A 74-year-old woman is brought to the emergency department with a 2-hour history of sudden… — USMLE Step 3

A 74-year-old woman is brought to the emergency department with a 2-hour history of sudden, severe, and diffuse abdominal pain accompanied by nausea and one episode of non-bloody emesis. Her medical history is significant for heart failure with preserved ejection fraction and paroxysmal atrial fibrillation. She admits she stopped taking her prescribed apixaban two weeks ago due to financial constraints. On examination, she appears in significant distress, writhing on the stretcher. Her temperature is $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), blood pressure is $102/64 \text{ mm Hg}$ , heart rate is $118/\text{min}$ and irregularly irregular, respiratory rate is $22/\text{min}$ , and oxygen saturation is $96\%$ on room air. Abdominal examination reveals a soft abdomen with mild, diffuse tenderness to deep palpation, but no guarding, rigidity, or rebound tenderness. Bowel sounds are hypoactive. Peripheral pulses are normal and symmetric. Which of the following diagnostic studies should be ordered concurrently as part of the immediate diagnostic sequence for this patient? (Select the THREE most appropriate options)

Computed tomography (CT) angiography of the abdomen and pelvisAnswer
Serum lactic acid levelAnswer
12-lead electrocardiogramAnswer
D
Mesenteric duplex ultrasonography
E
Transthoracic echocardiography
F
Upright and supine plain abdominal radiographs

Answer

The most appropriate concurrent diagnostic steps are Computed tomography (CT) angiography of the abdomen and pelvis, a Serum lactic acid level, and a 12-lead electrocardiogram.

This patient presents with the classic triad for acute mesenteric ischemia: sudden onset of severe abdominal pain, pain out of proportion to physical examination findings, and a high-risk embolic source (atrial fibrillation without anticoagulation). The survival of this patient depends on rapid diagnosis and intervention. The standard of care requires concurrent execution of multiple diagnostic steps. Computed tomography (CT) angiography of the abdomen and pelvis is the gold standard imaging test and should be obtained immediately to visualize the mesenteric vasculature. Concurrently, a serum lactic acid level must be drawn to assess for systemic hypoperfusion and advanced bowel necrosis. Finally, a 12-lead electrocardiogram is mandatory to formally evaluate the atrial fibrillation with rapid ventricular response and rule out concurrent acute coronary syndrome, which could complicate imminent surgical or endovascular interventions.

Step-by-Step Solution

Analyze the clinical presentation.

The patient has sudden, severe abdominal pain out of proportion to physical exam findings, with a history of atrial fibrillation off anticoagulation. This is the classic presentation of acute mesenteric ischemia (superior mesenteric artery embolism).

Identifying the primary working diagnosis dictates the urgency and type of the diagnostic workup.

Determine the definitive imaging modality.

Select CT angiography of the abdomen and pelvis.

CT angiography is highly sensitive and specific for mesenteric vessel occlusion and can rule out other catastrophic causes of acute abdomen.

Identify necessary concurrent laboratory testing for risk stratification.

Select serum lactic acid level.

Elevated lactate indicates significant tissue hypoperfusion and bowel infarction, which accelerates the need for emergent laparotomy versus endovascular intervention.

Assess concurrent systemic and cardiovascular risks.

Select 12-lead electrocardiogram.

The patient is tachycardic and irregularly irregular. An ECG evaluates the rhythm and checks for concurrent myocardial infarction (demand ischemia), which is critical prior to taking an elderly patient to emergency surgery.

Key Concept

The initial diagnostic sequence for suspected acute mesenteric ischemia requires concurrent definitive imaging (CT angiography), assessment of ischemic severity (lactate), and evaluation of precipitating or concurrent cardiovascular conditions (ECG), avoiding suboptimal tests that delay surgical intervention.

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