The American College of Cardiology (ACC) and the American Heart Association (AHA) have revised their original 1991 guidelines for coronary artery bypass surgery. The revised recommendations, developed by the ACC/AHA Task Force on Practice Guidelines, are based primarily on data published since 1989. The executive summary of the ACC/AHA practice guidelines on coronary artery bypass surgery is published in the September 28, 1999 issue of Circulation and the complete guidelines are published in the October 1999 issue of the Journal of the American College of Cardiology. Both versions are also available on the AHA Web site (http://www.americanheart.org).

In addition to providing specific recommendations, the guidelines discuss morbidities (neurologic events, mediastinitis and renal dysfunction) associated with bypass surgery and methods for predicting postoperative outcome. The greatest risk correlates with the urgency of the operation, advanced age and one or more previous coronary bypass surgeries.

The guidelines also summarize data that compare the outcomes of medical therapy with surgical and percutaneous revascularization. The following summarizes comparative data on surgical versus medical therapy.

Comparison of Medical Therapy and Surgical Revascularization

According to the ACC/AHA guidelines, a meta-analysis of seven trials with a total enrollment of 2,649 patients allows comparison of outcomes after five and 10 years of follow-up. Among all participants, the survival rate of surgical patients after 10 years of follow-up was 4.3 months longer than the survival rate of medically treated patients. The 15-year cumulative survival rate for left main coronary artery disease was 44 percent in patients who underwent bypass surgery, compared with a cumulative survival rate of 31 percent in patients who were treated medically. In patients with three-vessel disease (50 percent or more stenosis in all three vessels), the overall extension of survival was seven months in surgical patients compared with medically treated patients. In patients with severe stenosis of the left anterior descending artery, the relative risk reduction caused by bypass surgery, compared with medical therapy, was 42 percent at five years and 22 percent at 10 years.

Comparison of Medical Therapy and Angioplasty

The ACC/AHA guidelines point out that comparative clinical trials of angioplasty and bypass surgery have excluded patients in whom survival was already shown to be longer with bypass surgery than with medical therapy. In addition, none of the trials was large enough to detect relatively modest differences in survival between the two techniques. Most of the trials did not include long-term follow-up (for five to 10 years). Another limitation of the data relates to the inclusion in clinical trials of only about 5 percent of screened patients with multivessel disease at enrolling institutions. Physicians chose not to enroll many patients with three-vessel disease in the trials; these patients were referred for bypass surgery. Patients with two-vessel disease tended to be referred for angioplasty rather than enrolled in the trials.

According to the ACC/AHA guidelines, the most striking difference between bypass surgery and angioplasty was the four- to 10-fold increased likelihood of reintervention after coronary angioplasty. Recent analysis of approximately 60,000 patients who received treatment in New York state provides data on three-year survival. In this population, bypass surgery was associated with longer survival in patients with severe stenosis of the proximal left anterior descending artery and/or three-vessel disease. Conversely, patients with one-vessel disease that did not involve the left anterior descending artery had improved survival with angioplasty.

Indications for Coronary Artery Bypass Surgery

As with other ACC/AHA guidelines, the following classification system is used for the recommendations:

Class I—Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective.

Class II—Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness or efficacy of a procedure.

Class IIa—The weight of evidence/opinion is in favor of usefulness/efficacy.

Class IIb—Usefulness/efficacy is less well established by evidence/opinion.

Class III—Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/effective and, in some cases, may be harmful.

The following is an excerpt of the section in the guidelines that enumerates the indications for coronary artery bypass surgery on the basis of the above-described classification system.

• Indications for coronary bypass surgery in patients with asymptomatic or mild angina

Class I—(1) Significant left main coronary artery stenosis. (2) Left main equivalent: significant (70 percent or more) stenosis of proximal left anterior descending (LAD) artery and proximal left circumflex artery. (3) Three-vessel disease (survival benefit is greater in patients with abnormal left ventricular function, such as with an ejection fraction of less than 0.50).

Class IIa—(1) Proximal LAD stenosis with one- or two-vessel disease, which becomes Class I if extensive ischemia is documented by noninvasive study and/or the ejection fraction is less than 0.50.

Class IIb—(1) One- or two-vessel disease not involving the proximal LAD, which becomes Class I in the case of a large area of viable myocardium and high-risk criteria on noninvasive testing.

• Indications for bypass surgery in stable angina

Class I—(1) Significant left main coronary artery stenosis. (2) Left main equivalent: significant (70 percent or more) stenosis of proximal LAD and proximal left circumflex artery. (3) Three-vessel disease (survival benefit is greater with left ventricular ejection fraction of less than 0.50). (4) Two-vessel disease with significant proximal LAD stenosis and either ejection fraction of less than 0.50 or demonstrable ischemia on noninvasive testing. (5) One- or two-vessel coronary artery disease without significant proximal LAD stenosis, but with a large area of viable myocardium and high-risk criteria on noninvasive testing. (6) Disabling angina despite maximal medical therapy, when surgery can be performed with acceptable risk. If angina is not typical, objective evidence of ischemia should be obtained.

Class IIa—(1) Proximal LAD stenosis with one-vessel disease, which becomes Class I if extensive ischemia is documented by noninvasive study and/or the ejection fraction is less than 0.50 percent. (2) One- or two-vessel coronary artery disease without significant proximal LAD stenosis but with a moderate area of viable myocardium and demonstrable ischemia on noninvasive testing.

Class III—(1) One- or two-vessel disease not involving significant proximal LAD stenosis, in patients who have mild symptoms that are not likely caused by myocardial ischemia or have not received an adequate trial of medical therapy and have only a small area of viable myocardium or have no demonstrable ischemia on noninvasive testing. (2) Borderline coronary stenoses (50 to 60 percent diameter in locations other than the left main coronary artery) and no demonstrable ischemia on noninvasive testing. (3) Insignificant (less than 50 percent diameter) coronary stenosis.

• Indications for bypass surgery in unstable angina/non–Q-wave myocardial infarction

Class I—(1) Significant left main coronary artery stenosis. (2) Left main equivalent: significant (70 percent or more) stenosis of proximal LAD and proximal left circumflex artery. (3) Ongoing ischemia not responsive to maximal nonsurgical therapy.

Class IIa—(1) Proximal LAD stenosis with one- or two-vessel disease, which becomes Class I if extensive ischemia is documented by noninvasive study and/or left ventricular ejection fraction is less than 0.50.

Class IIb—(1) One- or two-vessel disease not involving the proximal LAD, which becomes Class I in the case of a large area of viable myocardium and high-risk criteria on noninvasive testing.

• Indications for bypass surgery in ST-segment elevation (Q-wave) infarction

Class I—None.

Class IIa—(1) Ongoing ischemia/infarction not responsive to maximal nonsurgical therapy.

Class IIb—(1) Progressive left ventricular pump failure with coronary stenosis compromising viable myocardium outside the initial infarct area. (2) Primary reperfusion in the early hours (six to 12 hours or less) of an evolving ST-segment elevation myocardial infarction.

Class III—(1) Primary reperfusion late (12 hours or more) in evolving ST-segment elevation myocardial infarction without ongoing ischemia.

• Indications for bypass surgery in poor left ventricular function

Class I—(1) Significant left main coronary artery stenosis. (2) Left main equivalent: significant (70 percent or more) stenosis of proximal LAD artery and proximal left circumflex artery. (3) Proximal LAD stenosis with two- or three-vessel disease.

Class IIa—(1) Poor left ventricular function with significant viable, noncontracting, revascularizable myocardium without any of the aforementioned anatomic patterns.

Class III—(1) Poor left ventricular function without evidence of intermittent ischemia and without evidence of significant revascularizable, viable myocardium.

• Indications for bypass surgery in life-threatening ventricular arrhythmias

Class I—(1) Left main coronary artery stenosis. (2) Three-vessel coronary disease.

Class IIa—(1) Bypassable one- or two-vessel disease causing life-threatening ventricular arrhythmias. (2) Proximal LAD disease with one- or two-vessel disease. Both entities in this class become Class I if the arrhythmia is resuscitated sudden cardiac death or sustained ventricular tachycardia.

Class III—(1) Ventricular tachycardia with scar and no evidence of ischemia.

• Indications for bypass surgery after failed angioplasty

Class I—(1) Ongoing ischemia or threatened occlusion with significant myocardium at risk. (2) Hemodynamic compromise.

Class IIa—(1) Foreign body in crucial anatomic position. (2) Hemodynamic compromise in patients with impairment of coagulation system and without previous sternotomy.

Class IIb—(1) Hemodynamic compromise in patients with impairment of coagulation system and with previous sternotomy.

Class III—(1) Absence of ischemia. (2) Inability to revascularize owing to target anatomy or no reflow state.

• Indications for bypass surgery in patients with previous bypass surgery

Class I—(1) Disabling angina despite maximal noninvasive therapy. (If angina is not typical, then objective evidence of ischemia should be obtained.)

Class IIa—(1) Bypassable distal vessel(s) with a large area of threatened myocardium on noninvasive studies.

Class IIb—(1) Ischemia in the non-LAD distribution with a patent internal mammary graft to the LAD supplying functioning myocardium and without an aggressive attempt at medical management and/or percutaneous revascularization.

The accompanying table summarizes management strategies to reduce perioperative and late morbidity and mortality in patients undergoing coronary artery bypass surgery.