Notes · Radiology · 13 October 2026

CT Pulmonary Angiography (CTPA) for Pulmonary Embolism

Definition

• CT Pulmonary Angiography (CTPA): A contrast‑enhanced, multidetector computed tomography (MDCT) study that visualizes the pulmonary arterial tree from the main pulmonary artery to subsegmental branches.
• Gold‑standard non‑invasive imaging modality for diagnosing pulmonary embolism (PE), replacing ventilation‑perfusion (V/Q) scan in most centres.

Epidemiology

• Global incidence of acute PE: 60–70 cases per 100 000 person‑years; in India, hospital‑based studies report 15–30 cases/100 000 admissions.
• Peak age: 50–70 years; slight female predominance in pregnancy‑related PE.
• Mortality without treatment: 30 % (within 1 month); falls to <5 % with early diagnosis and anticoagulation.

Aetiology / Risk Factors (Virchow’s triad)

• Stasis: prolonged immobilisation (post‑operative, long‑haul travel), heart failure, atrial fibrillation.
• Endothelial injury: recent surgery, trauma, central venous catheters, malignancy‑related invasion.
• Hypercoagulability: inherited thrombophilia (Factor V Leiden, prothrombin G20210A), antiphospholipid syndrome, pregnancy, oral contraceptives, malignancy, COVID‑19 infection.
• Additional Indian context: high prevalence of tuberculosis‑related pleural disease, dehydration in hot climates, and use of traditional herbal medicines with unknown pro‑coagulant effects.

Pathophysiology

• Thrombus formation in deep veins → embolisation to pulmonary arterial tree.
• Obstruction → increased right ventricular (RV) afterload, RV dilatation, interventricular septal shift, reduced left ventricular preload → systemic hypotension.
• Ventilation‑perfusion mismatch: perfusion defect with preserved ventilation → hypoxaemia and dyspnoea.
• Release of vasoactive mediators (serotonin, thromboxane) causes pulmonary vasoconstriction, worsening RV strain.

Clinical Features (high‑yield)

• Classic triad (rare): dyspnoea, pleuritic chest pain, haemoptysis.
• Common presentations:
  • Sudden onset dyspnoea (often at rest)
  • Tachypnoea, tachycardia, hypoxaemia (SpO₂ < 90 %)
  • Pleuritic chest pain, especially on deep inspiration
  • Syncope or presyncope in massive PE
  • Unexplained hypotension (SBP < 90 mmHg) → massive PE
• Physical signs: clear lungs, accentuated P2, RV heave, peripheral oedema in chronic thrombo‑embolic disease.

Investigations

Initial bedside work‑up

• Wells score or Revised Geneva score → pre‑test probability.
• D‑dimer: high sensitivity; negative result rules out PE in low‑intermediate probability patients.

Imaging – role of CTPA

Ancillary tests

• Echocardiography: RV dysfunction in massive PE.
• CT pulmonary angiography with dual‑energy: perfusion maps, useful in chronic thrombo‑embolic pulmonary hypertension (CTEPH).
• Ventilation‑perfusion (V/Q) scan: alternative when CTPA contraindicated.

Management (Guideline‑based, 2023 ESC & 2022 ACCP)

1. Risk stratification (based on haemodynamics, RV dysfunction, biomarkers).

   • High‑risk (massive): hypotension/shock.
   • Intermediate‑risk (sub‑massive): RV dysfunction or elevated troponin without shock.
   • Low‑risk: no haemodynamic compromise, normal RV, normal biomarkers.

2. Anticoagulation – initiated as soon as PE is suspected, before imaging if no contraindication.

   • Initial: Low‑molecular‑weight heparin (LMWH) 1 mg/kg SC q12h, or unfractionated heparin (UFH) infusion (target aPTT 1.5–2.5×).
   • Oral agents: Direct oral anticoagulants (DOACs) – rivaroxaban, apixaban, edoxaban, dabigatran – can be started after LMWH/UFH loading (per 2022 ACCP).

3. Reperfusion therapy (high‑risk PE)

   • Systemic thrombolysis: alteplase 100 mg IV over 2 h (or 0.6 mg/kg ≤ 50 kg).
   • Catheter‑directed thrombolysis or mechanical thrombectomy if contraindication to systemic thrombolysis or failed thrombolysis.

4. Surgical embolectomy – reserved for refractory massive PE or contraindication to thrombolysis.

5. Supportive care

   • Oxygen supplementation (target SpO₂ > 94 %).
   • Fluid restriction; cautious fluid bolus only if hypotension with low preload.
   • Vasopressors (norepinephrine) for persistent shock.

6. Duration of anticoagulation

   • Provoked PE (e.g., surgery, immobilisation): 3 months.
   • Unprovoked or recurrent: minimum 6 months; consider indefinite therapy after risk‑benefit assessment.

7. Follow‑up

   • Repeat CTPA not routinely required; consider if clinical deterioration or to assess CTEPH after ≥ 3 months.

Complications

From Pulmonary Embolism

• Cardiogenic shock and cardiac arrest (massive PE).
• Right‑ventricular failure → systemic venous congestion, hepatic congestion.
• Chronic thrombo‑embolic pulmonary hypertension (CTEPH) – occurs in ~4 % of survivors; may need pulmonary endarterectomy.

From CTPA (procedure‑related)

• Contrast‑induced nephropathy – risk ↑ with eGFR < 60 mL/min/1.73 m², diabetes, dehydration.
• Allergic reactions – mild urticaria to anaphylaxis; pre‑medicate high‑risk patients.
• Radiation exposure – cumulative dose concerns in young females; use dose‑saving protocols.

High‑Yield Exam Points

• CTPA is the first‑line test for suspected PE in patients with moderate‑to‑high clinical probability and no contraindication to iodinated contrast.
• Negative CTPA essentially rules out clinically significant PE (NPV > 98 %).
• Subsegmental PE: treat if symptomatic, proximal DVT present, or high‑risk patient; otherwise consider observation.
• RV/LV diameter ratio > 0.9 on CTPA = imaging marker of RV dysfunction → up‑grades to intermediate‑high risk.
• D‑dimer cut‑off can be age‑adjusted (age × 10 µg/L for > 50 y) to improve specificity.
• DOACs are now preferred over vitamin‑K antagonists for most PE patients without cancer or severe renal impairment (per 2022 ACCP).
• Pregnancy: CTPA is acceptable after the first trimester if needed; fetal dose ≈ 0.1 mGy (well below teratogenic threshold).
• Contra‑indication to anticoagulation → consider IVC filter only if PE is life‑threatening and anticoagulation cannot be given.

Practice questions

1. A 62‑year‑old man presents with sudden dyspnoea, tachycardia (110 bpm) and SpO₂ = 88 % on room air. Wells score is 6.5. Which investigation is most appropriate next?
   Answer: CTPA — high pre‑test probability warrants definitive imaging.

2. On CTPA, the RV/LV diameter ratio is 1.1 with a central filling defect in the right main pulmonary artery. According to ESC 2023, this patient belongs to which risk category?
   Answer: Intermediate‑high risk — RV dysfunction on imaging without systemic hypotension.

3. A 35‑year‑old pregnant woman (28 weeks) with suspected PE cannot receive iodinated contrast. What is the preferred alternative imaging modality?
   Answer: Ventilation‑perfusion (V/Q) scan — safe in pregnancy when CTPA contraindicated.

AI-assisted study material for exam revision. Always confirm with standard textbooks and current guidelines; not medical advice.