Keywords
coronary artery bypass graft, CABG, anastomosis
Step 1
Surgical Anatomy
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The named epicardial coronary arteries that serve as the distal anastomotic targets for coronary artery bypass grafting (CABG) are most commonly located just deep to the epicardial fat and superficial to the myocardium. The arteries, usually the left-sided vessels, may be located more deeply within the myocardium (intramyocardial). A straighter course on coronary angiography may suggest an intramyocardial location.
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The left anterior descending (LAD) coronary artery courses superficially to the interventricular groove, providing diagonal branches to the anterior wall.
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The ramus intermedius (RI) artery arises between the LAD and left circumflex artery (LCx) and can often be identified near the base of the left atrial appendage.
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The LCx arises from the left main coronary artery as the left main artery bifurcates to give off the LAD in the atrioventricular groove. The LCx provides obtuse marginal branches that supply the lateral and inferolateral myocardium, usually terminating near the lateral margin of the left ventricle.
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The right coronary artery (RCA) originates anteriorly from the aortic root and courses in the atrioventricular groove prior to crossing the acute margin of the heart and bifurcating into the posterior descending artery (PDA) and posterolateral ventricular branch (PLVB).
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Right or left coronary dominance refers to the artery from the which the PDA originates.
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The most commonly used conduits for CABG include the left and right internal mammary arteries (alternatively termed the internal thoracic artery ), radial artery, and reversed greater saphenous vein (GSV).
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The left internal mammary artery (LIMA) originates from the proximal left subclavian artery opposite the thyrocervical trunk and courses approximately 1.5 cm lateral to the sternocostal junction. Proximally, the LIMA passes inferiorly and medially behind the subclavian vein, where the phrenic nerve usually crosses from lateral to medial as it courses to the pericardium. Care must be taken during proximal harvest of the LIMA to avoid phrenic nerve injury and resultant diaphragmatic dysfunction. The midportion of the LIMA is superficial, lying just deep to the endothoracic fascia, and can be visualized or palpated most easily in this location. Below the sixth rib, the transversus thoracis muscle covers the posterior aspect of the internal mammary artery (IMA). Near the junction of the xiphoid process and body of the sternum, the IMA bifurcates into the musculophrenic and superior epigastric arteries. The IMA is accompanied by paired internal mammary veins that combine to form a single vein proximally.
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The radial artery originates from the brachial artery, coursing under the brachioradialis muscle proximally and in the lateral forearm deep to the distal deep fascia. From the antecubital fossa, the artery courses from medial to lateral. Care must be taken during harvest of the distal radial artery to avoid injury to the superficial radial nerve and lateral antebrachial cutaneous nerve.
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The GSV is located on the medial side of the lower extremity, coursing superficial to the medial malleolus at the ankle and running deep to the subcutaneous fat as it courses more proximally. At its most proximal portion, the GSV drains into the common femoral vein at the saphenofemoral junction.
Step 2
Preoperative Considerations
1
Preoperative Preparation
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The medical history should focus on comorbid conditions that could increase perioperative risk and conduit selection (e.g., history of stroke, gastrointestinal bleeding, liver disease, diabetes mellitus, obesity, chronic obstructive pulmonary disease, renal failure, peripheral arterial disease).
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The surgical history should delineate any prior chest surgery and procedures that could affect conduit selection (e.g., radial artery catheterization, varicose vein stripping).
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The physical examination should aim to identify any comorbid conditions not obtained during the history and to identify any potential caveats that could alter surgical planning. Bilateral upper extremity blood pressures should be obtained to identify possible subclavian stenosis, which could impair IMA flow. The skin overlying the chest wall and conduit harvest sites should be examined for any evidence of infection, prior irradiation, and scars from prior procedures. Auscultation for a carotid bruit may indicate the presence of stenosis. Radial pulses should be palpated and, in case radial artery harvest is planned, an Allen test should be performed. The presence of an arteriovenous fistula for hemodialysis has been reported to cause steal from the ipsilateral IMA and should be taken into consideration. Femoral, pedal, and posterior tibial pulses should be identified in case an alternative cannulation strategy is needed or for placement of an intraaortic balloon pump. The lower extremities should be inspected for venous stasis changes and large varicosities.
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Routine complete blood counts, coagulation studies, and serum chemistry tests should be performed. A baseline electrocardiogram should be obtained. Preoperative transthoracic echocardiography will provide data regarding ventricular function and any additional valvular pathology that might require concomitant intervention. In addition to providing the coronary anatomy for bypass planning, left heart catheterization can also serve to delineate left ventricular function, aortic valve pathology, and mitral regurgitation. A baseline chest x-ray can identify possible aortic calcification, and a noncontrast computed tomography (CT) scan of the chest may be obtained to evaluate for the presence of a porcelain aorta definitively. Routine carotid duplex ultrasonography is not mandated, but should be considered in patients with symptoms of stroke or a transient ischemic attack, presence of a carotid bruit, or significant left main coronary artery stenosis. If there is concern based on the history or physical examination regarding the radial artery or GSV conduit, duplex ultrasonography can aid in identifying the suitability of these conduits preoperatively.
2
Intraoperative Preparation
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Patients are placed in the supine position on the operating table. The upper extremities should be secured parallel to the torso and appropriately padded to prevent compressive nerve injury. In the case of planned radial artery harvest, the ipsilateral arm should be abducted 45 to 60 degrees from the patient.
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Hemodynamic monitoring should include placement of a noninvasive blood pressure cuff, radial arterial catheter (opposite the site of the planned radial arterial harvest site), and central venous catheter in the internal jugular vein. Placement of a pulmonary artery Swan-Ganz catheter should be based on discussion between the surgeon and anesthesiologist and is generally used for higher-risk patients. A transesophageal echocardiography probe may be passed after induction of general endotracheal anesthesia. Near-infrared spectroscopy (NIRS) monitoring may be performed if there are risk factors or significant cerebrovascular disease. All hair should be removed from incision sites with an electric razor. Electrocardiographic leads, defibrillator pads, and electrocautery grounding pads should be placed away from all potential incision sites. Placement of a roll perpendicular to the spine across the scapulae may facilitate sternotomy and IMA harvest. Bolsters placed under the knees or lower extremities with slight external rotation of the legs may facilitate GSV harvest.
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Perioperative antibiotics such as a first-generation cephalosporin, with the addition of vancomycin if methicillin-resistant Staphylococcus aureus (MRSA) colonization is documented, should be administered within 30 minutes prior to incision. Skin preparation with an iodophor solution or chlorhexidine gluconate should be performed from the chin to the toes, with circumferential preparation of the lower extremities.
Step 3
Operative Steps
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The following discussion details the procedure of CABG using a pedicled IMA graft, with reversed GSV or free radial artery grafting. Alternative conduits, including the gastroepiploic artery, inferior epigastric artery, and lesser saphenous vein may be used, but are not described here. Alternative strategies and approaches for CABG are described elsewhere in the text.
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A standard median sternotomy is performed. To facilitate harvest of the IMA, a variety of self-retaining sternal retractors are available to elevate the ipsilateral sternal edge. Once the sternum has been elevated, the mediastinal pleura is freed from the endothoracic fascia. The pleura may be opened widely into the pleural space to facilitate exposure or may be left intact once it has been freed several centimeters beyond the lateral edge of the IMA. The IMA can be harvested using a pedicled technique in which the IMA is harvested with the endothoracic fascia and paired veins or using a skeletonized technique. Using a pedicled technique, the endothoracic fascia is opened laterally to the paired mammary veins, creating a 1.5- to 2-cm pedicle. Dissection can be carried out using electrocautery or with scissors. The IMA and its paired veins should be gently dissected free from the chest wall using hemoclips to ligate intercostal branches. Care should be taken to avoid thermal injury with excess use of electrocautery or IMA dissection with excessive manipulation of the artery. Dissection of the proximal 3 cm of the IMA is where phrenic nerve injury is most likely to occur. Both the left IMA and right IMA can be harvested in a similar fashion, but the harvester should be aware that the mammary vein may cross medially earlier on the right side, and intersection of the phrenic nerve and IMA occurs more proximally on the right side. The skeletonized approach is preferred when bilateral IMA harvest is planned to avoid devascularization of the sternum and when IMA length may be an issue. Sharp dissection and avoidance of electrocautery is preferred during skeletonization of the IMA to minimize the risk of thermal injury. When skeletonizing the IMA, the endothoracic fascia is incised sharply, and the IMA is dissected free from the paired veins. The fascia is opened longitudinally under the IMA proximally and distally along the course of the artery. The artery may be bathed in a vasodilator solution such as papaverine until ready for use. The chest wall should then be inspected for hemostasis ( Fig. 3.1 ).
