A Simple Step Towards Better Stent Deployment

The idea of achieving an optimal stent deployment is a simple one: a stent deployed in a lesion has to reach its nominal size which should be close to the measured vessel size, taking into account that the plaque is still there and that the adventitia can be dilated at a certain extent. However, in the current clinical practice there are several drawbacks leading to a high incidence of “suboptimal” stent expansion. First, the final dimensions of a successfully deployed stent evaluated by angiography are very often below its “nominal” dimension. Several studies using an intravascular ultrasound (IVUS) evaluation demonstrated stent under-expansion in 20–60% of cases.(1–3) In one study that focused on angiographic stent evaluation, only 11% of stents obtained a desired IVUS stent area (> 9 mm2) — this despite an optimal angiographic results.4 Furthermore, there is a definite relation between stent expansion and restenosis. Our group has shown in the past an impact on the incidence of stent restenosis by achieving strict criteria to optimize stent expansion, e.g., obtaining an in-stent MLD of 90% or more of the reference segment with symmetric and completed stent apposition would decrease stent restenosis.5 IVUS appears as the most practical and reliable tool to guide optimal stent expansion. Unfortunately, in studies in which this approach was used, the achievement of the expected result was below the expectations,6 and when the IVUS strategy was compared to the angiography-guided strategy, no angiographic or clinical benefit could be demonstrated in the OPTICUS trial (Randomized comparison of coronary stent implantation under ultrasound or angiographic guidance to reduce stent restenosis).7 IVUS-guided optimization of tubular stents could be performed with comparable angiographic and clinical long-term results: six-month restenosis rate (24.5% with IVUS guidance versus 22.8% with angiographic guidance; p = 0.68), minimal lumen diameter (1.95 ± 0.72 mm versus 1.91 ± 0.68 mm; p = 0.52), and percent diameter stenosis (34.8 ± 20.6% versus 36.8 ± 19.6%; p = 0.29), respectively. At 12 months, neither major adverse cardiac events (relative risk, 1.07; 95% CI 0.75 to 1.52; p = 0.71) nor repeat interventions (relative risk 1.04; 95% CI 0.64 to 1.67; p = 0.87) were reduced in the IVUS-guided group. However, these results could be explained by good stent deployment using optimal balloon-to-artery ratio by very experienced operator by angiography alone. As a matter of fact, the immediate MLD had only a 0.11 mm difference favoring IVUS-guided stenting (3.02 vs. 2.91), despite a significance in the statistical evaluation. The RESIST (REStenosis after Ivus guided STenting)8 study, randomized patients after successful stent implantation were divided into two groups: Group A had no further dilation, and Group B had additional balloon dilation until achievement of IVUS criterion for stent expansion. At the end of the procedure, there was no significant difference in the minimal luminal diameter, but the stent lumen cross-sectional area (CSA) was significantly larger in Group B (7.16 ±2.48 vs. 7.95 ± 2.21 mm2; p = 0.04). At 6 months, there was no significant difference in the restenosis rate, (28.8%9 in Group A vs. 22.5%3 in Group B; p = 0.25), but according to the observed difference in the restenosis rate, the power of the study was only 40%. The difference in MLD was also not significant (1.60 ± 0.65 mm in Group A vs. 1.70 ± 0.64 mm in Group B; p = 0.20), whereas the lumen CSA was 20% larger in the IVUS-guided group (4.47 ± 2.59 vs. 5.36 ± 2.81 mm2; p = 0.03). Lumen CSA was the only predictor of restenosis by multivariate logistic regression analysis. The major point of this study is that there was not enough statistical power and that the stent CSA was still suboptimal to achieve a significant decrement in restenosis rate. On the contrary, the CRUISE (Can Routine Ultrasound Influence Stent Expansion) study10 demonstrated a significantly lower TLR in patients with IVUS-guided stenting compared to angiography guided stenting at 9-month follow-up (8.5% versus 15.3%; p 9 mm2 (46% versus 11%; p = 0.02) and more patients fulfilled AVID (Angiography-directed Versus Ivus-Directed coronary stent placement) study criteria for stent expansion (70% versus 32%; p = 0.048). Although there were no acute complications, no stents achieved a nominal size in spite of over-dilatation, and no differences in clinical variables were seen at 1-year follow-up. Thus, what is the value of this study? To understand this point, we should review some previously published studies. A recent study15 evaluated the reference vessel diameter in coronary arteries according to the method of measurement used: angiography was compared with by intravascular ultrasound. The study was done in 419 lesions in small vessels (vessel size of 2.75 mm, large group). The mean difference between the intravascular ultrasound and the angiographic reference diameter (IVUS-Angio) was 1.3 ± 0.5 mm in the small group and 1.0 ± 0.6 mm in the large group (p 1.0 mm occurred in 71% of cases in the small group and in 49% in the large group (p

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