What is the most appropriate next step in managing a 45-year-old gravida 4, para 1, abortion 0, living children 3 (G4P1031) woman with dyspnea and shortness of breath (SOB) on exertion, past medical history of hypothyroidism on levothyroxine, with symptoms persisting despite azithromycin treatment for presumed bronchitis 50 days ago, now presenting with rales in the right lung, oxygen saturation dropping to 86% on room air, sinus tachycardia, T-wave inversion, and right bundle branch block on electrocardiogram (EKG), and hypertension with a blood pressure of 150/90?

Immediate CT Pulmonary Angiography (CTPA) to Rule Out Pulmonary Embolism

This patient requires urgent CT pulmonary angiography as the most appropriate next step, given her high-risk clinical presentation with hypoxemia, EKG findings consistent with right heart strain (T-wave inversion in lead III and right bundle branch block), and persistent dyspnea despite prior treatment. 1

Clinical Reasoning for Acute Pulmonary Embolism

This presentation is highly concerning for pulmonary embolism (PE) based on multiple high-risk features:

• Right heart strain pattern on EKG: The combination of sinus tachycardia, T-wave inversion in lead III, and right bundle branch block strongly suggests acute right ventricular pressure overload 1
• Significant hypoxemia with exertion: Oxygen saturation dropping to 86% on room air with ambulation indicates impaired gas exchange 1
• Unilateral lung findings: Rales isolated to the right lung may represent pulmonary infarction or hemorrhage 1
• Persistent symptoms despite antibiotic therapy: The 50-day history with no improvement after azithromycin argues against infectious bronchitis 1

Why CTPA is the Appropriate Next Step

CT pulmonary angiography should be performed immediately as it provides definitive diagnosis of acute PE with high sensitivity and specificity, and can identify alternative diagnoses such as pneumonia or malignancy. 1

Key advantages of CTPA in this scenario:

• Directly visualizes pulmonary arterial thrombi down to subsegmental level 1
• Can assess right ventricular size and function, providing prognostic information 1
• Identifies alternative pulmonary pathology (pneumonia, mass, interstitial lung disease) 1
• Does not require the patient to be stable enough for transport to nuclear medicine 1

Why Not Other Tests First

Echocardiography, while useful for assessing right heart function and pulmonary hypertension, cannot definitively diagnose or exclude acute PE and should not delay definitive imaging. 1

• D-dimer testing has limited utility in this moderate-to-high pretest probability scenario and would not change management 1
• V/Q scanning is reserved for patients with contraindications to CT contrast or for chronic thromboembolic disease evaluation, not acute PE diagnosis 1
• Empiric anticoagulation without imaging confirmation is inappropriate given the need for definitive diagnosis and risk stratification 1

Critical Management Considerations

If PE is confirmed on CTPA:

Immediate anticoagulation should be initiated with therapeutic-dose low molecular weight heparin, unfractionated heparin, or direct oral anticoagulant based on hemodynamic stability and renal function. 1

• Risk stratification is essential: The presence of right heart strain on EKG with hypoxemia suggests intermediate-high or high-risk PE 1
• Patients with hemodynamic instability (systolic BP <90 mmHg or requiring vasopressors) require consideration for systemic thrombolysis or catheter-directed therapy 1
• Even if hemodynamically stable, this patient's right heart strain pattern warrants close monitoring in a higher acuity setting 1

Common Pitfalls to Avoid:

• Do not attribute persistent dyspnea to "bronchitis" when symptoms fail to improve with antibiotics - this delays diagnosis of life-threatening conditions like PE 1
• Do not rely on the absence of traditional risk factors (no recent surgery, no travel) - up to 30% of PE cases occur without identifiable provocation 1
• Do not dismiss PE because there is no lower extremity edema or JVD - these findings are neither sensitive nor specific for PE 1
• The patient's obstetric history (G4P1031) may indicate prior pregnancy complications that could represent unrecognized thrombotic events 1

Follow-up After Acute PE Management

If PE is confirmed and treated, this patient will require follow-up evaluation at 3-6 months to assess for chronic thromboembolic pulmonary hypertension (CTEPH), given the prolonged symptom duration. 1

• Clinical assessment should include evaluation of persistent dyspnea and functional limitation 1
• V/Q scanning is recommended at follow-up if symptoms persist, as it has superior sensitivity for detecting chronic thromboembolic disease compared to CTPA 1
• Referral to a pulmonary hypertension expert center is indicated if V/Q scan shows mismatched perfusion defects 1

Alternative Diagnosis Consideration

If CTPA is negative for PE, the differential diagnosis should include:

• Pulmonary arterial hypertension (PAH): The hypertension, exertional dyspnea, and right heart strain pattern could represent PAH, which would require echocardiography followed by right heart catheterization for definitive diagnosis 1, 2
• Interstitial lung disease: Though less likely given the acute presentation 1
• Pneumonia with parapneumonic effusion: The unilateral rales warrant consideration, though the prolonged course makes this less likely 1

Right heart catheterization would only be indicated after CTPA excludes acute PE and if echocardiography suggests pulmonary hypertension, as it is required to definitively establish PAH diagnosis before initiating specific therapy. 1, 2