Coronary Stents

Stents are small metal tubes implanted in the heart's arteries to improve the flow of blood to the muscle. A stent is implanted after a balloon angioplasty. Stents have been used widely in cardiovascular diseases in the last decade but in the last several years they have been in the news for safety concerns.

The mechanism of angioplasty is such that the artery is injured by the inflation of the balloon. This injury dilates and stretches the artery and improves blood flow. The first stents were developed to treat this injury. In up to 10 percent of angioplasty cases, the results were suboptimal and required urgent surgery to fix the problem or a repeat trip to the cath lab in the middle of the night to reopen the artery. After the initial procedure, up to 40 percent of patients returned to the cath lab for a repeat angioplasty because of re-narrowing of the treated segment. This re-narrowing is caused by buildup of scar tissue in the artery and a collapse of the expanded arterial wall.

The development of coronary stents allowed the cardiologist to treat areas of suboptimal expansion and cover small tears in the arterial wall to prevent abrupt closure of the segment. Unfortunately this did not reduce the numbers or repeat procedures as the stents were also associated with scar formation, or restenosis, in 25 to 30 percent of patients. This restenosis was more common in diabetics, long segments of blockages, smaller arteries and in complex anatomy.

The development of drug eluting or drug coated stents reduced the need for repeat procedures dramatically. The drug eluting stent is mechanically no different than the conventional stent except for the addition of a fine layer of polymer and drug coating the stent. The currently approved drug eluting stents in the United States are Taxus (paclitaxel coating), Cypher (Sirolimus coating) and Endeavor (Zotarolimus). After implantation, the drug is slowly released into the arterial wall to inhibit the scar formation. These stents went into wide use shortly after approval in the US and, at their pinnacle, were implanted in almost 90 percent of cases. The rates of repeat procedures were decreased to less than 10 percent.

Research data published in the summer of 2006 ignited a firestorm of controversy with drug eluting stents. At the time there was concern that the drug and polymer were inhibiting the formation of normal tissue in the stents and the possibility of stent clotting or thrombosis was underestimated. After 2 additional years of follow up there appears to be no difference in the long-term rates of stent thrombosis between drug eluting and older bare stents. There is, however, a higher risk or stent thrombosis after implantation of a drug eluting stent if the patient is not taking aspirin and clopidogrel (or ticlopidine). This combination of medications reduces the chance of clot formation inside the stent. It is currently recommended that all patients with a drug eluting stent take dual anti-platelet therapy for a total of 12 months unless they have a high risk of bleeding, in which case 6 months is appropriate. Factors that increase the chance of stent clotting are premature discontinuation of aspirin or clopidogrel, kidney failure, diabetes, complex anatomy and low heart function. Patient education is a major factor in compliance with these medications and I suggest that you consult your cardiologist before stopping any medications, especially if you have a drug eluting stent.