- During an 18-month period 11 patients were seen at the Toronto Western Hospital Pain Clinic 4 months to 5 years after internal mammary artery (IMA) bypass with a specific cluster of chest wall symptoms and signs confined to the site of IMA graft harvesting. Sympathetic ganglia blocks produced dramatic but temporary relief of symptoms in two of the most severely affected patients. In two other patients seen quite early after surgery, use of transcutaneous electrical stimulation produced considerable and permanent decrease of symptoms within 3 weeks. Such a chronic pain syndrome has not been previously reported in the literature. We postulate that IMA bypass surgery may be associated with a specific pain syndrome. This syndrome may arise from injury to the anterior branches of the intercostal nerves at the site of graft harvesting. Possible neurophysiologic mechanisms are discussed.