**Core Concept**
Subclavian steal syndrome is a condition that occurs when there is a significant stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery. This leads to a reversal of blood flow in the vertebral artery, causing a "steal" of blood from the ipsilateral arm.

**Why the Correct Answer is Right**
The reversal of blood flow in the vertebral artery is due to the higher pressure in the aorta compared to the pressure in the subclavian artery. As a result, blood flows from the vertebral artery into the subclavian artery, causing a decrease in blood flow to the arm. This can lead to symptoms such as arm fatigue, weakness, and coolness.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the location of the stenosis or occlusion, which is crucial for the development of subclavian steal syndrome.

**Option B:** This option is incorrect because it does not mention the vertebral artery, which is a key component of subclavian steal syndrome.

**Option C:** This option is incorrect because it mentions a different vascular territory (the carotid artery) and does not accurately describe the pathophysiology of subclavian steal syndrome.

**Clinical Pearl / High-Yield Fact**
Subclavian steal syndrome can be diagnosed using Doppler ultrasound, which can demonstrate the reversal of blood flow in the vertebral artery. It is essential to identify this condition promptly, as it can lead to serious complications such as arm ischemia and neurological deficits.

**Correct Answer: D. Stenosis or occlusion of the subclavian artery proximal to the origin of the vertebral artery.**