One of the first signs of the worst form of PADPeripheral Artery Disease, a potentially life threatening disease where plaque, like calcium, builds up along blood vessel walls, narrowing the arteries and reducing blood flow to the legs and feet., called critical limb ischemiaAlso potentially known as CLI, the most severe and deadly form of peripheral artery disease. (CLI), can be a nonhealing wound or ulcerUlcers (or wounds) can occur when there is poor blood flow in your legs or feet. Poor blood flow causes cells to die and damages tissue, often on the feet and legs. These types of wounds can be slow-healing..