| Abstract|| |
Aims and Objectives: Left internal mammary artery (LIMA) is the preferred arterial conduit for coronary artery bypass grafting. Various pharmacological agents are known to increase LIMA blood flow. Sympathetic blockade mediated by stellate ganglion block (SGB) has been used to provide vasodilatation in the upper extremities and in the treatment of refractory angina. We investigated effect of left stellate ganglion block (LSGB) on LIMA diameter. Materials and Methods: In 30 diagnosed patients of triple vessel coronary artery disease, LSGB was given under fluoroscopic guidance by C6 transverse process approach using 10 ml of 1% lignocaine. LIMA diameter was measured before and 20 min after the block at 2 nd , 3 rd , 4 th and at 5 th rib level. Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were recorded before and 20 min after the block. Results: The LIMA diameter increased significantly at 2 nd (2.56 ± 0.39 vs. 2.99 ± 0.40; P < 0.0001), 3 rd (2.46 ± 0.38 vs. 2.90 ± 0.40; P < 0.0001), 4 th (2.39 ± 0.38 vs. 2.84 ± 0.41; P < 0.0001) and 5 th rib level (2.35 ± 0.38 vs. 2.78 ± 0.40; P < 0.0001). No statistically significant change occurred in HR, SBP, DBP and MAP before and 20 min after LSGB. Conclusions: LSGB significantly increased the LIMA diameter. The LSGB can be considered as an alternative to topical and systemic vasodilators for reducing vasospasm of LIMA.
Keywords: Left internal mammary artery; Left stellate ganglion block; Quantitative coronary analysis
|How to cite this article:|
Gopal D, Singh NG, Jagadeesh A M, Ture A, Thimmarayappa A. Comparison of left internal mammary artery diameter before and after left stellate ganglion block. Ann Card Anaesth 2013;16:238-42
|How to cite this URL:|
Gopal D, Singh NG, Jagadeesh A M, Ture A, Thimmarayappa A. Comparison of left internal mammary artery diameter before and after left stellate ganglion block. Ann Card Anaesth [serial online] 2013 [cited 2020 Jan 25];16:238-42. Available from: http://www.annals.in/text.asp?2013/16/4/238/119161
This article is accompanied by an invited commentary by Dr. Mukul Chandra Kapoor
| Introduction|| |
The internal mammary artery (IMA) is the preferred graft for myocardial revascularization because of its superiority over venous grafts owing to long-term patency, lower mortality rates and improved post-operative outcomes. ,, However, conduit spasm is a recognized complication of coronary artery bypass surgery mainly affecting arterial conduits, a major concern that can lead to acute myocardial ischemia and may contribute to reduced graft patency.  The mechanism of graft spasm remains unclear. Topical application or systematic administration of many pharmacological agents has been shown to reverse or prevent graft spasm, ,, but side-effects are reported with the use of these agents. Regional techniques like thoracic epidural anesthesia have shown to increase IMA blood flow by sympathetic inhibition.  Stellate ganglion block (SGB) with local anesthetics has been widely used to provide pain relief, to treat vascular spastic disorders of upper limb, chronic pain conditions and treatment of refractory angina. ,,, The SGB has also been used for increasing radial artery (RA) blood flow and preventing RA spasm by sympathetic blockade in coronary artery bypass surgery.  Although the effects of topical and systemic vasodilators on blood flow in the IMA have been investigated, there is limited literature regarding the impact of SGB on IMA blood flow. We investigated the effects of left stellate ganglion block (LSGB) on left internal mammary artery (LIMA) diameter.
| Materials and Methods|| |
The study was approved by the Institutional Ethics Committee. After explaining the complications associated with LSGB procedure, informed consent was obtained from patients undergoing coronary angiography (CAG). Before starting the procedure, intravenous access was secured and monitoring was started with electrocardiogram, invasive blood pressure and pulse oximetry in all the patients. Patients with existing coagulopathy, recent myocardial infarction, unstable angina, pathological bradycardia (heart rate [HR] < 60 beats/min), glaucoma, decreased ventricular function (ejection fraction < 40%), left main coronary artery disease, emergency CAG, pre-existing contralateral phrenic nerve palsy and bloody tap were excluded. LSGB was given to patients who were found suitable for elective coronary artery bypass grafting (CABG) and where selective LIMA angiography is routinely done. Overall 30 patients were studied. In these patients, selective LIMA angiogram was repeated 20 min after LSGB.
In catheterization laboratory CAG was performed by the standard femoral approach. Selective injection of the native coronary arteries was performed by diagnostic Judkin 6F catheters. Patients showing significant coronary artery disease on CAG and suitable for CABG, selective angiography of LIMA was performed using 6F IMA catheter. After obtaining the baseline LIMA angiogram, LSGB was given by C6 transverse process approach under fluoroscopic guidance. All angiographies were performed with manual injection using non-ionic contrast medium.
Technique: Fluoroscopic C6 transverse process approach for LSGB
Patients were positioned supine with a thin pillow under head, the neck was slightly extended, the head was rotated slightly to the right side and the patients were asked to open mouth slightly. The needle insertion site was located with the finger between the trachea and the carotid sheath. The C6 vertebral body level was identified at the level of the cricoid cartilage. The anterior tubercle of the C6 vertebra, Chassaignac tubercle (carotid tubercle) was then identified after retracting the carotid sheath and sternocleidomastoid muscle laterally. Pressure was applied with the palpating finger to reduce the distance between the skin and tubercle and to depress the dome of the pleura to reduce risk of pneumothorax. The needle was inserted towards the Chassaignac tubercle and after contact; it was redirected and advanced inferomedially towards the body of C6. After touching the body of C6, the needle was withdrawn 1-2 mm to bring it out of the longus colli muscle while still staying within the pre-vertebral fascia. After negative aspiration, 1-2 ml of non-ionic contrast agent was injected and spread was visualized under fluoroscopy. After confirming the subfascial location of the injection, the local anesthetic was administered. A total volume of 10 ml of 1% lignocaine was injected. , Correct placement of the needle and injection of lignocaine was confirmed by prompt increase in the skin temperature of the ipsilateral arm, nasal stuffiness, hoarseness of voice and the onset of Horner's syndrome. The same anesthesiologist performed all the blocks. The systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and HR were monitored during the procedure and up to 2 hours after the LSGB. LIMA diameter was measured at the level of 2 nd , 3 rd , 4 th and 5 th rib by quantitative coronary analysis (QCA). The radiographer who measured the LIMA diameter was blinded. In all patients, QCA was performed with Philips Alura FD 10 software connected to a digital cardiac imaging system (DCI, Philips, The Netherlands). After selecting a well opacified image, calibration was performed using the diagnostic IMA catheter as a reference diameter. Defined length of LIMA was then selected at 2 nd , 3 rd , 4 th , and 5 th rib level and its minimum luminal diameter, maximum luminal diameter and mean diameter were calculated before and after the LSGB. Mean diameter was chosen for the study.
Serial changes in LIMA diameters were compared by means of Student's t-test for paired data at the level of 2 nd rib, 3 rd rib, 4 th rib and 5 th rib. A two-tailed probability level of less than 0.05 was considered significant. All results were expressed as mean ± standard deviation. Statistical analysis was performed using MedCalc software version 12.2.1.
| Results|| |
Transient short lived and minor side effects such as Horner's syndrome, hoarseness of voice, dryness of mouth, nasal stuffiness were noted, which were the indicators of successful block. None of the patients had any serious complication during or after the procedure. The hemodynamic parameters - HR, SBP, DBP and MAP measured before and 20 min after LSGB, during selective angiography were similar between the groups and there was no significant difference (P > 0.05) [Table 1].
LSGB had a significant effect on diameter of LIMA. The LIMA diameter increased significantly 20 min after LSGB. The increase in LIMA diameter at the level of 2 nd , 3 rd , 4 th , and 5 th rib is shown in [Table 2] and [Figure 1].
|Figure 1: Left internal mammary artery diameter before and after left stellate ganglion block at different rib levels|
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| Discussion|| |
The arterial grafts are the preferred conduits for myocardial revascularization.  Among arterial grafts LIMA and RA are most commonly used for revascularization. The main drawback of arterial conduits is perioperative graft spasm; however, its precise mechanisms are not clear. The possible explanations described in the pathogenesis of graft spasm are endothelial injury, local manipulation of the artery, temperature changes, and release of vasoconstrictor substances.  Native coronary artery spasm in early post-operative period are due to α-adrenergic activity, endothelium dysfunction, increased blood pH, systemic hypothermia, local manipulation of the artery, increased platelet activity, release of vasoconstrictor substances, increased plasma vasopressin levels, histamine release and local increase in potassium levels. 
The RA is more prone to spasm as its medial layer thickness is greater than that of LIMA. , Various drugs such as calcium channel blockers, papavarine, nitrates, etc., have been used to reduce arterial vasospasm. ,, SGB may also play an important role in management of LIMA spasm. The stellate ganglion contributes fibers to the nerve bundles located along the internal thoracic (mammary) artery.  The presence of nerve fibers along the internal thoracic artery may have clinical significance in surgical treatment of myocardial ischemia.  Studies have shown that human IMA and RA contain mainly α1-adrenoceptors and the α-adrenoceptor agonist-induced contraction is mainly mediated by activation of the α1-adrenoceptors. ,, Thus, sympathetic blockade of these nerves is the rationale for treatment of perioperative as well as post-operative spasm. The human IMAs as well as RAs express predominantly α1-subtype adrenergic receptors; therefore, α-adrenergic receptor agonist-induced contraction is mainly mediated by activation of the α1-adrenergic receptors.  Investigators have also identified and characterized the α1-adrenergic receptors in human IMA by radio-ligand binding analysis. ,
The various methods to confirm successful LSGB are expression of Horner's syndrome, nasal stuffiness and increases in skin temperature and perfusion index.  Doppler ultrasound-guided, computerized tomography guided and fluoroscopy guided SGB are additional methods available to enhance the accuracy of the sympathetic block on lower cervical and upper thoracic segments. , We observed increase in skin temperature of ipsilateral hand, change of voice and nasal stuffiness in all our patients following LSGB. Serious complications associated with a SGB include intra-arterial or intravenous injection, epidural spread of local anesthetic and pneumothorax. However, properly performed SGB is safe and an easy procedure and the complications are rare with an incidence of 0.17%.  Fluoroscopy guided SGB is known to enhance safety.  In this study, using fluoroscopy guided SGB; none of the patient had any serious complication during or after the procedure. The study by Yildirim et al.,  showed that pre-emptive SGB increased RA blood flow and prevented RA spasm, which improved the surgical outcome in patients undergoing CABG. The authors showed significant increase in RA blood flow using a pulsed-wave Doppler ultrasound blood flow-meter. The authors suggested that increase in RA blood flow could be due to cervical sympathetic block. In our study, LIMA diameter was measured by QCA and there was an increase in LIMA diameter after LSGB, which could be mediated by α1-adrenergic receptor sympathetic blockade. Although we did not measure the blood flow, the flow through LIMA should have increased as the flow is directly proportional to radius (radius (r) = diameter/2) (Hagen Poiseiulle law). Onan et al.,  showed that thoracic epidural anesthesia increases LIMA blood flow by inhibiting sympathetic stimulation, which might occur through expression of some endothelial vasoactive mediators that increase nitric oxide. They performed immunohistochemical study on LIMA specimen to evaluate expression of vascular endothelial growth factor (VEGF) inducible nitric oxide synthase (i-NOS) and adenosine A2B receptors. They concluded that increased expressions of VEGF, i-NOS and adenosine A2B-receptor will increase nitric oxide expression and hence increase in LIMA blood flow.
Various pharmacological agents (such us nitrates, calcium channel blockers and papavarine), which are used for prevention of LIMA spasm have limitations.  Chester et al., have described long-term benefits of SGB (relief for about 5 weeks) in severe chronic refractory angina.  Furthermore, SGB have been used for long-term pain relief in chronic pain conditions such as chronic regional pain syndrome , and phantom limb pain. , We did not measure duration of LSGB but because of its application in chronic pain conditions we can assume that action of LSGB on LIMA will last for long duration. However, further studies are needed to confirm duration of action of SGB on LIMA. In our study, patients had stable hemodynamics after LSGB. Other studies have shown that LSGB has only small effect on the left ventricular function in awake dogs before and after induction of heart failure and in patients without cardiovascular disease. , Koyama et al.,  also reported that SGB suppressed cardiac sympathetic function without affecting blood pressure.
The limitations of the study are actual LIMA blood flow was not measured. The assessment of the nitric oxide expression on the LIMA and the examination of α-adrenergic receptors and its subtypes were not done. We did not record the duration of action of SGB.
In conclusion, LSGB increases LIMA diameter by sympathetic blockade. Hence, LSGB may be useful in prevention of perioperative LIMA vasospasm. LSGB is expected to increase the LIMA flow, its patency and thus may improve surgical outcome. However, further studies are required on a larger group to quantify increases in LIMA flow and the duration of action with LSGB and to compare effects of LSGB with other pharmacological modalities.
| Acknowledgment|| |
The authors would like to acknowledge the help provided by Dr. C.N Manjunath, Director and HOD, Dr. B.C Srinivas and Dr. Prabhavati, Professors, dept. of Cardiology, Sri Jayadeva Institute of Cardiovascular Sciences and Research, Bangalore.
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Department of Cardiac Anesthesia, Sri Jayadeva Institute of Cardiovascular Sciences and Research, 9th Block, Jayanagar, Bangalore - 560 069, Karnataka
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2]