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[The significance of internal thoracic artery-left anterior descending coronary artery bypass grafting in postoperative angiographic studies--with reference to indication of ITA and factors of string sign].

Internal thoracic artery (ITA) graft for myocardial revascularization has shown superior long-term patency. However, several reports pointed out that the flow capacity of ITA was questionable and the string sign of ITA graft was sometimes observed in the findings of postoperative angiography when the stenosis of the coronary artery was of a lesser degree. We studied pre- and postoperative angiographic findings of 101 patients who underwent ITA grafting to the left anterior descending coronary artery. Postoperative angiography showed that the blood flow from the ITA graft ran through the site of anastomosis only towards the distal end when preoperative stenosis of the native left anterior descending coronary was less than 75%. ITA flow ran bidirectionally (retrogradely and antegradely) when stenosis was within 75 to 90%. Many cases with stenosis of greater than 90% showed the progression of the native lesion, that is, total obstruction of the left anterior descending coronary artery. It becomes clear by statistical study that the postoperative progression of native proximal lesion of the left anterior descending coronary artery correlates neither with the morphological state of the coronary artery nor sites of lesions, but the severity of stenosis. A conclusion has been drawn from angiographic study, that the blood flow from the ITA graft run into two directions; towards the distal and the lesion of the left anterior descending coronary artery, if the free flow through ITA was about 60 ml/min and at the same time, preoperative stenosis of coronary artery was 75% or more.