Carotid Disease And CABG

The causes of a stroke during surgery are many, but they can be grouped under three general headings:

1. 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 obstruction 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.

2. Bleeding into the Brain: 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.

3. Embolus to the Brain: An abnormal clump of material traveling through the blood vessels is called an embolus. 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 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.

Atherosclerosis in the Carotid Arteries

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.

Carotid and Coronary Artery Disease

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 situations, 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 has yielded lower operative death and stroke rates while providing better long-term relief from stroke.

In summary, 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.