A 45-year-old woman on oral contraceptives presents with acute dyspnea and chest pain. CTPA shows a small subsegmental pulmonary embolism in the right lower lobe with no evidence of right ventricular dysfunction. D-dimer is elevated. Which is the most appropriate next investigation to guide management decisions?

Explanation

## Investigation Choice in Subsegmental PE Without RV Dysfunction **Key Point:** In a hemodynamically stable patient with subsegmental PE and **no RV dysfunction on CTPA**, compression ultrasound of the lower extremities (CUS) is the most appropriate next investigation. Identifying concomitant proximal DVT directly influences the decision to anticoagulate in subsegmental PE, where the benefit of anticoagulation is otherwise uncertain. ### Why Compression Ultrasound? 1. **Subsegmental PE management dilemma**: Unlike proximal PE, subsegmental PE (SSPE) does not automatically mandate anticoagulation in all patients. The 2019 ESC and 2016 ACCP guidelines both acknowledge clinical uncertainty and recommend individualized decision-making. 2. **DVT presence changes management**: If a proximal DVT is identified on CUS, anticoagulation is clearly indicated regardless of the small clot burden on CTPA. If CUS is negative, a surveillance strategy (without anticoagulation) may be considered in low-bleeding-risk patients. 3. **Risk factor context**: This patient is on oral contraceptives — a known prothrombotic state — making DVT identification particularly relevant for both acute management and long-term decisions (e.g., stopping OCP, duration of anticoagulation). ### Why NOT the Other Options? - **Option A (Repeat CTPA in 24 hours)**: Not standard practice; exposes the patient to additional radiation and contrast without clear benefit in a stable patient. - **Option B (Echocardiography)**: The stem explicitly states "no evidence of right ventricular dysfunction" on CTPA. Performing echo to assess RV function would be **redundant** given this information is already available. Echo is indicated when RV status is unknown or equivocal, not when CTPA has already excluded RV dysfunction. - **Option D (ABG)**: Provides oxygenation data but does not guide anticoagulation decisions or alter management in a hemodynamically stable patient with known SSPE. ### SSPE Management Algorithm (ACCP/ESC) ``` SSPE confirmed on CTPA ↓ No RV dysfunction, hemodynamically stable ↓ Perform CUS of lower extremities ↓ Proximal DVT found? → YES → Anticoagulate → NO → Consider surveillance vs. anticoagulation based on bleeding risk ``` **High-Yield:** Per ACCP 2016 (Chest guidelines) and ESC 2019, CUS is specifically recommended in SSPE to detect proximal DVT, which is the single most important factor guiding the anticoagulation decision when clot burden is small and RV function is preserved [Harrison's Principles of Internal Medicine, 21e, Ch. 297; ACCP Chest 2016;149(2):315–352]. **Clinical Pearl:** When CTPA already confirms absence of RV dysfunction in SSPE, echocardiography adds no incremental diagnostic value. The pivotal question becomes: "Is there a proximal DVT?" — answered by compression ultrasound.