Which statement is true regarding Subclavian steal phenomena?

The statement that Subclavian steal phenomena is caused by arterial obstruction proximal to the vertebral artery is correctly identified. This phenomenon occurs due to significant stenosis or obstruction in the subclavian artery, typically before it branches off into the vertebral artery. When the subclavian artery is blocked or narrowed, the body compensates by redirecting blood flow. In this case, flow from the vertebral artery (which usually supplies blood to the posterior circulation of the brain) is reversed, effectively "stealing" blood flow to maintain perfusion to the affected limb. This can lead to various symptoms, including arm claudication, dizziness, or even vertigo, especially when the arm is elevated or exerted.

The other statements do not accurately describe the characteristics of Subclavian steal phenomena. It does not usually result in severe symptoms for all patients; many may be asymptomatic. The condition can affect either side of the body and is not exclusive to the right side. Furthermore, while it might be less common than other vascular issues, it is not classified as a rare occurrence. Thus, the understanding of this phenomenon's underlying cause is crucial for proper diagnosis and management in vascular technology.