Mastering UKMLA & PLAB 1: Diagnosing Aortic Dissection with Precision
This article delves into a high-yield topic from recent UKMLA and PLAB 1 exams, focusing on the clinical recognition and management of aortic dissection, a life-threatening condition that tests your ability to identify and prioritize diagnostic investigations in emergency settings.
PLAB 1 Exam Question: Aortic Dissection Case
A 62-year-old man presents to the Emergency Department with sudden-onset severe chest pain radiating to his back. He describes the pain as "tearing." His blood pressure is 180/90 mmHg in the right arm and 150/85 mmHg in the left arm. He is haemodynamically stable and has no significant past medical history.
Which is the most appropriate initial investigation?
A. CT angiography
B. Transthoracic echocardiography
C. Chest X-ray
D. Coronary angiography
E. MRI of the thorax
Answer with an explanation is provided below.
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Breaking Down the Diagnosis: Why CT Angiography is Crucial
Key Features of Aortic Dissection:
Pain characteristics: Sudden, severe, and "tearing," often radiating to the back.
Inter-arm blood pressure difference: A classic finding due to the involvement of different arterial branches.
Risk factors: While not present in this case, history of hypertension, connective tissue disorders (e.g., Marfan syndrome), or previous cardiovascular disease are common.
CT Angiography: The Gold Standard
Accuracy: Highly sensitive and specific, CT angiography provides detailed visualization of the aorta, including the dissection flap, entry tear, and extent of involvement.
Speed and Availability: Readily accessible in emergency departments, ensuring rapid diagnosis in stable patients.
Guides Management: Determines whether the dissection is Type A (requiring urgent surgery) or Type B (medical management).
Why the Other Options Are Less Suitable
B) Transthoracic Echocardiography (TTE):
Limitations: Less sensitive for dissection involving the descending aorta. It is a better option in unstable patients when CT is unavailable.
Role: May support bedside diagnosis in critical settings but lacks comprehensive imaging.
C) Chest X-Ray:
Findings: Can show a widened mediastinum or pleural effusion but is neither diagnostic nor specific for aortic dissection.
Use: Only as a preliminary investigation when CT is delayed.
D) Coronary Angiography:
Purpose: Evaluates coronary artery disease, not aortic dissection. Performing this in a dissection case could worsen the condition.
E) MRI of the Thorax:
Drawbacks: While detailed, MRI is not ideal for emergencies due to its longer scan time and limited availability in acute settings.
Management of Aortic Dissection
Immediate Steps:
Confirm the Diagnosis: CT angiography is performed immediately.
Blood Pressure Control:
Target BP: Aim for systolic BP <120 mmHg.
First-Line Drugs: IV beta-blockers (e.g., esmolol, labetalol) to reduce heart rate and aortic wall stress.
Definitive Treatment:
Type A Dissection: Emergency surgical repair to prevent rupture or cardiac tamponade.
Type B Dissection: Medical management, including strict BP control, unless complications (e.g., organ ischaemia, rupture) arise.
Follow-Up Care:
Monitoring: Regular imaging (CT or MRI) to assess for progression or complications.
Long-term BP Control: Essential to reduce recurrence risk.
PLAB/UKMLA Exam Tips: Key Learning Points
Aortic dissection is a clinical emergency: Prompt recognition of symptoms (e.g., tearing chest pain and inter-arm BP difference) is critical.
Imaging hierarchy: CT angiography is the investigation of choice in stable patients.
Management pathways: Distinguish between Type A and Type B dissections for appropriate intervention.
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