Eur J Cardiothorac Surg 2006;29:948-951
© 2006 Elsevier Science NL
Sympathetic stimulation increases the blood flow through the in situ right gastroepiploic artery graft after off-pump coronary artery bypass graft surgery
Ho-Geol Ryu
a
,
Jae-Hyon Bahk
a
,
*
,
Ki-Bong Kim
b
a Department of Anesthesiology, Seoul National University Hospital, Seoul National University College of Medicine, 28 Yongon-dong Chongno-gu, Seoul 110-744, Republic of Korea
b Department of Thoracic and Cardiovascular Surgery, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Republic of Korea
Received 21 November 2005;
received in revised form 27 February 2006;
accepted 10 March 2006.
* Corresponding author. Tel.: +82 2 2072 2818; fax: +82 2 747 5639. (Email: bahkjh{at}snu.ac.kr).
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Abstract
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Objective: The right gastroepiploic artery is gaining popularity as an in situ arterial graft for coronary artery bypass surgery. Unlike the internal thoracic artery, the right gastroepiploic artery is a visceral artery and has a vasoconstrictive tendency in response to sympathetic stimulation. We hypothesized that blood flow through the in situ right gastroepiploic arterial graft might be compromised after sympathetic stimulation. Methods: Thirty patients scheduled for off-pump coronary artery bypass surgery using the left internal thoracic artery and the right gastroepiploic artery as in situ arterial grafts were enrolled. Blood flow through both arteries was measured by transit time flow before (T1), during (T2), and after noradrenalinee infusion (T3). Results: After sympathetic stimulation, blood flow of both the right gastroepiploic artery (30.1 ± 13.9 mL/min at T1 vs 36.2 ± 17.5 mL/min at T2; P
= 0.001) and left internal thoracic artery grafts (37.3 ± 19.1 mL/min at T1 vs 41.8 ± 18.2 mL/min at T2; P
= 0.01) was increased significantly. However, blood flow in proportion to cardiac output increased only in the right gastroepiploic artery graft (P
= 0.01). Conclusions: Sympathetic stimulation increases, rather than compromises, blood flow through the right gastroepiploic artery graft after coronary revascularization.
Key Words: Right gastroepiploic artery • Sympathetic stimulation • Blood flow • Coronary artery bypass • Off-pump
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1. Introduction
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Two current issues in coronary artery bypass surgery are total arterial revascularization and off-pump coronary artery bypass surgery (OPCAB) [1–3]. The internal thoracic artery (ITA) has shown excellent results in total arterial revascularization [4,5]. The right gastroepiploic artery (RGEA) is another attractive arterial graft because its anatomic location and vessel diameter allows it to be used as an in situ graft to the posterior coronary arteries in patients with multi-vessel disease [2–4]. Reports concerning the patency of RGEA grafts thus far have been somewhat controversial but promising [4,6–9].
The RGEA is a visceral vessel supplying blood flow to the stomach. When sympathetic tone increases during exercise or emotional stress, blood flow to visceral organs is diverted to muscles and vital organs [10]. Consequently, coronary blood flow through the RGEA graft may be compromised and fail to meet demands in sympathetically activated states [11].
The purpose of this study was to evaluate the effect of sympathetic stimulation on blood flow through an RGEA graft in comparison to an ITA graft after OPCAB.
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2. Methods
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2.1 Patient selection
This study was approved by the institutional review board of Seoul National University Hospital, and written informed consent was obtained from each participating patient.
Thirty patients scheduled for elective OPCAB using the ITA and the RGEA as in situ arterial conduits were included. Patients who showed celiac trunk narrowing on preoperative angiography, who needed intra-aortic balloon pump support, who were converted to cardiopulmonary bypass intraoperatively, and whose left ventricular ejection fraction was <40% were excluded from the study. Patients who did not satisfy the criteria for normally functioning grafts after anastomosis [12] were also excluded.
2.2 Anesthesia and patient monitoring
General anesthesia was induced with etomidate, midazolam, vecuronium, rocuronium, and sufentanil and maintained with midazolam, vecuronium, and sufentanil with positive pressure ventilation using oxygen and medical air. Systemic arterial pressure, central venous pressure, pulmonary artery pressure, electrocardiography, oxygen saturation, and continuous cardiac output (Edwards Lifesciences, Irvine, CA, USA) were monitored throughout the operation.
2.3 Surgical technique and study protocol
All patients underwent OPCAB through a median sternotomy incision. The ITA and the RGEA were harvested in a skeletonized fashion using scissors or the tip of a cold cautery device as previously described [9].
The RGEA was approached from the posterior aspect of greater omentum, and dissected proximally to the pylorus and then leftward two thirds of the distance along the great curvature of the stomach. All branches on each side of the stomach and omentum were occluded with the use of two surgical clips and were divided with scissors. Throughout the dissection, the grafts were sprayed with warm diluted papaverine solution to minimize spasm and to prevent desiccation. After systemic heparinization, the grafts were clipped distally. The grafts were then immersed in a 10-mL syringe filled with warm diluted papaverine solution (1 mg/mL) and allowed to dilate until use. Intraluminal injection of papaverine solution was not used. The ITA graft was anastomosed to the left anterior descending artery or one of its branches and the RGEA graft was anastomosed to the right coronary artery or one of its branches. The patients were heparinized with an initial dose of 1.5 mg/kg of heparin and periodically received supplemental doses to maintain an activated clotting time of >300 s. All procedures and measurements were performed by one surgeon (Kim K.-B.).
When all anastomoses were finished and the vital signs stable for 10 min (T1), blood flow through the ITA and the RGEA grafts was measured using transit time flow measurement (TTFM; BF1001, Medi-Stim AS, Oslo, Norway) and the measuring points were marked. Thereafter, noradrenaline infusion was 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 [13]. When the heart rate or mean arterial pressure remained stable for 10 min in response to noradrenaline infusion (T2), blood flow through both arteries was measured at the locations previously marked by the surgeon and noradrenaline infusion was discontinued. Ten minutes after discontinuation of noradrenaline infusion (T3), blood flow through both arteries was measured again at the same locations. Blood flow measurements using TTFM were performed twice at each point and averaged.
2.4 Statistical analysis
Data were analyzed using SPSS, version 12.0 (SPSS, Chicago, IL, USA). Paired t-test was used to compare data before and after noradrenaline infusion. All results were expressed as mean ± standard deviation, and a P-value of less than 0.05 was considered to be statistically significant.
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3. Results
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Patient characteristics are summarized in Table 1
. There were no significant changes in hemodynamic variables except mean blood pressure during noradrenaline infusion (Table 2
). All variables returned to their baseline values (T1) after cessation of noradrenaline infusion (T3). Blood flow through the RGEA graft increased significantly after noradrenaline administration (30.1 ± 13.9 mL/min vs 36.2 ± 17.5 mL/min, P
= 0.001). Blood flow through the ITA graft also increased significantly after noradrenaline administration (37.3 ± 19.1 mL/min vs 41.8 ± 18.2 mL/min, P
= 0.01). When blood flow in proportion to cardiac output (blood flow/cardiac output) was calculated, it increased in the RGEA graft (0.0066 ± 0.0037 vs 0.0076 ± 0.0035, P
= 0.01) and did not change significantly in the ITA graft (0.0082 ± 0.0046 vs 0.0087 ± 0.0036, P
= 0.354) after noradrenaline administration.
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4. Discussion
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This study revealed that sympathetic stimulation increased, rather than compromised, blood flow through the RGEA graft after OPCAB.
Although the RGEA has been used as a suitable conduit for coronary artery bypass surgery because of its low surgical risk, high patency rate, and excellent patient outcome [7–9], it has a tendency for vasospasm because of its high muscularity [14,15] and different autonomic regulation [10]. In vitro studies demonstrated that the vasoconstriction response to noradrenaline was more intense in the RGEA than in the ITA [16,17]. Consequently, coronary blood flow through an RGEA graft may be compromised and fail to meet demands in sympathetically activated states [11].
One clinical study demonstrated that dobutamine significantly increased both the ITA and RGEA graft flow velocity as measured by a directly implanted Doppler miniprobe after coronary artery bypass grafting [18]. However, there have been no clinical studies evaluating blood flow through a skeletonized RGEA graft under controlled sympathetic stimulation. The RGEA is the fourth branch originating from the celiac artery that supplies blood to the liver, stomach, duodenum, and parts of the small intestine. Under sympathetic stimulation, the arterioles of the visceral vessels constrict and blood flow is diverted to vital organs or muscles. Because the RGEA graft is transected at its distal end for revascularization, it lacks arterioles, the major contributor of increasing systemic vascular resistance. Therefore, blood flow may be diverted towards the RGEA graft from the other branches of the celiac artery.
The present study showed that blood flow through the RGEA and the ITA grafts both increased significantly during noradrenaline infusion. This suggested that the increased blood flow of the skeletonized RGEA graft might result from the increased systemic vascular resistance based on the maintained cardiac output. When blood flow in proportion to cardiac output (blood flow/cardiac output) was calculated, it increased only in the RGEA graft and did not change significantly in the ITA graft. This suggested that the RGEA graft received an increased proportion of cardiac output despite the possibility of vasoconstriction after noradrenaline administration.
Noradrenaline infusion might reduce the RGEA diameter and affect the increased graft flow in this study. When the vasoconstriction effect to the RGEA during noradrenaline administration was calculated using Poiseuille's law, a 6 mL/min increase in the RGEA flow and 19 mmHg increase in mean blood pressure in the present study suggested an approximately 8% reduction in the RGEA radius based on the assumption of unaltered coronary vascular resistance and blood viscosity.
Among the various blood flow measurement techniques such as electromagnetic flow meters and ultrasound-based flow meters (Doppler, TTFM), TTFM has been used with increasing frequency intraoperatively because it is noninvasive, simple, quick, reproducible, and representative of the real flow within the graft [19,20]. Since the introduction of TTFM at our institute, we derived criteria to predict abnormal grafts [14]. By using these criteria, the sensitivity of TTFM to detect graft flow abnormality was 96.2%. In the present study, blood flow measurements using TTFM were performed twice at each point and averaged.
There are limitations to the present study that must be recognized. First, this study was performed intraoperatively while the patient was under general anesthesia. Care must be taken before interpretation and application to other clinical situations. Second, we used papaverine topically during the surgery, although intraluminal injection of papaverine solution was avoided. The potent vasodilatory effect of papaverine may have affected the results of the study. Topical lipophilic papaverine applied to the perivascular fat of the RGEA prevented vasoconstriction for up to 2 h [21].
In conclusion, this study demonstrated that sympathetic stimulation increased, rather than compromised, both the absolute blood flow and blood flow in proportion to cardiac output through the RGEA graft after coronary revascularization.
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Footnotes
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This study was presented as an abstract at the 2004 American Society of Anesthesiologists meeting in October 2004.
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Abstract
1. Introduction
