Chapter 21. Myocardial Revascularization with Cardiopulmonary Bypass

Coronary artery disease (CAD) remains the single largest killer of Americans, accounting for almost half a million deaths per year. It imposes a particular burden on the elderly, with more than 80% of all CAD deaths occurring in those over age 65.1 The magnitude of this impact takes on great significance because it is expected that the number of Americans older than 65 years of age will double over the next two decades.2 If you add to this aging population the anticipated increase in the prevalence of important risk factors for CAD such as diabetes mellitus and obesity, the population at risk for CAD can only be expected to increase.

Myocardial revascularization represents an effective treatment strategy shown to prolong survival. Techniques of revascularization include percutaneous coronary intervention (PCI) and coronary artery bypass graft surgery (CABG), which can be performed with or without cardiopulmonary bypass. Current techniques for CABG can be carried out with low perioperative morbidity and mortality, with excellent long-term outcomes despite an increasing risk profile.3 Coronary artery bypass graft surgery with cardiopulmonary bypass remains the standard by which the other techniques (ie, PCI, off-pump CABG) are measured.4,5 It is expected that it will continue to be a cornerstone in the management of CAD in the foreseeable future.

The modern era of myocardial revascularization with cardiopulmonary bypass began in 1954 when Dr. John Gibbon reported the development of the cardiopulmonary bypass machine.6 An additional seminal advance occurred with the development of coronary angiography by Mason Sones at the Cleveland Clinic in 1957, which opened the door to the elective treatment of coronary atherosclerosis by means of direct revascularization.7 Initial reports by Rene Favaloro and Donald B. Effler on their techniques to treat clinical events associated with stenotic lesions of the coronary arteries culminated in the first large series of aorto-to-coronary artery venous grafts reported in 1969.8 Simultaneously Dudley Johnson of Milwaukee published a series of 301 patients in 1969.9 The success of these techniques was soon demonstrated in larger series initiating the modern era of coronary artery surgery.

The indications for CABG are reviewed in detail in Chapter 19. In brief, the indications established by the American Heart Association and American College of Cardiology (AHA/ACC) consensus panel are based predominantly on the results of trials comparing surgical revascularization with medical therapy for patients with chronic stable angina.10 Three major trials, the Coronary Artery Surgery Study (CASS), the Veterans Administration Coronary Artery Bypass Cooperative Study Group, and the European Coronary Surgery Study (ECSS), demonstrated the greatest survival benefit of revascularization to be among those patients at highest risk of death from the disease itself as defined by the severity of angina and/or ischemia, the number of diseased vessels, and the presence of left ventricular dysfunction.11–13

Prediction of risk-adjusted outcomes permits both the surgeon and the patient to weigh the potential benefits of operation against risks of perioperative morbidity and/or mortality. The patient's comprehension of benefit versus risk is paramount to informed consent before coronary artery bypass surgery. Accurate risk-adjusted prediction of postoperative morbidity and mortality also provides an important quality improvement tool to understand and examine the variability in institutional and individual surgeon performance.

A number of cardiac surgery databases have been used to develop risk models for predicting operative morbidity and mortality in patients undergoing CABG.10 One of the more user-friendly risk assessment tools is that provided by the STS Risk Calculator (http://www.sts.org/quality-research-patient-safety/quality/risk-calculator-and-models/risk-calculator), which provides an assessment of individual patient operative risk derived using the Society of Thoracic Surgeons (STS) database (Table 21-1). The STS risk algorithm is proprietary and is based on data voluntarily submitted by participating centers on 503,478 patients undergoing isolated CABG in the United States from 1997 to 1999; the application is available for public use.

Overall, the average risks of 30-day operative death and major complication for patients reported to the STS database undergoing CABG from 1997 to 1999 were 3.05 and 13.4%, respectively. Specific complications included stroke (1.6%), renal failure (3.5%), reoperation (5.2%), prolonged ventilation (5.9%), and sternal infection (0.63%). Risk models were developed using multivariate analysis to stratify the strength of the association from among 30 potential preoperative risk factors for mortality and major complications as shown in Tables 21-2 and 21-3. Except for deep sternal wound infection, the development of any of these complications correlated with an increased risk-adjusted operative mortality.14

A preliminary sense of operative mortality can be derived simply from an understanding of the core variables most predictive of risk in the aforementioned data sets. The strongest predictors of operative mortality include nonelective surgery, low ejection fraction, and prior heart surgery. Chronic comorbidities are also associated with an increased operative mortality after coronary bypass, including treated diabetes, peripheral vascular occlusive disease, chronic renal insufficiency, and chronic obstructive pulmonary disease (COPD).10

Patient Evaluation

Regardless of the risk model applied, there is no substitute for clinical evaluation of the patient. Unfortunately, all too often the assessment focuses disproportionately on coronary anatomy and insufficiently on the nature, duration, and severity of ischemic symptoms, as well as signs and symptoms of congestive heart failure (CHF). In addition, history of or coexisting cerebrovascular and/or peripheral vascular disease, malignancy, sternal radiation, COPD, diabetes mellitus, or renal and/or hepatic insufficiency can have major impact on the operative morbidity and even mortality, not all of which are captured in risk models.

Current medications and dosages with special attention to antiplatelet agents such as clopidogrel must be reviewed. Operation in the setting of recent clopidogrel use is associated with excessive bleeding and need for reoperation.15 Most surgeons recommend 5 days from the last administered dose of clopidogrel before undertaking CABG with cardiopulmonary bypass.

Physical examination of the lungs and heart should focus on the stigma of ischemic and valvular heart disease. Cardiac murmurs warrant further evaluation. Additionally, the adequacy of presternal soft tissues to permit wound closure should be considered and evidence of venous varicosities or prior vein stripping may impact plans for conduit harvest. Peripheral pulses should be documented as their presence or absence may impact from which leg to harvest the vein or place an intra-aortic balloon pump. A detailed neurologic examination of the ulnar, radial, and median nerves should be document in the case of planned radial artery harvest.

Diagnostic evaluation should be directed by the clinical assessment, but at a minimum should include a renal panel (creatinine), complete blood count, and chest x-ray. The ECG should be reviewed for evidence of previous myocardial infarction and conduction abnormalities. Radiologic evaluation should rule out concomitant neoplasm, active pulmonary infection, and/or ascending aorta calcification; the latter should be further assessed with a noncontrast CT scan because it will impact the location for arterial cannulation and aortic cross-clamp placement.

Hemodynamically significant coronary artery lesions on angiography are conventionally defined as those lesions with a 50% loss of arterial diameter, which is sufficient to impair coronary blood flow reserve and distal coronary pressure.10 An assessment should be made of left ventricular function and regional wall motion abnormalities as well as the presence and degree of valvular abnormalities, including aortic stenosis and mitral regurgitation either with left heart catheterization or echocardiography (our preferred method).

It is in the surgeon's best interest to develop a good relationship with the patient and his or her significant others. Specifics including the risks, benefits, and alternatives to surgery need to be discussed to permit an informed decision. Ideally, this discussion is held in the presence of the patient's significant others, because patients often have difficulty absorbing the details of the discussion at the time related to the stress of the situation. Should the patient experience a major complication or mortality, it is often the patient's significant others with whom the surgeon will most often interact. Additionally, anticipated need for postoperative rehabilitation, as well as the tempo and time course of recovery is also of interest to all parties. A clear understanding of the expectations for the perioperative period will reduce everyone's anxiety about surgery and may promote early patient recovery. Good rapport with patients and their significant others is also the physician's best protection from litigation should untoward events occur.

Internal Thoracic Artery

The left internal thoracic artery (ITA) as a bypass graft to the left anterior descending coronary artery has been proven to provide superior early and late survival and better event-free survival after CABG.24 The unparalleled long-term patency and better clinical outcomes associated with the use of the ITA make it the conduit of first choice for anastomosis to the left anterior descending coronary artery in almost all patients regardless of age, and establish an argument to use the right ITA as conduit to other targets as well.

Characteristics

The ITA demonstrates remarkable resistance to development of atherosclerosis, which may be in part attributable to a greater resistance of its endothelium to harvest injury as compared with the saphenous vein. Under electron microscopy examination thrombogenic intimal defects are essentially nonexistent in the ITA but are commonly detected in venous grafts.16 Perhaps more significantly, however, is the nonfenestrated internal elastic lamina of the ITA that may inhibit cellular migration, thereby preventing initiation of intimal hyperplasia. In addition, the medial layer of the ITA is thin, with fewer smooth muscle cells and a lesser proliferative response to known mitogens such as platelet-derived growth factor and pulsatile mechanical stretch.17,18

The endothelium of the ITA is itself unique as well. With a significantly higher basal production of the vasodilators nitric oxide and prostacyclin, the ITA demonstrates a favorable response to pharmacologic agents commonly used in the postoperative period. For instance, the ITA shows vasodilation in response to milrinone and yet does not vasoconstrict in response to norepinephrine.19 Furthermore, nitroglycerin causes vasodilation in the ITA, but not in the saphenous vein.20 The endogenous secretion of such vasodilators may also have a “downstream” effect on the coronary vasculature, explaining the common observation that the native coronary vessel itself often appears relatively protected from progressive atherosclerotic disease distal to the anastomosis. Finally, the ITA exhibits remarkable remodeling over time, adapting to the demand for increased flow by often increasing in diameter over time as observed on late postoperative angiograms, a phenomenon mediated by the endothelium.21

Surgical Anatomy of the Internal Thoracic Artery

The ITA arises from the undersurface of the first portion of the subclavian artery opposite the thyrocervical trunk. The left ITA originates as a single artery in 70% of patients and as a common trunk with other arteries in 30%. In contrast, the right ITA originates as a single artery in 95% of cases.22 At the level of the clavicle and the first rib, the ITA passes at first downward and medially behind the subclavian vein and lateral to the innominate vein. In this area, the phrenic nerve crosses the ITA from its lateral to its medial side, before contacting the pericardium. The phrenic nerve crosses anterior to the ITA 66% of the time on the left and 74% of the time on the right.22 It is important to keep these relations in mind to avoid phrenic nerve injury during proximal ITA harvest.

Below the first costal cartilage the ITA descends almost vertically and slightly laterally at a short distance from the margin of the sternum. The ITA lies posterior to the cartilages of the upper six ribs and the intervening internal intercostal muscles. In the upper chest there is a bare area of variable length where the ITA is covered only by the endothoracic fascia and parietal pleura. Below this level the transversus thoracis muscle covers the posterior surface of the ITA. The mean distance of the left ITA from the sternal margin at the level of the first intercostal space is 10.5 ± 3.2 mm, whereas at the level of the sixth intercostal space the distance increases to 20.0 ± 6.7 mm. The right ITA is slightly closer to the sternal margin than the left ITA. At the level of the sixth rib the ITA bifurcates into its terminal branches: the musculophrenic and superior epigastric arteries. The length of the ITA in situ ranges from 15 to 26 cm, with a mean of 20.4 ± 2.1 cm; the left ITA is slightly longer than the right.22 A pair of internal mammary veins accompanies the ITA; at the most superior portion these veins form a single vessel, which runs medial to the artery and drains into the innominate vein.

Pedicled Harvest Technique

After the sternum is divided, the left ITA is harvested using an internal mammary retractor to expose of the internal mammary bed (Fig. 21-1). Excessive distraction of the sternal leaves can cause costal fractures or dislocation of the costosternal joints, resulting in severe postoperative pain as well as brachial plexus injury. The parietal pleura and loose connective tissue with accompanying fat is dissected away from the chest wall. It is our preference to enter the left pleural space to allow easier exposure of the ITA, especially in its most proximal aspect, and to permit the ITA to fall into a more lateral and posterior path upon wound closure. Slightly rotating the operating table to the patient's left and decreasing the patient's tidal volume can aid in the visualization.

The ITA is identified lateral to the border of the sternum by inspection of the bare area or by palpation in the area of artery covered by muscle. It can be harvested using either a pedicled, semiskeletonized, or a skeletonized technique. When taken as a pedicle, the dissection plane can be started in the bare area of the ITA at the level of the third or fourth rib or at the level of the lower sternum. The intercostal space is avoided as the initial point of exposure because it contains the branch vessels. The endothoracic fascia is incised medially for a distance of about 4 cm using the Bovey electrocautery at low setting (ie, 20). The pedicle is carefully separated from the chest wall using gentle blunt dissection with the Bovey electrocautery tip. Exposure can be enhanced by pushing the pedicle away with closed forceps or by gently grasping the fascia. The ITA is a fragile vessel and the conduit should never be grasped with the forceps. Gentle posterior traction on the pedicle allows exposure of arterial and venous branches, which should be clipped and divided.

After the pedicle has been freed for about 4 cm, the endothoracic fascia is incised laterally, allowing the pedicle to fall away from the chest wall. Dissection is continued proximally and distally to the level of the subclavian vein and ITA bifurcation. Attention should be given to avoid injury to the phrenic nerve during the proximal exposure. Once the dissection is completed, the patient is heparinized and the pedicle sprayed with a papaverine solution (1 cc [30 mg] of papaverine added to 9 cc of saline). Three minutes after heparinization, the distal ITA is doubly clipped just proximal to the bifurcation and the artery divided. An atraumatic bulldog clamp is applied to the distal end of the artery. Alternatively, the pedicle may be left in situ and transected just before using the conduit.

Skeletonization of the Internal Thoracic Artery

Sternal blood flow decreases significantly after pedicled ITA harvest. Skeletonized harvest, however, reduces the degree of sternal ischemia. Two prospective randomized studies assessing sternal blood supply using bone scan with single photon emission computed tomography after skeletonized and pedicled harvest have demonstrated significant reduction in sternal vascularity after pedicled harvest, whereas skeletonized harvest resulted in minimal change in sternal blood supply. Multivariate analysis found harvesting technique to be the only factor responsible for postoperative sternal ischemia.23,24

Low rates of sternal wound infection have been reported using skeletonized bilateral ITA harvest. Matsa and associates observed a deep sternal wound infection rate of 1.7% among 765 patients undergoing bilateral skeletonized ITA harvest. Of note, sternal complications occurred in only 2.6% of 231 diabetic patients in this study, which was not significantly different from that of the nondiabetic patients.25 In Calafiore and coworkers' review of 842 patients undergoing bilateral skeletonized ITA harvest compared with a historical nonskeletonized bilateral ITA control group, skeletonized harvest was associated with a reduced incidence of sternal wound complications (4.5%) versus pedicle harvest (1.7%). Diabetic patients in the study derived the greatest benefit from skeletonized harvest with respect to sternal wound complications: 10% in the pedicle harvest versus 2.2% in the skeletonized harvest groups.26

Using the skeletonized harvest technique, only the artery is mobilized, leaving the internal thoracic venous plexus intact. Although skeletonization is a technically more demanding and time-consuming procedure, it increases luminal diameter and free flow compared with a pedicled graft, and also provides a longer conduit.26 Some surgeons have expressed concerns regarding functional integrity, vasoreactive profile, and early and long-term patency; however several investigators have shown no difference in endothelial integrity, endothelial-dependent or neurogenic-dependent vasoreactivity between the techniques of pedicle or skeletonized harvest.27–29 Furthermore, there does not appear to be any difference with respect to early and midterm patency.30,31

Patency

The superior late patency of an ITA graft to the left anterior descending coronary artery compared to a saphenous vein graft (SVG) was initially demonstrated by Barner and colleagues in the 1985.32 Superior patency translates into improved 10-year survival (LITA-to-LAD artery 82.6% versus SVG-to-LAD artery 71%) with less incidence of myocardial infarction (MI), hospitalization for cardiac events, and cardiac reoperations.33 The superior performance of ITA grafts appears to persist in the current era despite the use of agents to improve vein graft performance. In the BARI trial the patency rates at 1 and 4 years for ITA grafts were 98 and 91% compared with vein grafts, which were 87 and 83%, respectively.34,35 The superior patency of the ITA becomes even more prominent with longer follow-up. In an angiographic study of 1408 symptomatic post-CABG patients, patency rates for the LITA at 10 and 15 years were 95 and 88%, respectively, whereas SVG patencies were 61 and 32% at the same time intervals.36

Radial Artery

The use of the radial artery (RA) as a conduit for coronary bypass was originally described by Carpentier and associates in 1973. Spasm of the artery was common during surgery and was managed by mechanical dilation. The initial results were disappointing with 32% of grafts occluded at 2 years.37 Accordingly, the RA was abandoned as a conduit for CABG. Acar and colleagues revived the use of the RA after several grafts, angiographically demonstrated to be “occluded” early postoperatively, were patent during restudy 15 years later. Acar postulated that harvest injury was responsible for the spasm/graft occlusion.38 Proponents of the RA as a conduit have demonstrated encouraging mid- and long-term results with a pedicled harvesting technique and pharmacologic manipulation to prevent radial artery vasospasm39 As a result, this conduit has enjoyed a remarkable resurgence of interest as a supplementary arterial conduit for coronary revascularization.

Characteristics

Histologically, the RA has a fenestrated internal elastic lamina and a thicker wall than the ITA with a higher density of myocytes in its media.40 The RA is also more likely to have atherosclerotic changes at the time of harvest than the ITA, with 28% of RAs having some degree of demonstrable atherosclerosis, as compared with only 6% of ITAs. Whether these differences indicate that the RA will prove more susceptible to graft atherosclerosis with reduced patency is unknown.41

Physiologically, the RA is equally sensitive to norepinephrine as the ITA; however, given its greater muscle mass, it generates a higher force of contraction, accounting for its well-recognized propensity for spasm.42 Fortunately, the RA also readily responds to a variety of vasodilators, including calcium channel blockers, papaverine, nitrates, and milrinone. In vitro, nitroglycerine appears to be the most effective agent for inhibiting and reversing RA spasm.43 Additionally, nitroglycerin has been shown to be better tolerated clinically, equally effective, and less expensive than diltiazem in prophylaxis of RA spasm after CABG in a prospective randomized trial.44

Surgical Anatomy of the Radial Artery

The RA originates from the brachial artery just proximal to the biceps tendon. In the proximal forearm the RA courses underneath the brachioradialis muscle. As it courses distally, it emerges from the lower surface of the muscle, becoming more superficial, and runs beneath the antebrachial fascia between the tendon of the brachioradialis muscle and the flexor carpi radialis muscle and anterior to the radius and pronator quadratus muscle. The recurrent radial artery originates from the lateral aspect of the RA soon after its origin from the brachial artery. Multiple small muscular branches emerge from the deep and lateral surfaces of the artery. At the wrist the RA gives rise to the palmar carpal branch, the dorsal carpal branch, the superficial palmar branch, and the deep palm.45 Throughout its course the RA is accompanied by a rich plexus of venae comitantes. The average length of the RA ranges between 18 and 22 cm with an internal diameter of 2 to 3 mm.46

Harvest Technique

It is most common to consider the patient's nondominant arm for harvest, partially out of concern for the impact of even subtle neurologic changes, and partially given the convenience of harvesting the left radial artery simultaneously with the left ITA. The extremity of interest must have adequate ulnar collateral circulation to ensure viability of the hand. Assessment of collateral circulation is best performed via noninvasive duplex ultrasonography.47 The RA of the dominant hand can also be harvested if needed. Tatoulis and associates reported 261 patients undergoing bilateral RA harvesting with safe functional outcomes of both extremities.48

The arm is prepped circumferentially and the hand wrapped in a sterile fashion. The upper extremity is place on an arm board perpendicular to the long axis of the operating table. As shown in Fig. 21-2, a medially curved incision is made on the skin overlying the RA from a point 2 cm proximal to the styloid process of the radius to a point 2 cm distal to the elbow crease and 1 cm medial to the biceps tendon. The subcutaneous tissue is divided with the cautery. The dissection can be initiated at either end depending on the surgeons' preference. The deep fascia of the forearm is incised directly over the RA.

The RA is harvested as a pedicle with minimal manipulation using sharp dissection, diathermy, or the harmonic scalpel (our preferred method). There are data to suggest that early graft flow is superior when the harmonic scalpel is used.49 On the proximal half of the forearm, gentle lateral retraction of the brachioradialis muscle aids exposure. At the distal end of the dissection the satellite veins are identified and divided. The proximal end of the dissection is marked by the radial recurrent artery branch and a large venous plexus in the medial aspect of the RA. It is our routine to leave the recurrent radial branch intact. The artery is divided proximally and distally and stored in a room temperature solution of lactate, nitroglycerin, and papaverine.

After the RA is removed from the forearm, hemostasis of the operative field is obtained and the arm is closed in multiple layers. A closed suction drain is placed, which we feel helps reduce postoperative seroma formation. A circumferential elastic wrap is applied. The arm is then abducted and secured to the table. Reports of endoscopic RA harvest are beginning to emerge with good functional and cosmetic results; nonetheless the impact of the technique on graft patency is unknown.50 We have not adopted the technique.

Two cutaneous nerves are of importance to note during RA dissection. The lateral antebrachial cutaneous nerve lies superficial to the belly of the brachioradialis muscle and runs close to its medial border. Placing the skin incision medial to the edge of the brachioradialis prevents potential injury. Damage to this nerve will produce paresthesias and numbness of the radial aspect of the volar forearm. The superficial branch of the radial nerve lies under the brachioradialis muscle and in the proximal two-thirds of the forearm runs parallel to the RA. Injury to this nerve will result in paresthesias and numbness of the thumb and the dorsum of the hand. The nerve can best be protected by avoiding excessive lateral retraction on the brachioradialis muscle.45,51 Transient paresthesias, numbness, and thumb weakness are common and are reported by almost a third of patients after RA harvest; fortunately, the symptoms gradually resolve with time so that after 1 year only 10% of patients have residual complaints with only 1% reporting their symptoms as severe.52–54

Patency

Acar and associates in 1992 reported on 122 radial grafts with a 100% patency rate at 2 weeks and 93% patency at 9 months.55 The results appear durable with reported patencies at 48 months of 89%. Several factors may affect RA graft patency, however, including both target artery runoff and competitive flow. In the prospective, randomized Radial Artery Patency Study, more severe target coronary artery stenosis was associated with lower rate of occlusion (>90% stenosis = 5.9% versus 70 to 89% stenosis = 11.8%).56 The graft failure rate is highest if the target vessel is the right coronary artery system, but this may be related more to the coronary artery than the bypass conduit; one study showed equal patency of radial artery and saphenous vein bypass grafts to the right coronary artery.57–59

The proximal radial artery can be sutured to the ITA as a T- or Y-graft (composite), sutured directly to the ascending aorta, or sutured to the proximal portion or hood of a separate vein graft. In addition, a segment of vein can be interposed between the aorta and proximal radial artery in an end-to-end fashion. Comparisons have been made between the T- or Y-graft and direct aortic anastomosis methods. Maniar et al. found at approximately 30 months follow-up, a significantly greater incidence of postoperative angiography for recurrent angina among patients with direct aortic anastomosis as compared with patients with composite anastomosis (19% versus 11%).59 There is controversy here, however, as Jung et al. found that 1-, 2-, and 5-year patency rates were significantly better with direct aortic anastomosis as compared with composite anastomosis.60 Importantly, it appears that the overall patency of radial artery grafts to ideal targets may be superior to that of saphenous vein bypass grafts at 5 years, 98% versus 86%.61

Other Arterial Conduits

A variety of arterial conduits have been used in patients in whom no other conduits are available. The gastroepiploic artery (GEA) for the most part is utilized as an alternative conduit or as part of an all-arterial revascularization strategy. Despite the enthusiastic support of a small cohort of surgeons, the widespread use of the GEA as a coronary conduit has not been adopted, perhaps because of the increased operative time and relative difficulty required to harvest the conduit, the potential for perioperative and long-term abdominal complications, and the lack of consensus on the long-term benefit for total arterial revascularization. Anecdotal use of the ulnar, left gastric, splenic, thoracodorsal, lateral femoral circumflex and inferior epigastric arteries as coronary graft conduits has been reported in the literature. The popularity of the RA, however, has in large measure superseded these options.

Greater Saphenous Vein

The saphenous vein continues to be one of the most commonly used conduits in coronary bypass grafting. Characteristics that have solidified the greater saphenous vein as a coronary artery bypass conduit include its ease of harvest, ready availability, versatility, resistance to spasm, and thoroughly studied long-term results. Unfortunately there is a loss of clinical benefit after CABG because of time-related attrition. Accordingly, there is interest in pharmacologic strategies to maximize early and late venous graft patency.

Prospective randomized trials have shown that early aspirin administration reduces mortality after CABG. Aspirin within 48 hours after CABG also reduces early postoperative complications, including mortality, myocardial infarction, stroke, renal failure, and bowel infarction.62 More recently, it has been recognized that lipid-lowering agents reduce the progression of graft atherosclerosis.63,64 Aggressive use of statins to achieve a low-density lipoprotein cholesterol <100 mg/dL decrease by one-third the number of grafts affected with atherosclerosis at angiographic follow-up and also decreased the need for repeat revascularization.63 With clear documentation of improved outcomes with these two pharmacologic strategies, systematic approaches to ensure their universal application are needed.10

Finally, in the future, gene therapy may allow modification of the venous vascular endothelium to avert development of intimal hyperplasia. Unfortunately, the PREVENT IV trial, testing whether short-term angiographic vein graft failure could be diminished with treatment of the saphenous vein before grafting with edifoligide (an oligonucleotide decoy that binds to and inhibits E2F transcription factors), demonstrated no impact of the treatment.65 The concept remains a valid one, however, and gene therapy will continue to be an exciting area of investigation in the future.

Harvest Technique

Saphenous vein harvest can be performed with an open or endoscopic technique. Open-vein harvest can be performed with a completely opened technique or bridged technique. In the completely open technique an extensile skin incision provides the best exposure of the vein and may allow for harvest with the least amount of surgical trauma, but that advantage comes at the risk of higher rates of wound complications and postoperative pain. Bridged skin incisions may decrease pain and wound complications but may also increase surgical manipulation of the vein conduit.

Open-vein dissection can be started either in the upper thigh, above the knee, or at the ankle (Fig. 21-3). Some surgeons prefer to harvest vein from the lower leg because of a more appropriate vein caliber and wall thickness, as well as greater distance from the perineum (a potential source of infection). Others prefer to harvest vein from the thigh, arguing improved wound healing, particularly among patients with distal peripheral arterial occlusive disease. We are not aware of any data supporting one location over another. Because of the greater amount of adipose tissue present in the thigh area, wound breakdown in that location may prove more of a nuisance to treat. The fundamentals of vein harvest are to procure the conduit with a minimal amount of trauma to the vein. Specifically, the vein should not be grasped with forceps, stretched, or overdistended, because patency rates may be related to endothelial damage induced during harvest and preparation of the conduit. Identification of the vein is easiest at the ankle, just lateral to the medial malleolus.

In the completely open technique, a skin incision directly over the trajectory of the vein is made, taking care not to create skin flaps. Purposeful, directed, sharp dissection is used to free the vein from the surrounding tissue. Side branches on the vein can initially be left long. Once dissection is completed, the vein is ligated and divided proximally and distally. A blunt-tipped vein cannula is inserted into the distal end of the vein and the vein gently flushed and dilated with a room temperature solution of plasmalyte. The side branches can be clipped flush with the vein at this time, taking care to avoid narrowing of the conduit lumen.

When using a bridged technique, several step incisions are performed over the course of the vein. Dissection of the vein is otherwise carried out in a similar fashion as describe above. Exposure of the vein with the bridge technique may be less than optimal. Caution is necessary here to avoid excessive tension or manipulation of the conduit as an adjunct to deal with less than adequate exposure of those segments of the vein covered by a skin bridge. For all techniques of vein harvest located in the lower thigh and more distal, care should be taken to avoid trauma to the saphenous nerve, which is in close proximity to the vein. Injury to the nerve can result in debilitating postoperative neuralgia.

Endoscopic vein harvest starts with a 1.5- to 2.0-cm skin incision in the medial aspect of the extremity above the knee (Fig. 21-4). Carbon dioxide insufflation for visualization and dissection is established. Dissection is directed toward the groin region as far proximally as possible and then distally as far as needed to obtain the required length of conduit. Side branches are divided by using bipolar cauterizing scissors. Once dissection is completed, small skin punctures are made at the limits of the dissection and the vein exteriorized, ligated, and divided. The vein is removed and otherwise prepared in the standard fashion. Following skin closure, the leg is wrapped with a circumferential elastic bandage.

Patency

Minimally invasive harvest of the saphenous vein using an endoscopic technique is gaining popularity because it greatly reduces the wound morbidity associated with the open harvest techniques. Endoscopic harvest decreases wound complication rates and produces an improved cosmetic result, although the operative time devoted to harvest is increased as are the number of defects to the harvested conduit requiring suture repair. Initial reports showed no detrimental effects of harvest technique on vein morphology, endothelial structure or function, or graft patency.66,67 However, in recent report of 3000 patients treated with CABG, endovascular vein harvest was associated with higher rates of vein-graft failure, death, myocardial infarction, and repeat revascularization.68

The polar opposite to endoscopic vein harvest is the “no-touch” technique in which the vein is removed with a pedicle of surrounding tissue. The harvested vein is not distended and it is stored in heparinized blood. In a randomized study of 104 patients using this technique, the angiographic patency at 18 months was 89% for conventional versus 95% for no-touch grafts. At 8.5 years, patency rates were 76% for the conventional group versus 90% for the no-touch group. Multivariate analysis showed that the most important surgical factors for graft patency were the technique of harvesting the conduit and the vein quality. By comparison, the patency of internal thoracic artery grafts was 90% in the study.69

Other Venous Conduits

Alternative venous conduits such as the lesser saphenous and/or upper extremity cephalic veins are usually secondary choices for conduit. If it is planned to use either of these veins, preoperative vein mapping can help guide conduit harvest. The lesser saphenous vein can be harvested in a supine position through a lateral approach by flexing the hip and medially rotating the knee or by an inferior approach with straight elevation of the extremity. A skin incision is usually started midway between the Achilles tendon and the lateral malleolus. Dissection is carried proximally up the leg to the popliteal fossa. Attention should be paid to avoid injuring the sural nerve.

The patency rate for arm veins is significantly lower than that of saphenous veins and for that reason they are considered conduits of last resort.70 For cephalic vein harvest, the arm is prepared and positioned as during radial artery harvest. Incisions are placed along the medial and superior aspect of the arm. The cephalic vein is relatively thin-walled in comparison with the greater saphenous vein and is predisposed to aneurysmal dilatation.

Procedures are done under general anesthesia with central venous access, radial arterial lines, and pulmonary artery catheters. Transesophageal echocardiography may be helpful for identifying unsuspected intracardiac lesions or aortic atherosclerosis, and for evaluating ventricular function at the end of the procedure. If ventricular function is poor, a femoral arterial line will facilitate later placement of an intra-aortic balloon pump (IABP). We routinely use a temperature-monitoring urinary catheter. The patient is positioned in the supine position with arms tucked at the side. Care should be taken to avoid peripheral nerve complications caused by pressure injury. The lower extremities are positioned with a slight external rotation and flexion of the knees. The patient is prepared and draped to include the lower neck, the chest, and abdomen between the anterior axillary lines, and the lower extremities circumferentially.

Incisions

By far the most common approach for CABG is via median sternotomy. Cannulation for cardiopulmonary bypass, managing aortic valve insufficiency, monitoring the left ventricle for distention, and evacuating air all are easier with the midline approach. The skin incision extends from a point midway between the angle of Louis and the sternal notch to just below the tip of the xiphoid process. The scalpel is used to extend the incision through the subcutaneous tissues down to the sternum. Extensive Bovey cautery to the subcutaneous tissues should be avoided because tissue destruction here may result in increased risk of wound complication. Charcoal does not bleed, but neither does it heal.

Special attention should be devoted to identifying the middle of the sternum. The middle of the sternal periosteum is noted and marked with cautery, although we avoid scoring the periosteum continuously from notch to xiphoid as this devascularizes the periosteum unless the saw passes exactly down the line. The interclavicular ligament is divided in the sternal notch, allowing palpation of the posterior aspect of the sternal manubrium. The xiphoid process is identified and divided in the midline with heavy scissors and the midline diaphragmatic muscle attachments divided. A finger should be inserted under the sternum to document a free space anterior to the pericardium. If there are no significant adhesions present, the sternum is divided with the oscillating saw. If the prepericardial space is adhered, the sternum should be divided using the microsagittal saw. The saphenous vein or the RA can be harvested simultaneous with the sternotomy. Once the sternum has been divided, the ITA is harvested as previously described.

Cannulation and Establishment of Cardiopulmonary Bypass

The pericardium is divided vertically down to the diaphragm and the inferior attachment of the pericardium to the diaphragm is divided transversely. The remnant of thymic tissue and pericardial fat is divided in the midline to the inferior aspect of the left innominate vein. Pericardial retraction sutures create a pericardial cradle or well to improve exposure of the ascending aorta and right atrium. The left pericardium is divided at the level of the great vessels toward the phrenic nerve to allow the completed ITA bypass graft to fall laterally into the pleural space away from the sternum. The distal ascending aorta is inspected and palpated for soft nonatherosclerotic areas suitable for arterial cannulation, root ventilation, proximal graft anastomoses, and aortic cross-clamp placement (Fig. 21-5). In some institutions epicardial ultrasound of the ascending aorta is performed. Now is the time to redirect the conduct of the operation should the aorta harbor areas of significant calcification, a topic of later discussion.

Systemic anticoagulation is achieved with the intravenous administration of 300 U/kg of unfractionated heparin and the adequacy of anticoagulation documented by an activated clotting time (ACT) over 450 seconds. In anticipation of aortic cannulation the systolic blood pressure should be reduced to about 100 mm Hg to minimize the risk of aortic dissection. Two partial-thickness concentric diamond-shaped purse-string sutures using 2-0 Ethibond suture are placed in the distal ascending aorta or proximal aortic arch, leaving enough room on the ascending aorta for all necessary proximal aortic work. The size of the purse strings should be large enough to accept the aortic cannula tip, usually 20-22 French. The ends of the sutures are passed through tourniquets that will be used for tightening the purse strings. The aortic adventitia within the purse strings is divided in preparation for aortotomy. The adventitia just superior to the planned aortotomy is grasped with a forceps and an aortotomy equal in size to the cannula tip is created with a no. 11 scalpel blade. Bleeding is easily controlled with slight inferior traction of the forceps on the adventitia. The aortic cannula is inserted and properly positioned, and the purse strings are tightened. The tourniquets are secured to the aortic cannula with a heavy silk tie and then the cannula is secured to the skin.

Placement of the aortic cannula can result in acute aortic dissection. Intraluminal positioning of the cannula is confirmed by watching for the cannula to fill with arterial blood. The aortic cannula is de-aired and connected to the arterial end of the pump tubing. An additional method to asses for the presence of aortic dissection is to have the perfusionist check the wave form and pressure of the arterial cannula pulse and to deliver a test infusion of 50 to 100 mL of fluid through the cannula. If an aortic dissection is present, often the test infusion will result in an increase in arterial cannula pressure.

Venous cannulation is accomplished with a two-stage venous cannula inserted in the right atrial appendage. A 2-0 Ethibond purse-string suture is placed around the tip of the right atrial appendage. The purse string should be wide enough for easy access of the selected venous cannula. An atriotomy is made with scissors at the tip of the appendage. Small bridging fibers of muscle are divided with scissors to permit easy entry of the cannula. The venous cannula is cautiously inserted, the tip of which should lie in the inferior vena cava. The purse-string suture is tightened and the tourniquet secured to the venous cannula with a heavy silk tie. The venous line is connected to the pump tubing.

An aortic root cannula is placed in the ascending aorta and retrograde cardioplegia cannula placed in the coronary sinus via the right atrium. The patient is placed on cardiopulmonary bypass at 2.4 L/min/m2 and may be perfused at normothermia or may be cooled to 34°C. Once the patient is on full bypass, flow ventilation is stopped. A left ventricle vent may be placed via the right superior pulmonary vein at this time if there is significant aortic regurgitation. Target vessels are easier to identify before cardioplegic arrest while they are fully distended in their native state. The locations of planned distal anastomoses are marked with a scalpel. The pump flow is turned down temporarily and the aortic cross-clamp applied just proximal to the arterial cannula and bypass flow returned to normal.

Cold blood cardioplegia (10 mL/kg) is administered and may be delivered antegrade, retrograde, or both, with special attention given during this time to look for evidence of aortic regurgitation such as a flaccid aorta and/or left ventricle distention. Two available options to treat significant aortic regurgitation include completion of the procedure using only retrograde cardioplegia or placement of a left ventricle vent via the right superior pulmonary vein (our preferred method). Rarely is aortic valve replacement required. Additional doses of cardioplegia (5 mL/kg) are given via the antegrade and retrograde catheters approximately every 20 minutes throughout the remainder of the cross-clamp period.

Location of Targets and Sequence of Anastomoses

Arteriotomy sites should be chosen proximal enough to offer the largest-sized coronary target but distal enough to avoid areas of obstruction or significant atherosclerotic disease. Arteriotomies at bifurcations should be avoided. Diseased vessels with an intramyocardial course can often be localized by noting epicardial indentation, accompanying epicardial veins, or a whitish streak within the myocardium. Sharp dissection of overlying tissue is required to identify the desired target site. Often a very diseased vessel will be less diseased in the intramyocardial segment.

The LAD coronary artery can be particularly difficult to identify when it has an intramyocardial course. It can be relatively easy to inadvertently enter the right ventricular cavity while dissecting in the interventricular fat plane. If such a ventriculotomy is small, it can be closed with fine 6-0 polypropylene sutures, keeping in mind that the right ventricle is a low-pressure chamber and deep bites of myocardium are not necessary. However, if the right ventricle has been opened for a distance, it is best repaired using interrupted, pledgetted 2-0 Prolene suture (MH needle) in a horizontal mattress fashion, passing the needle under the ITA-LAD anastomosis. If difficulty is encountered in identifying an LAD artery, a fine probe may be passed retrograde via a small transverse arteriotomy into the LAD artery at the apex of the heart. The tip of the probe can be palpated in the proximal portion of the artery and cut down on appropriately. The distal arteriotomy is repaired with interrupted fine suture (7-0 or 8-0 Prolene). The repair can be done with or without a small vein patch.

The distribution of cardioplegia is usually relatively uniform; however, the sequence of anastomoses may be planned based on ischemic regions if myocardial protection is a particular concern. Grafting the most ischemic area first, using a distal-proximal routine, will permit early antegrade delivery of cardioplegia through the graft to the area of myocardial ischemia. Alternatively, the sequence of anastomoses may be dictated by the quality of the conduit itself, matching the best conduit to the most important territories. It is customary to perform the left internal thoracic artery-to-LAD artery anastomosis last to avoid tension and potential disruption of the anastomosis.

Arteriotomy

The choice of the site of arteriotomy is critical. Opening into a plaque may force endarterectomy, whereas injury to the posterior wall with the knife transforms a straightforward anastomosis into a complex repair. Silastic tapes placed proximally and distally around the coronary artery may help to stabilize the vessel, a technique often employed when grafting the distal right coronary artery or when there is significant back bleeding from the opened vessel. The arteriotomy is performed with a fine scalpel blade and extended with fine Pott's scissors proximally and distally. The arteriotomy should match the conduit diameter, and should be at least 1.5 times the luminal diameter of the distal coronary artery (Fig. 21-6).

Anastomotic Technique

The goal of the anastomosis is to join the conduit and the target vessel with precise endothelial approximation affording minimal resistance to flow. The wall of the vessel should be handled with care, avoiding endothelial injury to prevent thrombotic complications. Coronary anastomoses are typically constructed with continuous 7-0 polypropylene suture. Sutures should be evenly spaced to prevent leaks at the conclusion of the anastomosis. In order to increase anastomotic area, we prefer to bevel the conduits at approximately 30 degrees and notch them at the heel. Anastomoses are performed with continuous suture. We prefer a continuous, parachuting technique initiated at the heel for virtually all anastomoses regardless of their configuration (ie, end-to-side versus side-to-side sequential anastomosis).

Venous conduit is brought onto the field with a mosquito clamp on the adventitia at the toe of the conduit. An end-to-side anastomosis is accomplished with continuous sutures (Fig. 21-7). Starting at the 3 o'clock position on the right side of the vessel, the suture is passed outside-in on the conduit and then inside-out at the corresponding location of the target coronary vessel. Two more sutures are taken before the heel (2 and 1 o-clock positions), one directly in the heel (12 o'clock), and then two more on the left side (11 and 10 o'clock positions) of the anastomosis before parachuting the conduit down to the target vessel.

The anastomosis is continued by placing additional sutures moving in a counterclockwise fashion around the anastomosis until the other thread is encountered. The technique encourages one to move out of the heel and toe areas of the anastomosis, minimizing the risk of narrowing the outflow. Care must be taken to prevent suturing the back wall of the coronary, and the proper amount of tension on the follow-through must be provided to avoid both leakage and a purse-string effect. Just before completion of the anastomosis, a 1-mm probe is passed proximally and distally to ensure patency. To prevent anastomotic tension and torsion, pedicled conduits (ie, left ITA) can be suture- fixated to the adjacent epicardium.

Sequential grafting permits efficient use of conduit and has the potential for increased flow in the conduit. When planning sequential anastomoses, the most distal anastomosis should be to the largest target vessel with the greatest outflow potential. If the reverse situation is created, the most distal anastomosis is at increased risk for failure, given the likelihood of preferential flow to the larger more proximal anastomosis.71,72 A clear disadvantage of sequential grafting is the reliance of two or more distal targets on a single conduit and proximal anastomosis, placing a potentially larger region of myocardium at jeopardy.72

Some surgeons avoid using the ITA for sequential grafting or as a donor for composite T- or Y-grafting of other conduits because of concerns of compromising critical ITA-to-LAD flow. However, several series have demonstrated successful use of the ITA for sequential grafting of stenotic diagonal coronary arteries with excellent results.73,74 The left ITA has also been used for multiple sequential anastomoses to the circumflex territory with grafting of the right ITA to the LAD artery.75 Sequential grafting has also been performed with the right GEA as well as the RA.76,77

When constructing a sequential anastomosis, it is our preference to complete the distal anastomosis first and move proximally (Fig. 21-8). We feel that this facilitates determination of optimal inter graft spacing. In the case of the LAD-diagonal graft, however, it is easier to move from proximal to distal, performing the diagonal anastomosis first. Sequential side-to-side anastomoses may be perpendicular or longitudinal. When constructing perpendicular anastomoses care must be taken not to make the arteriotomies too long, as there is risk of creating a “gull-wing” deformity and placing the graft at jeopardy. Arteriotomies in both the conduit and target are made in the direction of the long axis of the vessel. The two incisions are then aligned perpendicular to one another and the anastomosis completed, creating a diamond-shaped anastomosis. The arteriotomy for longitudinal anastomosis may be made as long as necessary without risk of distorting the conduit. Typically, the longitudinal anastomosis is begun at the heel as previously described.

Coronary endarterectomy predated CABG as a direct surgical approach to relieving coronary occlusive disease. Coronary endarterectomy has been relegated to a position of secondary importance, however, thanks to the reliable and reproducible results obtained with CABG. Recently there has been increased interest in endarterectomy techniques, because the patient population coming to CABG has a greater atherosclerotic burden owing to diabetes, hyperlipidemia, and advanced age.78 Most commonly, the need for endarterectomy arises intraoperatively when no soft site can be identified for arteriotomy or a vessel has been inadvertently opened in an extensively diseased area not amenable to grafting. Occasionally, endarterectomy is undertaken electively in patients with diffuse and extensive coronary disease with no other choices except transplantation.

The perioperative risk of CABG with endarterectomy is higher than that for CABG alone in most studies. In a retrospective study of 1478 patients, the reported mortality rate with endarterectomy was 3.2%, which was higher than for CABG alone (2.2%). Perioperative MI rate was also higher in the endarterectomy group, 4.2% versus 3.4%. The risk of mortality appears to increase when multiple vessels require endarterectomy: single-vessel endarterectomy mortality = 1.8% versus multiple-vessel endarterectomy mortality = 5.5%.79,80 There has been controversy regarding the risk of endarterectomy of the LAD, with some studies showing increased risk whereas others demonstrate no increased risk.79–81

The late results of endarterectomy are inferior to those of routine CABG, with reported 3-year patency for ITA grafts to endarterectomized LAD targets ranging from 74 to 80%.82,83 Despite this, angina relief is remarkably good initially. Unfortunately, the rate of recurrent angina is somewhat higher than after uncomplicated CABG; reported recurrence of angina is 25% at 5 years after endarterectomy.79,84 The reported 5-year survival following coronary endarterectomy ranges from 76 to 83%.79,84 Among patients in whom bypass to more distal nondiseased segments is not possible, coronary endarterectomy with subsequent bypass offers a viable alternative to leaving a territory ungrafted.

Technique

The technique of endarterectomy requires that the central core be extracted adequately in order to relieve obstruction of the branch vessels. Patency of a graft to the endarterectomized vessel depends upon the adequacy of runoff and therefore the distal endpoints of the endarterectomy core must be smoothly tapered. If the core fractures leaving behind disease in side branches, distal counter-incisions may be needed to obtain a satisfactory result.

The RCA is the vessel most often endarterectomized, usually at the level of its bifurcation. A manual eversion endarterectomy is performed after entering at the vessel approximately 1 cm proximal to the crux. A circumferential plane of dissection between the core and the adventitia is developed with a fine coronary spatula. The core is transected proximally and gently grasped with DeBakey forceps while the spatula is used to tease the adventitia away from the core. The core is regrasped hand over hand as distally as possible to avoid fracture. When the crux is reached, the posterior descending artery and the left ventricular branch are endarterectomized separately. If endarterectomy of the proximal segment of the RCA is needed, we prefer to use an open technique because it is difficult to obtain nice tapering of the core at the takeoff of the acute marginal branches with a retrograde eversion endarterectomy. The vessel wall is then reconstructed with a long hood created with the bypass conduit of choice.

We prefer open extended technique when the LAD is endarterectomized (Fig. 21-9). The vessel is opened as far proximal as possible if endarterectomy is anticipated. If the vessel has been opened in its mid-portion before it is apparent that endarterectomy is necessary, we extend the incision in the adventitia proximally before developing the endarterectomy plane. Retrograde eversion endarterectomy is dangerous because branch vessels will not be opened. Once the core is separated from the adventitia, it is transected proximally at the heel and the vessel is opened beyond the takeoff of the major diagonals to permit individual eversion endarterectomy of each of the branches. The segment is reconstructed with a long hood of the conduit of choice or a vein patch into which the ITA is anastomosed. The circumflex artery is the most infrequently endarterectomized vessel. Its rapid branching pattern makes satisfactory endarterectomy difficult. We tend to begin with an eversion technique, focusing our efforts on opening the largest distal branches as much as possible.

Proximal anastomoses of saphenous vein or RA to the aorta are performed after the distal anastomoses under the same cross-clamp clamp. Our preferred technique is to complete each respective bypass graft in a distal anastomosis-proximal anastomosis fashion. Completion of the each respective bypass graft allows antegrade cardioplegia down the completed graft, aiding in myocardial protection. The single cross-clamp technique results in longer cross-clamp times than with the partial occlusion clamp method. However, the partial occlusion clamp technique requires additional aortic manipulation and has been associated with a higher risk of neuropsychological deficits as compared with the single-clamp technique.85

Anastomotic Technique

Once an appropriate site for aortotomy is identified, the fatty tissue overlying the aorta is removed (Fig. 21-10). An arteriotomy is created with a no. 11 blade, and a 4.0-mm punch used to create a circular aortotomy. The size of the punch may vary depending on the size of the conduit graft. The graft is measured to length with the aorta, right heart, and pulmonary artery full of blood. The graft is cut and the proximal aspect of the conduit beveled and notched at the heel. A running 5-0 polypropylene suture is used for a venous graft and a 6-0 polypropylene suture for an arterial conduit. The long axis of the graft is aligned at an appropriate angle to the ascending aorta. The anastomosis can be completed with continuous stitches. Symmetry in the spacing of sutures is paramount to obtain a hemostatic anastomosis. Free arterial grafts may also be sutured to the hood of a vein graft with continuous 7-0 Prolene suture.

Composite Grafts

As an alternative to proximal anastomosis to the aorta, a free graft can be anastomosed proximally to the pedicled ITA (Fig. 21-11). This technique has the theoretical advantage of providing a more physiologic arterial pressure waveform by attaching the conduit to a third-order vessel rather than to the aorta. Composite grafting is also a useful tool for the hostile, calcified ascending aorta or when there is a limited length of conduit available. It is also advantageous when there is a marked mismatch between aortic wall thickness and arterial conduit size.

A combination of composite and sequential grafting allows the opportunity to perform complete arterial revascularization with only ITA or with ITA and other arterial conduits (Fig. 21-12). Multiple configurations of Y- and T-grafts can be devised to best suit the anatomic characteristics of each patient. The LITA has been shown to have more than sufficient flow reserve to supply flow to the entire coronary circulation.86 The free right ITA, the RA, or other arterial conduit can be based in this manner.

All-arterial Y-grafts are usually planned in advance and constructed before the initiation of cardiopulmonary bypass. Special care must be taken during construction of composite grafts to avoid tension, rotational torsion, or narrowing of the inflow anastomosis. Disadvantages include technical difficulty and reliance upon a single inflow source for two or more distal targets.

Ascending aortic atherosclerosis has been consistently identified as a very important risk factor for stroke in multiple series. Epiaortic ultrasound can be performed to define the extent of atherosclerosis of the ascending aorta and its likelihood of embolization. Patients with severe atherosclerosis of the ascending aorta may require alternative strategies to prevent embolization of aortic atheroma. If the ascending aorta is hostile, we favor cannulation of the right axillary artery. The axillary artery is a good option to achieve arterial inflow by using a chimney side graft. If needed, aortic clamping may be performed in areas free of atheroma, usually in the more proximal ascending aorta.

Coronary revascularization can be achieved with a variety of methods. Using a “no-touch”technique, revascularization can be done using only pedicled arterial conduits, and if proximal anastomoses are required they can be based off pedicled conduits or brachiocephalic vessels. Distal anastomoses can be performed under cold fibrillatory arrest without aortic cross-clamping, and they also can be accomplished using off-pump techniques. Proximal anastomoses can be performed under deep hypothermic circulatory arrest or after graft replacement of the ascending aorta if there are large mobile atheromas.87

Weaning from Cardiopulmonary Bypass

On completion of all anastomoses, the aortic cross-clamp is removed and a stable heart rhythm established. Some advocate allowing the heart to recover on full bypass for 10 minutes for each 60 minutes of aortic cross-clamp time. During this time of recovery the patient is prepared for transition from supported circulation to native circulation. The aortic root vent and retrograde catheters are removed and the sites repaired with suture. The bypass grafts are checked for kinks, twists, or tension and for presence of hemostasis. The patient must be rewarmed to normothermia if cooled and the acid-base status and electrolyte abnormalities corrected. We place temporary atrial and ventricular pacing wires on all patients.

Weaning from cardiopulmonary bypass is otherwise the same as for other cardiac surgical cases. Issues particular to CABG include attention to avoid overdistention of the heart, which may place grafts on tension and disrupt anastomoses. If air has entered the heart, bubbles may pass into the aorta and down the bypass grafts causing arrhythmias and regional wall motion abnormalities. Treatment involves continued recovery on bypass and increasing the perfusion pressure as a means to drive the bubbles through the coronary circulation. Persistency of regional wall motion abnormalities may require bypass graft revision or placement of additional bypass grafts.

Operative Mortality

The risk profile of patients requiring isolated CABG in the United States has changed significantly in the past decade. Patients are older, with a greater number of comorbidities, decreased LVEF, and a higher burden of atherosclerotic disease; however, early outcomes after CABG continue to improve. The STS database demonstrates that despite an increase in expected mortality from 2.6 to 3.4% (relative increase 30%) in the decade of the 1990s, the observed mortality has actually decreased from 3.9 to 3.0% (relative decrease 23%).3

Similar observations have been made using the Veterans Affairs mandatory national database, where the unadjusted mortality rate for isolated CABG fell from 4.3% in 1989 to 2.7% in the year 2000.88 In the private sector similar trends have been observed. In an analysis of outcomes of patients undergoing isolated CABG in the HCA system, a nationwide for-profit health care system involving 200 hospitals in 23 states, Mack and associates reported an ongoing decrease in unadjusted operative mortality among 51,353 patients, 80% of whom received CABG with cardiopulmonary bypass. In this study the operative mortality decreased from 2.9% in 1999 to 2.2% in 2002.89

Causes of Death

In a multicenter prospective study performed by the Northern New England Cardiovascular Disease Study Group, 384 deaths among 8641 consecutive patients undergoing isolated CABG between 1990 and 1995 were analyzed with respect to the mode of death. The mode of death was defined as the seminal event that precipitated clinical deterioration and ultimately resulted in the patient's demise. Heart failure was judged to be the primary mode of death for 65% of the patients, followed in frequency by neurologic causes (7.3%), hemorrhage (7%), respiratory failure (5.5%), and dysrhythmia (5.5%). The greatest variability in mortality rates observed across surgeons in the study was attributable to differences in rates of heart failure.90 Cardiac causes were also identified by Sergeant and colleagues as the most common causes of death in a series 5880 patients undergoing CABG between 1983 and 1988.91

Operative Morbidity

Myocardial Dysfunction

Postoperative myocardial dysfunction and cardiac failure after CABG may be related to preoperative ischemic injury, inadequate myocardial protection, incomplete revascularization, or postoperative graft failure. The spectrum of myocardial injury varies from subtle degrees of global myocardial ischemia to transmural infarction. The incidence of myocardial injury identified varies with the sensitivity of the method used for detection as well as the threshold set. Some studies have reported perioperative myocardial infarction rates as high as 10% of patients with associated worse clinical outcomes (death, MI, or revascularization).92

Some elevations of cardiac-specific enzymes are ubiquitous after CABG; however, most would agree that elevations in creatinine kinase-myocardial bound (CK-MB) greater than five times the upper limit of normal (ULN) value are considered significant. In a prospective study of 2918 patients undergoing CABG, 38% of patients had a CK-MB >5 ULN and 17% had a CK-MB >10 ULN with an incidence of new Q-wave MI of 4.7%.93 Troponin may be a more sensitive marker than CK-MB, but its role in large populations of CABG patients is still to be defined.94 Prominent elevations of CK-MB and troponin have been associated with global ischemia, MI, low cardiac output, and increased operative mortality, as well as increased midterm and long-term mortality.93,94

Transient myocardial dysfunction necessitating low-dose inotropic support for a short period of time is also common after CABG. Significant postoperative myocardial dysfunction manifest clinically as low cardiac output syndrome may be defined by the need for postoperative inotropic support or intra-aortic balloon pump support to maintain a systolic blood pressure >90 mm Hg or a cardiac index >2.2 L/min. The reported incidence of low output syndrome varies depending on the defining criteria and has a reported incidence of 4–9%.95,96 Low output syndrome has been shown to be a marker for increased operative mortality by 10- to 15-fold.97 Independent predictors of low output syndrome in order of importance include: LVEF <20%, reoperation, emergency operation, female gender, diabetes, age older than 70, left main disease, recent MI, and triple-vessel disease.96

Adverse Neurologic Outcome

Neurologic deficits after coronary surgery are divided into two types: type 1 deficits include major neurologic deficits, stupor, and coma; type 2 deficits are characterized by deterioration of intellectual function and memory. The incidence of type 1 deficits was reported to be 1.6% in a large review by the Northern New England Cardiovascular Disease Study Group with 1-, 5-, and 10-year survival rates significantly reduced in affected patients.98 Perioperative mortality is similarly increased among those with type 1 injury at over 24%.99 Type 2 deficits are more difficult to characterize and may be more related to the underlying atherosclerosis than to the bypass operation per se. In one nonrandomized study, there was no evidence that the cognitive test performance of coronary artery bypass grafting (CABG) patients differed from that of heart healthy control groups with coronary artery disease over a 1-year period.100

Predictors of neurologic deficits included advanced age (≥70 years of age), and history or presence of severe hypertension. Independent predictors of type 1 deficits included proximal aortic atherosclerosis, history of prior neurologic disease, need for IABP, diabetes, unstable angina, and perioperative hypotension. Predictors of type 2 deficits included history of alcohol consumption, dysrhythmias, prior CABG, peripheral vascular disease, congestive heart failure (CHF), and perioperative hypotension. Similar predictors of adverse neurologic outcomes have been observed in other studies.101

Deep Sternal Wound Infection

Deep sternal wound infection occurs in 1 to 4% of CABG patients and carries a mortality rate of 25%.102 Proven methods to reduce postoperative wound complications include the use of preoperative showers with chlorhexidine gluconate on the evening and morning before the procedure, prophylactic intranasal application of mupirocin given on the evening and the morning before the procedure and twice daily for 5 days postoperatively, hair clipping the morning of surgery, and administration of intravenous prophylactic antibiotics before skin incision.103–105 Application of a cyanoacrylate-based microbial skin sealant may further reduce surgical site infection.106

Obesity and diabetes are strong independent predictors of mediastinitis. Insulin-dependent diabetics are especially susceptible to deep sternal wound infection.107–109 Recent data suggest that tight glycemic control in the postoperative period decreases the risk of mediastinitis in the diabetic population.110,111 Other preoperative variables independently associated with an increased incidence of deep sternal wound infection include reoperation, longer operative times, reexploration for bleeding, and blood transfusions.108,109,112

The use of bilateral ITAs had been implicated as a risk factor for sternal would complications, especially in diabetics.113 However, this risk appears to be mitigated in part by using a skeletonized ITA harvesting technique.114 Bilateral ITA harvest should likely be avoided in obese diabetic women, in cases of repeat sternotomy, and in patients with severe COPD, because they exhibit a higher risk of deep sternal wound infection even with skeletonization of the ITA.25,115

Acute Renal Failure

Acute renal failure ensuing after CABG with cardiopulmonary bypass is an ominous event. In a prospective observational study conducted at 24 university centers in the United States, including data on 2222 CABG patients,116 renal dysfunction not requiring dialysis occurred in 6.3%, and renal dysfunction requiring hemodialysis developed in 1.4%. Mortality was directly related to postoperative renal function. Patients with no renal dysfunction had 0.9% mortality.116 Postoperative renal dysfunction increased mortality to 19% if no dialysis was needed and increased mortality to 63% if hemodialysis was required. Patients with large creatinine increases (≥ 50%) after CABG surgery also have higher 90-day mortality.117

Independent predictors of postoperative renal dysfunction included increasing age, CHF, reoperation, diabetes mellitus, chronic renal insufficiency, prolonged cardiopulmonary bypass time, and low cardiac output.116 These findings were confirmed in another series of 42,733 patients with similar incidence and mortality associated with postoperative renal dysfunction.118 One in four patients with preoperative chronic renal insufficiency (creatinine >1.6 mg/dL) will require renal replacement therapy post-CABG, and patients at highest risk are older than 70 years and have a baseline creatinine >2.5 mg/dL.119

Continuous infusion of low-dose recombinant human B-type natriuretic peptide (nesiritide) from the start of cardiopulmonary bypass has been evaluated as a method to effectively maintain postoperative renal function. In the prospective, randomized, NAPA Trial, 272 patients with ejection fraction ≤ 40% undergoing CABG who receive nesiritide experienced a significantly attenuated peak increase in serum creatinine and a greater urine output during the initial 24 hours after surgery. In addition, they had a shorter hospital stay and lower 180-day mortality.120 Similar renal protective results were noted in a randomized trial using human atrial natriuretic peptide in 251 patients. The treated group had fewer postoperative complications, lower serum creatinine, and higher urinary creatinine and creatinine clearance. The maximum postoperative creatinine level and percent increase of creatinine were also significantly lower in the treatment group. No patient in the natriuretic group required hemodialysis.121 We are awaiting further study before adopting natriuretic peptides in our routine CABG practice.

Long-Term Outcomes

Long-term outcomes of surgical myocardial revascularization depend on the complex interaction of patient-related and procedure-related factors. Important patient-related factors include anatomic distribution of the CAD, the extent and severity of coronary atherosclerosis, the physiologic impact of ischemia on ventricular function at the time of the original operation, age, gender, overall health status, severity of atherosclerotic burden throughout the body, the presence and severity of associated comorbidities, development of operative complications such as stroke, and need for permanent hemodialysis. The progression rate of native coronary atherosclerosis after surgery and the development of coronary bypass graft failure are of extreme importance in the development of post-CABG angina recurrence, MI, need for reintervention, and cardiac-related mortality. Procedure-related factors that influence long-term outcomes include completeness of revascularization, myocardial protection, and selection of bypass conduits.

Sergeant and colleagues at the Gasthuiberg University Hospital of the Katholieke Universiteit (KU) Leuven, Belgium have provided several reports detailing clinical outcomes after myocardial revascularization.122–125 From 1971 to 1993, 9600 consecutive CABG patients were prospectively followed with special attention to clinical outcomes after surgical myocardial revascularization; the investigators achieved a 99.9% complete follow-up in this cohort. Clinical outcomes prospectively followed included mortality, return of angina, MI, and coronary reintervention.122

Defining the return of angina as the first occurrence of angina of any intensity or duration unless it was associated on the same day with MI or death, and recording the severity of this event, was also recorded. The overall non–risk-adjusted freedom from return of angina was 95% at 1 year, 82% at 5 years, 61% at 10 years, 38% at 15 years, and 21% at 20 years. The data suggest that if followed long enough after CABG, the return of angina is almost inevitable; by 12 years one-half of operated patients had return of angina. The initial episode of recurrent angina was rated as mild in 59% of patients.123 In the Bypass Angioplasty Revascularization Investigation (BARI) trial of 914 patients with symptomatic multivessel disease randomly assigned to receive CABG, freedom from angina was 84% at 5 and 10 years.126

The overall non–risk-adjusted freedom from MI after CABG at the KU Leuven was 97% at 30 days, 94% at 5 years, 86% at 10 years, 73% at 15 years, and 56% at 20 years.124 The overall non–risk-adjusted freedom from a coronary reintervention, either PCI or reoperative CABG, was 99.7% at 30 days, 97% at 5 years, 89% at 10 years, 72% at 15 years, and 48% at 20 years (125). In the BARI trial, freedom from subsequent coronary reintervention intervention at 10 years was 80%.126

Overall risk-unadjusted survival after CABG in the KU Leuven experience was 98% at 30 days, 92% at 5 years, 81% at 10 years, 66% at 15 years, and 51% at 20 years. Mortality after CABG was characterized by an initial period of high risk in the first month after surgery, then risk declined to its lowest at 1 year after the operation, and thereafter the mortality risk rose slowly and steadily for as long as the patient was followed. This slow and steady rise in the risk of death over time paralleled that of the general population when matched for sex, age, and ethnicity.125 In the BARI trial, survival was 89% at 5 years and 74% at 10 years.126

The occurrence of ischemic clinical events after CABG negatively influences survival. In the KU Leuven study, overall survival was lessened by return of angina, with an observed survival of 83% at 5 years and 54% at 15 years; the more intense the severity of angina at its return, the greater its influence on survival.123 The occurrence of MI after CABG has a greater negative effect on survival. Observed long-term survival after post-CABG infarction at the KU Leuven was 80% at 30 days, 65% at 5 years, 52% at 10 years, and 41% at 15 years.124

Progression of Disease in Native Coronary Arteries

Progression of atherosclerosis in the native coronary arteries continues after CABG. Bourassa and associates studied the progression of atherosclerosis in the native circulation 10 years after surgery and found that progression of CAD occurs in approximately 50% of nongrafted arteries.127 The rate of progression of disease in nongrafted arteries was no different from that of grafted arteries with patent grafts; however, progression was more frequent in grafted arteries with occluded grafts. Progression of preexisting stenoses in native coronaries was more frequent than appearance of new stenoses, and it was related to the severity of the preexisting stenosis only in nongrafted arteries.

Progression of native CAD was associated with deterioration in left ventricular function. Native coronary atherosclerosis progressed at a similar rate to that of equally diseased arteries in nonoperated patients.127 Low levels of high-density lipoprotein cholesterol and elevated levels of plasma low-density lipoprotein cholesterol correlated with native disease progression and development of new atherosclerotic lesions.128,129 Diabetes has been related to accelerated atherosclerosis. The VICTORY trial will be the first cardiometabolic study to evaluate the antiatherosclerotic and metabolic effects of rosiglitazone is post-CABG patients with type 2 diabetes in patients 1 to 10 years after CABG.130

Vein Graft Failure

Although the use of the saphenous vein helped popularize coronary bypass grafting, the propensity of the saphenous vein graft to fail over time has been the limiting factor of the procedure. It has been reported that approximately 15% of vein grafts occlude in the first year after CABG, and by 6 and 10 years after surgery patency rates fall to approximately 75% and approximately 60%, respectively.18 Three entities are responsible for saphenous vein graft failure: thrombosis, intimal hyperplasia, and graft atherosclerosis

Thrombosis accounts for graft failure within the first month after CABG, and graft occlusion is found on angiography in 3 to 12% of all venous grafts. Even when performed under optimal conditions, the harvesting of venous conduits is associated with focal endothelial disruption. In particular, the high pressure distension used to overcome venospasm during harvesting causes prominent endothelial cell loss, medial damage, activation of local factors (ie, fibrinogen) influencing hemostasis. Additionally, the inherent antithrombotic properties of veins are comparatively weak. The propensity for early graft occlusion resulting from these prothrombotic effects may, on occasion, be amplified by technical factors that reduce graft flow, including intact venous valves, anastomotic stricture, or graft implantation proximal to an atheromatous segment.18

Intimal hyperplasia, defined as the accumulation of smooth muscle cells and extracellular matrix in the intimal compartment, is the major disease process in venous grafts between 1 month and 1 year after implantation. Nearly all veins implanted into the arterial circulation develop intimal thickening within 4 to 6 weeks, which may reduce the lumen by up to 25%. Intimal hyperplasia rarely produces significant stenosis per se; more importantly, however, is that it may provide the foundation for later development of graft atheroma.131

Progression of atherosclerosis in aortocoronary saphenous vein grafts is frequent and represents the predominant cause of late graft failure after CABG. Vein graft atherosclerosis may begin as early as the first year, but is fully developed only after about 5 years. Ten years after surgery, 50 to 60% of SVGs will be occluded and one-half of still patent grafts will show angiographic evidence of atherosclerosis; two-thirds of these lesions will have a luminal diameter reduction of 50% or greater. Vein graft atherosclerosis is the leading cause for reintervention following CABG, more so than progression of disease in native coronary arteries.18

Although the risk factors predisposing to vein graft atherosclerosis are broadly similar to those recognized for native coronary disease, the pathogenic effects of these risk factors are amplified by inherent deficiencies of the vein as a conduit when transposed into the coronary arterial circulation. A multifaceted strategy aimed at prevention of vein graft disease is emerging, elements of which include: continued improvements in surgical technique; more effective antiplatelet drugs; increasingly intensive risk factor modification, in particular early and aggressive lipid-lowering drug therapy; and a number of evolving therapies, such as gene transfer and nitric oxide donor administration, which target vein graft disease at an early and fundamental level. At present, a key measure is to circumvent the problem of vein graft disease by preferential selection of arterial conduits, in particular the internal mammary arteries, for coronary bypass surgery whenever possible.18

Extended Use of Arterial Grafting

Bilateral Internal Thoracic Artery Graft

In contrast to the easily demonstrated survival benefit conferred by an ITA graft to the LAD artery, it was more difficult to demonstrate a survival benefit to a second arterial graft. Buxton and colleagues studied 1243 patients undergoing primary CABG with bilateral ITA grafts compared with 1583 patients with single ITA grafts. This group demonstrated a 15% absolute improvement in actuarial survival rates 10 years after CABG with the use of bilateral ITA grafts, as compared with the use of a single ITA graft (10-year survival for bilateral ITA was 86 ± 3% versus 71 ± 5% for a single ITA).131 Lytle and colleagues similarly demonstrated an improvement in survival at 12 years (79 versus 71%) as well as superior reoperation-free survival (77 versus 62%) among 2001 bilateral and 8123 single ITA graft patients.132 The impact of selection bias in these studies is difficult to control, however, and although some surgeons have embraced bilateral ITA grafting, it still represents a small minority of cases reported to the STS database.

Complete Arterial Revascularization

The better long-term results achieved with the use of bilateral ITAs and the well-known time-related attrition in patency of venous conduits encouraged the exclusive use of arterial conduits for myocardial revascularization. Complete arterial revascularization can be achieved by a variety of strategies, including composite grafting using exclusively ITAs or secondary arterial conduits such as the RA and the GEA. The use of sequential anastomotic techniques maximizes the utilization of arterial conduits. Although technically demanding, sequential grafting can be performed safely and with excellent long-term results with reported 96% patency rates of 7.5 years of follow-up on 1150 sequential ITA anastomoses.133

Tector has championed complete arterial revascularization using bilateral ITAs in a T configuration with end-to-side anastomosis of one ITA as a free graft to the side of the second ITA, which is left as a pedicled graft, combined with liberal use of sequential anastomoses. In his series of 897 patients overall survival was 75%, and freedom from reintervention was 92% 8 years after revascularization.134 Barner has reported similar encouraging results with composite grafting using one ITA and one RA.135 Data from randomized studies are beginning to emerge supporting improvement in early outcomes with complete arterial revascularization compared with conventional CABG. Muneretto and associates randomized 200 patients to complete arterial revascularization (left ITA to the LAD artery and composite grafts with the right ITA, RA, or both) versus conventional CABG (left ITA to the LAD artery and SVGs). In midterm follow-up (20 months) superior event-free survival (freedom from non-fatal MI, angina recurrence, graft occlusion, need for percutaneous transluminal coronary angioplasty, and late death) was demonstrable in the complete arterial revascularization patients compared to conventional CABG.136

The same group conducted a second randomized trial comparing complete arterial revascularization to conventional CABG (ITA to LAD artery and SVG) in 160 patients older than 70 years of age undergoing first time nonemergent CABG. Early mortality was similar, but at 16 ± 3 months, there were significantly fewer graft occlusions and recurrences of angina among the complete arterial revascularization group. Independent predictors of graft occlusion and angina recurrence were use of SVGs, diabetes, and dyslipidemia.137 The result of longer follow-up of these trials is still awaited.

Coronary artery bypass graft surgery with myocardial perfusion remains an excellent treatment strategy for myocardial ischemia. As the population grows older and acquires more relevant comorbidities, the risk of treatment will increase. New techniques and conduit choices, however, are proving effective as the associated morbidity and mortality of operation continue to decline. Alternative techniques such as off-pump CABG and PCI continue to be assessed against the current, best treatment option, CABG with cardiopulmonary bypass.

1. Coronary artery disease is the number one killer of Americans.

2. Coronary artery bypass is advantageous over medical therapy in patients with left main coronary artery stenosis, three-vessel disease with left ventricular dysfunction, two-vessel disease with proximal left anterior descending disease, and in patient with severe ischemia and multivessel disease.

3. The STS risk model for postoperative morbidity and mortality can be found on the STS web site (www.sts.org) and includes 30-day stroke and death rates of 1.6% and 3%, respectively.

4. The left internal mammary to left anterior descending coronary artery bypass graft confers a survival advantage to coronary artery bypass patients. In the BARI trial, patency rates at 1 and 4 years were 98% and 91%, respectively.

5. Skeletonization of the internal mammary artery is associated with reduced incidence of sternal wound complications.

6. Radial artery grafts have better 5 year patency (98% versus 86%) than saphenous vein grafts.

7. Cognitive test performance of patients after coronary artery bypass grafting is no different from that of heart healthy control groups over a 1-year period.

8. Freedom from angina after coronary artery bypass grafting in the BARI trial was 84% at 5 and 10 years.

9. Bilateral compared to single internal mammary artery bypass grafting is associated with improved survival, but the benefit is not noted until about 10 years after operation.