Assessment Of Left Internal Mammary Artery Graft Flow And Patency Using Transthoracic Doppler Echocardiography

Background and Objective Coronary artery bypass graft( CABG)surgery is an effective treatment for most of the patients with coronary artery disease. The left internal mammary artery (LIMA) is the conduit of choice to the left anterior descending (LAD)artery, which reduces the risk of cardiac events and improves the survival rate of patients with coronary artery disease because of its high patency rate. Thereby how to evaluate the patency of LIMA graft is an important examination in the follow-up period of CABG patients. Coronary angiogram is invasive, which prevents its routine use as a quality control tool in the postoperative setting. Transthoracic Doppler echocardiography (TDE) has been available recently, and has developed as a complementary check-up for coronary angiogram. The objective of this study was to evaluate the LIMA flow characteristics and. identify the variables that may affect Doppler flow patterns, and to assess the patency of internal mammary artery graft with transthoracic Doppler echocardiography in patients after coronary artery bypass surgery.Material and Methods Sequential 115 patients were enrolled in this study, including 46 patients who were on the early stage post CABG, 28 patients had coronary angiogram. The mean age was 68.51±10.00.The TDE examinations were performed with a digital ultrasonographic unit (Sequoia 512, Acuson Inc., Mountain View, California, U.S.A.) using 14 MHz and 4.25MHz transducers. After routine echocardiographic examinations, LIMA grafts were conducted. Each LIMA graft was detected from its original segment , thoracic segment, to its anstomosis location. The systolic peak velocity (SPV), diastolic peak velocity(DPV), systolic velocity time integral(SVTI), diastolic velocity time integral (DVTI) for each segment were measured respectively. Theratio of diastolic peak velocity to systolic peak velocity (D/S) and diastolic fraction were calculated( DF ). Right internal mammary arteries were also checked in the patients who were on the early stage post CABG as a control. A compared study was done in patients who had coronary angiogram.Results 1 The detectable rates of LIMA graft's original segment and thoracic segment were around 94%. The appearance percentage was around 82% in the anstomosis of the LIMA graft. Three segments of the LIMA grafts were detectable in 79% of the patients. Compared with coronary angiography, the accuracy of TDE to evaluate internal mammary artery graft patency of was 96.4%.2 The right internal mammary artery had systole predominant forward flow. When grafted, even on the early stage, LIMA flow became biphasic(systolic and diastolic), with a diastole predominant flow.3 D/S ratio increased from 0.70 proximally to 1.76 distally. The pattern of LIMA flow near the anstomosis was similar with that of coronary artery.4 There were no statistically significance among measurements at distal segment of LIMA graft, anstomosis and distal left anterior descending artery of patent graftsC/^O.OS). D/S and DF and the DPV ratio of the anastomosis to the proximal LAD were indices on assessing graft stenosis. Occluded grafts had absent flow or systolic dominant pattern.5 Apart from the two factors of LIMA side branches and probe position, the combined effect of a poor LAD target and competitive LAD flow was associated with a significantly decreased PDV and DVTL A LIMA perfusing a poor LAD target or the presence of competitive LAD flow was associated with a significantly diminished PDV. PDV and DVTI had positive relations with LAD stenostic degree and LAD collateral vessels. D/S and DF were not affected.Conclusions1 TDE is an adoptable, reliable and noninvasive investigation of LIMA graft patency, especially using multiple segments detection.2 The diastolic component increases from graft proximal part to distal part, while the systolic component decreases. Apart from the two factors of LIMA side branches and probe position, LAD stenostic degree, LAD target and LAD collateral vessels IAD affect LIMA graft diastolic flow.3 Patent LIMA graft flow becomes diastole dominant pattern after CABG. The appearance of anstomosis of the LIMA graft provides the straight prove for judging the grafts patency. When detected absent flow or systolic dominant flow pattern, which may means occluded grafts.