(i) Principle :In CABG, a new route of blood flow is created by using a piece of blood vessel (graft). One end of the graft is attached to the aorta or one of its branches and the other end of the graft is attached to the diseased coronary artery beyond the blockage. Thus, the obstruction is bypassed.
(ii)Types of Graft : The graft may be an artery or a vein. Arterial grafts are considered superior as these remain patent for a longer period. Commonly used arterial grafts are :
(a) Left internal mammary artery (LIMA) : This lies in the chest itself.
(b) Right Internal Mammary Artery (RIMA).
(c) Radial Artery : It is obtained from the forearm.
(d) Right Gastroepiploic Artery : It lies in the abdomen and is used less frequently.
Among the vein grafts, long saphenous vein is used most frequently. It is obtained from leg and thigh of the patient. Selection of the grafts is based upon the nature of blockage, condition of coronary arteries and function of the heart.
(iii) Approaches and techniques :The traditional the and commonly used technique involves an incision down the front of the chest through the breastbone or sternum. This incision is called a “median sternotomy”. Sometimes a smaller incision is used on the left side of the chest. This technique is referred to as “Minimally invasive coronary artery bypass” or MICAB. In MICAB, it is expected that patient will have less pain and faster recovery. Most commonly, the patient is attached to the heart lung machine and the heart is stopped during CABG. In selected cases, the heart lung machine is not used and CABG is performed on a beating heart.
(iv) Risks and complications :Though CABG is a safe operation, about 5% patients develop some form of complications. It is a major operation and depending upon the condition of the patient, there is a small but definite risk to the life. Other potential complications of CABG include bleeding or infection, stroke (which is primarily related to age and history of previous stroke), kidney failure (related in large measure to the kidney function before the surgery), and heart attack during or after the surgery. The risk of complications generally depends upon age, general health, smoking history, specific medical conditions, and most importantly, the heart function.
(v) The outcome of surgery and long term success :The operation abolishes angina in almost all patients and minimizes the risk of future heart attacks. However, some patients may have residual angina even after CABG, but it is of lesser severity. CABG is also known to prolong the expected survival (life-span) in a specific subgroups of patients. One should understand clearly that CABG does not abolish or retard the process of coronary artery disease. It only provides a remedy for the harmful effects of the disease. Thus, it is possible that a patient may develop symptoms again, either due to progression of coronary artery disease or due to involvement of the grafts in the disease process. Vein grafts are particularly susceptible for involvement in the disease process and about 50% of the vein grafts may be blocked by 10 years.