November 17th, 2010
05:10 PM ET

What causes new blockages to form so quickly?

Every weekday, a CNNHealth expert doctor answers a viewer question. On Wednesday, it's Dr. Otis Brawley, a chief medical officer for the American Cancer Society.

Question asked by Angi Garton of Chariton, Iowa:

My mother had triple bypass surgery one year ago. She was having chest pain again and hospitalized. There are more blockages, one right below a bypass and 70 percent blockage through a bypass. Also one bypass has failed. Her cholesterol and blood pressure are in good ranges and under control. What would have caused the new blockages so quickly from a year ago?

Expert answer

Unfortunately, it is rather common for a patient to have blockages in the coronary arteries and in the bypass after a coronary artery bypass graft (or CABG).

The heart muscle is threatened when one or more of the arteries carrying oxygenated blood through it is partially or completely blocked. It can be blocked by a cholesterol plaque, a blood clot or a combination of the two. Heart muscle beyond the blockage cannot get enough oxygenated blood. This can cause the chest pain called angina. Prolonged decreased blood flow can cause death of heart muscle which is referred to as a myocardial infarction or a heart attack.

Minor blockages of the coronary artery are treated with medications that dilate the arteries and lower blood pressure which decreases the workload and oxygen requirement of the heart. More severe blockages have to be treated with an angioplasty, angioplasty and placement of a stent, or with a coronary artery bypass graft. Angioplasty is when a catheter is passed, usually from the femoral artery in the groin up to the heart and a balloon-like device is placed in the coronary artery to the level of the partial occlusion and inflated to open the blockage. A stent, a tiny tube, can be left behind to keep the artery open. A coronary artery bypass is an open-chest surgery. A surgeon takes a piece or graft of artery or vein from elsewhere in the body. The graft is then stitched into the coronary artery so that blood can detour around the blockage. Think of a CABG as creating a detour or alternative route for blood flow around a partial or completely blocked artery. All of these treatments are designed to allow muscle beyond the blockage to get oxygenated blood.

When CABG is done the surgeon may choose to use the saphenous vein from the leg or the internal mammary artery (IMA) from the chest and armpit for the bypass graft. The condition of the patient is factored into the decision to use one or the other. In surveys more than 80 percent of CABGs are done with the right or left internal mammary artery. In the first five years after surgery, the internal mammary artery grafts are less likely to occlude compared with the saphenous vein.

In studies of several thousand people getting CABG using the saphenous vein, 10 percent have graft occlusion within the first few weeks to a year after surgery. It occurs in 35 to 40 percent by five years after the operation and 40 to 50 percent at 10 years. Factors that predispose to saphenous vein graft disease, include the size of the vein graft. Smaller diameter veins being at higher risk. Remember women are likely to have smaller vein grafts and are thus at higher risk than men. Other risk factors include length of the vein grafted (longer being at higher risk), smoking history before and after surgery, hypertension in the weeks after surgery, and lipid abnormalities in the weeks after surgery. Interestingly diabetes and poor blood sugar control appear to have little role as a risk factor for early occlusion of the grafts but is a risk factor later.

One percent of left internal mammary artery grafts and six percent of right IMA graphs develop blockages within three months of surgery. Over the long term, 10 to 15 percent of internal mammary grafts develop occlusion. Factors that increase risk of IMA occlusion include the area of the heart that needs to be grafted and the severity of the blockages being bypassed. A more severe blockage in a coronary artery correlates with decreased chances of a blockage in the graph presumably because of higher blood flow in the graph.

IMA grafts are generally preferred because they have a higher long-term patency rate. Sometimes the internal mammary artery cannot be used, necessitating the use of the saphenous vein. In select cases, some surgeons are now using the radial artery from the forearm or the the right gastroepiploic artery (from the stomach).

Studies show that one can decrease risk of occlusion of both the veinous and arterial grafts and the coronary arteries by aggressively reducing LDL-cholesterol with statin therapy and possibly through blood pressure control to low normal levels. Patients also generally benefit from low-dose aspirin therapy, some doctors prefer the antiplatelet agent clopidogrel instead of aspirin. Avoidance of smoking, controlling the serum glucose in diabetes is also important. Unfortunately these reduce but do not eliminate risk of occlusion.

I will discuss angioplasty and cardiac stents next week.

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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.