Coronary Artery Bypass Grafting
Michael E. Jessen
HISTORY/BACKGROUND
Coronary arterial bypass grafting (CABG) is a surgical technique used to improve myocardial blood supply by creating vascular conduits that allow blood flow past obstructive lesions in the coronary arteries. The technique appeared after the introduction of selective coronary arteriography by Sones in 1958 and has seen considerable evolution over six decades. Although the first conventional coronary bypass operations were performed using a saphenous-vein graft by Sabiston in 1962 and using a left internal thoracic artery graft by Kolesov in 1964, it was the pioneering work of Rene Favaloro that led to the broad acceptance of the operation for treatment of ischemic heart disease.1 The operation has since undergone modifications to include other bypass conduits to avoid the use of cardiopulmonary bypass and to utilize less invasive techniques (Figure 86.1). Today it remains the most commonly performed cardiovascular operation in the world and is one of the most rigorously studied operations in history. By current guidelines, CABG represents the most highly recommended procedure for the treatment of ischemic heart disease in patients with complex coronary artery disease, left main coronary artery stenosis, depressed left ventricular (LV) systolic function, and some associated conditions such as diabetes mellitus.2,3
INDICATIONS FOR CORONARY ARTERIAL BYPASS GRAFTING
Clinical Indications and Coronary Anatomy Considerations
In broad terms, CABG is used today for treating patients with significant coronary artery disease to achieve control of angina or to prolong survival, or both.4 CABG remains one of the most effective means for control of angina, and disabling angina is a Class I indication for CABG. In patients with multivessel coronary disease, CABG offers better relief of angina than guideline-directed medical therapy (GDMT), and when compared with both medical therapy and percutaneous coronary intervention (PCI), CABG reduces the incidence of subsequent myocardial infarction and the need for additional revascularization.5
Many contemporary indications for CABG focus on the survival benefit that has been observed with CABG compared with GDMT. CABG prolongs survival in patients with several defined coronary anatomic conditions. CABG is indicated in patients with >50% stenosis of the left main coronary artery with or without symptoms of angina. PCI is occasionally used in these patients, although results may be less favorable (see discussion below). CABG also appears to improve survival in patients with >70% stenosis in three major coronary arteries or with >70% stenosis in two major coronary arteries when one is the proximal left anterior descending (LAD). These benefits may be seen in asymptomatic patients, those with mild or stable angina, and those found to have high-risk criteria on stress testing, abnormal intracoronary hemodynamic evaluation, or sizeable (>20%) perfusion defects on myocardial perfusion stress imaging.4 CABG has been extensively compared to revascularization by PCI. A discussion of trials comparing these treatment options is provided later in the chapter.
Survival benefits of CABG are more apparent in patients with impaired LV function. A meta-analysis of 20 studies, including 54,173 patients, comparing CABG and PCI in patients with decreased left ventricular ejection fraction (LVEF) found significantly lower hazard ratios for mortality (HR 0.763; 95% confidence interval [CI] 0.678-0.859; P < .001), myocardial infarction (HR 0.481; 95% CI 0.365-0.633; P < .001), and repeat revascularization (HR 0.321; 95% CI 0.241-0.428; P < .001) in the CABG group than in the PCI group.6 These data support the selection of CABG over PCI to improve survival in this higher risk subset. The mechanism behind this benefit may be a reduction in new myocardial infarction.7
Patients diagnosed with acute ST-segment elevation myocardial infarctions (STEMI) typically undergo urgent coronary arteriography and PCI. A small portion of these patients have coronary anatomy that is unsuitable for PCI or coronary occlusions that cannot be opened. Patients with these conditions and evidence of ongoing myocardial ischemia can benefit from emergency CABG, although the peri-procedural risk is higher than when CABG is performed electively. Similarly, patients who develop an acute coronary occlusion with ongoing ischemia while undergoing an elective PCI procedure should be considered for emergency CABG to preserve LV function providing their risk profile is not prohibitive.
Patients who present with non-ST segment elevation myocardial infarctions (NSTEMI) are typically treated medically initially. However, those who experience ongoing ischemia that is unresponsive to medical therapy can be treated with urgent revascularization. This is most commonly accomplished by PCI, but CABG has an important role in this
group of patients. In an observational study that included 5112 patients presenting with STEMI or unstable angina between 2000 and 2016, propensity score-matching analysis was used to compare early outcomes and all-cause mortality in groups treated with PCI or CABG.8 Multivariable analysis showed that CABG was independently associated with a significant 65% reduction in 10-year mortality (P < .001). Interestingly, this long-term advantage was seen among male patients and not female patients. Thus, CABG has an important role in the treatment of a wide range of patients with disabling angina, high-risk coronary anatomy, STEMI and NSTEMI, and impaired LV systolic function.
group of patients. In an observational study that included 5112 patients presenting with STEMI or unstable angina between 2000 and 2016, propensity score-matching analysis was used to compare early outcomes and all-cause mortality in groups treated with PCI or CABG.8 Multivariable analysis showed that CABG was independently associated with a significant 65% reduction in 10-year mortality (P < .001). Interestingly, this long-term advantage was seen among male patients and not female patients. Thus, CABG has an important role in the treatment of a wide range of patients with disabling angina, high-risk coronary anatomy, STEMI and NSTEMI, and impaired LV systolic function.
 FIGURE 86.1 Milestones in the evolution of CABG surgery—the history of CABG can be traced to the 1940s, when the Vineberg procedure was introduced as an effective strategy to treat symptomatic angina. Since then, great strides have been made optimizing CABG surgery techniques, including off-pump surgery and less invasive surgical revascularization techniques. CABG, coronary arterial bypass grafting; IMA, internal mammary artery; LAD, left anterior descending coronary artery; LIMA, left internal mammary artery; RIMA, right internal mammary artery; SVG, saphenous vein graft. (Reprinted by permission from Nature: Caliskan E, de Souza DR, Böning A, et al. Saphenous vein grafts in contemporary coronary artery bypass graft surgery. Nat Rev Cardiol. 2020;17(3):155-169. Copyright © 2019 Springer Nature.) |
Special Subgroups
Important survival benefits from CABG may accrue in other subgroups of patients. One group that has received much
scrutiny is patients with diabetes mellitus. The Future Revascularization Evaluation in Patients with Diabetes Mellitus: Optimal Management of Multivessel Disease (FREEDOM) trial randomized 1900 diabetic patients with multivessel coronary artery disease to PCI or CABG (Table 86.1).9 The primary composite outcome of death, myocardial infarction, and stroke at 5 years was significantly higher with PCI as compared with CABG (26.6% vs 18.7%, P = .005). Notably, a significant reduction in all-cause mortality (16.3% vs 10.9%, P = .049) and myocardial infarction (13.9% vs 6.0%, P < .001) was observed with CABG, although the incidence of stroke was higher (2.4% vs 5.2%, P = .03). At 1 year, repeat revascularization was significantly higher in the PCI group (13% vs 5%, P < .0001). All events were higher in patients with insulin-dependent diabetes as compared with non-insulin-dependent diabetes, including the primary end point (29% vs 19% at 5 years, P < .001). In a study of 943 FREEDOM patients with extended follow-up, all-cause mortality rate was higher in the PCI group compared with CABG (23.7% vs 18.7%, P = .076).10 CABG is considered the preferred revascularization option in patients with diabetes.
scrutiny is patients with diabetes mellitus. The Future Revascularization Evaluation in Patients with Diabetes Mellitus: Optimal Management of Multivessel Disease (FREEDOM) trial randomized 1900 diabetic patients with multivessel coronary artery disease to PCI or CABG (Table 86.1).9 The primary composite outcome of death, myocardial infarction, and stroke at 5 years was significantly higher with PCI as compared with CABG (26.6% vs 18.7%, P = .005). Notably, a significant reduction in all-cause mortality (16.3% vs 10.9%, P = .049) and myocardial infarction (13.9% vs 6.0%, P < .001) was observed with CABG, although the incidence of stroke was higher (2.4% vs 5.2%, P = .03). At 1 year, repeat revascularization was significantly higher in the PCI group (13% vs 5%, P < .0001). All events were higher in patients with insulin-dependent diabetes as compared with non-insulin-dependent diabetes, including the primary end point (29% vs 19% at 5 years, P < .001). In a study of 943 FREEDOM patients with extended follow-up, all-cause mortality rate was higher in the PCI group compared with CABG (23.7% vs 18.7%, P = .076).10 CABG is considered the preferred revascularization option in patients with diabetes.
Revascularization to Improve Survival: Recommendations: Class I
CABG to improve survival is recommended for patients with significant (≥50% diameter stenosis) left main coronary artery stenosis (Level of Evidence: B).
CABG to improve survival is beneficial in patients with significant (≥70% diameter) stenoses in three major coronary arteries (with or without involvement of the proximal LAD artery) or in the proximal LAD plus 1 other major coronary artery (Level of Evidence: B).
Revascularization to Improve Symptoms: Recommendations Class I
CABG to improve symptoms is beneficial in patients with one or more significant (≥70% diameter) coronary artery stenoses amenable to revascularization and unacceptable angina despite GDMT (Level of Evidence: A).
CABG in Patients With Acute Myocardial Infarction: Recommendations Class I
Emergency CABG is recommended in patients with acute MI in whom (1) primary PCI has failed or cannot be performed, (2) coronary anatomy is suitable for CABG, and (3) persistent ischemia of a significant area of myocardium at rest and/or hemodynamic instability refractory to nonsurgical therapy is present (Level of Evidence: B).
Emergency CABG is recommended in patients undergoing surgical repair of a postinfarction mechanical complication of MI, such as ventricular septal rupture, mitral valve insufficiency because of papillary muscle infarction and/or rupture, or free wall rupture (Level of Evidence: B).
Emergency CABG is recommended in patients with cardiogenic shock and who are suitable for CABG irrespective of the time interval from MI to onset of shock and time from MI to CABG (Level of Evidence: B).
TABLE 86.1 Kaplan-Meier Estimates of Key Outcomes at 2 Years and 5 Years After Randomization | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Some retrospective studies have suggested a survival benefit with CABG in patients with mild-to-moderate chronic kidney disease (CKD) and end-stage renal disease (ESRD). A recent study examined mortality in 971 veterans with incident ESRD, who underwent CABG (N = 582) or PCI (N = 389) up to 5 years prior to dialysis initiation. Compared to PCI, patients who underwent CABG had a 34% lower risk of death (P = .002) after initiation of dialysis.11 Although randomized trials are needed, CABG appears to be the preferred revascularization option in patients with advanced kidney disease.
SURGICAL TECHNIQUES
The majority of coronary bypass operations are performed through a median sternotomy incision, with the patient cannulated for cardiopulmonary bypass via the ascending aorta and
right atrium. Bypass conduits, most commonly the left internal thoracic artery and greater saphenous vein, are harvested, the aorta is cross clamped, and the heart is arrested with a potassium-containing cardioplegia solution to achieve a diastolic arrest, reduce myocardial oxygen demand and provide a bloodless operating field. Bypass grafts are constructed to allow blood flow beyond coronary obstructions, the cross clamp is removed, cardiac activity is reestablished, and the patient is weaned from cardiopulmonary bypass. Surgical drains are placed, the sternum is reapproximated with wires, and the incisions are closed. While this framework comprises the commonest form of the operation, several noteworthy variations are applied.
right atrium. Bypass conduits, most commonly the left internal thoracic artery and greater saphenous vein, are harvested, the aorta is cross clamped, and the heart is arrested with a potassium-containing cardioplegia solution to achieve a diastolic arrest, reduce myocardial oxygen demand and provide a bloodless operating field. Bypass grafts are constructed to allow blood flow beyond coronary obstructions, the cross clamp is removed, cardiac activity is reestablished, and the patient is weaned from cardiopulmonary bypass. Surgical drains are placed, the sternum is reapproximated with wires, and the incisions are closed. While this framework comprises the commonest form of the operation, several noteworthy variations are applied.
Conduits for Coronary Bypass Grafts
The most common conduit used for bypass grafting is the greater saphenous vein. However, vein grafts become diseased or occluded over time at significant rates. Vein graft failure occurs in three distinct phases: (1) early (<1 month) graft occlusion results from graft thrombosis owing to technical imperfections in the construction of the graft, poor runoff in the target vessel, or vein graft endothelial injury during harvest; (2) intermediate (1-12 months) graft stenosis attributable to development of intimal hyperplasia near anastomotic sites; and (3) late graft disease (>12 months) from the development of atherosclerosis in the vein graft itself (Figure 86.2). Up to 15% of saphenous-vein grafts occlude by 1 year, and angiographic studies have shown a 40% to 50% occlusion rate at 10 years. Clinical outcomes are worse when graft occlusion occurs, with higher rates of recurrent angina, myocardial infarction, and need for repeat revascularization. Vein graft patency is improved with the use of antiplatelet therapy.
 FIGURE 86.2 Deployed stabilization device for off-pump coronary artery bypass surgery. |
Vein grafts can be harvested through open incisions or through endoscopic approaches.
Randomized trials have shown no difference in cardiovascular outcomes between these methods, although wound complications are reduced with endoscopic vein harvesting.12
The left internal mammary artery (LIMA) is unquestionably the preferred conduit for use in CABG, and grafting of the LAD with this conduit is firmly entrenched as the standard of care. This construct results in the highest 10-year patency rate (>90%), survival, and freedom from cardiac events compared with any other conduit. The LIMA can be harvested as a pedicle graft or as a “skeletonized” graft that may offer greater length and lower sternal complication rates. The vast majority of LIMA grafts are placed as in situ grafts, although the LIMA can be used as a free graft or Y-graft in select situations.
Owing to superior results observed with the LIMA graft, surgeons have considered the use of bilateral internal mammary artery (IMA) grafting as a mechanism to further improve CABG outcomes. A number of observational studies and meta-analyses have suggested high graft patency rates, superior survival rates, and lower rates of recurrent angina, late myocardial infarction, and hospitalization for cardiac events in patients undergoing CABG with multiple arterial grafts compared with single arterial grafts. However, the multicenter, prospective randomized Arterial Revascularization Trial (ART trial), in which patients were randomly assigned to undergo single or bilateral IMA grafting did not identify significant differences in mortality or rates of adverse cardiovascular events between groups at 10 years of follow-up.13 In this trial, patients with bilateral IMA grafting sustained a significantly higher rate of sternal wound complications. Interpretation of the study has been complicated by a high crossover rate (14% of patients allocated to bilateral IMA actually received a single IMA) and by the fact that 22% of patients allocated to single IMA receiving an additional radial artery.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
