An evaluation of the intraoperative transit time measurements of coronary bypass flow

Objective: The intraoperative measurement of the coronary bypass flow enabl es the identification of technical errors while the sternum is still open. The transit-time flow method is able to effectively measure the internal th oracic artery graft flow. The aim of the present study was to analyze the f actors which affected the bypass flow rate. Methods: We measured the blood flow of 291 in situ internal thoracic artery (ITA) and 190 saphenous vein ( SV) grafts constructed in 171 patients undergoing coronary artery bypass gr afting from December 1996 to March 2000 using this method during the surger y. All patients underwent postoperative coronary angiography before the pat ients were discharged. The blood Row rate of all bypass grafts constructed was assessed after the patients were weaned from cardiopulmonary bypass. Re sults: The mean flow rate of all ITA grafts was 65.1 +/- 36.7 ml/min and th at of all SV grafts was 56.4 +/- 29.9 ml/min. According to analyses using c orrelation tests, the graft flow was found to significantly correlate with the grafted perfusion areas and the diameter of the bypassed coronary arter ies. However, no significant difference was observed between the flow rates of the ITA grafts with and without stenosis or string phenomenon, but sign ificant (P < 0.0001) correlation was observed between the occurrence of a s tring sign and the degree of proximal stenosis of the recipient coronary ar tery. Regarding SV grafts, the mean flow rate of occluded grafts (29.2 <plu s/minus> 20.5 ml/min) was significantly (P < 0.0001) less than non-occluded grafts (56.4 <plus/minus> 29.9 ml/min). Conclusions: The bypass flow was a ffected by such a large number of factors that only measuring the bypass fl ow rate could not sufficiently predict either stenosed or narrowed grafts. However, ITA grafts bypassed to the coronary arteries with less stenosis we re shown to more easily become narrowed. (C) 2001 Elsevier Science B.V. All rights reserved.