Is a computed tomography angiogram (CTA) useful in a patient with deep vein thrombosis (DVT) on anticoagulation therapy with Eliquis (apixaban) who has increased oxygen requirements, tachycardia, and fever, but is unable to verbalize symptoms due to a speech impediment?

Should You Get a CTA in This Patient Already on Anticoagulation?

Yes, you should obtain a CTA chest to evaluate for pulmonary embolism in this patient despite already being on anticoagulation. The combination of DVT, increased oxygen requirements, and inability to communicate symptoms creates a high-risk scenario where PE must be definitively ruled out or confirmed, as it will directly impact management decisions regarding escalation of therapy or alternative interventions 1.

Why CTA is Indicated Despite Anticoagulation

The presence of anticoagulation does not eliminate the need for diagnostic imaging when PE is clinically suspected. Several critical management decisions depend on confirming or excluding PE 1:

• Treatment escalation decisions: If PE is confirmed with signs of right ventricular strain, you may need to consider thrombolytic therapy or mechanical thrombectomy rather than continuing standard anticoagulation alone 2, 1
• Prognostic stratification: CTA provides crucial information about RV/LV ratio, pulmonary artery diameter, and septal deviation that predict short-term mortality and need for ICU-level care 2, 3
• Alternative diagnoses: CTA frequently reveals other causes of respiratory deterioration (pulmonary edema, pneumonia, pleural effusion) that would change management entirely 2, 4

Clinical Context Supporting CTA

Your patient has multiple concerning features that elevate PE probability 1:

• Known DVT source: Established lower extremity thrombus significantly increases PE risk
• Objective deterioration: Increased oxygen requirements represent measurable clinical worsening, not subjective symptoms
• Communication barrier: The speech impediment prevents reliable symptom assessment, making objective imaging even more critical 1
• Confounding factors: While fever and tachycardia could be from infection, they could equally represent PE—you cannot safely attribute them to infection without excluding PE 1

What CTA Will Tell You That Changes Management

CTA provides actionable information beyond simple PE presence or absence 2, 3:

• Clot burden and location: Central vs. subsegmental PE determines whether advanced reperfusion strategies are appropriate 2
• RV dysfunction markers: RV/LV ratio >1.0, septal bowing, and PA trunk diameter predict hemodynamic decompensation and mortality 2, 3
• Treatment failure assessment: If PE is confirmed despite therapeutic anticoagulation, this indicates either medication non-adherence or true treatment failure requiring indefinite anticoagulation or IVC filter consideration 1

Critical Pitfalls to Avoid

Do not assume current anticoagulation precludes PE or makes imaging unnecessary 1:

• Breakthrough embolic events occur due to non-adherence, inadequate dosing, or true treatment failure
• The 10 mg BID apixaban dose is appropriate for acute VTE treatment, but absorption issues, drug interactions, or timing errors can result in subtherapeutic levels 5, 6
• Delaying imaging in a patient with DVT and new respiratory deterioration risks missing a potentially fatal PE 1

Do not rely on D-dimer testing in this scenario 1:

• D-dimer has no utility in a patient with known DVT already on anticoagulation
• The pretest probability is already high enough to warrant direct imaging 7

Do not wait for clinical deterioration before imaging 1:

• The patient is already showing objective worsening (increased O2 requirements)
• CTA findings of RV dysfunction predict which patients will decompensate, allowing preemptive intervention 2, 3

Practical Considerations

CTA is the definitive test with 96-99% sensitivity and specificity for PE 2:

• Modern multidetector CTA detects emboli down to 2-3 mm in subsegmental arteries 2
• The false-negative rate is extremely low, and outcome studies show no adverse events in patients with negative CTPA who remain untreated 2, 8
• Additional findings beyond PE are identified in 78% of cases, often providing alternative or concurrent diagnoses 4

If renal function is a concern, V/Q scan is an acceptable alternative, though less informative regarding RV function and alternative diagnoses 9. However, given the critical need for prognostic information in this deteriorating patient, CTA remains preferable if renal function permits 2, 9.