Clinical Professor of Surgery Harvard University
The most dreaded complication of coronary artery bypass grafting, other than death, is the occurrence of stroke during the surgery. Unfortunately, as the average age of patients having bypass surgery has risen during the past twenty years, so has the chance of having a stroke. For patients less than age fifty years, the risk of stroke after coronary artery bypass grafting is less than 1 percent; for those patients more than age eighty years, the risk approaches 8 percent to 10 percent.
The causes of a stroke during surgery are many, but they can be grouped under three general headings.
Problems with Blood Flow to the Brain
Although cardiopulmonary bypass with the heart-lung machine rarely causes poor blood flow to the brain, certain unusual circumstances can occur.
Each time the left ventricle contracts, it ejects blood from the
heart and causes a pulse In the arteries throughout the body. The brain, however, is sensitive to the loss of regular pulse, and the heart-lung machine provides a more continuous flow than the normal pulsing flow from the heart. Because there is a lack of pulsation, it is particularly important that an adequate blood pressure be maintained when the patient is receiving assistance from the heart-lung machine to ensure the brain gets enough blood. Partial or complete ob struction of one or both carotid arteries, which supply blood to the brain, can lead to compromised blood flow to the brain while the heart-lung machine is working.
One of the startling and very fortunate findings in heart surgery is that, despite the high doses of very potent blood thinners (anticoagulants) required when the heart-lung machine is used for coronary artery bypass grafting, bleeding into the brain is extremely rare. In fact, it almost never occurs during the operation and thus can be discounted as a cause of stroke during the operation.
An abnormal clump of material traveling through the blood vessels is called an embo-lus. The possible sources of material traveling to the brain include blood clots from inside the heart, debris from plaque in the aorta or the carotid arteries, and
STROKES, CAROTID ARTERY DISEASE, AND CORONARY BYPASS SURGERY
particles of material or air from the heart-lung machine.
Surgeons have recently focused their attention on atherosclerosis in the aorta and in the carotid arteries.
Physicians currently have numerous strategies to deal with atherosclerosis when it occurs in the aorta near the heart. This area is of great importance to the surgeon because it is where the blood-return tubes from the heart-lung machine are usually inserted, where coronary bypass grafts may be sewn, and where other clamps and tubes may need to be placed to protect the heart muscle during the operation.
In the carotid arteries, the accumulation of atherosclerotic plaque is unfortunately quite common in older patients. When more than half of the carotid artery is obstructed with atherosclerotic material, the risk of stroke begins to climb.
In patients with at least 60 percent obstruction of their carotid artery, a carotid endarterectomy, or surgical clearing of the artery, yields much greater freedom from subsequent strokes than continued medical therapy. A carotid endarterectomy is performed through an incision in the neck. During the procedure, the atherosclerotic accumulation can be removed directly and the artery incision closed.
The subsequent freedom from strokes is obtained not only by patients who have symptoms from their carotid obstructions but also by those who do not have symptoms from them. Thus, the mere presence of a substantial carotid artery blockage can justify a carotid endarterectomy even if the patient does not have symptoms. Unfortunately, the first symptom of advancing carotid artery blockage may be a full stroke.
Patients who have substantial carotid artery disease in addition to coronary artery disease are at a much higher risk of stroke during coronary artery bypass grafting if nothing is done to correct the carotid artery disease.
The issue for surgeons in the last several years has been timing the two operations (carotid endarterectomy and coronary artery bypass graft) when a patient has both forms of artery disease. Several approaches have been tried, including performing one of the operations first, followed by the other. In some situ ations, this may seem to be an acceptable choice, particularly if the disease in one of the arterial systems is very severe and that in the other system is not.
However, recent surgical research has indicated that for the majority of patients with severe disease in both arterial systems, a combined operation is probably the best approach. During such an operation, the blocked coronary arteries are bypassed, and the diseased carotid artery is treated. This approach in our institution and other surgical centers has yielded lower operative death and stroke rates while providing better long-term relief from stroke. One study has demonstrated that doing the two procedures after the same anesthesia induction rather than as separate operations is much more cost effective.
In summary, evidence is accumulating that patients with severe disease in both their coronary and carotid arteries are generally better treated with a combined operation. Continuing studies are being performed that will test whether this combined approach is more effective than the staged approach in all surgical centers. The goal remains lowering the incidence of stroke during surgery, still the most devastating nonfatal complication of coronary artery bypass surgery.
Minimally Invasive Coronary Artery Revascularization
Michael Mack, M.D.
Assistant Clinical Professor of Surgery University of Texas SW Medical School Dallas, Texas
ONE OF THE MAJOR CAUS-|es of surgical trauma is the method of entry into the body. Large incisions tend to result in greater trauma, whereas the pain and some complications associated with surgery can possibly be lessened if the physician gains entry through a smaller incision. This approach has led to the concept of "less invasive surgeiy," a relatively new method of surgery that is accomplished through a few small "keyhole" incisions using a video camera attached to a telescope.
Because of the unique complexities of heart surgery—including the necessity of the heart-lung machine, operating on a moving organ, and the need to sew tiny blood vessels together — cardiac surgery was the last surgical specialty to adopt these new concepts. Starting in 1995, however, a few surgeons began performing coronary artery bypass grafting (CABG) through a three-inch incision between the ribs on the left side of the breast bone. The procedure was performed on a
beating heart rather than on a stopped heart, and the minimally invasive direct coronary artery bypass (MIDCAB), or "keyhole" form of cardiac surgery, was born. The "direct" in the acronym means that although the bypass was performed through a small incision, it was done while viewing the heart directly rather than with a scope.
This form of surgery has two benefits for postoperative recovery: Patients do not undergo as much discomfort as a large incision would cause, and the heart-
lung machine, which can contribute to the undesirable side effects of heart surgery, is not used.
At first, the MIDCAB operation was basically limited to a single bypass on the front surface of the heart and, because the heart was still moving, the connection of the bypass was technically challenging, and the results of the procedure were appropriately questioned. This issue was largely solved by the introduction of "stabilizers," which are mechanical feet placed against the surface of the heart. This produces a local area of immobilization and allows for precise sewing while the remainder of the heart continues to beat and support the circulation.
In 1995, the Port-Access™ device was introduced by Heartport, Inc., of Redwood, California. This device allows the surgeon access to the heart through a smaller incision while still using the heart-lung machine. It allows not only CABG operations but also surgery on the mitral valve inside the heart. Both are performed through a
New surgical techniques are allowing surgeons to access the heart through much smaller incisions on the side of the chest. Commonly called "keyhole" surgery, this is possible for a number of different heart operations.
three-inch incision on either the left (CABG) or right (mitral valve) side of the sternum. In addition to the ability to use the heart-lung machine without opening the chest, this procedure offers the ability to safely stop the heart with a balloon catheter placed in the aorta just above the heart.
In 1998, there were about forty-five thousand beating-heart operations performed in the United States (7 percent of all CABGs) and four thousand Port-Access procedures. Findings being published in early 1999 in the medical literature give some early indication that acceptable results may be obtained by these new approaches.
Currently, most of the focus in the field of minimally invasive cardiac surgery is on the off-pump coronary artery bypass (OPCAB) procedure. In the OPCAB operation, multiple coronary arteries can be bypassed. Although the breastbone is still divided, the heart-lung machine is not utilized, and newer generation stabilizers are used to immobilize each artery to be bypassed in turn while the heart continues to beat. Many experts in the field predict that within five years, more than 50 percent of all CABG surgery will be performed by using this approach.
The field of minimally invasive cardiac surgery is less than four years old, and the early results are promising. However, the results have not yet withstood the test of time. Accurate measurement of its role in managing heart disease will require further comparison, not only with conventional bypass surgery, but also with the "least invasive" form of coronary bypass, percutaneous transluminal coronary angioplas-ty (PTCA).
All four heart valves are seen from above here. The pulmonary valve is seen on top with the aortic valve immediately below it. The two red dots depict where the coronary arteries originate in the aorta just above the aortic valve. The two lower valves are the tricuspid, on the right, and the mitral valve on the left. The two illustrations show the valves during two stages of the heart cycle.
Was this article helpful?