Peripheral Arterial Disease

Peripheral arterial disease (PAD) is a manifestation of systemic atherosclerosis affecting the arteries supplying the lower extremities, most commonly the superficial femoral artery (most frequent site of stenosis), the aortoiliac segment, and the infrapopliteal (tibial) arteries. The pathogenesis mirrors coronary atherosclerosis: endothelial injury from hypertension, tobacco toxins, hyperglycemia, and dyslipidemia increases endothelial permeability, allowing LDL cholesterol to infiltrate the subintimal space. Oxidized LDL triggers monocyte recruitment and differentiation into macrophages that engulf lipid, becoming foam cells. Smooth muscle cell migration, proliferation, and extracellular matrix deposition create a fibrous cap over the growing lipid-rich necrotic core. Progressive plaque growth narrows the arterial lumen, reducing blood flow. During exercise, skeletal muscle oxygen demand increases 10-20 fold, but the stenotic artery cannot increase flow to match demand, producing the hallmark symptom of intermittent claudication -- reproducible cramping pain in the calves, thighs, or buttocks that occurs with walking and resolves within 2-5 minutes of rest. The Fontaine classification stages PAD progression: Stage I (asymptomatic), Stage II (intermittent claudication), Stage III (rest pain), and Stage IV (tissue loss/gangrene). The ankle-brachial index (ABI) is the...