A 64-year-old man is brought to the emergency department via ambulance due to the sudden o… — USMLE Step 3

A $64$ -year-old man is brought to the emergency department via ambulance due to the sudden onset of excruciating, "tearing" chest pain that radiates to his interscapular region. The pain began $1$ hour ago while he was watching television. He has a history of poorly controlled hypertension, type 2 diabetes mellitus, and a $40$ -pack-year smoking history. On arrival, he appears pale, diaphoretic, and lethargic. His temperature is $36.8^\circ\text{C}$ ( $98.2^\circ\text{F}$ ), blood pressure is $80/50\text{ mm Hg}$ in the right arm and $115/65\text{ mm Hg}$ in the left arm, heart rate is $124/\text{min}$ , and respiratory rate is $24/\text{min}$ . Cardiopulmonary examination reveals a faint diastolic decrescendo murmur at the right upper sternal border. An electrocardiogram demonstrates sinus tachycardia with voltage criteria for left ventricular hypertrophy but no acute ischemic changes. Portable chest radiography shows a widened mediastinum. Initial laboratory studies reveal a serum creatinine concentration of $2.9\text{ mg/dL}$ . Which of the following is the most appropriate next step in diagnostic imaging?

A
Computed tomography angiography of the chest
B
Magnetic resonance angiography of the chest
C
Non-contrast computed tomography of the chest
D
Invasive ascending aortography
Transesophageal echocardiographyAnswer

Answer

Transesophageal echocardiography

The patient's presentation is classic for an acute aortic dissection, which is a life-threatening emergency. The standard initial diagnostic test for a stable patient with suspected aortic dissection is computed tomography angiography (CTA). However, this patient presents with hemodynamic instability (hypotension, tachycardia, lethargy) and acute renal failure (elevated creatinine). Hemodynamic instability precludes safe transport to the CT or MRI scanner, as the patient requires continuous monitoring and immediate access for resuscitation. Furthermore, his acute kidney injury makes iodinated contrast administration highly risky. Transesophageal echocardiography (TEE) is the modality of choice in this scenario. TEE can be performed rapidly at the bedside (in the emergency department or operating room), provides excellent visualization of the ascending aorta and aortic valve, and does not require intravenous contrast.

Step-by-Step Solution

Analyze the patient's clinical presentation and identify the primary differential diagnosis.

Sudden-onset tearing chest pain radiating to the back, unequal blood pressures in the upper extremities, a new murmur of aortic regurgitation, and a widened mediastinum strongly suggest an acute aortic dissection.

Recognizing the classic triad of aortic dissection (tearing pain, pulse/blood pressure differentials, and widened mediastinum) is the first step in determining the necessary diagnostic workup.

Assess the patient's physiologic stability and identify specific contraindications to standard imaging.

The patient is hemodynamically unstable (blood pressure

80/50\text{ mm Hg}

, lethargy) and has evidence of acute kidney injury (creatinine

2.9\text{ mg/dL}

Imaging must be selected based on the patient's ability to tolerate transport, lie flat for extended periods, and clear nephrotoxic contrast agents safely.

Select the imaging modality that provides definitive diagnosis without exacerbating the patient's clinical decline.

Transesophageal echocardiography (TEE) is chosen because it is performed at the bedside, requires no iodinated contrast, and offers excellent sensitivity for proximal aortic dissections.

Unstable patients should not leave the emergency department or resuscitation area for prolonged imaging studies like CT or MRI, and nephrotoxic agents must be avoided in acute renal failure.

Key Concept

In patients with suspected acute aortic dissection who are hemodynamically unstable or have a contraindication to iodinated contrast (e.g., severe renal dysfunction), bedside transesophageal echocardiography is the most appropriate initial diagnostic imaging modality.

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