Stents are small, metal scaffolds similar in size and shape to the spring found in a ballpoint pen (Figure 3). Stent implantation is not appropriate for every artery.
Before stent implantation, the blocked artery usually is treated and dilated with one or more angioplasty balloons. A stent, tightly mounted on a special angioplasty balloon, is then guided to the site of the blockage. The angioplasty balloon is inflated to stretch open the stent and implant it into the walls of the blocked artery (Figure 4). The balloon is deflated and removed, and the stent remains permanently in place to hold the artery open (Figure 5).
A drug-eluting stent is coated with an agent that inhibits restenosis. The Cypher® stent is coated with an antibiotic called sirolimus (also called rapamycin), which is slowly released into the artery for about 30 days after implantation.
Sirolimus is a "cytostatic" drug, which means it inhibits cell growth and division, and T-cell activation and proliferation. T-cells initiate an inflammatory response that commonly follows implantation, and inflammation can lead to restenosis.
With uncoated stents, restenosis occurs in 15–25 percent of patients. The restenosis rate in patients who receive a drug-eluting stent is about 3–4 percent. These patients require fewer repeat procedures (e.g., additional angioplasty, bypass surgery) and have a lower risk for heart attack.