Emergency medical services transport a 62-year-old male to the resuscitation bay following… — USMLE Step 3

Emergency medical services transport a 62-year-old male to the resuscitation bay following the abrupt onset of excruciating, anterior chest pain that radiates directly to his upper back. The patient describes the pain as "ripping" in quality. He has a history of long-standing, non-adherent hypertension. On arrival, he is lethargic but arousable, pale, and profusely diaphoretic. Vital signs include a heart rate of $124/min$ , a respiratory rate of $24/min$ , and a blood pressure of $78/45\text{ mm Hg}$ . Physical examination reveals a prominent early diastolic decrescendo murmur auscultated over the right second intercostal space. His left radial pulse is weak and delayed, while the right is bounding. The initial 12-lead electrocardiogram indicates sinus tachycardia without ischemic ST-segment changes. Large-bore intravenous lines are secured, and fluid resuscitation is initiated. Which of the following is the single most appropriate initial imaging modality to establish the diagnosis?

Transesophageal echocardiographyAnswer
B
Computed tomography angiography of the chest
C
Transthoracic echocardiography
D
Magnetic resonance angiography of the chest
E
Coronary angiography

Answer

Transesophageal echocardiography

The clinical presentation of sudden-onset, ripping chest pain radiating to the back, an asymmetric pulse examination, and a new early diastolic murmur (indicating acute aortic regurgitation) is a classic manifestation of an acute aortic dissection. When evaluating a patient for an acute aortic syndrome, the choice of definitive diagnostic imaging is dictated entirely by their hemodynamic stability. This patient is in profound shock, with a blood pressure of

78/45\text{ mm Hg}

. Transporting a hemodynamically unstable patient out of the resuscitation bay to the radiology suite for a computed tomography (CT) scan is strictly contraindicated due to the high risk of acute decompensation and cardiac arrest in an environment with limited monitoring and resuscitative capabilities. Transesophageal echocardiography (TEE) is the imaging modality of choice for establishing the diagnosis in unstable patients. It can be performed rapidly at the bedside or concurrently in the operating room as surgeons prepare for a sternotomy. TEE provides excellent sensitivity and specificity (approaching 99%) for identifying an intimal flap and can concurrently evaluate for critical complications such as pericardial tamponade, severe aortic valve regurgitation, and proximal coronary artery involvement.

Step-by-Step Solution

Analyze the clinical presentation.

The patient presents with sudden-onset ripping chest pain, a pulse differential, and a new murmur of aortic regurgitation.

These findings are highly indicative of an acute Stanford Type A aortic dissection.

Assess the patient's hemodynamic status.

The patient is in profound shock, evidenced by a blood pressure of

78/45\text{ mm Hg}

, tachycardia, lethargy, and diaphoresis.

Hemodynamic stability is the critical pivot point that dictates whether a patient can safely leave the resuscitation bay for advanced imaging.

Select the optimal imaging modality based on stability guidelines.

Transesophageal echocardiography is selected to establish the diagnosis.

It provides near 100% sensitivity for detecting an intimal flap and can be performed immediately at the bedside or in the operating room without jeopardizing the patient's safety.

Key Concept

In patients with suspected acute aortic dissection, the choice of diagnostic imaging depends on hemodynamic stability; unstable patients require bedside transesophageal echocardiography (TEE), while stable patients undergo computed tomography angiography (CTA).

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