Lorraine D. Cornwell, MD, Ourania Preventza, MD and Faisal Bakaeen, MD

1. What are the indications for coronary artery bypass grafting (CABG)?

    According to the latest published guidelines from the American College of Cardiology Foundation/American Heart Association (ACCF/AHA), class I indications for CABG include significant left main stenosis and three-vessel coronary artery disease (CAD). Class I indications also include two-vessel disease involving the proximal left anterior descending (LAD) artery. CABG should be considered as a reasonable treatment strategy (class IIa) in patients with proximal LAD artery disease, and in 2-vessel disease without proximal LAD artery disease but with extensive ischemia.

    After myocardial infarction (MI), primary surgical revascularization should be considered in patients not suitable for percutaneous coronary intervention (PCI), patients who have failed PCI, or patients with ongoing ischemia or symptoms. After a transmural infarct, mechanical complications such as a postinfarction ventricular septal defect (VSD), acute mitral regurgitation (MR) as a result of papillary rupture, and free-wall pseudoaneurysm should be considered as indications for primary surgical intervention.

2. How does CABG compare with medical management for CAD?

    Three early prospective randomized trials comparing CABG with medical therapy were conducted in the late 1970s and were reported in the early 1980s. The Veterans Affairs (VA) cooperative trial, European Coronary Surgery Study (ECSS), and Coronary Artery Surgery Study (CASS) showed long-term superiority of surgery over medical therapy in patients with left main (LM) artery CAD, significant CAD involving the LAD artery, and multivessel disease.

3. How does CABG compare with stents?

    The Arterial Revascularization Therapies Study (ARTS) was the largest trial comparing CABG with bare metal stents in patients (1) with ejection fraction (EF) greater than 30% and (2) where there was consensus between surgeon and cardiologist that the disease was suitable for both therapies. The study showed improved event-free survival in the CABG group at 1, 2, and 5 years.

4. What about with drug-eluting stents (DES)?

    Drug-eluting stents have reduced the problem of restenosis, but data directly comparing DES with CABG is limited and still relatively short-term. In a registry study from the New York state cardiovascular database, CABG resulted in improved survival at 3 years compared with DES for patients with double- and triple-vessel disease. ARTS II randomized patients to DES or CABG, and showed that the primary composite outcomes at one year were similar. The international SYNTAX trial, involving 85 centers and 1800 patients with multivessel or left main CAD, recently published 3-year follow-up data in 2011. This showed worse outcomes in the PCI group as compared to the CABG group at 3 years, with increased composite major adverse cardiac and cerebrovascular events (MACCE: death, stroke, MI, or repeat revascularization). Although there was no significant difference in all-cause mortality and stroke at 3 years, MI and repeat revascularization were both increased in the PCI group. The study concluded that patients with more complex disease (three-vessel CAD with intermediate-high SYNTAX scores and LM artery CAD with high SYNTAX scores) have an increased risk of MACCE with PCI, and CABG is the preferred treatment option.

5. What is the SYNTAX score?

    The SYNTAX score derives from a scoring system developed by the SYNTAX trial investigators to quantify the extent and complexity of CAD based on findings at cardiac catheterization. Scores are divided into tertiles: low (0-22), intermediate (23-32), and high (≥33), with higher scores representing more extensive and complex CAD. The SYNTAX score was found to correlate with PCI risk and outcome, but not with CABG risk and outcome. Patients with higher SYNTAX scores generally benefited from a revascularization strategy of CABG in preference to PCI. This is reflected in current guidelines, which state that it is reasonable to choose CABG over PCI as a revascularization strategy in patients with complex three-vessel disease and high SYNTAX scores (class IIa recommendation).

6. Which patients benefit most from CABG?

    The decision for surgery is made based on the comprehensive evaluation of the patient. Anatomic considerations that favor recommendation for CABG include presence of significant LM or proximal LAD coronary artery disease, multivessel CAD, and presence of lesions not amenable to stenting. The presence of diabetes also favors surgical revascularization over stenting in operable patients. Depressed ejection fraction has been recognized as an additional indication for CABG.

    Although the coronary anatomy may be suitable for bypass, each patient’s comorbidities should be considered in the overall risk-benefit analysis. Preoperative renal insufficiency, peripheral vascular disease, recent MI, or recent stroke, as well as emergency operation and cardiogenic shock, have been identified as factors that increase mortality.

7. What is the cardiopulmonary bypass (CPB) pump, and how is it used?

    The “pump” involves temporarily placing a patient on a machine to supply circulation and oxygenation during an operation, so that the heart can be stopped to facilitate the procedure. The bypass circuit consists of the tubing, a collection chamber, oxygenator, heater-cooler machines to control temperature, and the pump. An aortic cannula is placed in the distal ascending aorta, and this is connected to tubing that will be used to bring artificially oxygenated blood from the pump back to the patient’s arterial bloodstream. A venous cannula is placed in the right atrium, and advanced down into the inferior vena cava, to collect venous blood and return it towards the pump. Once the venous blood is oxygenated, it is pumped back into the arterial line to the patient’s aorta. A perfusionist runs the pump under the direction of the surgeon.

8. Why is heparin required for CPB?

    The CPB circuit is thrombogenic, and systemic anticoagulation is required to prevent clotting and embolization. The standard anticoagulant is heparin (300 U\kg), which is administered to produce a target activated clotting time (ACT) of greater than 480 seconds. In patients with previously documented heparin-induced thrombocytopenia, direct thrombin inhibitors have been used for anticoagulation. Heparin is used in off-pump CABG at partial dose. After termination of CPB and decannulation, heparin-related anticoagulation is reversed with protamine.

9. How is the heart stopped while on CPB?

    The heart is stopped by placing a completely occluding cross-clamp across the ascending aorta, below the aortic cannula, eliminating arterial blood flow to the coronary arteries. Cardioplegia solution is then used to induce arrest of the heart, and can be given antegrade and/or retrograde. Components of cardioplegia solution are varied in different institutions but include potassium to achieve diastolic arrest. Cardioplegia solution administered into the aortic root, via a small cannula below the cross-clamp, is delivered in an antegrade fashion to the myocardium via the coronary ostia. Retrograde cardioplegia is also used frequently, by infusing cardioplegia solution into the coronary sinus with backward filling of the cardiac veins to reach the myocardium, and is especially important in situations where antegrade may not be as effective, such as with severe CAD and aortic valve insufficiency. Most commonly, cold cardioplegia at 4° C is administered intermittently in 15- to 20-minute intervals. Blood can be mixed to the crystalloid component of cardioplegia in a 4:1 mix to provide oxygenated blood to the myocardium and to buffer the pH of the tissue (Fig. 21-1).

10. How is the myocardium protected during cardiac arrest during bypass surgery?

    Myocardial ischemia occurs when the aortic cross-clamp is applied, at which time the coronary arteries no longer perfuse the myocardium. Strategies to protect the myocardium during this time include cooling the heart, unloading the ventricle, and arresting the heart. Systemic cooling of the heart and the body is accomplished with the cardiopulmonary bypass machine. Direct cooling of the heart is also accomplished with cold cardioplegic solution and topical ice solution. Unloading the ventricles is accomplished by the CPB machine, which empties the heart. The greatest decrease in oxygen demand (by as much as 80%) occurs with the diastolic arrest of the heart using cardioplegia solution, which eliminates the electrical and mechanical work of the myocardium.

11. What are the benefits of using the internal mammary artery for bypass?

    Use of the internal mammary artery (IMA) was first described by Kolessov in 1967, but its impact on survival wasn’t noted until the mid-1980s. Left IMA (LIMA) anastomosed to the LAD artery has an approximately 90% patency at 10 years and offers an advantage in both survival and freedom from reoperation. The current guidelines for CABG include a class I recommendation for use of the LIMA to bypass the LAD artery when bypass of the LAD artery is indicated (Fig. 21-2).

12. What about other arterial conduits?

    The right IMA (RIMA), radial artery, gastroepiploic artery, and inferior epigastric arteries have also been used as bypass conduits, and some surgeons have favored all-arterial strategies for bypass grafting, with hopes to improve long-term patency over saphenous vein grafts (SVG). However, these other arterial grafts have not duplicated the success of the LIMA to the LAD artery. The radial artery has been recently evaluated in several randomized trials using follow-up angiography, and results are mixed, with some showing a small incremental benefit in patency over SVG at 1 year. A recent VA cooperative study randomized 733 patients to radial artery versus saphenous vein graft, and showed equivalent graft patency at one year (89% in each group). Because the important question is long-term patency, 5 year patency rates will be the subject of ongoing investigations.

13. What is the long-term patency of the saphenous vein?

    The saphenous vein is readily available and relatively easy to procure, provides multiple graft segments, and is the most common bypass graft used other than the LIMA. The major limitation of the SVG is its long-term patency. Early attrition of up to 15% can occur by 1 year, with 10-year patency traditionally cited at 60%. Early patency has been shown to be improved by use of aspirin postoperatively. SVG can be harvested using a single long leg incision, multiple short incisions with intervening skin islands, or endoscopic techniques. Early patency has largely been found to be equivalent both clinically and angiographically between open and endoscopic techniques.

14. What is off-pump CABG, and what are the differences between on-pump and off-pump CABG?

    Off-pump bypass is CABG surgery performed without use of the CPB machine. The heart remains beating throughout the procedure, and stabilizers and coronary occlusion and shunts are used to perform the bypass graft to native coronary artery anastomoses (Fig. 21-3). Because off-pump surgery avoids CPB, it should lessen the side effects of the extracorporeal circulation, such as activation of inflammatory mediators, coagulopathy, and risk of embolic events. Surgeons have debated the merits of off-pump verses on-pump bypass for many years, and the goal of demonstrating differences between the two techniques in hard endpoints, such as mortality, stroke, and renal failure, has been elusive. In fact, the literature largely shows equivalency in these major early outcomes. In some studies, slightly shorter lengths of hospital stay and lower transfusion rates have been noted with off-pump surgery.

    Surgeons that prefer on-pump bypass surgery argue that the use of CPB allows maintenance of hemodynamic stability and aids in complete revascularization. The motionless and bloodless field allows precise and exact anastomoses. Off-pump revascularization on a beating heart is technically more demanding, especially with small or diffusely diseased targets, and the technical difficulty may result in decreased long-term patency of the grafts.

    The technique of off-pump revascularization can be particularly useful in selected cases, such as in patients with a heavily calcified aorta (often called a “porcelain aorta”). In experienced centers, patency rates of the bypass grafts performed on-pump versus off-pump should not differ greatly. Most centers use off-pump selectively. In the United States, currently approximately 80% of CABG operations are performed on-pump using CPB, whereas 20% are performed off-pump.

15. What are minimally invasive, robotic, and hybrid CABG procedures, and what are their current roles in coronary revascularization?

    Minimally invasive CABG involves the use of smaller incisions, sometimes with videoscopic guidance, and is often referred to by the acronym “MICS,” for minimally invasive cardiac surgery. The most common minimally invasive bypass surgery is known as the “MID-CAB,” which consists of a single vessel LIMA to LAD artery, done through a small left anterior thoracotomy, using off-pump technique. The rationale for such minimally invasive operations is that avoiding a full sternotomy should help avoid some serious potential complications of CABG, such as mediastinitis, and allow for quicker recovery, because patients could theoretically return to full activity and lifting sooner, without the risk for sternal dehiscence. However, mini-thoracotomy, which usually employs rib spreading, can sometimes be more painful for the patient than a median sternotomy, and the benefits of such techniques are not well established. Some surgeons have also pursued multivessel off-pump “MICS” CABG through mini-thoracotomy, but such efforts are technically very demanding and may have substantial risk without proven benefit.

    There has been a good deal of fanfare about robotic cardiothoracic surgery over the past decade. Robotic CABG consists of robotically controlled endoscopic instruments and a three-dimensional camera set up through ports placed in the patient’s chest, controlled remotely by a surgeon sitting at a console in the same operating room. For CABG, the robotic instruments are often used mainly to mobilize the internal mammary artery, but can also be used to perform the anastomoses; however, this is technically very challenging and has no proven benefit over hand-sewn anastomoses. High cost and cumbersome setup, in addition to technical difficulties and lack of evidence for overwhelming benefit, have limited the applicability of robotics to coronary surgery.

    Some centers have popularized performing “hybrid” procedures, where a patient will receive a single-vessel CABG with LIMA to LAD artery, most commonly using a mini-thoracotomy, and other non-LAD artery coronary lesions will be treated with coronary stents, either at the same or staggered settings. One rationale for this strategy is to attempt to capitalize on the high long-term patency and mortality benefit demonstrated with the LIMA to LAD artery graft, while avoiding the downside of sternotomy. In the current CABG guidelines, hybrid CABG has a class IIa indication if there are limitations to traditional CABG, such as heavily calcified aorta, poor target vessels, lack of suitable conduit, or unfavorable LAD artery for PCI. Otherwise, indications for hybrid CABG are deemed class IIb, or a “may be reasonable alternative,” in an attempt to improve the overall risk-benefit ratio. These techniques are used in a minority of CABG procedures performed in the US.

16. What complications can occur following CABG?

    Operative mortality is currently less than 2% overall, and less than 1% in low-risk patients. Sentinel complications include stroke, MI, renal failure, respiratory failure, and mediastinitis (see the following question). The incidence of each is approximately 1% to 5% and varies with age and preoperative comorbidities of the patient.

    Atrial fibrillation is the most common complication after cardiothoracic surgery, with an incidence of 20% to 40%. The incidence of atrial fibrillation increases with age, duration of CPB, presence of chronic obstructive pulmonary disease (COPD), and preexisting heart failure, among other risk factors. The peak incidence of postoperative atrial fibrillation is between 2 to 4 days after surgery, is usually self-limited, and usually resolves over time as the inflammatory state of the heart improves. Use of beta-adrenergic blocking agents (β-blockers) postoperatively is routine and is useful to decrease the risk of atrial fibrillation. Goals of therapy are rate control and conversion to normal sinus rhythm, if possible. Anticoagulation may be advisable if timely conversion cannot be accomplished, or if the arrhythmia recurs intermittently.

17. Who is at risk for mediastinitis?

    Mediastinitis is a deep surgical-site infection following sternotomy. The infection involves the sternal bone and underlying heart and mediastinum. The organism most commonly recovered is Staphylococcus, but gram-negative organisms can also be found. The incidence of mediastinitis has been reported in the past to be 1% to 4%, but a recent Society of Thoracic Surgeons (STS) database study has shown an incidence less than 1%. The incidence of mediastinitis increases with the presence of diabetes, morbid obesity, COPD, and when bilateral mammary harvesting is performed. Perioperative prophylactic antibiotics, proper skin preparation and clipping, and active control of hyperglycemia in the postoperative setting are important measures believed to decrease the incidence of mediastinitis.

18. What causes strokes during coronary bypass?

    Incidence of stroke (type I neurologic deficit) in the perioperative period after cardiac surgery is 1% to 6% and varies with age. The risk of stroke is dependent on the atherosclerotic burden in the cerebrovascular circulation and in the aorta. Atherosclerotic plaques in the ascending aorta can be the source of atheroemboli during aortic cannulation, cross-clamping, or manipulation of the ascending aorta. Microemboli may also be due to fat and to air that can arise during extracorporeal circulation. Regional hypoperfusion can occur in the brain as a result of intracranial and extracranial vascular lesions when there are significant fluctuations in the blood pressure during on-pump or off-pump surgery.

19. What is a type II neurologic deficit?

    A type II neurologic deficit is a neurocognitive change after CABG, and its true incidence remains controversial. Changes in intellectual abilities, memory, and mood are often based on subjective assessment and often difficult to quantitatively evaluate. Reported incidence ranges widely from 2% to 50%. Studies have shown decreases in neurocognitive functioning after CABG, but in small series, similar declines over time have been noted in on-pump, off-pump, PCI, and CAD “control patients” not undergoing intervention.

20. How should clopidogrel be managed preoperatively?

    Preoperative clopidogrel use increases blood transfusion during cardiac surgery and increases the risk of reoperation after surgery for mediastinal bleeding. The current recommendation is to avoid clopidogrel for 5 days before CABG, unless the need for urgent or emergent revascularization for ongoing ischemia exceeds the risk of bleeding.

21. What factors are important in the follow-up of CABG patients?

    Secondary prevention and control of atherosclerotic risk factors are important in maintaining the long-term clinical success of the operation. Use of statins, β-blockers, and aspirin is advised in all post-CABG patients who do not have strong contraindications to those medications. Angiotensin-converting enzyme (ACE) inhibitors are also recommended in patients with low left ventricular ejection fraction (less than 40%). In addition, control of hypertension and diabetes, and smoking cessation are also essential aspects of secondary prevention.

22. What is the incidence of recurrent disease requiring redo-CABG?

    Reoperation may be required because of progression of native coronary disease or failure of previous grafts. The incidence of reoperation in studies has been reported to be approximately 10% by 10 years, although aggressive secondary prevention and advances in the use of PCI for the treatment of native and graft disease may decrease the need for reoperation. Redo CABG is technically more challenging. Scarring of the mediastinum increases the risk of complications, including damage to the LIMA graft. Lack of suitable bypass conduits is also a concern in patients undergoing redo bypass surgery.

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