Competitive flow in arterial composite grafts and effect of graft arrangement in Off-Pump coronary revascularization

Background

We sought to investigate the incidence of competitive flow in arterial composite grafts and to delineate the effect of the location of moderately stenotic branch, the extent of the revascularized territories and the arrangement of in situ and free arterial grafts in off-pump coronary artery bypass grafting (OPCAB).

Methods

Three hundred eighteen patients who underwent OPCAB with aorta no-touch technique using the composite graft with totally arterial materials between December 2000 and March 2003 were studied. A total of 362 composite grafts were used. We reviewed their coronary angiography before and early after operation. Competitive flow was defined as the phenomenon that at least one of the distal anastomotic sites of the composite graft was not opacified in in situ graft angiography, but clearly opacified in native coronary angiography. The number of distal anastomoses was 3.47 ± 0.93 per patient and 2.87 ± 0.81 per composite graft.

Results

Early patency rate of the distal anastomotic sites of composite grafts was 98.7%. Competitive flow was found in 53/362 (14.6%) composite grafts, and graft occlusion occurred in 13/362 (3.6%) composite grafts. In the multivariate analysis of 362 composite grafts, 75% stenosis in right coronary artery (RCA) territory (p < 0.0001) and the number of distal anastomoses (p = 0.004) were significant predictors of competitive flow and graft occlusion. Multivariate analysis of 318 patients demonstrated that 75% stenosis in RCA territory (p < 0.0001) and the total number of distal anastomoses (p = 0.003) were statistically significant predictors of competitive flow and graft occlusion. The use of more than two in situ grafts and the shape of composite graft (branched or straight) did not have significant correlation with the outcome.

Conclusions

Coronary artery revascularization using composite arterial grafts provided satisfactory early patency rates with an acceptable incidence of competitive flow. Because the implication of competitive flow in an arterial composite graft may differ from that in conventional bypass grafts unpredictably, long-term follow-up is mandatory.     

Intraoperative flow measurement in composite Y arterial grafts.

OBJECTIVE: Total arterial myocardial revascularization may be achieved by using the 'Y-graft' techniques with different free arterial conduits anastomosed off the side of an in situ internal thoracic artery to reach distal coronary segments. This study was assessed to measure intraoperative graft flow, resistance and clinical outcomes. METHODS: Seventy-six patients who underwent coronary artery bypass grafting during a time period of 27 months were enrolled in this prospective study. All patients received sequential grafting by using both internal thoracic arteries, inferior epigastric and right gastroepiploic artery joined as a composite Y graft. Intraoperative graft flow, resistance and derived variables were measured. RESULTS: All patients except one showed good flow (ml/min and waveform) in either branch of composite graft. In one case, a low-flow situation through the graft was registered requiring surgical correction. Temporary occlusion of either branch did not significantly affect flow in the other side of the arterial Y. Mid-term follow-up (3 and 15 months) and angiographic studies showed a high graft patency rate. CONCLUSION: Composite arterial grafts provide excellent early and mid-term clinical results. Flow reserve of the left internal thoracic artery did not affect blood flow and resistance on either branch of the Y graft when temporary occlusion on the other side of the arterial Y was performed.     

Comparison of the flow capacity of free arterial grafts and saphenous vein grafts for coronary bypass surgery

There is controversy regarding the flow reserve and capacity of arterial conduits to meet the needs of the myocardium. This study compared flow in 22 free arterial bypasses to 15 saphenous vein grafts in procedures involving twenty patients. To assess the maximal flow possible, (flow capacity) graft flow was measured using a calibrated pump while perfusing blood cardioplegia through the conduit and distal anastomosis during cardiac arrest (no competitive flow). This assessment was subsequently confirmed with whole blood during myocardial contraction while on cardiopulmonary bypass. Twenty-two free arterial grafts were used; 15 right internal mammary artery grafts, 4 right gastroepiploic grafts, 3 inferior epigastric artery grafts, and 3 sequential bypasses. Free arterial conduit flow ranged from 50 to 180cc/ml, with an average flow of 102.5+/-28.5ml/min as compared to saphenous vein graft flow, 102+/-28 ml/min. No correlation of flow with the conduit size was found. Arterial graft flow demonstrated a mild correlation with the size of the native coronary artery bypassed (R=0.47, P相似文献   

Composite arterial Y graft has less coronary flow reserve than independent grafts

BACKGROUND: It is not known whether a composite Y graft of the left internal thoracic artery can provide sufficient blood flow to the whole left coronary system. The aim of this study was to compare regional myocardial blood flow (MBF) and coronary flow reserve after coronary artery bypass grafting using arterial composite Y graft or independent arterial grafts. METHODS: Positron emission tomography was performed at rest and after dipyridamole infusion using oxygen-15-labeled water 2 weeks after coronary artery bypass grafting. Regional MBF was calculated in seven segments of the left ventricle. Coronary flow reserve was defined as the ratio of MBF after dipyridamole infusion to MBF at rest. In the Y graft group (n = 22), a free arterial graft to obtuse marginal arteries was anastomosed to the proximal side of in situ left internal thoracic artery, which was anastomosed to the left anterior descending artery. In the independent graft group (n = 13), left anterior descending and obtuse marginal arteries were independently revascularized using in situ left internal thoracic artery and a free arterial graft. RESULTS: There was no difference between the groups in MBF at rest. Coronary flow reserve in the Y graft group was lower than that in the independent group in the anterobasal (1.43 +/- 0.07 versus 1.90 +/- 0.13, p = 0.038), apical (1.24 +/- 0.06 versus 1.64 +/- 0.12, p = 0.003), septal (1.34 +/- 0.05 versus 1.75 +/- 0.13, p = 0.023), and lateral regions (1.19 +/- 0.04 versus 1.66 +/- 0.09, p = 0.001). CONCLUSIONS: Although arterial composite Y graft improved MBF at rest, it was not as effective as independent grafts for improving coronary flow reserve soon after coronary artery bypass grafting.     

Blood flow measurement in PTFE grafts

In vascular surgery peroperative control of the result of reconstruction is essential. PTFE-grafts have been known to be "resistant" to flow registration with electromagnetic flowmetry because of the electrical isolation. Similarly, intraoperative Doppler registration has been impossible because of the attenuation of the ultrasound in the graft wall. The leading disturbances are obviously caused by air in the graft material and are not caused by the material itself. By squeezing the graft carefully between the thumb and forefinger, blood slowly penetrates the wall colouring it red. The squeezing is performed intermittently to avoid occlusion of the graft. Excellent flow registration is obtained after less than 2 min squeezing of the thin walled graft, while at least 5 min squeezing is necessary to obtain signals from thick walled grafts. To obtain satisfactory ultrasound signals more squeezing is necessary.     

Baseline flow in coronary bypass grafts

BACKGROUND: The purpose of the study is to estimate the total blood flow in coronary artery bypass grafts. METHODS: In a 3-year period 102 patients having a standardized coronary artery bypass grafting (CABG) with the left internal mammary artery (LIMA) anastomosed to the left anterior descending artery and a sequential vein grafted to the remaining diseased coronary arteries were included in the study, 21 females and 81 males. In females a mean of 3.9 anastomosis (range 2-5) were performed and in males a mean of 4.2 (range 2-6) were performed. Flow in the bypass grafts was measured with the transit-time method before termination of cardiopulmonary bypass. RESULTS: Females: LIMA 31 mL/min, vein graft 74 mL/min (26 mL/min per anastomosis), cumulated flow 105 mL/min. Males: LIMA 31 mL/min, vein graft 93 mL/min (29 mL/min per vein anastomosis), cumulated flow 124 mL/min. CONCLUSION: Conventional CABG may restore half of the normal resting coronary artery blood flow (250 mL/min).     

Use of arterial grafts for coronary revascularization

Objectives: The aim of this study was to evaluate the performance and the quality of arterial grafts for coronary artery bypass grafting at The Heart Institute of Japan, Tokyo Women’s Medical University.Patients and Methods: From January 1970 to March 1998, 2987 arterial grafts, including left and right internal thoracic arteries, gastroepiploic artery, radial artery and inferior epigastric artery, were used in 1673 patients. In the same period, 1225 saphenous vein grafts were used. Early graft patency was angiographically determined. Also, histological evaluation of operative specimens and preoperative angiographic evaluation of arterial grafts were performed.Results: The total number of hospital deaths was 38 (2.3%). Of 4212 grafts, 3919 grafts (93%) were evaluated angiographically and 3714 of 3919 grafts were patent (94.8%). The patency rate of internal thoracic artery was better than that of gastroepiploic artery (p < 0.0001), radial artery (p = 0.0005) and saphenous vein grafts (p < 0.0001). However, the patency rate of gastroepiploic artery was better than that of saphenous vein grafts (p = 0.04), while no significant difference was detected between gastroepiploic artery and rdial artery. Only one internal thoracic artery specimen obtained at surgery showed atherosclerotic change, but all gastroepiploic artery specimens had moderate to severe atherosclerotic changes with CD68-positive cell infiltration. Only one patient’s left internal thoracic artery out of 200 was not angiographically useable as a conduit, while multiple stenotic lesions in gastroepiploic artery were observed.Conclusions: In the graft selection for CABG, the primary choice is internal thoracic artery and the secondary choice is right internal thoracic artery, from the standpoint of histological and angiographic evaluation, gastroepiploic artery and/or radial artery, depending on the target anastomotic site, degree of stenosis, and in situ or free use is the third choice.     

Blood flow velocity of internal mammary artery and saphenous vein grafts to the coronary arteries

Doppler-derived blood flow velocity measurements were used to characterize the hemodynamics of 66 internal mammary artery grafts and 60 saphenous vein grafts to the coronary arteries at operation. Pulsed Doppler spectral analysis of centerstream graft flow demonstrated predominantly diastolic flow with a variable, multiphasic flow pattern in systole. The magnitude and configuration of the graft flow velocity waveform varied with graft type and whether the runoff was to single or multiple arteries. At operation, peak diastolic flow velocity was greater (P less than 0.0001) in internal mammary artery grafts to a single outflow artery (71 +/- 2 cm/sec) compared with single vein grafts (31 +/- 4 cm/sec). Sequential grafts demonstrated increased flow velocity and forward flow throughout the pulse cycle, indicative of low outflow resistance. Analysis of the phasic flow patterns permitted an assessment of functional graft patency. Technical errors (anastomotic stricture, internal mammary pedicle torsion) were identified in three grafts with low or absent diastolic flow. Vasospasm of the internal mammary artery was associated with high flow velocity throughout the pulse cycle. Observed differences in patency and the development of intimal hyperplasia between internal mammary artery and saphenous vein grafts may be related to graft hemodynamics.     

Improved surgical field for composite arterial grafts.

A simple method to obtain a motionless surgical field with excellent exposure and access to perform internal thoracic or radial artery composite grafts for myocardial revascularization is described.     

Flow capacity of inferior epigastric artery in composite arterial grafts

BACKGROUND: In the effort to expand the use of arterial conduits for myocardial revascularization, 'Y-graft' techniques are utilized with increasing frequency, although the physiology of this type of composite arterial grafts is not yet fully understood. The aim of this study was to measure changes in blood flow through a 'Y-graft' constructed by anastomosing a segment of inferior epigastric artery (IEA) off the side of an in situ internal thoracic artery (ITA). METHODS: Twenty-two patients who underwent CABG were enrolled in this prospective study. Exclusion criteria were age > 70 years, poor left ventricular function (Ejection Fraction < 0.25) and need for associated cardiac procedures. Blood flow in the TrA-IEA 'Y-graft' was measured in the operating room after completion of left ITA to left anterior descending artery (LAD) and IEA to marginal or diagonal branch anastomoses. Follow-up evaluation was performed at 3 and 12 months postoperatively. RESULTS: After completion of surgery, blood flow in ITA and IEA as measured downstream from the Y anastomosis was 45+/-7 and 39+/-6 ml/min respectively. Temporary occlusion of either branch did not significantly affect flow in the other side of the arterial Y. All patients were discharged from the hospital in excellent condition. At follow-up no cases of angina recurrence were recorded. CONCLUSIONS: Composite ITA-IEA arterial grafts provide excellent short-term clinical results. Blood flow on either side is not affected by run off in the other side branch. Information from this study may be used to understand the role that undivided ITA side branches play in reducing flow rate in an ITA graft harvested during minimally invasive CABG procedures.     

Instantaneous diastolic pressure-flow relationship in arterial coronary bypass grafts

OBJECTIVE: The objective of this study was to describe the diastolic pressure-flow relationship and to assess critical occlusion pressure in arterial coronary bypass grafts in human beings. METHODS AND RESULTS: Fifteen patients were studied following elective surgical coronary artery bypass grafting. Flow in the left internal mammary artery bypass to the left anterior descending artery was measured and simultaneously, aortic pressure, coronary sinus pressure and left ventricular end-diastolic pressure were recorded. The zero-flow pressure intercept as a measure of critical occlusion pressure was extrapolated from the linear regression analysis of the instantaneous diastolic pressure-flow relationship. Mean diastolic flow was 46 +/- 17 mL min(-1), mean diastolic aortic pressure was 60.5 +/- 10.0 mmHg. Diastolic blood flow was linearly related to the respective aortic pressure in all patients (R-values 0.7-0.99). The regression lines had a mean slope of 2.1 +/- 1.2 mL min(-1) mmHg(-1). Mean critical occlusion pressure was 32.3 +/- 9.9 mmHg and exceeded mean coronary sinus pressure and mean left ventricular end-diastolic pressure by factors of 3.1 and 2.6, respectively. CONCLUSIONS: Our data demonstrate the presence of a vascular waterfall phenomenon in the coronary circulation after internal mammary artery bypass grafting. Critical occlusion pressure in arterial grafts considerably exceeds coronary sinus pressure as well as left ventricular end-diastolic pressure and should thus be used as the effective downstream pressure when calculating coronary perfusion pressure. Our data further suggest that the slope of diastolic pressure-flow relationships provides a more rational approach to assess regional coronary vascular resistance than conventional calculations of coronary vascular resistance.     

Pressure characteristics in arterial grafts for coronary bypass surgery

The haemodynamic properties of arterial grafts were studied by measuring the pressure waveform at the tip of the grafts in 28 patients who underwent coronary artery bypass surgery (CABG). The internal thoracic and gastroepiploic arteries were harvested as pedicles for CABG. Pressure wave of the ascending aorta and arterial grafts were simultaneously recorded with an electrocardiogram under stable haemodynamic conditions before cardiopulmonary bypass. Systolic, diastotic and mean pressures were measured, and mean systolic and diastolic pressures calculated for systolic and diastolic areas divided by time. The ascending aorta showed high sustained diastolic pressure that decreased gradually. Pressures in the internal thoracic and gastroepiploic artery grafts had narrow contours and decreased rapidly. Pressure waveforms in the internal thoracic and gastroepiploic artery grafts had a notch between the systolic and diastolic contours. There was no difference in systolic pressure between the ascending aorta and internal thoracic and gastroepiploic artery grafts. Diastolic pressures were 64(9), 55(7), and 51(6) mmHg in the ascending aorta and internal thoracic and gastroepiploic artery, respectively. Mean(s.d.) pressures were 75(9), 65(9) and 59(7) mmHg in the ascending aorta and internal thoracic and gastroepiploic artery grafts, respectively. Diastolic and mean pressures in the internal thoracic artery grafts were significantly lower than in the ascending aorta but significantly higher than in the gastroepiploic artery grafts. The mean(s.d.) calculated diastolic pressure in the internal thoracic artery grafts was significantly lower than in the ascending aorta but significantly higher than in the gastroepiploic artery grafts. The inferior capacity of flow through the arterial grafts may be mainly attributable to reduced diastolic pressure, which is caused by anatomical characteristics. Arterial grafts originating from a systolic-dominant circulation far away from the heart have a limited ability to supply blood to the diastolic-dominant coronary circulation.