Balloon angioplasty deforms the coronary artery to overcome an acute thrombus or a stenotic atheroma. The forceful enlargement by its nature causes dissection in the vessel intima and distention of the adventitia. The defects in the endothelium allowed a thrombus to form, and an occlusion of the artery can occur. The stretched elastic adventitia also has a tendency to recoil.
These two effects could cause abrupt closure of the vessel about five percent of the time with balloon angioplasty, which could cause myocardial infarction and possibly require emergent bypass surgery. Even if acute closure did not occur, neointimal proliferation and vascular remodeling would lead to in-stent restenosis (ISR) more than 50 percent of the time, with recurrence of the patient's ischemic symptoms for up to six months post-procedure. Stents were developed to provide a scaffold and help counter the acute closure and ISR, but suffered from difficulties with a higher rate of early in-stent thrombosis because of exposed metal in the coronary artery lumen, which is extremely thrombogenic. (Table 1.)
Drug-eluting stents (DES) used the antimitotic chemotherapeutic agents sirolimus and paclitaxel. The coating allowed for a controlled long-acting local drug delivery to stop the cell hyperplasia and proliferation, and showed significant reduction of ISR compared with bare-metal stents. Drug-eluting stents, however, came with an increased risk of late in-stent thrombosis. The same anti-proliferative properties that helped DES prevent restenosis also delayed the endothelialization of the stent, leaving the thrombogenic stent exposed to blood much longer than bare-metal stents. The development dual--antiplatelet therapy with aspirin and the thienopyridine class of antiplatelet medications (clopidogrel, Plavix) proved a potent inhibitor without excessive bleeding complications.
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