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why do predilation before stenting?

Before stent implantation, predilation with a balloon that is slightly undersized relative to the reference vessel diameter is a safe strategy that gives the operator useful information such as the pressure needed to expand the lesion. Using a slightly undersized balloon also leaves an indi- cation of the lesion so the stent can be optimally positioned. Predilation also allows for the vessel to be fully re-pressurized with restored flow, which often produces vasodilation. It is not uncommon to find a vessel enlarged after balloon dilation. This enlargement results in the operator selecting a larger stent than would have been chosen initially. Alternatively, an operator may choose to go directly to stenting without balloon predilation. Although this method is usually success- ful, stents cannot always be delivered to the lesion site because of tor- tuosity or calcifications. In these cases, exchange for a balloon catheter, predilation, and/or exchange for a stiff guidewire may be needed. It is disconcerting to the operator to place a stent directly in a lesion only to find that the stent cannot be fully expanded because of heavy calci- fication. Undersized stents may be selected because of unappreciated flow-mediated vasodilation.