A 65-year-old man with a history of smoking and hyperlipidaemia presents with acute onset of severe pain and coldness in the right foot. On examination, the right foot is pale and pulseless below the inguinal ligament. What is the most appropriate investigation to confirm acute limb ischaemia and guide immediate management?

Explanation

## Investigation of Choice for Acute Limb Ischaemia **Key Point:** In acute limb ischaemia (ALI), urgent CT angiography or conventional angiography is the investigation of choice because it provides rapid, definitive anatomic diagnosis and allows immediate therapeutic intervention (thrombolysis or thrombectomy) without delay. ### Why Urgent Angiography in ALI? Acute limb ischaemia is a vascular emergency with a "golden window" of 6–8 hours for salvage. Investigations must be rapid and actionable: 1. **Speed** — CT angiography can be performed in minutes; conventional angiography allows simultaneous diagnosis and intervention 2. **Diagnostic accuracy** — shows exact site of occlusion (embolus vs. thrombosis vs. dissection) 3. **Therapeutic potential** — angiography enables immediate catheter-directed thrombolysis or mechanical thrombectomy 4. **No time for duplex** — duplex is operator-dependent and time-consuming; not suitable in emergency 5. **High sensitivity** — >95% for acute occlusion ### Clinical Presentation Clues This patient has the **6 Ps of acute limb ischaemia**: - **Pain** (severe, acute onset) - **Pallor** (pale foot) - **Pulselessness** (absent pulses) - **Paresthesia** (may develop) - **Paralysis** (may develop if not treated) - **Perishing cold** (coldness) ### Comparison of Investigations in ALI | Investigation | Role in ALI | Limitation | |---|---|---| | **CT Angiography** | First-line; rapid, non-invasive diagnosis | Contrast nephropathy risk; no therapeutic option | | **Conventional Angiography** | Gold standard; diagnostic + therapeutic | Invasive; requires expertise; time to setup | | **Duplex Ultrasonography** | Not suitable in ALI | Operator-dependent; time-consuming; cannot guide intervention | | **ABI** | Not useful in ALI | Does not diagnose acute occlusion; time-wasting | | **MR Angiography** | Too slow for ALI | Lengthy acquisition; not suitable for emergency | **Clinical Pearl:** In many centres, conventional angiography is preferred over CT in ALI because it allows immediate catheter-directed thrombolysis or thrombectomy without a second procedure. However, CT angiography is acceptable if it enables faster diagnosis and transfer to the interventional suite. **High-Yield:** The decision between CT and conventional angiography depends on local expertise and availability. The key principle is: **do not delay intervention with prolonged imaging**. If conventional angiography can be set up quickly, it is preferred; otherwise, CT angiography followed by urgent intervention is acceptable. **Warning:** Duplex ultrasonography, while excellent for chronic PAD, is NOT appropriate in acute limb ischaemia because it is time-consuming and operator-dependent. ABI is also not useful because it does not diagnose acute occlusion.