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Coronary Artery Bypass Surgery: 
Scientific and Clinical Aspects

National Institutes of Health
Consensus Development Conference Statement
December 3-5, 1980

Conference artwork, a diagram of a human heart with the title at the top of the page.

This statement is more than five years old and is provided solely for historical purposes. Due to the cumulative nature of medical research, new knowledge has inevitably accumulated in this subject area in the time since the statement was initially prepared. Thus some of the material is likely to be out of date, and at worst simply wrong. For reliable, current information on this and other health topics, we recommend consulting the National Institutes of Health's MedlinePlus http://www.nlm.nih.gov/medlineplus/.

This statement was originally published as: Coronary Artery Bypass Surgery: Scientific and Clinical Aspects. NIH Consens Statement 1980 Dec 3-5;3(8):1-12.

For making bibliographic reference to the statement in the electronic form displayed here, it is recommended that the following format be used: Coronary Artery Bypass Surgery: Scientific and Clinical Aspects. NIH Consens Statement Online 1980 Dec 3-5 [cited year month day];3(8):1-12.

Introduction

A Consensus Development Conference was held at the National Institutes of Health on December 3-5, 1980 to consider the status of coronary artery bypass surgery in relation to five specific questions:

  1. What is the overall management of coronary artery disease--that is, in what context should coronary artery surgery be considered?
  2. What constitutes a reasonable diagnostic workup before recommending medical or surgical therapy?
  3. What is known about long-term survival after coronary artery bypass surgery in specific patient groups?
  4. What is known about the long-term quality of life after coronary artery bypass surgery?
  5. What is the range of success rates for the procedure in various settings, and what factors may be important in influencing this outcome?
 What Is the Overall Management of Coronary Artery Disease -- That Is, in What Context Should Coronary Artery Surgery Be Considered?

Coronary heart disease may be recognized by the physician as the clinical syndromes of angina pectoris, acute myocardial infarction, sudden cardiac arrest, or ischemic cardiomyopathy. It may also be recognized in an asymptomatic form by detection of electrocardiographic evidence of prior myocardial infarction not recognized during the acute episode or by characteristic abnormalities of the electrocardiogram during exercise testing of apparently healthy persons. Once suspected by the physician, the diagnosis may be confirmed with various levels of certainty by one or more special diagnostic tests. The tests most commonly used include the electrocardiogram recorded during and after monitored graded exercise, in some institutions radionuclide studies of myocardial perfusion and ventricular function at rest and in response to exercise, and coronary arteriography with left ventricular angiography. In addition to confirming the diagnosis, such studies may provide information about the pathology and anatomy of the coronary arteries, the functional condition of the left ventricle, and the overall response of the circulation to stress. These data may be combined with those obtained from the medical history and physical examination and with detailed knowledge of the natural history of the disease derived from many long-term follow-up studies of patients having such tests, to form definable subsets of persons with widely different prognoses. Since a fundamental aspect of advanced coronary heart disease is a greatly increased probability of sudden death or myocardial infarction, such prognostic information strongly influences the decision on whether to add coronary artery bypass surgery to the overall lifelong medical management recommended. If the combined data indicate that the patient is at high risk of sudden death or infarction--for example, if the patient has severe stenosis of the main trunk of the left coronary artery or severe and proximal stenosis of multiple major coronary branches--surgery is given especially serious consideration. On the other hand, if the studies indicate no critical stenosis of any major coronary branch, surgery is clearly not indicated and medical treatment is advised.

A very large percentage of patients fall between these extreme examples. In these patients, recommendations for medical or surgical therapy are based on two fundamental questions. The first question, often the most anxiety provoking to the patient, relates to which course will provide the greatest protection from disabling myocardial infarction or death. The second question relates to which course will permit a satisfactory quality of life according to the patient's own standards. The answers to these questions are highly judgmental. The answer to the first is largely based on the physician's interpretation of a large volume of sometimes contradictory data of extraordinary complexity. The answer to the second is largely based on the individual response to medical therapy and on the patient's priorities.

It is common practice for the physician and patient, when faced with this problem, to initiate comprehensive medical therapy with subsequent periodic reevaluation of the indications for surgical intervention based on the patient's response. It is critical to recognize that appropriate, comprehensive medical care of the patient with coronary heart disease requires an intensive effort on the part of the physician, involving consideration of almost every aspect of the patient's life. It requires careful education of the patient and spouse on the nature of the disease and its management to allow adequate self-care on a continuing basis and to allow the patient to participate knowledgeably in major decisions affecting his or her life. It requires optimal control of risk factors for atherosclerosis and modification of the patient's lifestyle. This may affect both work and leisure activities. It may require long-term administration of such potent medications, as nitroglycerine, beta-adrenergic blocking drugs, long-acting nitrates, antiarrhythmic agents, and digitalis. Effective and safe use of these therapeutic agents requires careful titration of dosage according to subjective and objective indexes. If, after such careful and intensive medical treatment, the patient believes that the quality of life is so adversely affected that other alternatives must be sought, then surgical therapy may be advised. It must also be recognized that in many cases dissatisfaction with the altered lifestyle imposed by the illness is the result of inadequate attention to the details of management; failure of the physician to educate the patient concerning appropriate use of the indicated medications may be a particularly important cause of this outcome.

In patients with chronic stable angina and good ventricular performance, the operative mortality associated with aorto-coronary revascularization of the heart, whether with autologous vein or artery, has progressively declined to 1 to 2 percent at major surgical centers. A corresponding decrease in perioperative myocardial infarction has been achieved. These results are assumed to relate to better management of anesthesia, more complete myocardial revascularization, and improved methods for protecting the heart during the period of coronary grafting. There seems to be no doubt that coronary bypass can improve myocardial perfusion. The patency of aorto-coronary saphenous-vein grafts has been 80 to 85 percent two years after operation. The procedure has been widely accepted for patients receiving medical therapy who have unacceptable symptoms and for certain other subsets of patients with coronary artery disease.  

What Constitutes a Reasonable Diagnostic Workup Before Recommending Medical or Surgical Therapy?

A reasonable diagnostic workup of a patient with angina pectoris depends on the clinical problem at issue. Instability and severity of angina, effect of the disease on the quality of life, cardiac function, and to a certain degree, age are all important in determining the workup of the patient. The workup should be done as efficiently as possible to provide definitive information on which clinical decisions can be based. Unnecessary and redundant procedures should be avoided.

In some patients the clinical picture indicates that definition of the coronary anatomy is needed to determine operability. It is agreed that patients with stable angina whose quality of life is significantly impaired by their symptoms should undergo coronary arteriography. Furthermore, in patients with unstable angina, coronary arteriography should be performed during the initial phase of hospitalization; if maximal medical therapy does not relieve symptoms, this procedure is considered urgent. There is consensus that coronary artery bypass is indicated in patients with unacceptable symptoms during appropriate medical treatment or with recurrent unstable angina, but the decision to operate must also depend on the results of invasive studies.

In patients with typical angina not sufficiently severe to dictate surgery for relief of symptoms, noninvasive cardiac testing may be carried out initially in an attempt to identify those at high risk for major cardiac events. However, there is lack of consensus on the value of noninvasive testing in the workup of such patients. Some physicians prefer coronary arteriography as the initial diagnostic procedure, particularly in the young patient. Others recommend exercise electrocardiography to identify patients with serious left main coronary artery or triple-vessel disease. Such patients will often have early or excessive ST-segment deviations, prolonged ST-segment depression into the recovery period, or decrease in blood pressure during the test. In this category of patients coronary arteriography should be carried out, and if high-risk disease is found, coronary artery bypass surgery should be considered. The use of radionuclide studies to identify high-risk patients with left main coronary artery or triple-vessel disease needs further evaluation.

There is a lack of consensus on the approach to evaluation of patients with questionable or atypical angina. Exercise electrocardiography may be helpful in identifying those with serious coronary disease; such identification may be enhanced by radionuclide studies in conjunction with exercise testing, particularly in patients with resting electrocardiographic abnormalities that impair interpretation of the exercise electrocardiogram. The presence of coronary artery disease may be indicated by transient defects in myocardial perfusion, by wall motion abnormalities, or by an abnormal response of the left ventricular ejection fraction to exercise. Further research is needed to determine the role of noninvasive testing when the presence of coronary artery disease is known or suspected.

Survivors of an acute episode of myocardial infarction are at high risk of sudden death during the first year after the infarction. Recent studies have demonstrated that the one-year mortality ranges from 10 to 15 percent of all survivors. Several investigators have reported that these patients can be divided into high-risk and low-risk subgroups on the basis of clinical information and such noninvasive testing as exercise electrocardiography, radionuclide studies of ventricular function, and ambulatory 24-hour electrocardiographic recording. It is believed that high-risk patients should undergo coronary arteriography and left ventricular angiography followed by surgical intervention if the coronary anatomy and left ventricular function are appropriate. It should be recognized, however, that the course of these patients undergoing surgery may differ from that in patients with stable or unstable angina and apparently similar coronary anatomy and ventricular function, in that the former group appears to have a greater tendency toward major ventricular arrhythmias. It is also recognized that there is are insufficient data to determine whether surgical intervention will reduce the mortality in this special subset of patients with coronary heart disease. Because of the relatively large number of patients in this high-risk post-myocardial infarction subset and the present uncertainty about their proper management, there is an urgent need for further investigation of this problem.

The problem of the patient with coronary disease presenting with congestive heart failure needs special consideration. It is important to determine whether a lesion amenable to surgery is contributing substantially to the heart failure--e.g., a ventricular aneurysm, severe mitral incompetence, or a ventricular septal defect resulting from myocardial infarction. Two-dimensional echocardiography or radionuclide ventriculography may be helpful in the evaluation of such patients.  

What Is Known About Long-Term Survival After Coronary Artery Bypass Surgery in Specific Patient Groups?

The impact of coronary artery bypass surgery on the survival of patients with coronary artery disease has been the focus of extensive debate since its introduction. Severe left ventricular dysfunction has been determined to have an adverse effect on survival, and comparisons between surgical and medical therapy must take this into account, as well as the anatomic location and extent of disease defined by coronary arteriography.

The difficulty of interpreting the results of surgical series by comparison with historical controls is well recognized. This type of comparison is especially hazardous in the assessment of coronary artery surgery because of marked differences between early and recent results for both surgically and medically treated patients. Several recently published series with long-term follow-up of patients undergoing coronary artery bypass have documented an impressively low operative mortality with a remarkable long-term survival. At the same time, other studies have noted a marked improvement in recent years in the survival of medically treated patients. Accordingly, it seems unlikely that the benefits of surgery, even in appropriately defined subgroups, can be assessed from studies that are not adequately controlled.

It is agreed that in patients with angina pectoris and more than 50 percent narrowing of the luminal diameter of the left main coronary artery, bypass surgery results in better survival than medical treatment, regardless of left ventricular function or the degree of angina pectoris. Survival rates after medical and surgical therapy were 60 and 89 percent, respectively, at four years in the Veterans Administration trial, and 67 and 89 percent, respectively, at five years in the European trial. Left main coronary artery stenosis of this severity is present in approximately 10 percent of patients undergoing coronary arteriography. (Since estimates of the prevalence of lesions based on coronary angiography depend on the criteria for angiography, considerable variability may exist among individual institutions.)

There are only a few prospective randomized trials and observational studies with concurrent medically treated controls for use in assessing the impact of surgery on survival. Furthermore, such results must be applied with caution to the overall population with symptomatic coronary artery disease treated in a variety of centers. This situation compounds the problem of judging the effects of coronary artery bypass on survival in patients with three-vessel disease, for whom conflicting data exist. Three-vessel coronary artery disease of surgical importance has been reported in 30 to 40 percent of angiographic studies. The initial report on the Veterans Administration Cooperative Randomized Trial did not demonstrate improved survival with surgery in patients with three-vessel disease, the majority of whom had moderate impairment of left ventricular function. However, if one accepts the analysis of the Veterans Administration data for the 10 hospitals (including 87 percent of the patients) in which the average operative mortality was 3.4 percent and eliminates the three outliers in which the average mortality of 23 percent, a substantially improved survival with surgery is observed. Evidence from some observational studies suggests improved survival in patients with three-vessel disease and moderate impairment of global left ventricular function, i.e., left ventricular ejection fraction in the range of 25 to 50 percent.

Data were reviewed that suggested improved survival after coronary artery grafting in patients with three-vessel disease and good left ventricular function, defined as left ventricular ejection fraction greater than 50 percent. The European Collaborative Randomized Trial has demonstrated improved survival for surgically treated patients in this subset. Although the differences observed in the European trial are impressive (the survival rate at 60 months was 82 percent for the medical group and 94 percent for the surgical group), there is consensus that confirmation of these findings in additional studies is needed before a firm conclusion can be reached on the question of improved survival in patients with three-vessel disease and good left ventricular function as defined above. Other smaller randomized trials and observational studies have yielded conflicting results in this subset.

The two large randomized studies examined do not provide evidence of improved survival with surgery in patients with two-vessel disease regardless of the status of the left ventricle, but some observational studies have suggested improvement in survival with surgery of patients with two-vessel disease and moderate impairment of left ventricular function. There is no evidence of improved survival after surgery in patients with single-vessel disease regardless of left ventricular functional status.

The available data are not considered adequate to support the conclusion of improved survival with surgery in patients with severely impaired left ventricular function, i.e., left ventricular ejection fraction less than 20 percent.

The National Heart, Lung, and Blood Institute Multicenter Randomized Unstable Angina Pectoris Trial, which excluded patients with left main coronary artery disease or persistent unstable angina, has failed to show improved survival of patients treated by urgent surgery, as compared with those treated exclusively by medical management, unless surgery was dictated by chronic symptomatology. The extent to which the results in this highly selected group of patients can be extrapolated to other patients with unstable angina has not been established.

It is important to reemphasize that surgery may still be appropriate in patient subsets in which evidence of improved survival with surgery is lacking, if symptoms of myocardial ischemia are sufficiently severe or if large areas of myocardium are in jeopardy. Further attempts should be made to identify other variables, currently unmeasured, that may affect survival and thus provide methods for more critical testing of therapeutic effectiveness.  

What Is Known About the Long-Term Quality of Life After Coronary Artery Bypass Surgery?

There are few objective criteria by which quality of life can be assessed after coronary artery surgery. The symptom of angina pectoris is reported to be relieved in 80 to 90 percent of patients undergoing surgery for chronic stable angina. Bypass has reduced the subsequent number of cardiac-related events, the amount of medication required, and the frequency of hospitalizations. The majority of patients have been able to increase their exercise capacity and improve their New York Heart Association functional class after operation. This observation has been documented by improvements in functional exercise testing, angina threshold, left ventricular wall motion, left ventricular ejection fraction during exercise, indexes of myocardial oxygen consumption during exercise and lactate extraction across the myocardium.

Theoretically, improvements in symptoms and functional capacity associated with coronary bypass should enable more patients to resume gainful employment. The consensus is that this expectation has not been realized. It is recognized that physicians do not make consistent recommendations to patients regarding exercise potential and employability after successful coronary bypass surgery. Factors extraneous to the patient-physician relationship, such as preoperative work status, availability of non-work income, perception of health, age, and level of education, and employer attitude, all appear to influence the postoperative employment status. Whether or not the patient returns to work after coronary surgery depends on too many non-medical factors to allow any conclusions regarding efficacy of therapy based on this characteristic.

It is reported that angina will recur or progress after bypass surgery in about 5 percent of patients per year. In approximately two-thirds of these patients, symptoms are related to closure of the vein graft or progression of disease in the native circulation. This may be related to persistent elevation of blood lipids or poor control of other risk factors. The mechanisms involved in progression of atherosclerosis in the coronary circulation and in grafts are important and require further investigation.

Similar results regarding quality of life have been observed in patients undergoing coronary bypass for unstable angina, but the reported follow-up data are of shorter period than those cited, which are based predominantly on patients with stable angina.  

What Is the Range of Success Rates for the Procedure in Various Settings, and What Factors May Be Important in Influencing This Outcome?

The institutional setting in which bypass grafting is performed may have an important influence on the success of the operation in various clinical subgroups. Excellence can be achieved in a variety of hospital settings, provided that appropriate medical and technical support is available to complement an experienced and skilled surgical team. The necessary features include expertly performed angiography in suitably equipped laboratories, the availability of other subspecialty resources, and appropriate laboratory and blood banking facilities.

Successful intraoperative management--reflected in low rates of mortality, perioperative infarction, and other postoperative complications--and short hospital convalescence, will depend not only on surgical skill and judgement but also on the availability of competent anesthesiologists, efficient extracorporeal support, optimal myocardial preservation techniques, and a minimal period of myocardial ischemia consistent with optimal revascularization.

Postoperative management requires a suitable intensive-care facility, dedicated personnel, and the availability of circulatory support systems.

With the experience that has been accumulated to date, the following hospital mortality and perioperative infarction rates can be expected.

In patients with chronic stable angina pectoris and normal or moderately impaired left ventricular function, a hospital mortality rate of 4 percent is generally attainable, and a rate of less than 1 percent is possible. The incidence of electrocardiographically documented perioperative infarction may approximate 5 percent.

In the syndrome of unstable angina pectoris, early results will depend on the institution's approach to management. A somewhat higher incidence of morbidity and mortality may result from earlier operative intervention, and lower risks may result from a longer period of stabilization and exclusion of patients with evolving infarctions. With initial stabilization and nonemergency operation, hospital mortality and perioperative infarction rates should approach those in patients with chronic stable angina pectoris. Even with early intervention, a hospital mortality of 6 percent is generally attainable, and perioperative infarction may approximate 10 percent.

Left main coronary artery involvement has been associated with high operative risks in the past. Except under emergency conditions, patients with this lesion can be treated surgically with morbidity and mortality rates only slightly higher than those in patients with chronic stable angina and a different coronary anatomy.

Bypass grafting in patients with severe left ventricular dysfunction has been associated with high operative morbidity and mortality. Recent improvements in perioperative management have lessened the risks. In patients with very severe myocardial dysfunction--that is, ejection fractions of less than 25 percent--a hospital mortality rate no greater than 15 to 20 percent is generally achievable.

At present there is insufficient information to identify the role of bypass surgery in patients with acute myocardial infarction or intractible ventricular arrhythmias, or in asymptomatic patients with jeopardized myocardium.

For all categories of patients, an average one-year graft patency of 85 to 90 percent should be achievable. The roles of anticoagulant and antiplatelet therapy, as well as other interventions which may affect late graft patency and retard the arteriosclerotic process, are not known at present and require further study.  

Conclusion

There is consensus of the panel that coronary artery bypass represents a major advance in the treatment of patients with coronary artery disease. Evidence has been presented to support the conclusion that an improvement in the quality of life, a decrease in myocardial ischemia, and an increase in survival have been demonstrated after coronary artery bypass in selected subsets of patients.  

Consensus Development Panel

Robert L. Frye, M.D.
(Chairman)
Chairman, Division of Cardiovascular Diseases
Mayo Clinic
Rochester, Minnesota
W. Gerald Austen, M.D.
Chief of Surgical Services
Massachusetts General Hospital
Boston, Massachusetts
Paul A. Ebert, M.D.
Professor and Chairman
Department of Surgery
University of California
San Francisco, California
Charles K. Francis, Jr., M.D.
Assistant Professor of Medicine
Co-Director, Cardiac Catheterization Laboratory
Division of Cardiology
Yale University School of Medicine
New Haven, Connecticut
Nicholas T. Kouchoukos, M.D.
Professor of Surgery
University of Alabama in Birmingham
Birmingham, Alabama
Paul Meier, Ph.D.
Department of Statistics
University of Chicago
Chicago, Illinois
Hiltrud S. Mueller, M.D.
Professor of Medicine and Chief of Cardiology
St. Louis University School of Medicine
St. Louis, Missouri
Elliot Rapaport, M.D.
Professor of Medicine
University of California, San Francisco
San Francisco, California
T. Joseph Reeves, M.D.
Director, Cardiovascular Laboratory
St. Elizabeth's Hospital
Beaumont, Texas
David C. Sabiston, Jr., M.D.
Professor and Chairman
Department of Surgery
Duke University Medical Center
Durham, North Carolina
William C. Sheldon, M.D.
Chairman, Department of Cardiology
Cleveland Clinic Foundation
Cleveland, Ohio
Robert L. Vitu, M.D.
Assistant Clinical Professor of Family Practice
College of Human Medicine
Michigan State University
East Lansing, Michigan
James H. Ware, Ph.D.
Associate Professor of Biostatistics
Harvard School of Public Health
Boston, Massachusetts

Special participants in the discussions of the Panel included the following:

Samuel Gorovitz, Ph.D.
Chairman, Department of Philosophy
University of Maryland
College Park, Maryland
David C. Levin, M.D.
Associate Professor of Radiology
Harvard Medical School
Boston, Massachusetts
William B. Stason, M.D.
Associate Professor of Health Policy and Management
Harvard School of Public Health
Boston, Massachusetts

Speakers

Martial G. Bourassa, M.D.
Department of Medicine
Montreal Heart Institute
Montreal, Quebec
CANADA
James Chesbro, M.D.
Mayo Clinic
Rochester, Minnesota
Delos Cosgrove, M.D.
Department of Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
Cleveland, Ohio
Gottlieb C. Friesinger, M.D.
Professor of Medicine
Director, Division of Cardiology
Vanderbilt University Medical Center
Nashville, Tennessee
Victor Froelicher, M.D.
Assistant Professor of Cardiology
University of California Medical Center
University Hospital
San Diego, CA
Glen W. Hamilton, M.D.
Professor of Medicine
Chief, Nuclear Medicine Section
Seattle Veterans Administration Medical Center
Seattle, Washington
Karl E. Hammermeister, M.D.
Assistant Chief of Cardiology
Veterans Administration Hospital
Seattle, Washington
Herbert N. Hultgren, M.D.
Chief, Cardiology Service
VA Medical Center
Palo Alto, California
J. Willis Hurst, M.D.
Professor of Medicine (Cardiology)
Chairman, Department of Medicine
Emory University Medical Center
Atlanta, Georgia
W. Dudley Johnson, M.D.
Milwaukee Heart Surgery Association
Milwaukee, Wisconsin
George C. Kaiser, M.D.
Department of Surgery
St. Louis University Hospitals
St. Louis, Missouri
Dean T. Mason, M.D.
Department of Cardiovascular Medicine
University of California at Davis School of Medicine
Davis, California
Henry McIntosh, M.D.
Watson Clinic
Lakeland, Florida
George C. Morris, Jr., M.D.
Professor of Surgery
Baylor College of Medicine
Houston, Texas
Albert Oberman, M.D.
Division of Preventive Medicine
University of Alabama
Birmingham, Alabama
John Ochsner, M.D.
Ochsner Clinic
New Orleans, Louisiana
Shahbudin H. Rahimtoola, M.D.
Professor of Medicine
Chief, Section of Cardiology
University of Southern California
Los Angeles, California
T. Joseph Reeves, M.D.
Director, Cardiovascular Laboratory
St. Elizabeth's Hospital
Beaumont, Texas
Robert A. Rosati, M.D.
Associate Professor of Medicine
Cardiovascular Division
Duke University Medical Center
Durham, North Carolina
Richard Russell, M.D.
Professor of Medicine
University of Alabama School of Medicine
Birmingham, Alabama
Hugh C. Smith, M.D.
Mayo Clinic
Rochester, Minnesota
Frank Spencer, M.D.
Professor and Chairman
Department of Surgery
University Hospital
New York, New York
Professor Edward Varnauskas
Department of Cardiology
Sahlgrenska Hospital
Gļæ½teborg
SWEDEN
James H. Ware, Ph.D.
Associate Professor
Department of Biostatistics
Harvard School of Public Health
Boston, Massachusetts
Robert E. Whalen, M.D.
Professor of Medicine
Director, Cardiovascular Disease Service
Department of Medicine
Duke University Medical Center
Durham, North Carolina
Vallee L. Willman, M.D.
Professor and Chairman
Department of Surgery
St. Louis University School of Medicine

Conference Sponsors

National Heart, Lung, and Blood Institute

National Center for Health Care Technology

Office of Medical Applications of Research

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