Evaluation of coronary remodeling after sirolimus-eluting stent implantation by serial three-dimensional intravascular ultrasound

Numerical investigations of the haemodynamic changes associated with stent malapposition in an idealised coronary artery

The deployment of a coronary stent near complex lesions can sometimes lead to incomplete stent apposition (ISA), an undesirable side effect of coronary stent implantation. Three-dimensional computational fluid dynamics (CFD) calculations are performed on simplified stent models (with either square or circular cross-section struts) inside an idealised coronary artery to analyse the effect of different levels of ISA to the change in haemodynamics inside the artery. The clinical significance of ISA is reported using haemodynamic metrics like wall shear stress (WSS) and wall shear stress gradient (WSSG). A coronary stent with square cross-sectional strut shows different levels of reverse flow for malapposition distance (MD) between 0mm and 0.12 mm. Chaotic blood flow is usually observed at late diastole and early systole for MD=0mm and 0.12 mm but are suppressed for MD=0.06 mm. The struts with circular cross section delay the flow chaotic process as compared to square cross-sectional struts at the same MD and also reduce the level of fluctuations found in the flow field. However, further increase in MD can lead to chaotic flow not only at late diastole and early systole, but it also leads to chaotic flow at the end of systole. In all cases, WSS increases above the threshold value (0.5 Pa) as MD increases due to the diminishing reverse flow near the artery wall. Increasing MD also results in an elevated WSSG as flow becomes more chaotic, except for square struts at MD=0.06 mm.

Intimal hyperplasia and vascular remodeling after everolimus-eluting and sirolimus-eluting stent implantation in diabetic patients: the randomized Diabetes and Drug-Eluting Stent (DiabeDES) IV Intravascular Ultrasound trial

OBJECTIVE

To evaluate the effects of the everolimus-eluting Xience™/Promus™ stent (EES) and the sirolimus-eluting Cypher™ stent (SES) on intimal hyperplasia (IH) in diabetic patients.

BACKGROUND

Patients with diabetes mellitus have increased risk of in-stent restenosis after coronary stent implantation due to intimal hyperplasia (IH).

METHODS

In a sub study of the Randomized Comparison of Everolimus-Eluting and Sirolimus-Eluting Stents in Patients Treated with Percutaneous Coronary Intervention (SORT OUT IV trial), serial intravascular ultrasound (IVUS) 10-month follow-up data were available in 88 patients, including 48 EES and 40 SES treated patients. IVUS endpoints included IH volume, in-stent % volume obstruction and changes in external elastic membrane (EEM) volume.

RESULTS

Compared with the SES group, IH volume was increased in the EES group [median (interquartile range): 2.8 mm(3) (0.0-12.6) vs. 0.0 mm(3) (0.0-1.1), P = 0.001]. In-stent % volume obstruction was increased in EES compared to SES [median (interquartile range): 1.6% (0.0-8.2) vs. 0.0% (0.0-1.0), P = 0.001]. Peri-stent external elastic membrane (EEM) volume: (post procedure vs. follow-up EES [300 mm(3) (219-491) vs. 307 mm(3) (223-482), P = 0.73] and SES [316 mm(3) (235-399) vs. 323 mm(3) (246-404), P = 0.05]) and peri-stent plaque volume: EES [163 mm(3) (103-273) vs. 184 mm(3) (115-291), P = 0.18] and SES [186 mm(3) (139-248) vs. 175 mm(3) (153-243), P = 0.26]) were unchanged in both groups. In the proximal reference segment a significant increase in plaque area was seen in the EES group only, without vascular remodeling.

CONCLUSION

In diabetic patients, EES stent implantation was associated with increased IH volume obstruction without involvement of vascular remodeling.

Optical coherence tomography evaluation of drug-eluting stents: a systematic review

AIMS

We performed a systematic review of studies reporting stent strut coverage and malapposition post implantation of different drug-eluting stent (DES), as assessed by optical coherence tomography (OCT).

METHODS

A review of publications and online databases in May 2011 retrieved 33 published studies reporting stent strut coverage and malapposition post-DES implantation using OCT: 24 for sirolimus-eluting stents (SES), 13 for paclitaxel-eluting stents (PES), 10 for zotarolimus-eluting stents (ZES), and two for everolimus-eluting stents (EES). The follow-up duration ranged from 3 months to 4 years. Stent strut coverage and malapposition were compared between DES at various time intervals post implantation.

RESULTS

Significant differences in stent strut coverage and malapposition exist between various DES. The SES had the highest frequency of uncovered struts at 3, 6, 9, and 12 months (13.1%, 10.9%, 8.1%, and 7.5%, respectively), followed by PES (5.5%, 4.4%, and 5.7% at 6, 9, and 12 months, respectively) and ZES (0.7%, 0%, and 0.5% at 3, 6, and 9 months, respectively) (P < 0.001 for all comparisons between stents). Only two studies reported 3.1% uncovered struts at 9 months with the EES. Stent strut malapposition at 6, 9, and 12 months was highest with SES (3.2%, 2.2%, and 1.2%, respectively) followed by PES (1.6%, 1.3%, and 0.9%, respectively), EES (0.46% at 9 months), and ZES (0.7% and 0.1% at 6 and 9 months, respectively).

CONCLUSIONS

SES had the highest rates of uncovered struts and malapposition, followed by PES and ZES. Such differences may explain the different clinical outcomes between various DES. © 2012 Wiley Periodicals, Inc.

Molecular mechanism of green microalgae, Dunaliella salina, involved in attenuating balloon injury-induced neointimal formation

The pathological mechanism of restenosis is primarily attributed to excessive proliferation of vascular smooth muscle cells (VSMC). The preventive effects of ethanol extract of Dunaliella salina (EDS) on balloon injury-induced neointimal formation were investigated. To explore its molecular mechanism in regulating cell proliferation, we first showed that EDS markedly reduced the human aortic smooth muscle cell proliferation via the inhibition of 5'-bromo-2'-deoxyuridine (BrdU) incorporation at 40 and 80 microg/ml. This was further supported by the G0/G1-phase arrest using a flow cytometric analysis. In an in vivo study, EDS at 40 and 80 microg/ml was previously administered to the Sprague-Dawley rats and found that the thickness of neointima, and the ratio of neointima:media were also reduced. EDS inhibited VSMC proliferation in a dose-dependent manner following stimulation of VSMC cultures with 15 % fetal bovine serum (FBS). Suppressed by EDS were 15 % FBS-stimulated intracellular Raf, phosphorylated extracellular signal-regulated kinases (p-Erk) involved in cell-cycle arrest and proliferating cell nuclear antigen. Phosphorylated focal adhesion kinase (p-FAK) was also suppressed by EDS. Also active caspase-9, caspase-3 and cleaved poly(ADP-ribose) polymerase (PARP) protein expression levels were increased by administration with EDS; the apoptotic pathway may play an important role in the regulatory effects of EDS on cell growth. These observations provide a mechanism of EDS in attenuating cell proliferation, thus as a potential intervention for restenosis.

Comparison of sirolimus and paclitaxel-eluting stents for complex coronary lesions: an intravascular ultrasound study

BACKGROUND/AIMS

Recent intravascular ultrasound (IVUS) studies of sirolimus-eluting stents (SES) and paclitaxel-eluting stents (PES) have demonstrated a significant reduction in neointimal hyperplasia (NIH) based on simple coronary lesions. In this study, we evaluated the efficacy of SES and PES using IVUS in complex coronary lesions.

METHODS

Eighty-seven patients in whom 95 drug-eluting stents (66 SES and 29 PES) were implanted in complex coronary lesions were enrolled in this study. Case selection was based on the availability of IVUS and quantitative coronary angiographic (QCA) examinations at the index procedure and at follow-up. The neointimal volume index (volume/length: NIVI) and percent neointimal volume (% NIV) were calculated. The longitudinal length of stented segments without IVUS-detectable NIH was also evaluated.

RESULTS

The baseline patient demographics were similar between the SES and PES groups. At follow-up, no significant differences were observed in the vessel, plaque, or stent volume indices between the two groups. However, the NIVI and % NIV were significantly lower in the SES group (p<0.01). The longitudinal length of stented segments without IVUS-detectable NIH was significantly higher in the SES group (p<0.01). The net gain was significantly larger in the SES group (2.3+/-0.7 vs. 2.0x0.6 mm, p=0.025), while the rate of major adverse cardiac events was similar between the two groups.

CONCLUSIONS

Although SES showed significantly greater suppression of NIH at follow-up, both stents were highly effective at inhibiting NIH in complex coronary lesions.

Late stent malapposition risk is higher after drug-eluting stent compared with bare-metal stent implantation and associates with late stent thrombosis

AIMS

Late stent malapposition (LSM) may be acquired (LASM) or persistent. LSM may play a role in patients who develop late stent thrombosis (ST). Our objective was to compare the risk of LASM in bare metal stents (BMS) with drug-eluting stents (DES) and to investigate the possible association of both acquired and persistent LSM with (very) late ST.

METHODS AND RESULTS

We searched PubMed and relevant sources from January 2002 to December 2007. Inclusion criteria were: (a) intra-vascular ultrasonography (IVUS) at both post-stent implantation and follow-up; (b) 6-9-month-follow-up IVUS; (c) implantation of either BMS or the following DES: sirolimus, paclitaxel, everolimus, or zotarolimus; and (d) follow-up for LSM. Of 33 articles retrieved for detailed evaluation, 17 met the inclusion criteria. The risk of LASM in patients with DES was four times higher compared with BMS (OR = 4.36, CI 95% 1.74-10.94) in randomized clinical trials. The risk of (very) late ST in patients with LSM (five studies) was higher compared with those without LSM (OR = 6.51, CI 95% 1.34-34.91).

CONCLUSION

In our meta-analysis, the risk of LASM is strongly increased after DES implantation compared with BMS. Furthermore, LSM seems to be associated with late and very late ST.

Comparison of intravascular ultrasonic imaging with versus without incomplete stent apposition at follow-up after drug-eluting stent implantation

BACKGROUND

Incomplete stent apposition (ISA) at follow-up has been reported to be more common after drug-eluting stent (DES) implantation than after bare-metal stent (BMS) implantation. The aim of this study was to use intravascular ultrasound (IVUS) to evaluate the coronary characteristics after drug-eluting stent implantation in patients with ISA at follow-up.

METHODS

From the IVUS database of our institute, a total of 89 patients with 125 native lesions who underwent DES implantation into de novo lesions with IVUS imaging at 6-month follow-up were identified, and 15 (16.9%) patients had documented ISA at follow-up by IVUS. The ISA group was compared with a matched control group of patients (n = 30) who had no evidence of ISA at follow-up.

RESULTS

Of the 15 documented ISA at follow-up after DES implantation, two located at the edge (within 5 mm from stent margin) while 13 in the body of the stent. The maximum area and arc of ISA measured 5.3 +/- 2.2 mm(2) and 163 +/- 67 degrees , respectively. In patients with ISA, the maximum EEM area of stent segment with ISA was significantly larger than the adjacent stent segment without ISA (24.1 +/- 3.3 vs. 20.1 +/- 3.1 mm(2), P = 0.002), while stent area, plaque plus media (P&M) area and intrastent lumen area were comparable (P > 0.05). Compared to the matched control cohort without ISA at follow-up, the maximum EEM area was also significantly larger (24.1 +/- 3.3 vs. 18.8 +/- 4.2 mm(2), P < 0.001), while the areas of reference EEM and lumen, stent, P&M behind the stent, intimal hyperplasia and intrastent lumen were all comparable between the two groups (P > 0.05).

CONCLUSION

ISA at follow-up after DES implantation for de novo coronary lesions was associated with a larger EEM area.

Randomized Comparison of Sirolimus and Paclitaxel Drug-Eluting Stents for Long Lesions in the Left Anterior Descending Artery

OBJECTIVES

The goal of this work was to verify whether the superiority of the sirolimus-eluting stent (SES) in inhibiting neointimal hyperplasia could be demonstrated in complex coronary lesions.

BACKGROUND

Both the SES (Cypher, Cordis, Miami Lakes, Florida) and the paclitaxel-eluting stent (PES) (Taxus, Boston Scientific, Natick, Massachusetts) have shown a marked reduction in neointimal hyperplasia compared with bare-metal stents. Intravascular ultrasound (IVUS) is the best method to assess arterial response to stent deployment, but few IVUS data are available comparing complex lesions treated with SES or PES.

METHODS

We prospectively randomized patients with complex lesions to SES or PES implantation. Intravascular ultrasound and quantitative angiography were performed post-procedure and at 9 months. Mean neointimal hyperplasia area (NIHA), percent of NIHA (NIHA%), mean peristent plaque area (PSPA), and percent of PSPA (PSPA%) were calculated. The primary end point was NIHA% at follow-up. Secondary end points included change in PSPA% and angiographic late luminal loss at follow-up.

RESULTS

Of the 100 patients enrolled, 42 receiving the SES and 43 receiving the PES had adequate IVUS assessment. Vessel, plaque, and lumen areas were comparable at follow-up, but NIHA% was significantly lower with SES than PES (7.4 +/- 4.2% vs. 15.4 +/- 8.1%; p < 0.001). A significant reduction in PSPA% was observed with SES (-4 +/- 10% vs. 0 +/- 8%; p = 0.01). Late loss was significantly lower with SES (0.16 +/- 0.19 mm vs. 0.32 +/- 0.33 mm; p = 0.003).

CONCLUSIONS

The SES shows a significantly higher inhibition of neointimal hyperplasia compared with PES in complex lesions. However, both stents have excellent IVUS and angiographic results at 9 months. A significant reduction in peri-stent plaque is observed only with SES.

Evaluation of four-year coronary artery response after sirolimus-eluting stent implantation using serial quantitative intravascular ultrasound and computer-assisted grayscale value analysis for plaque composition in event-free patients

OBJECTIVES

This study sought to evaluate the long-term arterial response after sirolimus-eluting stent implantation.

BACKGROUND

Sirolimus-eluting stents are effective in inhibiting neointimal hyperplasia without affecting plaque volume behind the stent struts at six months.

METHODS

Serial quantitative intravascular ultrasound and computer-assisted grayscale value analysis over four years were performed in 23 event-free patients treated with sirolimus-eluting stents.

RESULTS

In the first two years, the mean plaque volume (155.5 +/- 42.8 mm3 post-procedure and 156.8 +/- 57.7 mm3 at two years, p = 0.86) and plaque compositional change expressed as mean percent hypoechogenic tissue of the plaque behind the stent struts (78.9 +/- 8.6% post-procedure and 78.2 +/- 8.9% at two years, p = 0.67) did not significantly change. However, significant plaque shrinking (change in plaque volume = -18.4 mm3, p = 0.02) with an increase in plaque echogenicity (change in percent hypoechogenic tissue = -7.8%, p < 0.0001) was observed between two and four years. The mean neointimal volume increased over four years from 0 to 8.4 +/- 5.8 mm3 (p < 0.0001). However, no further statistically significant change occurred between two and four years (7.0 +/- 6.7 mm3 vs. 8.4 +/- 5.8 mm3, p = 0.25).

CONCLUSIONS

Between two and four years after sirolimus-eluting stent implantation, peri-stent tissue shrank with a concomitant increase in echogenicity. These intravascular ultrasound findings suggest that late chronic artery responses may evolve for up to four years after sirolimus-eluting stent implantation. In addition, the fact that the neointima does not significantly change from two to four years may suggest that the biological phenomenon of a delayed healing response has begun to subside.

A New Polymer Concept for Coating of Vascular Stents Using PTFEP (poly(bis(trifluoroethoxy)phosphazene) to Reduce Thrombogenicity and Late In-Stent Stenosis

OBJECTIVES

We sought to evaluate the new polymer PTFEP (poly(bis(trifluoroethoxy)phosphazene) for (1) its ability to reduce thrombogenicity and late in-stent stenosis and (2) its effect on endothelialization in a rabbit iliac artery model.

MATERIALS AND METHODS

Nanocoated ( approximately 50 nm) and bare stainless-steel stents were implanted bilaterally in the iliac arteries of 30 New Zealand White rabbits (1, 4, 8, 12, and 16 weeks follow-up) and evaluated by angiography, light, and scanning electron microscopy.

RESULTS

Bilateral stent placement was successful in 27 of 30 rabbits. Thrombus depositions occurred in none of the 27 coated but in 4 of the 27 bare stents (P=0.037). A normal angiogram was obtained in 18 of 22 coated stents at risk for restenosis (follow-up >or=4 weeks) but only in 13 of 22 bare stents (P=0.023). Marked restenosis (luminal loss >30%) was found in 6 bare stents (P=0.011) but not in any coated stents. The neointima was 47.7-73.9 mum on coated and 66.9-115.2 mum on bare stents (statistically significant at 4, 8, and 16 weeks). Scanning electron microscopy detected full endothelialization in all stents from 4 weeks on (22 stents in both groups).

CONCLUSION

PTFEP nanocoating successfully showed thromboresistance and reduced late in-stent stenosis. Endothelialization was equal in both stent types. Studies in more human-like models and human feasibility studies in human arteries are encouraged.

Simvastatin does not inhibit intimal hyperplasia and restenosis but promotes plaque regression in normocholesterolemic patients undergoing coronary stenting: a randomized study with intravascular ultrasound

BACKGROUND

Restenosis after coronary stenting is mainly caused by intimal hyperplasia. Both experimental and clinical studies suggest that statins may be able to inhibit intimal hyperplasia and, therefore, in-stent restenosis (ISR), by mechanisms beyond lipid lowering.

METHODS

In a 12-month study, we randomized 71 normocholesterolemic patients to 20 mg simvastatin or no treatment, 2 weeks before elective coronary stenting. Patients were evaluated by quantitative coronary angiography and intravascular ultrasound, immediately after the index procedure and at the 12-month catheterization.

RESULTS

Binary ISR was present in 15% and in 18% of simvastatin-treated patients and controls, respectively (P = NS). Intimal hyperplasia did not differ significantly between the 2 groups (3.6 +/- 1.8 vs 3.8 +/- 2.3 mm3/mm, 34% +/- 15% vs 35% +/- 23% for simvastatin vs controls, P = NS). However, persistent plaque decreased with simvastatin but increased in controls (-4.0 +/- 4.0 vs +1.6 +/- 3.8 mm3/mm, -14% +/- 10% vs +6% +/- 12%, P < .05). The same behavior was shown by intermediate plaques at nonstented sites (-2.5 +/- 3.0 vs +1.0 +/- 3.0 mm3/mm, -10% +/- 8% vs +9% +/- 9%, P < .05). Major adverse events at 12 months were present in 11% and 24% of simvastatin-treated patients and controls, respectively (P = .20).

CONCLUSIONS

In normocholesterolemic patients undergoing coronary stenting, simvastatin does not prevent intimal hyperplasia or ISR, but it promotes atherosclerotic regression both at stented and at nonstented sites.

Elucidating the Inhibitory Mechanisms of Magnolol on Rat Smooth Muscle Cell Proliferation

The pathological mechanism of percutaneous transluminal coronary angioplasty-induced restenosis has been attributed to outgrowth of vascular smooth muscle cells. Pretreatment with antioxidants has been shown to reduce restenosis. Magnolol, an active compound of Magnolia officinalis, has exhibited approximately 1,000 times more potent antioxidant effects than alpha-tocopherol. In this study, we demonstrate, using cytometric analysis, an approximate 61% reduction of smooth muscle cells progressing to the S-phase by 0.05 mg/ml of magnolol. A BrdU incorporation assay also showed a significant reduction (73%) of DNA synthesis using 0.05 mg/ml of magnolol. The protein level of the proliferating cell nuclear antigen was suppressed by approximately 48% using 0.05 mg/ml of magnolol. This was in agreement with the promoter activity of nuclear factor-kappa B, which was also attenuated by 0.05 mg/ml of magnolol. Since receptor interacting protein and caspase-3 protein expression levels were both increased by magnolol in a dose-dependent manner, the apoptotic pathway may mediate the inhibition of cell growth. Our finding that malondialdehyde formation was significantly inhibited by 0.05 mg/ml of magnolol further supported the antioxidant effect of magnolol. These studies suggest that magnolol might be a potential pharmacological reagent in preventing balloon injury-induced restenosis.

Impact of peri-stent remodeling on in-stent neointimal proliferation in acute myocardial infarction

Fifty stented lesions in 50 patients with acute myocardial infarction were studied by intravascular ultrasound (IVUS) before and just after stent implantation and at follow-up. Volumetric IVUS analyses revealed that greater peristent positive remodeling after stent implantation was associated with less neointimal proliferation and greater luminal gain at follow-up.

Drug-Eluting Stents

Coronary interventions have revolutionized the treatment of coronary artery disease (CAD). Stents, which were used initially for the complications arising from coronary angiography gradually, came to occupy a more prominent role in coronary interventions. However, restenosis remained a limiting factor from a therapeutic point of view. Recent development of drug-eluting stents is a step toward overcoming this problem. This development has elicited a great interest in both physician as well as patient communities. We have reviewed the available medical evidence regarding drug-eluting stents.