Stents and Plaque

If a blockage exists, that is about 15mm long or greater, and the composition is very hard plaque, too hard for a wire to penetrate, are there any tools which can attack the plaque which do not require to be guided along a wire? If not, does this mean that all such blockages have to rely on bypass surgery?
Also, if stents block, is it normally through scar tissue? or is usually due to the re-formation of plaque? Can blocked stents be cleared relatively safely and does it make any difference if there is more than one stent joined end to end?

Many thanks for your very valuable support.

[CCF HeartMD3]

ed34,
Interventional cardiologists have many tools (such as special wires and burr devices) that they can use to attempt to open arteries that have been blocked for long periods of time (known as chronic total occlusion). Some centers which have considerable experience (Patrick Whitlow at Cleveland Clinic and David Kandzari at Piedmont Heart) have had very good success in opening these type of blockages.

When stents clog, they do so either because of clot formation within the stent or the formation of scar tissue within the stent itself. The treatment depends whether the blockage is caused by scar tissue (known as restenosis) or clots (known as thrombosis). Longer stents or those placed end to end are at higher risk of clogging.