Although coronary artery bypass surgery is clearly effective in relieving angina pectoris, research evidence that it prolongs life has been inconsistent. Bypass surgery has been shown to improve survival in patients who have left main coronary artery disease or triple-vessel disease with impaired ventricular function, but whether other patient groups live longer after this surgery is not clear. Conservative interpretations of the results of various trials have led some authorities to conclude that many bypass procedures performed are avoidable.

Three factors were associated with a significant survival benefit following surgery, the extent of coronary disease, the patient's overall medical risk and the year of the operation. Patients with more extensive coronary obstruction treated surgically had the greatest improvement in survival. Patients with a poor prognosis because of factors other than the extent of coronary obstruction, older age, severe angina, had a greater absolute improvement in survival after coronary bypass surgery than did those who were treated medically.

Improved survival after surgery is not confined to select subgroups of patients. Therapeutic recommendations must be based on individualized assessment of expected risks and benefits of surgery.