Prime Minister Manmohan Singh [Images] will undergo a second by-pass surgery on Saturday at the All India Institute of Medical Sciences. Dr Ramakanta Panda, a noted cardiac surgeon with Asian Heart Institute, Mumbai [Images], will be among the team of doctors who will perform the surgery on the 76-year-old prime minister.

But, what does a repeat (redo) by-pass surgery actually mean?

In layman's terms, "Think of a road. If you are going on a road and there is a big traffic jam, you take the car from a different route and you join back later on the main road. When you have a blockage in your artery, we take another artery from a different place and we connect it to the original artery, below the blockage. Hence, the blockage gets by-passed," said Dr Aashish Contractor, Head of Department, preventive cardiology & rehabilitation, Asian Heart Institute.

"The blockages, which are present in the arteries, remain as they were. The 'graft' which provides the 'new blood supply' is connected below your old blockages; thereby providing adequate blood to the heart muscle. The blockage is still existent in the system but it gets by-passed. To do this by-pass, we normally take an artery from the chest or we can also take an artery from the arm or leg as needed. That's what a by-pass surgery is.

"A redo by pass surgery is the same except that it is being done after one by-pass surgery has already been performed in the past. The difference is that a redo by-pass surgery is harder. Now there are lesser places to connect the artery -- old grafts that you have used cannot be used again, one has to come up with new grafts. Performing a redo by-pass surgery requires far more skill. It is a more challenging and demanding surgery when it is a second time," Dr Contractor said.

On being asked if extra care needed to be taken by a patient who is undergoing a redo by-pass surgery, he said, "Post surgery care has to be taken whether it is a first by-pass surgery or second. The patient needs to be extra careful. The patient is normally suggested three to six weeks of rest."

"To perform the surgery, the chest-bone is cut open and stitched together after surgery. It is quite normal to feel some pain or altered sensations in the chest region for a few months after surgery. However, this pain is different from the pain of 'angina', which a patient might have experienced before surgery," Dr Contractor explained.