Limitations of Coronary Stenting

The preprocedural arterial lumen size remains a major issue in stenting procedures. A meta-analysis of the Benestent-I and STRESS-I/II trials showed that arteries less than 2.6 mm and greater than 3.4 mm in diameter (the smallest and largest quintiles treated) did not have better restenosis rates than arteries treated with conventional PTCA (119). A pooled analysis of quantitative angiographic data from the TIMI 4 and TIMI 10 trials shows that 69% of patients presenting with acute MI had a proximal reference segment diameter (PRSD) > 2.75 mm, and 56% had a PRSD > 3.0 mm (117). Despite recent advances in stenting techniques, the fact that smaller vessels may derive reduced benefits from coronary stenting due to greater risks of subacute thrombosis and intimal hyperplasia remains a significant challenge in coronary stenting.

Another challenge associated with stenting involves the treatment of in-stent restenosis. Although balloon angioplasty is the most common method of treating in-stent restenosis and is associated with a greater than 90% procedural success rate, it has been observed to have a high rate of restenosis (54%) (120). This is perhaps because balloon angioplasty of in-stent restenosis works by compressing and extruding the intimal tissue rather than by expanding the stent.

Although the stenting of highly thrombotic lesions is generally avoided, in a small trial stents were placed in 86 thrombus-containing lesions in patients with ACS. Despite this, there was a low rate of subacute thrombosis (1%) and restenosis (33%) (121). In addition to the risk of subacute thrombosis, other potential limitations of stenting include side branch occlusion, stent embolization, and inadequate access to more distal disease and significant side branches post-stent-implantation, the occasional inability to deliver a stent to the target lesion, and the potential for the wire to become entrapped in stents while recrossing. The impact of stenting on subsequent bypass procedures is unknown.

Many new stent designs currently under investigation include welded tubular stents, integrated flexible-coil stents, interlocking coil-strut stents, self-expanding stents, and radiation-emitting stents. Although it is unlikely that any single design will be suitable for all patients, diversity in composition and structure are likely to offer the interven-tionalist a wide variety of options in the future.

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