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Femoro popliteal bypass is a major lower extremity arterial reconstruction with the goal of establishing blood flow due to any form of obstructive lesions in the blood vessels.
The greater saphenous vein (GSV) is the most commonly utilized autogenous graft for doing peripheral arterial bypass operations as it has superior long term patency compared to synthetic grafts.
With regarding to the outcome, as long as the grafted vein portion is healthy and disease free, it can last lifelong. There is usually no need to replace the graft, unless the underlying disease process remains uncontrolled and overtime affects the graft.
Hence you should continue any treatment suggested by your doctors which might help to control the condition, and prevent any possible damage in the future.
I hope this helps.