by Syed Tasnim Raza
The author indicts coronary artery bypass operations, which are performed widely by claiming that they “provided little or no improvement in survival rates over standard medical and lifestyle treatment except in the very sickest patients.”
Let me start by giving a little historical perspective, slightly different then the author's recalling. Until 1896, surgeons were too afraid to even attempt suture of the heart. In that year Ludwig Rehn of Frankfurt repaired a stab wound to the heart of a young man, who survived, thus beginning the era of heart surgery. From then until the 1950's most attempts at heart operations were largely unsuccessful. It is only after the development of the Heart-Lung machine (John Gibbon 1952) and it's further improvement at the University of Minnesota and the Mayo Clinic, between 1955 and 1960, that the modern era of heart surgery began. Coronary Artery Disease (CAD), which is blockage of coronary arteries by atherosclerotic plaques and can result in a heart attack was recognized mostly by indirect methods or post-mortem, until 1958, when selective coronary angiography was developed at the Cleveland Clinic. Before then it was the symptoms of CAD namely angina which was clinically recognized and attempts at surgical treatment for angina had been made since 1930's including denervation of the heart, surgically causing inflammation of the membrane surrounding the heart (pericardium), hoping that it would result in formation of new blood vessels (Beck's operation) and in 1960's implantation of Internal mammary artery into the muscle of the left ventricle with the hopes that new blood vessels would form (Vineburg operation). All these operations were unsuccessful and are of historical interest only. It was only after selective coronary angiography was possible in 1958, that Favalaro developed the operation that is now referred to as coronary artery bypass graft (CABG, pronounced cabbage) surgery. The first successful operation was performed in late 1967. The results of this operation were such a vast improvement over any other treatment then available that it was taken up by surgeons everywhere and by early 1990's over half a million such operations were being performed annually throughout the United States.
At this point it is important to describe briefly the anatomy of coronary arteries and how the severity of disease is described. Two coronary arteries come off as the first branches of the aorta, the left and the right. The left coronary artery has a short trunk (left main), which divides into two large branches, the left anterior descending (LAD) and the left circumflex (LCX). The LAD courses on the anterior surface of the heart and gives branches to the anterior wall (diagonal branches) and to the inter-ventricular septum (thick muscle in between the left and right ventricles). The LCX goes around the back of the heart on the left side and gives branches to the free wall of the left ventricle (marginal branches). The right coronary artery (RCA) comes off the front of the aorta, courses around the right side and to the back of the heart, where it gives off branches to the left ventricle and the posterior one third of the inter-ventricular septum. Atherosclerotic plaques can develop anywhere in these arteries and can range from less than 50% to 99% or can totally occlude the said artery (100%). Only blockages greater than 50% of the cross-sectional area of the coronary artery are considered clinically significant. If greater than 50% blockage occurs in the short left main trunk it is simply referred to as left main disease. The LAD, LCX and the RCA are three equal sized arteries and blockages in one, two or all three of them is referred to as one, two or three vessel coronary artery disease (CAD).
When blockages in the coronary arteries become significant they obstruct blood flow to the ventricular muscle supplied by the particular artery. Lack of blood flow to the heart muscle causes chest pain or angina. Initially the pain may only come when the person is physically active and there is relative lack of blood flow for the increased demand during exercise. If the pain is predictable with activity and is relieved quickly with rest and has been going on for weeks or months it is referred to as chronic stable angina. If it is a new symptom, or comes on even at rest or wakes up a person from sleep, it is referred to as unstable angina. The plaques in the coronary arteries are generally smooth, but may rupture under stress, attracting platelets to start sticking to the plaque to smooth it out again. These platelets and other blood cells form a clot, which may cause total obstruction of the blood flow, causing a heart attack or death of the muscle involved. Such an event causes changes on the electrocardiogram (ECG) and these events are now called acute coronary syndrome (ACS).
The VA Coop study referred to by the author was started in 1972 and was the first randomized clinical trial (RCT), the gold standard for evidence-based medicine, comparing CABG to standard medical therapy. This trial clearly showed that CABG surgery in patients with blockages greater than 50% in the left main coronary artery have a significant survival advantage over medical treatment. Every subsequent trial has confirmed this finding.
Because of the intense public interest in this operation and the number of cases increasing rapidly, the National Institute of Health (NIH) sponsored the largest randomized multi-center clinical trial till then, comparing CABG to medical treatment of coronary artery disease in patients with chronic stable angina, called the Coronary Artery Surgical Study (CASS), during the late 1970's. This study excluded patients with left main disease. Patients with unstable angina were also excluded. This study showed survival advantage for CABG surgery in patients who had 3-vessel disease, were diabetics and had compromised ventricular function. Ventricular function is measured by the percentage of blood ejected by the left ventricle when it contracts, referred to as ejection fraction (EF), normal value being 50% or higher.
The European Cooperative Study was the next major randomized clinical trial confirming the findings of CASS and also showed survival advantage for CABG surgery in selected patients with 2-vessel CAD.
A study from the Duke University, based on their registry data for patients with coronary artery disease, though not randomized, showed that patients with blockages in the proximal portion of the LAD, before any of it's branches came off, also had a significant survival advantage with CABG over medical therapy.
In late 1990's, another NIH-sponsored multi-center, randomized clinical trial, with its principal site at Columbia University Medical Center, compared early revascularization (read CABG surgery) to standard medical treatment for patients who presented in shock following an acute heart attack, called SCHOCK trial. While the death rates for both groups remain high, this trial also showed significant survival advantage for CABG surgery over standard medical treatment.
In late 1970's, David Greene from Buffalo General Hospital compared the survival of patients after CABG with age and sex-matched cohort from Life-insurance tables and found the patients after CABG with survival comparable to the age and sex-matched population with no known CAD.
In mid-1980's, John Kirklin, a pioneer heart surgeon, headed a joint committee of the American Heart Association and the American College of Cardiology to review the literature on CABG and produced the guidelines for operating on patients with coronary artery disease. This review and guidelines were simultaneously published in Circulation and the Journal of the American College of Cardiology and have remained the gold standard of surgical treatment of CAD.
Unstable angina is considered suggestive of a coming heart attack and coronary angiography is indicated in such patients. If significant coronary artery disease is found on angiography, revascularization of the culprit arteries by either angioplasty or bypass surgery is considered standard therapy to prevent heart attack and thus prevent damage to ventricular muscle and the resultant heart failure.
To summarize therefore, let me state that there is ample scientific evidence to support revascularization of coronary arteries whether by CABG or angioplasty in patients with left main disease, 3 vessel disease with poor ventricular function, in patients with critical disease of proximal LAD, in patients with unstable angina or acute coronary syndrome and in patients who present with shock after an acute heart attack. These conditions remain the indication for CABG at present.
Coronary artery surgery is the most extensively studied surgical operation ever. Heart surgery and heart surgeons are also the most highly scrutinized operations and surgeons in all of medicine. In 1989, New York State began a ‘voluntary' reporting system for all hospitals and surgeons in New York and the results are published in the press annually. It ranks the hospitals and the surgeons according to the mortality rates for the previous three years. It forces the hospitals to improve their results and has forced many surgeons to re-evaluate their practices. Many other States have followed the example set by New York.
The Society of Thoracic Surgeons (STS), one of the two professional societies of American heart surgeons also started a program of voluntary data collection and now over 90% of all heart surgery programs subscribe to this group. The STS database with millions of patients has become a large repository of information, which is generating dozens of studies based on large populations of patients. It is now considered a model for other specialties to follow, especially when we are heading towards pay-for-performance era in medicine.
The principles of continuous quality improvement include action, data collection, analysis, and improved action. Cardiac surgeons are the best example of such quality improvement programs. There are very few operations, which have been subjected to such rigorous trials as CABG and other heart operations. Is there abuse in the system? I am sure there is, but it is a very small percentage of the good that most cardiac surgeons are doing, based on the best evidence for the time, and continuing to collect data, analyze and improve the surgical options.
I do agree with the author that, “We need interventions, especially lifestyle changes or medications, that address the causes of atherosclerosis.” We must do more as a profession to prevent the disease rather than simply treating those who already have developed the disease. As a society we are suffering from many bad habits particularly in what we eat, which is causing ever-increasing incidence of diabetes, hypertension, coronary artery disease and such. Prevention of these chronic ailments will take a much larger national effort and infusion of funds. In the meantime we must continue to provide treatment according to the best evidence for those who have already developed atherosclerosis of coronary arteries, whether it is continued medical therapy, angioplasty or CABG surgery.
Syed Tasnim Raza, MD, is Associate Professor of Clinical Surgery at Columbia University Medical Center, New York City.