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a Department of Anesthesiology and Pain Medicine, Seoul National University Hospital, Seoul, Korea
b Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, Seoul, Korea
Accepted for publication September 17, 2009.
* Address correspondence to Dr Kim, Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, 28 Yeongeon-dong, Chongno-gu, Seoul, 110-744, Korea (Email: kimkb{at}snu.ac.kr).
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsCommentReferences |
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Methods: Enrolled were 28 patients who were scheduled for revascularization with a Y-composite graft (end-to-side anastomosis of the right gastroepiploic artery to the in situ left internal thoracic artery graft). After all planned anastomoses were completed in each patient, blood flow in the right gastroepiploic artery composite graft and the internal thoracic artery graft (proximal and distal to the right gastroepiploic artery graft) was measured before and after continuous norepinephrine infusion.
Results: Blood flow in right gastroepiploic artery (26.4 ± 15.8 vs 33.8 ± 18.0 mL/min, p = 0.0004), proximal left internal thoracic artery (47.5 ± 21.2 vs 61.6 ± 23.4 mL/min, p < 0.0001), and distal left internal thoracic artery (20.1 ± 12.1 vs 26.8 ± 14.6 mL/min, p < 0.0001) grafts increased after norepinephrine infusion. In addition, the proportion of blood flow in right gastroepiploic artery grafts based on the blood flow in proximal left internal thoracic artery grafts was preserved (57.2% ± 24.7% vs 55.1% ± 25.6%, p = 0.607).
Conclusions: Blood flow in right gastroepiploic artery composite grafts after off-pump coronary artery bypass grafting was preserved during norepinephrine infusion.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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There is a concern that because the composite graft only emanates from a single blood source, it may not supply sufficient blood flow to a wider area of myocardium [4, 5]. In addition, RGEA grafts tend to spasm because of the high muscularity of the RGEA [6, 7]. In vitro studies demonstrated that RGEA grafts showed a greater propensity for vasoconstriction in response to various vasoconstrictors compared with other arterial grafts [8, 9]. The aim of this study was to elucidate the effect of sympathetic stimulation on absolute blood flow and the proportion of blood flow through a RGEA composite graft that was anastomosed to the side of the left ITA.
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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The study enrolled 28 patients scheduled for elective off-pump coronary artery bypass (OPCAB) grafting using the free RGEA as a Y-composite graft anastomosed to the side of the in situ left ITA (Table 1). Excluded were patients who showed celiac trunk narrowing on preoperative angiographic evaluation, who needed intra-aortic balloon pump support, who converted to cardiopulmonary bypass during OPCAB, or whose left ventricular ejection fraction was less than 0.40. Also excluded were patients who did not meet the criteria for normally functioning grafts after anastomoses [10].
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Surgical Technique and Study Protocol
All patients underwent OPCAB through a median sternotomy incision. The ITA and RGEA were harvested in a skeletonized fashion using scissors or a cold cautery device, as previously described [11]. Throughout the dissection, the grafts were sprayed with warm diluted papaverine solution to minimize spasm and prevent desiccation. After systemic heparinization, the grafts were clipped distally. The ITA graft was immersed in a 10-mL syringe filled with warm diluted papaverine solution (1 mg/mL) and allowed to dilate until use. The RGEA graft was wrapped in gauze soaked in warm dilute papaverine solution. Intraluminal injection of papaverine solution was not performed.
The Y-composite graft was constructed before the distal anastomosis was started. The RGEA was divided at its proximal section and anastomosed to the side of the left ITA in a Y fashion using an 8-0 polypropylene continuous suture. The ITA graft was anastomosed to the left anterior descending artery or diagonal branch, and the composite RGEA graft was anastomosed to the diagonal branches, obtuse marginal branches, or distal branches of the right coronary artery. Patients received an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time exceeding 300 seconds.
When all anastomoses were finished and vital signs were stable for 10 minutes, blood flow through the left ITA proximal and distal to the RGEA anastomosis site and the RGEA graft was measured (T1) by transit time flow measurement (TTFM; BF1001, Medi-Stim AS, Oslo, Norway), and the measuring points were marked. Norepinephrine infusion was then started at a rate of 0.005 µg/kg/min and increased every minute by 0.005 µg/kg/min until a 15% increase in heart rate or mean arterial pressure was achieved [12]. When heart rate or mean arterial pressure remained stable for 10 minutes in response to the norepinephrine infusion (T2), blood flow through both arteries was measured again at the locations previously marked, and norepinephrine infusion was discontinued. Blood flow measurements using TTFM were performed three times at each point and averaged.
One surgeon (Ki-Bong Kim) performed all procedures and measurements.
Statistics
Because a previous study showed the average flow difference through in situ RGEA grafts after sympathetic stimulation was 6 ± 11 mL/min [13], a sample size of 28 was used to detect the difference of 6 mL/min at 80% power and at a type I error of 0.05. A paired t test was used to compare the flows before and after norepinephrine infusion. All results were expressed as mean ± standard deviation, and a value of p < 0.05 was considered statistically significant. Statistical analysis was performed with the SPSS 12 software (SPSS Inc, Chicago, IL).
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Blood flow in the RGEA (26.4 ± 15.8 vs 33.8 ± 18.0 mL/min, p = 0.0004), proximal left ITA (47.5 ± 21.2 vs 61.6 ± 23.4 mL/min, p < 0.0001), and distal left ITA (20.1 ± 12.1 vs 26.8 ± 14.6 mL/min, p < 0.0001) grafts was significantly increased after norepinephrine infusion (Table 2). The proportion of blood flow through the RGEA grafts compared with that through the proximal left ITA grafts did not change after norepinephrine infusion (57.2% ± 24.7% vs 55.1% ± 25.6%, p = 0.607).
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentReferences |
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Greater freedom from reinterventions and enhanced long-term survival rates have been demonstrated when bilateral ITAs are used rather than a single ITA graft in surgical revascularization for multivessel coronary artery disease [1–3]. However, the use of bilateral ITAs as in situ grafts sometimes does not achieve complete arterial revascularization in patients with multivessel coronary disease. Construction of a Y-composite graft further increases the length of the ITA and allows the extensive use of bilateral ITA grafts to revascularize the right coronary system as well as the left coronary system [14].
On the basis of the superior advantages of ITA grafts, other arteries such as the radial artery and the RGEA have been used in myocardial revascularization. One previous study [15] demonstrated a significantly lower patency of pedicled RGEA composite grafts than radial artery grafts and discouraged the use of RGEA composite grafts. In contrast, another study [16] demonstrated satisfactory clinical and early patency results of skeletonized RGEA composite grafts. Encouraged by a previous study [11] demonstrating excellent early and 1-year patency rates of skeletonized in situ RGEA grafts, we extended the use of the skeletonized RGEA to the construction of a Y-composite graft anastomosed to the left ITA.
There has been a concern that RGEA grafts tend to spasm because of the RGEA's high muscularity [6, 7]. In vitro studies demonstrated that the vasoconstriction response to noradrenaline was more intense in the RGEA than the ITA [8, 9]. This contrasts with a previous study [13] that showed sympathetic stimulation increased blood flow through in situ RGEA grafts after coronary revascularization. That result, along with the results of the present study, suggested that blood flow through RGEA grafts seemed to be pressure dependent and increased by norepinephrine infusion through the mechanism of increased systemic blood pressure.
Because the blood flow of the composite RGEA graft only emanates from the left ITA, there is a concern that composite RGEA grafts may not supply sufficient blood flow to a wider area of myocardium [4, 5]. Although composite grafts provided a more than twofold reserve of blood flow through the grafts [17], they were not as effective as independent grafts for improving coronary flow reserve soon after CABG [4]. The concern is amplified in sympathetically stimulated circumstances, and no clinical studies have evaluated blood flow through the RGEA composite graft under controlled sympathetic stimulation. The present study showed that blood flow through composite RGEA grafts anastomosed to the side of left ITA was preserved during norepinephrine infusion both in absolute flow and in proportion to flow through ITA grafts. These results provided a rationale for the safe use of norepinephrine in patients undergoing CABG using the RGEA graft.
Some limitations of the present study must be recognized. First, this study was performed under general anesthesia with an open chest. Caution must be taken when extrapolating the results to clinical situations. Second, the use of topical papaverine during the operation might have affected the results because the effect of topical papaverine persists up to 2 hours [18].
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