Internal Thoracic Artery Graft Flow Research Articles

Intraoperative Internal Thoracic Artery Graft Flow Measurement Ipsilateral or Contralateral to the Arteriovenous Fistula in Hemodialysis Patients During Coronary Artery Bypass Graft Surgery

Intraoperative Internal Thoracic Artery Graft Flow Measurement Ipsilateral or Contralateral to the Arteriovenous Fistula in Hemodialysis Patients During Coronary Artery Bypass Graft Surgery

Immediate improvement of left internal thoracic artery graft flow after subclavian artery stenting.

We report a case of treatment of subclavian-coronary steal syndrome with stenting and immediate improvement of left internal mammalian artery flow.

Vascular adaptation of the internal thoracic artery graft early and late after bypass surgery

Flow mismatch between the supplying artery and the myocardial perfusion region has been observed in patients with internal thoracic artery grafts. Thus coronary flow changes of arterial (internal thoracic artery grafts) and saphenous (saphenous vein grafts) bypass grafts were studied early and late after coronary artery bypass grafting. Thirty patients undergoing elective bypass surgery (internal thoracic artery and saphenous vein grafts) were studied intraoperatively and (17 patients) 3 to 10 months postoperatively. Coronary flow was measured intraoperatively with the transit-time Doppler scanning technique. Postoperatively, flow velocity and coronary flow reserve were determined with the Doppler flow wire technique. Quantitative angiographic analysis was used to determine vessel size for calculation of absolute flow. Intraoperatively, internal thoracic artery graft flow was significantly lower than saphenous vein graft flow (31 +/- 8 vs 58 +/- 29 mL/min, P < .01). Postoperatively, internal thoracic artery graft flow increased significantly to 42 +/- 24 mL/min at 3 months and to 56 +/- 30 mL/min (P < .02 vs intraoperative value) at 10 months, respectively. However, saphenous vein graft flow remained unchanged over time (58 +/- 29 to 50 +/- 27 mL/min at 3 months and 46 +/- 27 mL/min at 10 months). Coronary flow reserve was abnormally low intraoperatively in the internal thoracic artery (1.3 +/- 0.3) and saphenous vein (1.6 +/- 0.5) grafts but increased significantly to normal values in both types of graft at follow-up. Bypass flow of the internal thoracic artery graft is significantly reduced intraoperatively when compared with that of the saphenous vein graft. However, 3 and 10 months after the operation, flow of the internal thoracic artery graft increases significantly and is similar to saphenous vein graft flow. This finding can be explained by an early flow mismatch of the native internal thoracic artery in the presence of a large perfusion territory. During follow-up, there is vascular remodeling of the internal thoracic artery, probably because of endothelium-mediated mechanisms.

Supraclavicular control of patent internal thoracic artery graft flow during aortic valve replacement

Background The mortality and morbidity of aortic valve replacement (AVR) after prior coronary artery bypass surgery (CABG) with patent left internal thoracic artery (LITA) is significant. The risk of LITA injury and inadequate myocardial preservation during the cross-clamp period may cause myocardial pump failure. Methods A total of 43 patients with a patent LITA graft underwent AVR. The patients were divided into the two groups. Group 1 included 19 patients who underwent AVR with deep hypothermia (20°C) without LITA clamping. Group 2 included 24 patients in whom LITA flow was controlled through supraclavicular occlusion and AVR performed with moderate hypothermia (28°C). Results Average cardiopulmonary bypass time (CPB) time was 118.79 ± 20.36 minutes in group 1 and 102.67 ± 9.66 minutes in group 2 ( p = 0.006). Average cross-clamp time was 53.79 ± 7.26 minutes in group 1 and 49.63 ± 6.7 minutes in group 2 ( p = 0.022). Inotropic support was required in 12 patients in group 1 and 4 patients in group 2 ( p = 0.002). Average intensive care unit stay was 4.68 ± 2.24 days in group 1 and 2.29 ± 0.46 days in group 2 ( p < 0.001). Average hospital stay was 11.84 ± 2.91 days in group 1 and 8.04 ± 2.38 days in group 2 ( p < 0.001). Mortality due to myocardial failure developed in 4 patients in group 1 but in none of the patients in group 2 ( p = 0.02). Conclusions Proximal control of LITA flow by extrathoracic supraclavicular occlusion reduces the incidence of myocardial failure due to nonhomogenous cardioplegia delivery to the anterior wall of the heart, resulting in improved myocardial protection and the elimination of the need for deep hypothermia.

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

The intraoperative measurement of the coronary bypass flow enables the identification of technical errors while the sternum is still open. The transit-time flow method is able to effectively measure the internal thoracic artery graft flow. The aim of the present study was to analyze the factors which affected the bypass flow rate. 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 grafting from December 1996 to March 2000 using this method during the surgery. All patients underwent postoperative coronary angiography before the patients were discharged. The blood flow rate of all bypass grafts constructed was assessed after the patients were weaned from cardiopulmonary bypass. The mean flow rate of all ITA grafts was 65.1+/-36.7 ml/min and that of all SV grafts was 56.4+/-29.9 ml/min. According to analyses using correlation tests, the graft flow was found to significantly correlate with the grafted perfusion areas and the diameter of the bypassed coronary arteries. However, no significant difference was observed between the flow rates of the ITA grafts with and without stenosis or string phenomenon, but significant (P<0.0001) correlation was observed between the occurrence of a string sign and the degree of proximal stenosis of the recipient coronary artery. Regarding SV grafts, the mean flow rate of occluded grafts (29.2+/-20.5 ml/min) was significantly (P<0.0001) less than non-occluded grafts (56.4+/-29.9 ml/min). The bypass flow was affected by such a large number of factors that only measuring the bypass flow rate could not sufficiently predict either stenosed or narrowed grafts. However, ITA grafts bypassed to the coronary arteries with less stenosis were shown to more easily become narrowed.

Effect of flow competition on internal thoracic artery graft: Postoperative velocimetric and angiographic study

Objectives: To assess the effects of competitive blood flow on internal thoracic artery grafts, we investigated postoperative flow velocity characteristics and angiographic findings of the grafts with various grades of native coronary artery stenosis. Methods: Fifty patients who had an internal thoracic artery graft to the left anterior descending artery underwent intravascular Doppler graft velocimetry during postoperative angiography. Patients were divided into 3 groups according to the grade of native coronary stenosis: group H (28 patients), 80% stenosis or greater; group M (16 patients), 60% to 79% stenosis; and group L (6 patients), 40% to 59% stenosis. Phasic flow velocity of the grafts was measured with an intravascular Doppler ultrasound–tipped guide wire during angiography. Graft flow volume was calculated from the diameter and the average peak velocity. Results: Average peak velocity (group H, 27.1 ± 8.6 cm/s; group M, 16.9 ± 3.9 cm/s; group L, 7.2 ± 3.7 cm/s), distal graft diameter (group H, 2.27 ± 0.23 mm; group M, 2.00 ± 0.28 mm; group L, 1.07 ± 0.27 mm), and calculated graft flow volume (group H, 33.1 ± 12.0 mL/min; group M, 16.2 ± 5.8 mL/min; group L, 2.3 ± 2.0 mL/min) significantly differed among the 3 groups. Graft flow in diastole and systole also differed among the 3 groups. Conclusions: Competitive blood flow reduces internal thoracic artery graft flow and diameter according to the grade of the native coronary artery stenosis. These data suggest that grafting the internal thoracic artery to the coronary artery with stenosis of a low grade can cause graft atrophy and failure. (J Thorac Cardiovasc Surg 2000;120:459-65)

Intraoperative monitoring of IMA flow: What does it mean?

This study examines whether the measurement of internal thoracic artery (ITA) graft flow can determine the adequacy of the ITA-left anterior descending coronary artery (LAD) anastomosis. To study a wide range of clinical problems, we used a computer simulation of the cardiovascular system. The model included a time-varying elastance model of the heart, a systemic circulation represented by a multielement nonlinear model of the aorta and its major branches, a nonlinear model of the LAD circulation, and a model of the ITA bypass graft. With a mild LAD stenosis, ITA graft flow was low and flow reversal occurred. As the percent stenosis increased, ITA flow and the percentage of ITA-to-total LAD flow increased. The ITA graft helped to maintain resting LAD blood flow. A partial obstruction (40%) at the ITA-LAD anastomosis reduced ITA graft flow at similar levels of LAD stenosis. However, overlap in flow values comparing a normal with a partially obstructed anastomosis occurred. Flow patterns in the ITA are highly dependent on the degree of stenosis of the LAD as well as the integrity of the anastomosis. The predictive power of ITA flow measurement increases with severe stenosis or total occlusion of the proximal LAD and with high coronary blood flow demands.

Internal thoracic artery graft function during exercise assessed by transthoracic doppler echography

Noninvasive quantitative assessment of internal thoracic artery (ITA) graft function at rest and during exercise is important in patients who have undergone coronary artery bypass grafting. Blood flow in the ITA graft was measured using transthoracic color Doppler echography before and after operation in 50 patients who underwent coronary artery grafting using an ITA to the left anterior descending artery. The patients were divided into three groups according to the degree of coronary stenosis and previous anterior myocardial infarction: Group 1 included 12 patients with severe (90% or more) coronary stenosis accompanied by anterior infarction. Group 2 included 26 patients with severe coronary stenosis without anterior infarction. Group 3 included 12 patients with moderate (75% or less) coronary stenosis without anterior infarction. Transthoracic echographic images of the ITA were obtained through the first intercostal space using a 7.5-MHz probe, and the diameter and cross-sectional area of the ITA were measured on B-mode imaging. Systolic, diastolic, and mean blood flow velocity and volume were measured by the Doppler method. Internal thoracic artery diameter increased significantly from 2.2 mm to 2.4 mm after operation. The ITA flow patterns in both flow velocity and volume changed from systolic-dominant to diastolic-dominant after operation. Postoperative ITA graft flow was 82 +/- 24 mL/min, 53 +/- 30 mL/min, and 31 +/- 15 mL/min (p < 0.01, group 1 versus 3; p < 0.05, group 1 versus 2) and percent diastolic fraction of ITA flow was 72%, 68%, and 62% (not significant) in groups 1, 2, and 3, respectively. Compared with intraoperative ITA flow, which was measured using an ultrasound transit-time flowmeter, postoperative ITA graft flow was increased in group 1, but not changed in group 2 or 3. The ITA graft flow was measured before and after exercise in 19 patients and was compared with ITA flow in 10 normal control subjects. The ITA graft flow increased significantly with exercise in all patients in the three groups. Percent diastolic fraction of ITA flow increased significantly with exercise in patients with severe coronary stenosis (groups 1 and 2), but decreased significantly in patients with moderate stenosis (group 3). Changes in native coronary artery and ITA graft may be predicted by assessing ITA flow pattern during exercise. Transthoracic color Doppler echography is a clinically useful noninvasive method of assessing ITA graft function at rest and during exercise.

Internal thoracic artery graft flow during exercise assessed by transcutaneous color Doppler echocardiography

Internal thoracic artery graft flow during exercise assessed by transcutaneous color Doppler echocardiography

Cardiac Pacing Induced Flow Responses in Internal Thoracic Artery and Saphenous Vein Coronary Artery Bypass Grafts

The flow reactivity of an internal thoracic artery (ITA) graft and a vein graft for multiple coronary beds in response to different modes of cardiac pacing remains unclear. These experiments were conducted in 14 anesthetized dogs with the ITA or the vein grafted to the circumflex coronary artery, off pump, using a brief local occlusion. The left main coronary artery was occluded, rendering the entire left ventricle totally dependent upon the ITA graft or the vein graft. When the left main coronary artery was occluded and the heart rate was 120 beats per min, graft flow was 93.4 +/- 9.6 ml per min in the ITA, and 96.1 +/- 10.4 ml per min in the vein graft. Atrial pacing to increase heart rates 25% to 150 beats per min increased both the ITA graft flow (110.3 +/- 9.7 ml per min, p < 0.05 versus flow in sinus rhythm) and the vein graft flow (109.8 +/- 7.9 ml per min, p < 0.05 versus flow in sinus rhythm). The increases in flow in both cases were not attributable to changes in perfusion pressure. In contrast, ventricular pacing to the same heart rate decreased systemic pressure slightly, but insignificantly. Despite the slight decrease in perfusion pressure, ventricular pacing increased ITA flow (107.9 +/- 8.4 ml per min, p < 0.05 versus flow in sinus rhythm), but the increase in vein graft flow was not significant compared with flow in sinus rhythm (102.1 +/- 7.3 ml per min, p = ns versus flow in sinus rhythm).(ABSTRACT TRUNCATED AT 250 WORDS)

Distal flow determinants in canine myocardium perfused through internal thoracic artery bypass grafts

The dynamic reactivity and the acute, recruitable flow capacity of an internal thoracic artery (ITA) graft remains unclear. These experiments were conducted in 20 anesthetized dogs with the left ITA grafted to the circumflex artery, off pump, using a brief local occlusion. The left main coronary artery was occluded, rendering the entire left ventricle, including anterior descending artery and circumflex regions, totally dependent on the ITA graft. When the left main coronary artery was occluded, the ITA flow immediately increased more than fivefold (93.4 +/- 9.6 mL/min; mean +/- standard deviation), representing an absolute flow value three times higher than ITA flow measured in situ on the chest wall (27.5 +/- 9.6 mL/min; p < 0.05 versus control), and the ITA graft provided total resting flow requirements (93.4 +/- 9.6 mL/min) for both left anterior descending and circumflex coronary artery perfusion territories at levels comparable with measured native flow values (y = (0.9555)x + 21.9272; r = 0.976; p < 0.05). Pharmacologic challenge with adenosine (0.2 mg.kg-1.min-1 intravenously) significantly increased the graft flow (120.3 +/- 18.7 mL/min; p < 0.05 versus control), but also significantly decreased the mean arterial pressure (85.4 +/- 5.0 versus 74.6 +/- 6.1 mm Hg; p < 0.05). Phenylephrine (0.003 mg.kg-1.min-1 intravenously) significantly decreased ITA graft flow (81.2 +/- 9.0 mL/min; p < 0.05 versus control) despite significantly increased perfusion pressure (84.8 +/- 6.3 versus 108.2 +/- 8.6 mm Hg; p < 0.05 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonic assessment of internal thoracic artery graft flow in the revascularized heart

We investigated the clinical applicability of the transittime ultrasound technique for quantitation of internal thoracic artery (ITA) graft flow in coronary artery bypass grafting. Intraoperative measurements of arterial and venous coronary graft flow were performed in 63 patients using an ultrasonic flowmeter. Native ITA blood flow was determined using a skeletonized segment of the ITA and a flexible perivascular flow probe. Simultaneous measures of ultrasonic blood flow from the proximal part of the ITA and free flow from the distal cut end of the ITA validated reliability. After coronary grafting, separate perivascular flow probes over the saphenous vein and ITA grafts were positioned to measure flows during cardiopulmonary bypass and immediately before the sternal closure. Mean native ITA flow was 7 ± 0.8 mL/min and ITA graft flow was 35 ± 4 mL/min, a fivefold increase after grafting to the coronary artery ( p < 0.001). Mean saphenous vein graft blood flow of 38 ± 4 mL/min was not significantly different from the mean ITA graft flow ( p = 0.37). Coronary blood flow via saphenous vein and ITA conduits was unaffected by the Cardiopulmonary bypass ( p = 0.73). No complications were directly caused by the flow measurements. Flow impedance resulting from pedicle twist at the distal anastomosis was easily detected in 2 patients using the ultrasonic flowmeter. We conclude that ITA graft flow can be quantitated intraoperatively by the transit-time ultrasound technique. Ultrasonic assessment of ITA graft flow in the revascularized heart may be a useful means of detecting immediate coronary graft failure caused by technical errors.

Effect of chronic native flow competition on internal thoracic artery grafts

Residual competitive flow from the native coronary artery has been proposed as a mechanism that reduces flow in an internal thoracic artery graft (ITA), resulting in narrowing and ultimately failure of the graft. Results from acute experiments have indicated that competitive flow from a fully patent native artery did not abolish ITA graft flow. The present study was designed to examine the consequences of dynamic flow competition between the native vessel and the ITA graft in a chronic model. Fifteen mongrel dogs underwent coronary artery bypass grafting using the pedicled left ITA anastomosed to the normal, fully patent circumflex (CFX) coronary artery. The procedure was performed through a sterile thoracotomy, without systemic cardiopnlmonary bypass, using a brief local occlusion to construct the anastomosis. Intraoperatively, ITA flow was measured in situ on the chest wall, before the pedicle was mobilized. Internal thoracic artery graft and distal CFX flow were measured after the anastomosis was completed, with and without brief occlusion of the proximal CFX. Angiography was performed 72 hours, 4 weeks, and 8 weeks later; graft patency and diameter were evaluated. After 8 weeks, open-chest direct flow measurements comparable with the intraoperative assessment were obtained. Two grafts (13%) occluded early, the technical result of poor anastomotic construction. In the 13 remaining animals, all grafts were widely patent at all time points. Internal thoracic artery flow in situ averaged 10.9 ± 7.8 mL/min (mean ± standard deviation), and was maintained after grafting (11.5 ± 4.4mL/min; p = not significant). Internal thoracic artery graft flow represented 38.7% of total distal CFX flow (11.5/29.7) acutely. Comparable flows were obtained after 8 weeks of chronic competitive flow (11.9/ 30.4; 39.1%; p = not significant). Even after 8 weeks, when the proximal CFX was occluded transiently, flow increased in the ITA graft to provide 95% of the distal CFX requirements (30.4 ± 7.8 mL/min with proximal CFX open versus 28.9 ± 11.6 mL/min with proximal CFX occluded). The results demonstrate that even after 2 months of maximal chronic flow competition from a fully patent native artery, ITA graft flow was maintained above in situ levels, and a recruitable flow reserve from the ITA graft could be demonstrated when the native vessel was occluded. The data suggest that ITA grafts are dynamic and may remain patent despite significant residual flow in the native vessel.