What is the most appropriate investigation for a 40-year-old woman with sudden onset right lower limb pain, absent distal pulses, diminished sensory and altered motor exams, normal lab values, stable vital signs except for tachycardia (heart rate 95/min), and atrial fibrillation on electrocardiogram (ECG)?

CT Angiography is the Most Appropriate Investigation

For this 40-year-old woman with acute limb ischemia (sudden onset pain, absent distal pulses, sensory and motor deficits) in the setting of atrial fibrillation, CT angiography (CTA) is the most appropriate initial investigation. 1, 2

Why CTA is the Optimal Choice

• CTA provides rapid, comprehensive anatomic detail of the entire lower extremity arterial circulation, including the level of occlusion, degree of atherosclerotic disease, and below-knee vessel patency—all critical information needed for immediate revascularization planning 1, 2

• The American College of Radiology explicitly recommends CTA as the preferred initial imaging modality for acute limb ischemia, with a rating of 7-8, because it is fast and reveals both the thrombosis and underlying atherosclerotic plaque to plan an appropriate treatment strategy 1, 2

• Time is tissue in this emergency—the principle of "time is tissue" applies, where delays beyond 4-6 hours increase the risk of permanent damage and limb loss 2, 3

• CTA allows immediate treatment planning without the delays associated with other modalities, and can guide the choice between endovascular versus surgical revascularization 2, 3

Clinical Context: This is Acute Limb Ischemia

• The presence of motor deficits (altered motor exam) indicates Rutherford Class IIb (immediately threatened limb), which requires intervention within 6 hours to prevent permanent tissue damage 1, 2

• Atrial fibrillation on ECG strongly suggests embolic etiology, which significantly increases the risk of thromboembolism causing acute arterial occlusion 2, 4

• The "6 Ps" are present: pain, pulselessness (absent distal pulses), paresthesias (diminished sensory exam), paralysis (altered motor exam), pallor, and poikilothermia (cold extremity) 2, 3, 5

Why Other Options Are Inadequate

Vascular Ultrasound (Option B)

• Duplex ultrasound is too time-consuming, operator-dependent, and limited in scope for acute limb ischemia evaluation in the emergency setting 1
• The American College of Radiology explicitly states that duplex US is limited by the need for operator expertise, poor accessibility of vessels, heavy calcification, and poor overall accuracy if multilevel disease is present 1
• Ultrasound cannot provide the comprehensive anatomic mapping of the entire arterial tree needed for revascularization planning in this emergency 1, 6

Conventional Angiography (Option C)

• While conventional angiography (DSA) remains the gold standard, it is generally reserved for immediate pretreatment evaluation and allows simultaneous diagnosis and treatment 1
• In patients with viable or marginally threatened limbs (Rutherford Class I or IIa), immediate arteriography is preferred, but CTA should be obtained first in most cases to guide the approach 1, 2
• The key distinction: conventional angiography is appropriate when you're proceeding directly to intervention, but CTA should be done first to plan the approach unless the limb is immediately threatened requiring emergency thromboembolectomy 1, 2

Embolectomy Without Imaging (Option D)

• Proceeding directly to embolectomy without imaging is only appropriate for immediately threatened limbs with Rutherford Class IIb (late presentation) or Class III (irreversible ischemia) where motor loss is severe 1, 2
• This patient has altered motor exam but intact femoral pulse, suggesting she is not in the most severe category requiring immediate surgery without imaging 1, 2
• Even in severe cases, brief CTA can be obtained rapidly (within 15-20 minutes) and provides critical information about the level of occlusion and treatment strategy 2, 3

Immediate Management Algorithm

1. Start systemic anticoagulation immediately with intravenous unfractionated heparin bolus and continuous infusion to prevent thrombus propagation while arranging imaging 2, 3

2. Obtain emergent vascular surgery consultation even before imaging is complete, as some patients may need to proceed directly to surgical thromboembolectomy 1, 3

3. Perform CTA of the entire lower extremity from aorta to pedal vessels to define anatomy and plan revascularization 2, 3

4. Proceed to urgent revascularization (endovascular-first approach preferred in most patients) based on CTA findings, with intervention within 6 hours for this Rutherford Class IIb presentation 2, 3

Critical Pitfalls to Avoid

• Do not delay anticoagulation while obtaining imaging or awaiting vascular consultation—heparin should be started within minutes of presentation 2, 3

• Do not order ABI as the primary investigation—while ABI is useful for screening chronic disease and post-intervention follow-up, it only confirms arterial occlusion but provides no information about location, cause, or treatment planning needed in acute limb ischemia 1, 2, 6

• Do not delay treatment for echocardiography—while useful later to identify embolic sources in atrial fibrillation patients, it is not part of the acute workup and should not delay revascularization 1, 2

• Do not dismiss the urgency based on stable vital signs—the limb viability clock is ticking regardless of hemodynamic stability 2, 3