What is the most appropriate investigation for an elderly female patient with a history of atrial fibrillation (A. fib) and recent unintentional weight loss, presenting with severe abdominal pain and decreased bowel sounds?

Abdominal CT Angiography is the Most Appropriate Investigation

In this elderly female with atrial fibrillation presenting with severe abdominal pain out of proportion to examination findings, abdominal CT angiography (CTA) with contrast is the definitive diagnostic test and should be performed immediately. 1, 2

Why CT Angiography is the Answer

CTA of the abdomen and pelvis is the gold standard investigation for acute mesenteric ischemia, offering 95-100% sensitivity and specificity for detecting vascular abnormalities. 2 This clinical presentation—atrial fibrillation, severe pain disproportionate to physical findings, and decreased bowel sounds—is the classic triad for acute mesenteric ischemia, which carries a 30-90% mortality rate if diagnosis is delayed. 2, 3

Technical Specifications

• A triple-phase CTA study (non-contrast, arterial, and portal venous phases) should be performed to identify the underlying cause of ischemia, evaluate for bowel complications, and exclude other diagnoses. 1
• CTA simultaneously evaluates both the mesenteric vasculature and bowel wall, allowing identification of arterial emboli (present in 40-50% of cases with atrial fibrillation), arterial thrombosis, venous thrombosis, and signs of bowel infarction. 1, 2, 3

Why the Other Options Are Inadequate

Lactate Levels (Option A)

• While elevated lactate >2 mmol/L is associated with irreversible intestinal ischemia and occurs in 88% of cases, lactate is a marker of advanced disease, not a diagnostic tool. 3
• Waiting for lactate elevation means waiting for bowel necrosis—by then, mortality approaches 60%. 1
• Lactate should be obtained as part of the workup but cannot replace imaging. 3

Plain X-ray of the Abdomen (Option B)

• Plain radiography is strongly NOT recommended for evaluating mesenteric ischemia, as 25% of patients have completely normal radiographs. 2
• Abnormal findings (pneumatosis, portal venous gas) appear only after bowel infarction has occurred, which is associated with extremely high mortality. 2
• The American College of Radiology states that plain radiography has low diagnostic yield with nonspecific findings that appear late in the disease course. 2

Abdominal Ultrasound (Option C)

• Ultrasound has no role in the acute evaluation of mesenteric ischemia. 1
• It cannot adequately visualize the mesenteric vessels or assess for arterial emboli, which is the most likely diagnosis in this patient with atrial fibrillation. 1, 3
• Ultrasound is appropriate for right upper quadrant pain (cholecystitis) but not for suspected mesenteric ischemia. 1

Critical Clinical Context

Why This Patient Needs Immediate CTA

• Atrial fibrillation accounts for approximately 50% of patients with embolic acute mesenteric ischemia. 2, 3
• The combination of atrial fibrillation, unintentional weight loss (suggesting chronic mesenteric ischemia progressing to acute-on-chronic), and pain out of proportion to examination is pathognomonic for mesenteric ischemia. 1, 3
• The soft abdomen with decreased bowel sounds is the classic "benign exam" that falsely reassures clinicians—this is a common pitfall, as severe pain with minimal physical findings is the hallmark of early mesenteric ischemia. 3

Time-Critical Nature

• Mortality rates approach 60% when diagnosis and intervention are delayed. 1
• CTA is fast, accurate, and noninvasive, and can guide immediate management by stratifying patients who need angiography versus emergent surgery. 2
• Early diagnosis before irreversible necrosis occurs is vital for survival. 2

Management Algorithm After CTA

Once CTA confirms the diagnosis:

• If arterial embolism is identified: Systemic anticoagulation (rating 8/9) plus transcatheter thrombolysis or aspiration embolectomy (rating 7/9) versus surgical embolectomy. 1
• If arterial thrombosis is identified: Angiography with transcatheter thrombolysis followed by angioplasty and stenting (rating 8/9). 1
• If bowel infarction is present: Immediate surgical exploration is mandatory. 1

The bottom line: Do not waste time with lactate levels, plain films, or ultrasound in this patient—proceed directly to CT angiography to save her life. 1, 2