The condition that leads to peripheral artery bypass surgery is peripheral artery disease (PAD). PAD is caused by atherosclerosis, a buildup of plaque, which is a hard, fatty substance. The plaque results from the high cholesterol circulating in blood and depositing in the inner layers of the arteries. Risk factors for plaque formation include smoking, high cholesterol, high blood pressure and high blood sugar levels. At some point, blood clots form due to the reduced flow of blood or because the plaque breaks causing a blood clot that can severely narrow or block arteries.