QUOTE: "I had gone through angiiogprahy in 2003, at that time there was 5% blockage in LAD and that was pushed out by pressure."
>>>"Pushed out be pressure", indicates there be a ballooning or bulging of the wall of blood vessel. It is possible the artery wall is thinner with additional plaque buildup. Also, visceral aneurysms may rupture and form clots that block blood flow, or they can compress a nearby nerve or vein and cause pain, numbness or swelling. If this occurs a bypass may be warranted. Under those conditions, a stent may not be an option.
If a thin wall in addition to the blockage is not an issue, Ed has the relevant response.
I think your first priority is to see what risk factors you still have in your life because your disease is still progressing. There is no 'cure' but you can slow the disease down or stop it getting worse if lucky. Obvious risks are smoking, bad diet, no exercise, stress, high blood pressure and high cholesterol.
With such a large blockage in your LAD, I don't think that you will be left with medication as an option. Chest pains means that your heart muscle is seriously lacking in Oxygen and surgical intervention will be necessary. I doubt if Nitro will open an artery with a 99% blockage sufficiently to give much/if any relief. The vessel will already be fully open around the blockage trying to increase blood flow.
So, your only two options will be either a bypass or Angioplasty. I am not sure why, but it seems much more common for people to have a bypass when there is a large blockage in the LAD. There are some precautions you can take to ensure your bypass will last many years, normally the rest of your natural life (If this is the chosen option). You could ask the surgeon to use both the arteries from inside your chest, rather than using veins from your legs. Arteries are much stronger than veins and are much more up to the job. The arteries used are the Left internal mammary artery and the right one, commonly known as the Lima and Rima to surgeons. You have two sets of arteries running inside your chest and taking one away for use in a bypass will give no side effects.