Friend of mine is in hospital now due to arterial stent becoming partially blocked. Took 5 years before he developed severe discomfort and pain in his chest and shoulder.
That said most of the clogging material is in the arteries not the venous return as filtration by the kidneys removes a lot of toxins.
Hypothetically, the stents in veins should last much longer.
Maybe a search on pubmed could provide us with an answer.