A 72-year-old hypertensive man presents with acute-onset severe chest pain radiating to the back and left arm. On examination, he is hypertensive (BP 165/95 mmHg), with a blood pressure differential of 20 mmHg between the two arms. Aortic dissection is suspected. Which investigation is most appropriate to confirm the diagnosis and assess the extent of dissection?

Explanation

## Investigation of Choice for Acute Aortic Dissection **Key Point:** Contrast-enhanced CT angiography (CECT) of the chest with ECG-gating is the first-line investigation for suspected acute aortic dissection in most centres due to high sensitivity, specificity, speed, and availability. ### Why CECT with ECG-Gating? 1. **Diagnostic Performance** - Sensitivity: 94–98% for acute dissection - Specificity: >95% - Detects intimal flap, true and false lumens, and entry/re-entry sites - Identifies branch vessel involvement (coronary, carotid, renal, mesenteric) - Assesses for aortic rupture, pericardial effusion, and haemothorax 2. **ECG-Gating Advantage** - Reduces motion artefact from aortic wall pulsation - Improves visualization of intimal flap - Enhances detection of subtle dissections - Essential for Type A dissection assessment 3. **Speed & Availability** - Performed in <5 minutes - Available in most hospitals 24/7 - Allows rapid triage to surgery (Type A) vs medical management (Type B) **Clinical Pearl:** The blood pressure differential between arms (≥20 mmHg) is a classic sign of aortic dissection involving the brachiocephalic or left subclavian artery. This finding increases pre-test probability and mandates urgent imaging. **High-Yield:** CECT is preferred over TOE and MRI because it is faster, non-invasive, and does not require intubation. TOE is reserved for intraoperative monitoring or when CECT is contraindicated (e.g., severe renal failure). MRI takes 30–60 minutes—unacceptable in acute dissection. ### Comparison Table: Investigations for Acute Aortic Dissection | Investigation | Sensitivity | Specificity | Time | Availability | Use Case | Limitation | | --- | --- | --- | --- | --- | --- | --- | | **CECT (ECG-gated)** | 94–98% | >95% | 5 min | 24/7 | First-line for acute dissection | Contrast allergy; renal failure | | **TOE** | 97–99% | >95% | 10–15 min | Limited availability | Intraoperative; bedside in ICU | Invasive; requires sedation; operator-dependent | | **Cardiac MRI** | >95% | >95% | 30–60 min | Limited availability | Chronic dissection; follow-up | Too slow for acute; contraindicated with metallic implants | | **Aortography** | >95% | >95% | 20–30 min | Limited availability | Rarely used; endovascular planning | Invasive; delays treatment; risk of catheter-induced dissection | | **Chest X-ray** | 60% | Variable | <1 min | Always available | Screening only; non-specific | Insensitive; cannot confirm dissection | **Mnemonic: CECT FAST** — **C**ontrast, **E**nhanced, **C**T for acute **T**horacic dissection, **F**ast diagnosis, **A**vailable 24/7, **S**ensitive & specific, **T**riage to treatment. ### Stanford Classification & Management Correlation ```mermaid flowchart TD A[Acute Aortic Dissection]:::outcome --> B{CECT shows involvement?}:::decision B -->|Ascending aorta ± descending| C[Type A Dissection]:::outcome B -->|Descending aorta only| D[Type B Dissection]:::outcome C --> E[Emergency surgery]:::action D --> F{Uncomplicated?}:::decision F -->|Yes| G[Medical management: BP/HR control]:::action F -->|No| H[Endovascular repair or surgery]:::action ```