noted in this patient could represent pneumonia, infarction, or simple post-operative atelectasis—CTA will definitively differentiate these 4, 5

Why Doppler Ultrasound is Inadequate

While leg vein imaging has a role in PE evaluation, it is insufficient as the sole investigation in this symptomatic post-operative patient: 1

• Doppler ultrasound only detects DVT, not PE itself—a negative study does not exclude PE 1
• A single normal leg ultrasound should not be relied upon for exclusion of subclinical DVT 1
• Leg ultrasound is most useful when positive (confirming VTE and justifying anticoagulation) or when used in patients with coexisting clinical DVT 1
• In patients with high clinical probability of PE and cardiopulmonary symptoms, direct lung imaging is mandatory 1, 2

Critical Management Considerations

Immediate Actions

• Do not delay CTA imaging—it should ideally be performed within 24 hours in non-massive PE 1
• Consider initiating heparin before imaging if clinical probability is high, as this patient's presentation suggests 1
• If massive PE with hemodynamic instability develops, CTA or echocardiography will reliably diagnose it, and thrombolysis becomes first-line treatment 1

Common Pitfalls to Avoid

• Do not assume atelectasis alone explains the symptoms—post-operative atelectasis is common but does not typically cause severe dyspnea with new RBBB 5, 6
• Do not rely on D-dimer testing in post-operative patients, as it has limited value due to expected elevation from recent surgery 1, 7
• Do not substitute leg ultrasound for lung imaging when PE is the primary concern based on cardiopulmonary symptoms 1, 2

Role of Echocardiography

• Transthoracic echocardiography can identify right ventricular dysfunction and is appropriate for suspected PE 1
• However, echocardiography has limitations: the McConnell sign (RV free wall hypokinesis with apical sparing) is neither sensitive nor specific for PE, and patients often require subsequent CTA for confirmation 1
• Echocardiography is most useful in massive PE with hemodynamic instability or when CTA is contraindicated 1

The answer is A: CTA chest is the most appropriate investigation for this patient.