**Core Concept:** Embolic stroke is a type of stroke caused by the blockage of blood vessels due to emboli, which are particles or structures that travel through the bloodstream and obstruct blood flow to the brain. This can be due to various causes, including a pulmonary embolism.

**Why the Correct Answer is Right:** In this case, the correct answer (D) is due to the patient having a pulmonary embolism, which is a common cause of embolic stroke. An agitated saline contrast during echocardiogram shows the presence of bubbles crossing into the left atrium, indicating a right-to-left shunt, which is a characteristic feature of a patent foramen ovale (PFO). A patent foramen ovale is a normal variant in approximately 20-25% of healthy individuals, particularly those with a history of childhood respiratory infections.

**Why Each Wrong Option is Incorrect:**

A. Deep vein thrombosis (DVT) is a common cause of embolic stroke, but in this scenario, the patient presents with acute bilateral lower extremity deep vein thrombosis (DVT) and not an embolic stroke.

B. The patient's symptoms are due to acute bilateral lower extremity deep vein thrombosis (DVT), which is a direct cause of DVT but not an embolic stroke.

C. This option is incorrect because it is not the primary cause of the patient's symptoms; instead, it is a potential complication of acute bilateral lower extremity deep vein thrombosis (DVT).

D. The correct answer, as described above, explains the patient's symptoms due to a right-to-left shunt from a patent foramen ovale (PFO) leading to a pulmonary embolism causing embolic stroke.

**Clinical Pearl:** A patent foramen ovale (PFO) can act as a conduit for emboli to travel from the right atrium to the left atrium, leading to cerebral embolism (embolic stroke). This is particularly relevant in patients with a history of childhood respiratory infections, as these can cause right-to-left shunt through the PFO, leading to a paradoxical embolism involving the lungs and brain.