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Kobayashi et al. (1)demonstrated the in vivo mechanical properties of the Radius stent, a self-expanding coronary stent. They studied the subsequent vessel response over time in a group of 62 patients randomized to either the Radius self-expanding stent or the Palmaz-Schatz balloon-expandable stent.
Using intravascular ultrasound studies after stent deployment and at six-month follow-up, the researchers concluded that the Radius stents continued to enlarge during the follow-up period (increased 24%) while the Palmaz-Schatz stents had remained unchanged. The expansion was accompanied by a greater amount of neointima than the Palmaz-Schatz stents (3.0 ± 1.7 mm2vs. 1.9 ± 1.2 mm2), resulting in similar late lumen loss in both configurations.
Our group has been intensively involved in the development of self-expanding stents, demonstrating the concept of long-term expansion in animal and clinical models (2–4). In a study published in 1999 we reported the first human experience with the nitinol self-expanding coil stent (5). In a series of 64 patients, we provided clinical and angiographic data on the effect of self-expansion during implantation and follow-up. Balloon angioplasty increased the minimal lumen diameter (MLD) from 1.07 ± 0.73 mm to 2.24 ± 0.57 mm; stent deployment further increased the diameter to 2.63 ± 0.48 mm, and within-stent balloon dilation to 2.96 ± 0.62 mm. Angiographic follow-up showed that the MLD was 2.15 ± 0.80 mm (late lumen loss of 0.81 ± 0.69 mm), and the mean stent diameter expanded to 3.58 ± 0.48 mm (self-expanding late stent gain of 0.62 ± 0.55 mm). The extent of this expansion was inversely related to the late lumen loss. Several patients presented a positive remodeling (i.e., their MLD increased at follow-up). A one year, 51 (80%) of 64 patients were event free.
The self-expanding nitinol stent exerts its acute effect on MLD through its intrinsic radial force aided by balloon expansion. Self-expanding stents do not reach their nominal diameter at implantation. The stent continues to expand until it reaches its nominal diameter over the follow-up period. The extent of this expansion is inversely related to the late lumen loss, which may be due to the continuous injury stimulus by the continued expansion. The balance between continued expansion and neointimal proliferation determines the late lumen loss, which is the critical parameter determining long-term stent performance. Kobayashi et al. (1)do not answer the main question arising from their excellent study. What is the place of self-expanding stents today, at the start of the era of the coated balloon-expandable stent?
Based on our results and those of the present study, despite the promising theoretical benefits of these continued expanding stents and because of the exaggerated neointimal proliferation, there is no net late gain compared to balloon-expandable stents. Methods to reduce intimal proliferation after implantation of self-expanding stents may include optimal size selection, acute implant methodology with respect to pre- and post-stent dilation and in situ pharmacologic methods to reduce this proliferation. Therefore, the possible success of such stents in coronary artery disease will critically depend upon our ability to limit the proliferative response to that stent. It is timely that a study combining an effective antiproliferative coating and a self-expanding stent will determine the role of long-term stent expansion, without the counterproductive intimal response.
- American College of Cardiology
- Kobayashi Y.,
- Honda Y.,
- Christie L.G.,
- et al.
- Roguin A.,
- Grenadier E.,
- Linn S.,
- Markiewicz W.,
- Beyar R.