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Ann Thorac Surg 2001;71:1210-1214
© 2001 The Society of Thoracic Surgeons
a Department of Surgery II, Division of Cardiovascular Surgery, Nippon Medical School, Tokyo, Japan
b Department of Internal Medicine I, Nippon Medical School, Tokyo, Japan
Accepted for publication November 28, 2000.
Address reprint requests to Dr Ochi, 1-1-5 Sendagi Bunkyo-ku, Tokyo, 113-8603, Japan
e-mail: ochi/surg2{at}nms.ac.jp
| Abstract |
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Methods. Angiographic and echocardiographic studies were conducted in 30 patients who had undergone coronary artery bypass grafting using both the internal thoracic and right gastroepiploic arteries. The luminal diameter of the arterial grafts was measured from the postoperative angiograms. The adequacy of the myocardial blood supply from the arterial grafts was evaluated by dobutamine stress echocardiography.
Results. With echocardiography, 14 patients exhibited an ischemic response in the gastroepiploic artery grafted region, whereas no patients exhibited an ischemic response in the internal thoracic artery grafted area. The luminal diameter of the gastroepiploic artery and a younger age were correlated with the ischemic response observed in the dobutamine stress echocardiography. A luminal diameter of the gastroepiploic artery of greater than 2.6 mm had the highest sensitivity and specificity for a nonischemic change.
Conclusions. To generate the maximal flow reserve, the luminal diameter of the gastroepiploic artery when used as a graft should be sufficiently large enough, nearly 3 mm at the anastomosis.
| Introduction |
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The GEA has a wide individual variation in its length and caliber. However, there has been little data presented providing criteria for the usage of this artery with regard to the characteristics of the flow capacity of the GEA. We assessed the flow capacity of the GEA by analyzing the results of the postoperative angiographic and dobutamine stress echocardiographic evaluations in patients who underwent coronary artery bypass grafting using both the GEA and the ITA.
| Material and methods |
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Sequential anastomoses were performed with the left ITA in 17 patients and with the GEA in 11 patients (Table 1).
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The GEA was brought into the pericardial cavity anterior to the stomach and liver. All patients were operated on by a single surgeon (MO).
An angiographic examination was performed from 3 to 21 months (mean, 6.8 months) postoperatively as a routine practice to confirm the status of the grafts, as well as that of the coronary arteries. All patients were informed of this preoperatively and all accepted to comply with the procedure. During the same period, all patients were offered the option of dobutamine stress echocardiography (DSE) to document the adequacy of the myocardial blood flow, and informed consent was obtained.
Protocol of the postoperative dobutamine stress echocardiography study
The protocol for the DSE [9] included infusion of nitroglycerin at 0.1 to 0.2 µg · kg-1 · min-1, followed by infusion of dobutamine at 4 µg · kg-1 · min-1 with stepwise increases to 8, 12, 16, 20, 25, and 30 µg · kg-1 · min-1 (infusion at each dose for 3 minutes). The electrocardiogram was monitored continuously, and the blood pressure, 12-lead electrocardiogram, and echocardiogram were recorded at baseline and at the end of each stage.
The following end points were applied to the DSE: (1) appearance of a new regional wall motion abnormality involving two or more wall segments; (2) attaining 85% of the target heart rate; (3) an ST-segment depression or elevation greater than 2 mm; (4) occurrence of significant chest pain; (5) an increase in the systolic blood pressure more than 200 mm Hg; (6) a decrease in the systolic blood pressure of 20 mm Hg or to less than 90 mm Hg; (7) appearance of complex ventricular arrhythmias; and (8) administration of the maximum dose of dobutamine.
Echocardiographic images were video-recorded and reviewed by at least two experienced cardiologists. The presence of an ischemic response to the DSE was diagnosed when one of the following involving two or more wall segments was identified: (1) development of asynergy in the patients without a wall motion abnormality at rest and (2) worsening of the wall motion abnormality in the patients with a wall motion abnormality at rest (ie, deterioration from hypokinesis to akinesis or dyskinesis).
Angiographic examination
Diagnostic angiographic catheters (5F) of various shapes were used through a transfemoral approach in all patients. All grafts were investigated for patency. The ITAs and GEAs were visualized selectively or semiselectively. Care was taken to obtain a cineangiogram in which both the distal segments of the arterial grafts around the anastomosis and the catheter could be seen in the same frame. Coronary angiograms were also obtained. Before angiography, a 2.5-mg bolus of isosorbide dinitrate was injected into the coronary arteries and arterial grafts to eliminate spasms.
The luminal diameter of the arterial grafts near the anastomosis was measured from the angiogram by comparing it with the lumen of a 5F angiographic catheter (1.67 mm) by means of computer-analyzed Quantitative Coronary Angiography (Cardio 500, KONTRON Elektronik GmbH, Munich, Germany).
The angiographic status of the arterial grafts was evaluated by classifying the pattern of the blood flow of the grafted coronary artery by the arterial graft as follows:
Statistical analysis
Statistical analysis was performed using SPSS10.0J (SPSS Inc, Chicago, IL). The distributions were analyzed by the Kolmogorov-Smirnov test and the variances of the data by the Levene test. Then, comparisons between the two groups were performed using the unpaired Students t test. The
2 test using the Fishers direct method was used for comparison of categoric data. A multivariate logistic regression analysis was performed using the patient characteristics and the difference between the ischemic and nonischemic changes in the GEA anastomosed region as independent covariates, by selecting a forward-stepping selection method with maximum likelihood estimates and default criteria. A receiver operator characteristic curve was used to optimize the sensitivity and specificity of using the diameter of the GEA to predict nonischemic change. Data were presented as mean ± standard deviation. All p values were two-tailed, and a p value of less than 0.05 was considered significant.
| Results |
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The status of the ITAs was: A dominant ITA in 19 patients, balanced condition in 7, and dominant coronary in 4 patients. The status of the GEAs was: A dominant GEA in 23 patients, balanced condition in 6, and dominant coronary in 1 patient. Residual nongrafted vessels in the right coronary system were identified in 5 patients.
Dobutamine stress echocardiography
In the DSE, no patients exhibited new wall motion abnormalities in the anteroseptal to lateral region where the ITAs were grafted. On the contrary, a new wall motion abnormality during the DSE was identified in 14 patients in the inferoposterior region where the GEA was anastomosed. Among these patients, 3 complained of chest pain with an ST-segment depression on the electrocardiogram during the DSE.
Patients were divided into three groups according to the results of the DSE and the presence of residual nongrafted vessels in the inferoposterior region on the angiogram (Table 2). Group I patients did not exhibit an ischemic change in the DSE and did not have residual nongrafted vessels in the inferoposterior region (N = 16). Group II patients exhibited an ischemic change in the DSE, but did not have residual nongrafted vessels in the inferoposterior region (N = 9). Group III patients exhibited an ischemic change in the DSE and had residual nongrafted vessels in the inferoposterior region (N = 5). The luminal diameter and angiographic status of the arterial grafts of the GEA in each group are shown in Tables 3 and 4.
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On univariate analyses, the age, body surface area, presence of hypertension, diabetes or hyperlipidemia, and history of smoking, or old myocardial infarction were not associated with an ischemic change. The variables observed during the DSE also were not associated with an ischemic change in the DSE. The only significant variable associated with an ischemic change was the luminal diameter of the GEA (Fig 1).
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| Comment |
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In the current study, ischemic wall motion abnormalities occurred in the DSE only in the region perfused by the GEA, even in the patients who exhibited acceptable angiographic findings for the GEA. Among the 9 patients in group II, 6 exhibited a definite angiographic dominancy of the GEA over the coronary artery. Furthermore, no wall motion abnormalities were induced in the DSE in the region perfused by the ITA. These results led us to assume that the flow capacity is apparently different between the GEA and ITA, especially under certain stress conditions.
There have been several reports on the free flow rate and the diameter of the GEA for the anastomosis measured intraoperatively [6, 18, 20, 21]. A large luminal diameter correlated with better flow rates. None of the previous reports, however, have demonstrated the adequacy of the flow capacity of the GEA under maximum stress conditions. The results in this study clearly indicate that the luminal diameter of the GEA should be large enough (2.6 mm or more) to meet the myocardial oxygen demand during exercise.
Many reports have warned that a GEA with a small diameter should not be anastomosed to a noncritically stenosed coronary artery because of the frequent occurrence of competitive flow between the coronary artery [8, 2224]. As mentioned previously, 6 patients in group II showed angiographic dominancy (Fig 3). In 4 of these patients, the GEA grafted coronary artery was totally occluded. Dominant GEAs were supposed to perfuse the entire vascular bed of the grafted coronary artery.
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The length of the GEA graft may influence its flow reserve. The distal segment of the GEA contains more smooth muscle cells and is smaller in diameter. Therefore, the distal segment of the GEA graft should be trimmed, because the distal segment of the arterial grafts is reactive and functions as a flow regulator [25]. Use of a shorter GEA graft has been advocated to obtain better blood flow [20].
However, the GEA has a wide individual variation in its length and caliber. In our series, 7 patients with a sequential graft of the GEA were included in the nonischemic group. Despite the need for a longer length of the GEA than that for nonsequential grafts, all these patients had GEAs with a luminal diameter of more than 3 mm. This indicates that the major determinant of the flow capacity of the GEA is its luminal diameter. As long as the luminal diameter of the GEA is large enough, the length of the GEA graft may not influence its flow reserve. Conversely, even if the length of the GEA is sufficient, a small luminal diameter is a contraindication to its use.
There was at least one residual nongrafted vessel of the right coronary artery in the group III patients. All the patients in group III had GEAs with a luminal diameter of more than 3 mm (range, 3.1 to 3.8 mm; mean, 3.6 mm). In 4 of these patients, the GEA graft was anastomosed to the totally occluded right coronary artery. Whether the ischemic change was the result of the inadequate flow reserve of the GEA or the nongrafted vessels remained ambiguous. However, even in group II patients, there was 1 patient whose GEA was 3.3 mm in diameter (Fig 1). The right coronary artery of this patient was totally occluded at the proximal segment and the remainder of it was perfused by the GEA. A possibility still exists that the ischemic response in the group III patients was attributable to the inadequate flow capacity of the GEA. There may be other factors that influence the flow capacity of the GEA as a graft [19]. Further study, for example, a measurement of the change in the flow velocity of the GEA under stress conditions using transcutaneous Doppler echocardiography [26], may give us a solution to this problem.
A possible explanation for why a younger age is an independent predictor for ischemic change in the DSE is an age-related reduction in the basal metabolic rate that reduces oxygen consumption of the heart [27, 28]. Aging is associated with a progressive loss of myocytes and an increase in the rate of degenerative change [29]. The structural and functional changes can affect the oxygen utilization of the heart.
In conclusion, considering the high occurrence of ischemic change in the GEA grafted region, which is not observed at all in the ITA grafted region, the flow capacity of the GEA differs from that of the ITA especially under maximal stress conditions. In that sense, the GEA should not be used routinely in the same way as the ITA. The luminal diameter of the GEA as a graft to the coronary artery should be more than 2.6 mm at the anastomosis, and adding the thickness of the arterial wall, the outer diameter should be 3 mm or more.
| Acknowledgments |
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| References |
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