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Postdilatation following Coronary Stent Deployment: Lesion
Postdilatation following Coronary Stent Deployment: Lesion and Proce
July 2008
First-generation balloon-expandable stents such as the Palmaz-Schatz stent were often deployed at low pressure using compliant delivery balloons. Overhang of the deployment balloon outside the stent increased the risk of edge dissection when high-pressure inflation was used. Intravascular ultrasound (IVUS) studies showed that stents deployed in this fashion were often underexpanded and postdilatation with higher pressures or larger balloons was required to optimize stent expansion.1 Postdilatation following stent implantation was shown to increase the mean stent minimal lumen diameter (MLD) by 16%, and the mean stent minimal cross-sectional area (CSA) by 35%.2,3
Improvements in stent design and delivery systems have enabled modern stents to be deployed at high pressure. This has resulted in a reduced use of postdilatation after stent deployment.4 The purpose of this study was to examine the use of postdilatation and its impact on stent expansion and lumen dimensions in patients undergoing coronary stenting using modern stent delivery systems.
Methods
Patient selection. We performed a prospective observational study documenting a series of native vessel percutaneous coronary interventional (PCI) cases reflecting routine clinical activity at our center. The data collection period ran from September 26, 2003 to October 12, 2004. Three consultant cardiologists agreed to take part in this study (RHS, RAP, JLM). All data relating to the PCI procedure were collected in real time by SA, who was present in the catheterization laboratory during the procedures. Trial-specific information was transcribed to a computer database system running as an adjunct to our routine clinical audit database tool. All procedures were performed according to agreed protocols, with the acquisition of specific angiographic images for subsequent offline quantitative coronary angiographic (QCA) analysis.
A total of 499 individual lesions in 391 patients treated with coronary stent implantation were recorded during the study period. Out of 499 cases, no reference vessel diameter (RVD) measurements were available in 8 cases and no MLD following postdilatation in 1 case. The remaining 490 lesions (representing 385 patients) were included in the analysis. Postdilatation was performed in 41.2% (202/490) of cases.
Angiographic evaluation. Digital angiographic records were analyzed offline by SA. QCA was performed using an automated edge detection system, CAAS II (Cardiovascular Angiography Analysis System, Pie Medical Imaging, Maastricht, The Netherlands). This system has been extensively validated in previous studies.5 Investigators were required to record paired orthogonal images of target lesion segments as part of routine PCI practice.
QCA was used to measure the RVD, diameter stenosis and the MLD within the stent before and after postdilatation. Optimal stent deployment was defined as a stent MLD ≥ 90% of the RVD. This was calculated as an average of the proximal and distal RVDs.
Procedural technique. All procedures were performed via the femoral or radial routes. Intravenous heparin was given at the start of the procedure to maintain an activated clotting time of 220–300 seconds. The choice of guidewires, balloons and stents was left to the discretion of the operators. The decision to carry out postdilatation was made by the operator based on the angiographic images available at the time of the procedure. The offline QCA analysis data were not available during the procedure.
All patients received aspirin 300 mg and clopidogrel 300–600 mg preprocedure. Aspirin 75 mg was continued indefinitely and clopidogrel 75 mg was continued for a minimum of 4 weeks post procedure.
Statistical analysis. We examined the ability of postdilatation to increase the stent MLD. This analysis consisted of comparing the MLD immediately after stent deployment with the final MLD using a paired t-test. The results were expressed as mean absolute and relative differences with 95% confidence intervals. We explored factors associated with an increase in the MLD following postdilatation. These included the use of predilatation, baseline RVD, stent deployment pressure, balloon vessel (BV) ratio of the postdilatation balloon and residual stenosis after stent implantation. The diameter of the postdilatation balloon was calculated from the manufacturer’s reference chart depending on the inflation pressure used. Residual stenosis after stent implantation was calculated as RVD - stent MLD/RVD x 100.
Categorical variables are presented as absolute values and percentages. Continuous variables are presented as a mean with standard deviation. All analyses were performed with SPSS version 11.0. A p-value 14 atm, p 1.23 was not associated with any significant improvement in the mean percentage increase in stent MLD with postdilatation (Table 3).
Residual stenosis after stent deployment in patients who underwent postdilatation. The mean (SD) residual stenosis after stent deployment was 13.98% (11.27), 95% CI 12.42–15.54%. The study population was divided into tertiles depending on the residual stenosis after coronary stenting. The mean (SD) percent increase in stent MLD with postdilatation was significantly greater in those cases where the residual stenosis was > 20% after stent deployment compared to those cases with a residual stenosis of 20% after stent deployment. Lesions with heavy calcification or large plaque burden are likely to have increased resistance to stent expansion. The immediate angiographic result after stent deployment should be carefully reviewed for stent underexpansion. Further studies are required to examine whether quantitative assessment of the post stent deployment images may improve patient selection for postdilatation. Fourth, a BV ratio of > 1.23 for postdilatation was not associated with any further benefit in increasing the stent MLD. Our practice is to use short (8–12 mm) noncompliant balloons for postdilatation with a nominal diameter 0.5 mm larger than the stent delivery balloon, deployed to ≥ 16 atm. Care should be taken to avoid vessel injury outside the stent margins with postdilatation.
Modern stent delivery systems use semicompliant balloons that are manufactured to achieve a certain nominal diameter at a specific pressure. Inflation of the balloon at pressures greater than nominal can result in a slight increase in the final diameter. Manufacturers provide a compliance chart for each device, which describes the expected stent diameter for a range of deployment pressures. These values are derived from calliper or other measurements of balloons inflated in air or in a water bath. Some manufacturers report only the compliance data of the delivery balloon without the stent. Studies have shown that the actual stent diameters achieved after deployment are much smaller than those predicted by the manufacturer’s compliance chart.11 Stent delivery balloon underexpansion is the principal reason for this shortfall. The semicompliant nature of modern stent delivery balloons may not be able to overcome the resistance of coronary lesions, particularly those with extensive fibrocalcified plaque. Noncompliant balloons are manufactured to achieve a nominal size, with little further increase in diameter despite increasing the inflation pressures.12 Noncompliant balloons that are oversized compared to the nominal stent diameter may achieve more uniform and greater expansion, resulting in better stent deployment. However, even noncompliant balloons are unable to overcome the resistance of very hard lesions, as shown by the 57% optimal expansion rate in those cases where postdilatation was performed. Sometimes a suboptimal stent may be acceptable when the lesion is unyielding to initial postdilatation, and further balloon inflations with oversized balloons may result in complications such as vessel dissection and perforation.
Randomized clinical trials have shown that drug-eluting stents (DES) reduce the in-stent restenosis and TVR rates compared to bare-metal stents.13 The local delivery of antiproliferative drugs prevents neointimal hyperplasia and late loss that occurs following coronary stenting. This may result in operators using adjunctive postdilatation less frequently after DES implantation compared with BMS. Our study showed that similar rates of postdilatation were used after DES and BMS deployment. Adequate DES expansion may be important to ensure optimal drug delivery, with close contact between the stent struts and the vessel wall. High-pressure postdilatation has been reported to be important in optimizing stent expansion in cases where DES are used for the treatment of in-stent restenosis.14 It has been reported that stent thrombosis after sirolimus-eluting stent implantation is associated with stent underexpansion.15 The authors showed that 80% of the cases with stent thrombosis had a stent MLA of
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