**Core Concept**
Atrial fibrillation can lead to paradoxical embolism, where a blood clot forms in the heart and is transported to the arterial circulation, causing a limb to become pulseless and ischemic. In this scenario, despite successful embolectomy, the patient's inability to dorsiflex his toes suggests compartment syndrome, a condition where increased pressure within a confined space compromises muscle and nerve function.

**Why the Correct Answer is Right**
Following a popliteal embolectomy, the patient's inability to dorsiflex his toes indicates ongoing ischemia or compartment syndrome. The anterior compartment of the leg contains the muscles responsible for toe dorsiflexion. In compartment syndrome, increased pressure within this compartment can compress the anterior tibial nerve and muscles, leading to muscle weakness and paralysis. Immediate fasciotomy is necessary to relieve pressure and restore blood flow to the affected muscles and nerves.

**Why Each Wrong Option is Incorrect**
**Option A:** Electromyography (EMG) is a diagnostic tool that measures the electrical activity of muscles. While EMG can confirm muscle damage, it is not a suitable immediate response to suspected compartment syndrome, where urgent decompression is necessary to prevent further damage.

**Option B:** Measurement of anterior compartment pressure would be a more appropriate step if the patient's symptoms were less severe or if there was no suspicion of compartment syndrome. However, given the patient's inability to dorsiflex his toes, immediate action is required to prevent permanent damage.

**Option C:** Elevation of the left leg might be beneficial in reducing swelling and pain but would not address the underlying issue of increased pressure within the anterior compartment.

**Clinical Pearl / High-Yield Fact**
In cases of suspected compartment syndrome, especially after a popliteal embolectomy, prompt recognition and treatment are critical to prevent permanent muscle and nerve damage. A simple, reliable method to diagnose compartment syndrome is the "5 Ps": Pain, Pallor, Pulselessness, Paraesthesia, and Paralysis.

**✓ Correct Answer:** D. Immediate fasciotomy