What is the initial investigation for a patient with atrial fibrillation (AF) presenting with acute severe abdominal pain, without abdominal distension or lower gastrointestinal (GI) bleeding?

Initial Investigation for Atrial Fibrillation Patient with Acute Severe Abdominal Pain

CT angiography (CTA) of the abdomen and pelvis with intravenous contrast is the initial investigation of choice for this patient. 1, 2

Rationale for CTA as First-Line Imaging

This clinical presentation—atrial fibrillation with acute severe abdominal pain out of proportion to physical examination findings—is the classic hallmark of acute mesenteric ischemia (AMI), specifically embolic mesenteric ischemia. 1, 2 Nearly 50% of patients with embolic AMI have atrial fibrillation, making this the most critical risk factor for mesenteric arterial embolism. 1, 2

CTA provides superior diagnostic accuracy with 94% sensitivity and 95% specificity for identifying arterial occlusion in AMI. 2 The American College of Radiology designates triple-phase CTA (non-contrast, arterial, and portal venous phases) as the optimal imaging modality because it: 1, 2

• Identifies the location and extent of arterial occlusion
• Evaluates bowel wall viability and detects complications (pneumatosis, portal venous gas, perforation)
• Excludes alternative diagnoses
• Guides immediate treatment decisions (endovascular vs. surgical intervention)

Why Other Imaging Modalities Are Inappropriate

Plain abdominal X-ray (Option A) is not recommended and should be avoided. 1 The World Society of Emergency Surgery gives plain radiography a strong recommendation against its use in evaluating intestinal ischemia (1B evidence). 1 Radiographs are normal in 25% of AMI cases and only become positive after bowel infarction has already occurred—at which point mortality is significantly higher. 1

Abdominal ultrasound (Option A) has no role in diagnosing mesenteric ischemia. 1 While ultrasound is appropriate for right upper quadrant pain (cholecystitis), it cannot visualize mesenteric vessels or assess bowel perfusion. 1

MRI (Option C) is inappropriate in this acute setting due to longer acquisition times, limited availability in emergency situations, and no demonstrated superiority over CTA for AMI diagnosis. 1

Critical Time-Sensitive Considerations

Time to diagnosis is the most important predictor of outcome in AMI, with mortality approaching 50% overall but improving dramatically with intervention within 5-10 hours of symptom onset. 2 This makes immediate CTA essential—do not delay for:

• Elevated creatinine levels (the risk of missing mesenteric ischemia far outweighs contrast nephropathy concerns) 2
• Additional laboratory testing beyond basic workup
• Plain radiographs or other preliminary imaging

Supporting Evidence from Clinical Practice

A retrospective study of 30 patients with atrial fibrillation presenting with acute abdominal pain found that 37% had CT findings related to their atrial fibrillation, including end-organ ischemia/infarction (27%) and anticoagulation-related hemorrhage (10%). 3 This demonstrates the high likelihood of embolic or hemorrhagic complications in this specific population, further supporting immediate contrast-enhanced CT.

Immediate Management After CTA

Once CTA confirms AMI: 2

• Initiate systemic anticoagulation immediately (appropriateness rating 8/9)
• Obtain immediate surgical consultation regardless of imaging findings
• Consider endovascular intervention first (angiography with aspiration embolectomy or thrombolysis) if no peritoneal signs are present

The absence of abdominal distension and lower GI bleeding in your patient suggests potentially viable bowel without perforation, creating a critical window for revascularization if AMI is present. 1