Cross-sectional Area Narrowing Research Articles

Why do Human Femoral Stents Fail? First In-man Pathology and Multimodality Imaging of Acute and Chronic Femoral Stenting in Human

Introduction: Lower extremity peripheral arterial disease (PAD) is a major cause of morbidity. Endovascular therapy remains the gold standard to treat PAD1. While pathology of coronary stenting has been well studied2, pathology of lower extremity femoral stenting remains poorly understood. The objective was to comprehensively evaluate the pathology of acute and chronic femoral stenting in symptomatic atherosclerotic patients and to understand the causes of stent failures (SF) using multi-modality imaging including micro-computed tomography (microCT). Methods: Twelve stents were obtained from 10 patients with history of PAD (mean age 74 ± 9.3; 7 male and three female); all the stented arteries underwent radiography, microCT and histologic assessment. Dissected arteries were embedded in Spurr and sawed at 3-5 mm intervals and Exact slides were prepared at 60 to 100 mm and a total of 78 sections examined following co-registration with microCT. Results are reported as median and interquartile (25 to 75th percentile, IQR). Results: Duration was 150 days (30 - 365, IQR), diameter was 5.90 mm (5.44 - 7.16, IQR) and stented length was 39.5 mm (27 - 107.5, IQR). Two of 12 stents were drug-eluting stents, 10 of 12 were bare-metal stents. Half of them were overlapping stents. Indications for stenting were intermittent claudication (40%), chronic limb ischemia (50%), and acute limb ischemia (10%). Morphometric analysis of the histologic sections showed stent success [(defined as < 75% cross sectional area narrowing and absence a thrombus (>30% narrowing from thrombus)] in 4 of 12 stents with 31.0% stenosis (22.16 - 35.0, IQR). The causes of SF in the remaining 8 were: stent-thrombosis (Figure 1), 3; in-stent restenosis, 2; and chronic total occlusions, 3, with 91.5% stenosis (78.3 - 100, IQR). Histologic malapposition3 occurred in 8 of the 12 stented lesions. Underlying nodular calcification (NC) was observed in half of the lesions, medial calcifications observed in 67% of cases with the median arch of calcification of 63° (0-283, IQR). Intimal calcification was observed in 11/12 cases, degree of calcification was 126° (38 - 248, IQR). The duration of implantation was divided into short-term (≤90 days) and long-term (>90 days) stenting. The extent of medial calcification was significantly different in short-term vs. long-term stenting [126° (18.0 - 195.8) vs 0 (0 - 2.25) respectively, p=0.003]. Malapposition (Figure 2) was observed more frequently in the short-term vs. long-term groups [50.0% (25.0 - 87.5) vs 0% (0-11.9) respectively, p=0.02]. Stent fractures were observed in 3 stents (3/11, 27.7%) and all of them were associated with SF. Also, SF had a higher medial injury score4: 2 (1 - 3, IQR) vs 1 (1 - 2, IQR), p=0.04. Conclusion: This descriptive histologic study is the first series of explanted human femoral stents, removed at surgery (n=10) and autopsy (n=2). Medial calcification and malapposition play an important role in long-term stent patency. Excessive injury and stent fracture also contributes to SF. Use of microCT in this study illustrates the advantages of high-resolution CT to detect SF, especially stent fractures. This study also enlightens the necessity to evaluate any explanted material in the future5.Figure 2Multi-modality imaging showing stent malapposition.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Disclosure: Sho Torii receives research grants from SUNRISE lab. Renu Virmani and Aloke V. Finn have received institutional research support from Abbott Vascular, Boston Scientific, Cook Medical, Cardiovascular Systems, Inc., Medtronic, and Terumo Corporation; Renu Virmani is a consultant for 480 Biomedical, Abbott Vascular, Medtronic, and W.L. Gore. Other authors report no conflicts of interest.

Human autopsy study of drug-eluting stents restenosis: histomorphological predictors and neointimal characteristics

Restenosis in drug-eluting stents (DESs) occurs infrequently, however, it remains a pervasive clinical problem. We interrogated our autopsy registry to determine the underlying mechanisms of DES restenosis, and further we investigated the neointimal characteristics of DESs and compared with bare metal stents (BMSs). Coronary lesions from patients with DES implants (n = 82) were categorized into four groups based on cross-sectional area narrowing: patent (<50%), intermediate (50-74%), restenotic (≥ 75% with residual lumen), and total occlusion (organized thrombus within the stent). Restenosis and occlusion were significantly dependent on the total stented length: restenosis (26.7 mm) and occlusion (25.7 mm) compared with patent DESs (17.3 mm). Further, restenotic and occluded lesions were located more distally in the coronary arteries and had greater vessel injury and uneven strut distribution suggesting local drug gradient. Multivariate analysis revealed that normalized maximum inter-strut distance was associated with DES restenosis (OR: 17.4, P = 0.04) while medial tear length was a predictor of DES occlusion (OR: 5.1, P = 0.03). No differences were observed between different DESs (sirolimus-, paclitaxel-, and everolimus-eluting stents) for restenosis and occlusion. Further, neointimal compositions of restenotic DESs demonstrated greater proteoglycan deposition and less smooth muscle cellularity over time, when compared with BMS with greater cell density and collagen deposition. Our study indicates the impacts of inadequate drug concentration due to wider inter-strut distance and vessel injury as primary mechanisms of DES restenosis and occlusion, respectively. Moreover, the differences in neointimal compositions between DESs and BMSs might serve as a potential target for the suppression of late neointima growth via inhibition of proteoglycans in DESs.

Quantitative Comparison of Amounts of Cross-Sectional Area Narrowing in Coronary Endarterectomy Specimens in Patients Having Coronary Artery Bypass Grafting to Amounts of Narrowing in the Same Artery in Patients with Fatal Coronary Artery Disease Studied at Necropsy

This study compares the amounts of cross-sectional area narrowing of the right coronary artery (RCA) in patients having endarterectomy of this artery at the time of coronary artery bypass grafting (CABG) to the amounts of narrowing in the same artery at necropsy in patients with fatal coronary artery disease (CAD). We examined histologically each 5-mm segment of endarterectomy specimens of the RCA in 39 patients having this procedure at the time of CABG and compared findings in them to the amounts of narrowing of 5-mm segments of the RCA in 141 patients with fatal CAD studied at necropsy. Of the 564 five-mm RCA segments in the endarterectomy patients, 371 (66%) were narrowed >75% in cross-sectional area by atherosclerotic plaque: another 112 (20%), 51% to 75%; 64 (11%), 26% to 50%, and 17 (3%), 1% to 25%. In contrast, of 2,699 five-mm segments of the RCA in 141 patients with fatal CAD, 1,217 (45%) were narrowed >75% in the cross-sectional area; another 966 (36%), 51% to 75%; 405 (15%), 26% to 50%, and 114 (4%), 1% to 25% by plaque. In conclusion, the amounts of severe narrowing found in coronary endarterectomy specimens excised at the time of CABG in live patients is at least as great as that found using the same technique in patients with fatal CAD studied at necropsy. This observation suggests that an even greater emphasis should be placed on primary prevention of atherosclerotic events and, indeed, of atherosclerotic plaques.

BILIRUBIN SUPPRESSES NEOINTIMA FORMATION BY INTERACTING WITH THE RETINOBLASTOMA TUMOR SUPPRESSOR PROTEIN PATHWAY

O386* Aims: Induction of heme oxygenase 1 (HO-1) ameliorates the development of chronic allograft arteriosclerosis, which normally involves oxidative stress and vascular smooth muscle cell (VSMC) proliferation. Bilirubin and biliverdin, generated during heme catabolism by HO-1, are potent antioxidants that play a role in maintenance of homeostasis. Based on the clinical observation that healthy individuals with higher levels of bilirubin develop less arteriosclerosis, we hypothesized that the bile pigments would inhibit VSMC proliferation in vitro and neointima formation in vivo. We used balloon injury (BI) as a model of the neointimal proliferation seen in transplant arteriosclerosis. Methods: BI was performed in the left common carotid artery of congenitally hyperbilirubinemic Gunn rats and congenic wild-type Wistar rats. The artery was harvested two weeks after BI, and neointima formation was assessed by quantifying intima/media ratio and luminal cross-sectional area narrowing (LCAN). In vitro, proliferation of primary vascular smooth muscle cells (VSMC) was measured by 3H-thymidine incorporation in the presence or absence of bilirubin/ biliverdin. Cell cycle progression was monitored by DNA content analysis; apoptosis by the Annexin V binding assay. Protein levels were detected by western blot. Immuncytochemistry was performed using antibody directed against the retinoblastoma tumor suppressor protein (pRb). Results: BI mediated neointima formation was significantly reduced in hyperbilirubinemic Gunn rats (serum bilirubin levels: 12.0 ± 2.5 mg/dl) as compared to control Wistar rats (LCAN 0.18 vs. 0.44; p < 0.05). Systemic administration of biliverdin, the precursor of bilirubin, to normal rats also suppressed neointima proliferation (LCAN 0.29 vs. 0.43; p < 0.05). In vitro, bilirubin inhibited VSMC proliferation in a dose-dependent manner. Bilirubin (200 μM) arrested VSMC cell cycle progression at the G0/G1 phase, while it did not increase apoptosis (p=0.2816). Inhibition of cell cycle progression was mediated by reduced phosphorylation of p38 MAPK and c-Jun NH2-terminal kinase 1/2 (JNK 1/2), down-regulation of cdk2, cyclins D1, E and A, and the resulting decreased phosphorylation of pRb. In nuclear extracts, lower total levels of pRb were found in bilirubin treated VSMCs, consistent with the findings that a significant portion of pRb was kept in the cytosol after bilirubin treatment as assessed by immunocytochemistry. Further, bilirubin treatment reduced expression levels of the transcription factor YY1, a zinc finger DNA-binding transcription factor known to regulate the expression of genes with important functions during cell growth and differentiation. The effects of bilirubin were independent of HO-1 expression, as demonstrated in HO-1−/− VSMCs. Conclusions: Biliverdin and bilirubin suppress both BI induced neointima formation in vivo and VSMC proliferation in vitro. Our data suggest that bilirubin treatment inhibits VSMC growth by impaired activation of p38 and JNK 1/2, resulting in two events. Firstly, the inhibition of pRb phosphorylation impedes the release of transcription factors such as YY1 that are important for VSMC growth. Secondly, there is reduced expression of the transcription factor YY1 itself, resulting in a suppressed capacity to induce DNA synthesis and transcriptional activity. Thus, administration of the bile pigments bilirubin and biliverdin may have a beneficial effect on VSMC proliferation in chronic allograft arteriopathy and may become a potent strategy for the treatment of chronic rejection.

Laryngo-Tracheal Anastomosis: Post-Operative Evaluation by Helical CT and Computerized Reformations

OBJECTIVE: Our purpose was to evaluate the role of post-operative helical computed tomography (CT) and computerized reformations in patients after laryngo-tracheal segmental resection with anastomosis. METHODS: Helical CT and computerized reformations were obtained in 11 consecutive patients who underwent laryngo-tracheal resection with anastomosis for obstruction or stenosis caused by longstanding intubation or tracheostomy. Post-operative computer assisted cross-sectional area, coronal and sagittal diameter measurements at the level of maximal narrowing of the trachea were compared with clinical assessment in all patients. The additive value of various coronal and sagittal computerized reformations over axial images was subjectively evaluated by a consensus of a thoracic radiologist and a neuroradiologist who were blinded to clinical information. RESULTS: Various degrees of restriction in daily activities were reported by patients with cross-sectional area narrowing of more than 50%, by 4/6 patients with cross-sectional area of less than 90mm2, by 4/5 and 4/6 patients with coronal or sagittal narrowing of more than 25% respectively, and by 4/5 patients with sagittal diameter of less than 12mm. All five patients with cross-sectional area stenosis of less than 50% assessed themselves as ‘asymptomatic’. Sagittal multi-planar and volume rendering reformations clarified or added additional information over axial images in all six patients with significant cross-sectional area stenosis (>50%). Volume rendering scores were significantly higher than minimal intensity projection reformations (P=0.01). CONCLUSION: Our preliminary results suggest that CT-based cross-sectional area and diameter measurements of the trachea represent a clinically helpful tool for post-operative evaluation of patients with tracheoplasty. The need for post-operative endoscopy may be obviated in some cases. Konen, E. et al. (2002). Clinical Radiology57, 820–825.

Laryngo-Tracheal Anastomosis: Post-Operative Evaluation by Helical CT and Computerized Reformations

OBJECTIVE: Our purpose was to evaluate the role of post-operative helical computed tomography (CT) and computerized reformations in patients after laryngo-tracheal segmental resection with anastomosis. METHODS: Helical CT and computerized reformations were obtained in 11 consecutive patients who underwent laryngo-tracheal resection with anastomosis for obstruction or stenosis caused by longstanding intubation or tracheostomy. Post-operative computer assisted cross-sectional area, coronal and sagittal diameter measurements at the level of maximal narrowing of the trachea were compared with clinical assessment in all patients. The additive value of various coronal and sagittal computerized reformations over axial images was subjectively evaluated by a consensus of a thoracic radiologist and a neuroradiologist who were blinded to clinical information. RESULTS: Various degrees of restriction in daily activities were reported by patients with cross-sectional area narrowing of more than 50%, by 4/6 patients with cross-sectional area of less than 90mm2, by 4/5 and 4/6 patients with coronal or sagittal narrowing of more than 25% respectively, and by 4/5 patients with sagittal diameter of less than 12mm. All five patients with cross-sectional area stenosis of less than 50% assessed themselves as ‘asymptomatic’. Sagittal multi-planar and volume rendering reformations clarified or added additional information over axial images in all six patients with significant cross-sectional area stenosis (>50%). Volume rendering scores were significantly higher than minimal intensity projection reformations (P=0.01). CONCLUSION: Our preliminary results suggest that CT-based cross-sectional area and diameter measurements of the trachea represent a clinically helpful tool for post-operative evaluation of patients with tracheoplasty. The need for post-operative endoscopy may be obviated in some cases. Konen, E. et al. (2002). Clinical Radiology57, 820–825.

Low molecular weight fucoidan prevents neointimal hyperplasia in rabbit iliac artery in-stent restenosis model.

Smooth muscle cell (SMC) proliferation within the intima is regulated by heparan sulfates. We studied a low molecular weight (LMW) fucoidan (sulfated polysaccharide from brown seaweed) on SMC proliferation in vitro and intimal hyperplasia in vivo. In vitro study revealed that LMW fucoidan reduces rabbit SMC proliferation and is internalized in SMC perinuclear vesicles. On rabbit iliac arteries perfused in vivo with fluorolabeled LMW fucoidan after angioplasty, the labeling was mainly located on sites of injury. Pharmacokinetic studies showed that LMW fucoidan exhibited in rats an elimination half-life of 56+/-25 minutes (n=8) after intravenous administration and a constant plasma rate for > or =6 hours after intramuscular administration. After stent implantation in their iliac arteries, rabbits were also treated with LMW fucoidan (5 mg/kg IM twice a day). Histomorphometric analysis at day 14 indicated that LMW fucoidan reduced intimal hyperplasia by 59% (1.79+/-0.4 versus 0.73+/-0.2 mm2, P<0.0001) and luminal cross-sectional area narrowing by 58% (0.38+/-0.08 versus 0.16+/-0.04, P<0.0001). Blood samples showed no anticoagulant activity due to LMW fucoidan. This natural polysaccharide with high affinity for SMCs and sustained plasma concentration markedly reduced intimal hyperplasia, suggesting its use for the prevention of human in-stent restenosis.

Plaque distribution and vascular remodeling of ruptured and nonruptured coronary plaques in the same vessel: an intravascular ultrasound study in vivo

OBJECTIVESThis study was designed to identify potential differences between the intravascular ultrasound (IVUS) characteristics of spontaneously ruptured and nonruptured coronary plaques.BACKGROUNDThe identification of vulnerable plaques in vivo may allow targeted prevention of acute coronary events and more effective evaluation of novel therapeutic approaches.METHODSIntravascular ultrasound was used to identify 29 ruptured plaques in arteries containing another nonruptured plaque in an adjacent segment. Intravascular ultrasound characteristics of these plaques were compared with plaques of computer-matched controls without evidence of plaque rupture. Plaque distribution was assessed by measuring the eccentricity of lumen location (inside the total vessel). Lumen cross-sectional area narrowing was calculated as [1 − (target/reference lumen area)] × 100%. A remodeling index was calculated as lesion/reference arterial area (>1.05 = compensatory enlargement, <0.95 = shrinkage).RESULTSAmong the three groups of plaques, there was no significant difference in quantitative angiographic parameters, IVUS reference dimensions and IVUS lumen cross-sectional area narrowing. There was a difference in plaque distribution; lumen location by IVUS was significantly more eccentric in ruptured than in nonruptured (p = 0.002) and control plaques (p < 0.0001). The arc of disease-free vessel wall was larger in ruptured than in control plaques (p < 0.0001). The remodeling pattern of ruptured and nonruptured plaques differed significantly from that of the control plaques (p = 0.0001 and 0.003); compensatory enlargement was found in 66%, 48%, and 17%, whereas shrinkage was found in 7%, 10% and 48%, respectively.CONCLUSIONSIntravascular ultrasound assessment of plaque distribution and vascular remodeling may help to classify plaques with the highest probability of spontaneous rupture.

Effect of percutaneous adenovirus-mediated Gax gene delivery to the arterial wall in double-injured atheromatous stented rabbit iliac arteries

Though the efficacy of intravascular gene transfer has been demonstrated in native vessels following acute injury, this methodology has not been validated in complex models of vascular injury that more closely mimic clinical angioplasty procedures. Previous studies have shown that Gax gene overexpression modulates the injury-induced remodeling of the vessel in rat carotid and normal rabbit iliac arteries. Here, we evaluated the effect of the Gax gene delivery in atheromatous stented vessels. Rabbits were fed 120 g daily of 1% cholesterol diet for 3 weeks. At 1 week they underwent initial injury on the external iliac artery, then balloon angioplasty was performed at 3 weeks at the same site with a 2.5 mm diameter channel balloon catheter (three times 1 min at 6 atm). Either saline (n = 4) or the control viral construct Ad-CMVluc (5 x 109 p.f.u.) (n = 5) or Ad-CMVGax (5 x 10(9) p.f.u.) (n = 4) was delivered with a poloxamer mixture via a channel balloon (6 atm, 30 min), and a 15 mm long Palmaz-Schatz stent (PS154) was then deployed at the site (1 min, 8 atm). Arteries were analyzed 1 month later. At 1 month, the Ad-CMVGax treated arteries exhibited a lower maximal intimal area (1. 15+/-0.1 mm2) than saline (1.87+/-0.15 mm2, P = 0.007) or Ad-CMVluc-treated vessels (1.98+/-0.31 mm2, P = 0.04). Likewise Ad-CMVGax-treated vessels displayed a lower maximal percentage cross-sectional area narrowing (35.1+/-3.5%) than saline (65.3+/-9.4%, P = 0.01) or Ad-CMVluc-treated vessels (62.7+/-6.7%, P = 0.02). Angiographic analysis revealed larger minimal lumen diameter in Ad-CMVGax treated arteries (2.0+/-0.1 mm) than saline (1.14+/-0.36 mm, P = 0.06) or Ad-CMVluc-treated vessels (1.23+/-0.25 mm, P = 0.02). Overexpression of the Gax gene inhibits neointimal hyperplasia and lumen loss in atheromatous stented rabbit iliac arteries.

Local Adenovirus-Mediated Delivery of Hirudin in a Rabbit Arterial Injury Model

Intravascular delivery of an E1/E3 deleted adenovirus encoding the hirudin protein reduces neointimal formation in the rat arterial injury model. Given the interspecies variability in response to adenoviral vectors, we tested this same construct in the hirudin-sensitive cholesterol-fed rabbit arterial balloon injury model. We hypothesized that local delivery of an E1/E3-deleted adenovirus encoding hirudin (Ad-Hir) in addition to early hirudin infusion would limit neointimal formation compared to early hirudin alone. Methods and Results: Local delivery of Ad-Hir, 2.5 × 10¹⁰ PFU/ml, using a double balloon catheter [n = 6 vessels (v)] produced a 79% reduction in vessel wall thrombin activity at 48 h after balloon angioplasty (BA) compared with vehicle (Veh, n = 6v; p = 0.05). In chronic experiments, hypercholesterolemic rabbits underwent femoral BA, and received either early hirudin alone (n = 9v) or early hirudin plus locally delivered Ad-Hir (early hirudin + Ad-Hir; n = 9v), an E1/E3-deleted adenovirus encoding β-galactosidase (early hirudin + AdGal; n = 7v), or Veh (early hirudin + Veh; n = 10v). Early hirudin + Ad-Hir did not limit the arterial response to injury versus the other groups at 4 weeks after BA. Plaque area, cross-sectional luminal area narrowing by plaque, and T cell infiltration were significantly increased in the adenovirus- versus non-adenovirus-treated arteries. Plaque area correlated with T cell density. Conclusion: Following BA in cholesterol-fed rabbits, local transduction with A-Hir produced a marked reduction in vessel wall-associated thrombin activity. However, this strategy increased rather than decreased the arterial response to BA injury. Our results suggest that the lack of therapeutic effect resulted from adenovirus-stimulated plaque formation, possibly resulting from a T cell-mediated inflammatory response.

Value of exercise electrocardiography in the detection of restenosis after coronary angioplasty in patients with one-vessel disease

Exercise treadmill testing (ETT) is considered an unreliable method for detection of restenosis after percutaneous transluminal coronary angioplasty (PTCA). The studies on which this belief is based have used quantitative coronary angiography (QCA) as a reference. The inherent limitations of angiography have been demonstrated by intravascular ultrasound (IVUS). To determine the value of ETT for detecting restenosis when IVUS criteria are used to define restenosis, we studied 29 patients with angiographically documented 1-vessel coronary disease (<35% stenosis in all nondilated segments) who underwent angioplasty. ETT was performed ≤2 weeks before follow-up angiography and IVUS imaging. Only patients without any abnormalities precluding an accurate reading of the ST segment during ETT were included. Restenosis was defined as a ≥50% diameter stenosis by QCA criteria and as a cross-sectional area narrowing of ≥75% by IVUS. The ETT was positive in 12 patients and restenosis was documented by QCA and IVUS in 38% and 48% of cases, respectively. Sensitivity, specificity, and positive and negative predictive values of ETT when QCA was used as a reference were 55%, 67%, 50%, and 71%, respectively. This corresponded to an accuracy of 62% when compared with QCA. Sensitivity, specificity, and positive and negative predictive values were 79%, 93%, 92%, and 82% when ETT was compared with IVUS, with an accuracy of 86% (p = 0.002). Thus, ETT is a reliable noninvasive method for detecting the presence of restenosis after PTCA in patients with 1-vessel coronary artery disease. The presence of ≥75% cross-sectional narrowing shown by IVUS is well correlated with ≥1-mm ST-segment depression at follow-up ETT after PTCA.

Early plus delayed hirudin reduces restenosis in the atherosclerotic rabbit more than early administration alone: potential implications for dosing of antithrombin agents.

A 2-hour infusion of r-hirudin at the time of balloon angioplasty limits restenosis in atherosclerotic rabbits. Because thrombin activity in the vessel wall after angioplasty remains high for 48 to 72 hours, we hypothesized that a second infusion of hirudin at 24 hours would reduce restenosis more than early treatment alone. Femoral atherosclerosis was induced in 35 rabbits by air desiccation injury and a high-cholesterol diet. At the time of angioplasty, rabbits were randomly assigned to 1 of 4 groups: controls: heparin bolus, saline infusion at 24 hours; early hirudin: hirudin bolus+2 hours' infusion, saline infusion at 24 hours; delayed hirudin: heparin bolus, hirudin infusion+/-bolus at 24 hours; and early+delayed hirudin: hirudin bolus+2 hours' infusion, hirudin infusion+/-bolus at 24 hours. Rabbits were euthanized after 28 days. The early+delayed hirudin treatment group had less loss of minimal lumen diameter by angiography at 28 days. By histomorphometry, cross-sectional area narrowing by plaque was least in the early+delayed treatment group compared with controls (P=0.0001), early hirudin (P=0.01), or delayed hirudin (P=0.001). The early+delayed hirudin group also had a significant reduction in absolute plaque area and an improvement in lumen area compared with the other groups. No differences were observed between treatment groups with respect to the cross-sectional area encompassed by the internal or external elastic laminae. Combined early+delayed administration of hirudin significantly reduces angiographic restenosis and cross-sectional area narrowing by plaque compared with early or late treatment alone. These results suggest that restenosis after balloon angioplasty is markedly influenced by thrombin-mediated events not only occurring early but also extending beyond the first 24 hours in this model.

PDGF-receptor tyrosine kinase blocker AG1295 selectively attenuates smooth muscle cell growth in vitro and reduces neointimal formation after balloon angioplasty in swine.

Signaling through protein tyrosine kinases (PTKs) is a major contributor to the transmission of mitogenic stimuli to the interior of the cell and nucleus. The present study was designed to determine the effect of the tyrphostin AG1295, a selective blocker of PDGF-receptor PTK, on the growth of porcine and human smooth muscle cells (SMCs) in culture, on the outgrowth kinetics of SMCs from porcine and human arterial explants, and on neointimal formation after balloon injury in pigs. SMCs for culture were obtained from porcine abdominal aortas, human internal mammary arteries, and endarterectomy tissue from a single human carotid artery. Addition of AG1295 to SMCs before PDGF stimulation completely inhibited PDGF-beta-receptor tyrosine phosphorylation without affecting the level of PDGF-beta-receptor. AG1295 resulted in a selective, reversible inhibition of SMC proliferation in culture (76%) with only mild (13.5%) inhibition of endothelial cell proliferation. The number of SMCs accumulating around explants of porcine carotid arteries and human endarterectomy specimens 12, 15, 19, 22, and 24 days after plating was reduced by 82% to 92% in AG1295-treated compared with nontreated specimens, and initiation of SMC outgrowth was markedly delayed. The numbers of cells accumulated 10 days after initiation of outgrowth were significantly lower in treated versus control explants. Local intravascular delivery of AG1295-impregnated polylactic acid-based nanoparticles (130+/-25 nm) to the site of balloon injury to porcine femoral arteries resulted in significant reductions in intima/media area ratio and luminal cross-sectional area narrowing by neointima compared with contralateral control arteries to which empty nanoparticles were applied (0.15+/-0.07 versus 0.09+/-0.03, P=.046 and 20+/-4% versus 10+/-4%, P=.0009, n=6 for both). The tyrphostin AG1295, a selective blocker of PDGF-receptor kinase, exerts a marked inhibitory effect on the activation, migration, and proliferation of porcine and human SMCs in vitro and an approximately 50% inhibitory effect on neointimal formation after balloon injury in porcine femoral arteries when delivered via biodegradable nanoparticles. Further studies appear to be warranted to evaluate the applicability of this novel approach to the interventional setting.

Predictors of luminal narrowing by neointima after angioplasty in atherosclerotic rabbits.

The present study was designed to identify the predictors of cross-sectional area narrowing by neointima (%CSAN-N) after balloon angioplasty (BA) in the cholesterol fed rabbit model. Angiographic, histomorphometric, and immunohistochemical data were analyzed from 91 femoral arteries of New Zealand white rabbits. Focal atherosclerosis was induced by air desiccation of the endothelium followed by a 2% cholesterol diet for 28 days. The rabbits received heparin (150 U/kg) at the time of BA (2.5 mm; three, 60-second, 10-atm inflations). Arteries were perfusion-fixed and excised 7 (n = 16), 14 (n = 11), 21 (n = 9), or 28 (n = 20) days after BA. Non-angioplastied arteries were de-endothelialized (cholesterol-fed [n = 12] or normal diet [n = 8]), non-injured but cholesterol-fed (n = 7), or normal (n = 8). Univariate regression across all groups showed that the absolute area of the lumen by histomorphometry (LA) correlated significantly with the area bounded by the external elastic lamina (EEL) (vessel size), but no correlation was found with the absolute area of neointima or media, the percentage disruption of the internal elastic lamina (IEL), or the percentage of neointima and media occupied by foam cells. However, %CSAN-N correlated significantly with the area bounded by the EEL, significantly with the absolute neointimal area, and negatively with the absolute LA (p < 0.0001). Significant correlations were also found between %CSAN-N and the % IEL disrupted, the area of neointima and media occupied by RAM-11 + foam cells, and the loss of alpha-actin positivity in the media (p < 0.0001). These studies show that neointimal formation contributes significantly to luminal narrowing 1 month after angioplasty in this model, that the degree of vascular injury and the extent of foam cell accumulation in the neointima and media are significant independent predictors of neointimal formation, and that the area of the neointima, and the percent narrowing by neointima, are important predictors of remodeling itself (EEL area). These predictors were not identifiable when the analysis was focused on the determinants of absolute luminal area alone.

Densitometric analysis of eccentric vascular stenoses: Comparison of CO 2 and iodinated contrast media

The authors compared the accuracies of CO2 and iodinated contrast material in the densitometric quantification of eccentric vascular stenoses. Five precision-machined eccentric phantom stenoses of 50%, 60%, 70%, 80%, and 90% cross-sectional area narrowing were integrated into a pulsatile ex vivo flow model, imaged with digital subtraction angiography (DSA), and analyzed with densitometry. Relationships between the actual and measured (densitometric) degree of cross-sectional area narrowing were evaluated by using linear regression analysis and paired Student t tests. Comparison measurements were obtained in en face and profile projections. In addition, the effect of iodinated contrast material concentration was evaluated over a range of dilutions (47-282 mg iodine per milliliter). CO2 yielded significantly more accurate results than did iodinated contrast material (282 mg iodine per milliliter) in the 50%, 60%, and 70% stenosis models when imaging was performed en face (P < .005). The best overall correlation was observed with CO2 DSA when imaging in profile (slope = 0.91, intercept = 2.42% actual stenosis, r = .99). The accuracy of densitometric stenosis estimation was inversely related to the concentration of iodinated contrast material. CO2 DSA densitometry, under the conditions of these experiments, yields quantitative measures of relative cross-sectional area narrowing that are comparable with, and under some circumstances surpass, those obtained with iodinated contrast material-based DSA. In this model, CO2 was more useful than iodinated contrast material in 50%-70% stenosis when imaging in the least-optimal plane of stenosis quantification, the en face projection.

Effect of thrombin inhibition with desulfatohirudin on early kinetics of cellular proliferation after balloon angioplasty in atherosclerotic rabbits.

Thrombin may have a pivotal role in restenosis after angioplasty. Hirudin, a potent thrombin inhibitor, reduces luminal narrowing by plaque after angioplasty in a rabbit model of atherosclerosis. Because cellular proliferation is believed to be an important mechanism for restenosis and thrombin has been shown to be a potent smooth muscle cell mitogen in vitro, we hypothesized that the mechanism of the effect of hirudin on limiting luminal narrowing by plaque occurs via inhibition of cellular proliferation. Femoral atherosclerosis was induced in 108 rabbits, and balloon angioplasty was performed. At angioplasty, group 1 rabbits (n=38) were treated with a 2-hour infusion of hirudin, and group 2 rabbits (n=41) were treated with heparin. Group 3 rabbits (n=29) were treated with hirudin (n=15) or heparin (n=14) and killed at 7 or 28 days to determine cross-sectional area narrowing by plaque and cellular proliferation with the use of bromodeoxyuridine labeling. At 29, 71, or 167 hours after angioplasty, group 1 and 2 rabbits were injected with 3H-thymidine and killed 1 hour later, and labeling indexes were determined. A significant increase in the index of 3H-thymidine-labeled nuclei was observed in the intima of "ballooned" arteries compared with "nonballooned" atherosclerotic arteries at both 30 hours (0.06+/-0.05 versus 0.01+/-0.01, P<.01) and 72 hours (0.10+/-0.06 versus 0.004+/-0.004, P<.01). By 7 days, the index of labeled cells was similar to baseline (0.04+/-0.03 versus 0.01+/-0.01, P=.12). Hirudin had no effect on the 3H-thymidine labeling indexes at any of the time points studied despite the fact that hirudin treatment in group 3 rabbits resulted in less cross-sectional area narrowing by plaque at both 7 and 28 days after angioplasty (41+/-16 versus 24+/-12 at 7 days and 60+/-21 versus 44+/-17 at 28 days, heparin versus hirudin; P<.03). Balloon angioplasty resulted in a marked increase in cellular proliferation that peaked at 72 hours. A 2-hour infusion of hirudin failed to reduce early 3H-thymidine labeling, suggesting that inhibition of cell proliferation within the first 7 days after angioplasty is not the predominant mechanism by which hirudin exerts its effect on limiting luminal narrowing by plaque 28 days after balloon angioplasty in this animal model.

Effectiveness of hirulog in reducing restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits.

Thrombin may play an important role in restenosis after balloon angioplasty (BA). Angiographic and pathologic restenosis have been shown to be reduced after BA in an atherosclerotic rabbit model using recombinant desulfatohirudin, a selective and direct thrombin inhibitor. We hypothesized that potent and specific thrombin inhibition with the synthetic peptide hirulog given intravenously at the time of angioplasty would reduce restenosis in rabbits, confirming a specific role of thrombin in restenosis. Focal femoral atherosclerosis was induced in 27 rabbits by air desiccation endothelial injury followed by a 2% cholesterol diet for 1 month. Rabbits received either heparin (150 units/kg bolus, n = 14) or hirulog (5 mg/kg bolus followed by 5 mg/kg/h for 2 h, n = 13) at the time of BA (2.5-mm balloon with three 60-second, 10-atm inflations 60 s apart). Angiograms performed before and after BA and before sacrifice were analyzed quantitatively. Rabbits were sacrificed 28 days after BA for quantitative histopathologic analysis. Minimum luminal diameter (mm) did not differ between treatment groups before (1.1 +/- 0.2 vs. 1.2 +/- 0.1 mm) or after (1.5 +/- 0.2 vs. 1.6 +/- 0.1) BA in arteries from heparin-versus hirulog-treated rabbits, respectively. At 28 days, however, minimum luminal diameter was significantly less (1.0 +/- 0.4 vs. 1.5 +/- 0.2, p = 0.0001) and percent stenosis was greater (0.46 +/- 0.25 vs. 0.22 +/- 0.08, p = 0.0002) in arteries from heparin- versus hirulog-treated rabbits, respectively. Similarly, quantitative histopathology showed less cross-sectional area narrowing by plaque in the hirulog group (56 +/- 24 vs. 42 +/- 21%, p = 0.04). A 2-hour infusion of hirulog at the time of angioplasty improved late angiographic luminal dimensions and reduced cross-sectional area narrowing by plaque in rabbits compared with heparin controls. Together with previous studies, this confirms a specific role for thrombin in restenosis after angioplasty.

Occult and frequent transmission of atherosclerotic coronary disease with cardiac transplantation. Insights from intravascular ultrasound.

Transplant coronary artery disease is a major cause of morbidity and mortality after cardiac transplantation. However, limited data exist regarding the potential contribution of coronary atherosclerosis in the donor heart to cardiac-allograft vasculopathy. We performed quantitative coronary angiography and intravascular ultrasound imaging in 50 of 62 consecutive heart-transplant recipients (40 men, 10 women, mean age, 53 +/- 9 years) 4.6 +/- 2.6 weeks after transplantation. The donor population consisted of 30 men and 20 women (mean age, 32 +/- 12 years). Ultrasound imaging visualized all three coronary arteries in 22 patients, two coronary arteries in 23, and one coronary artery in 5. Ultrasound imaging detected coronary atherosclerosis (intimal thickness > or = 0.5 mm) in 28 patients (56%). However, the angiography was abnormal in only 13 patients (26%). The sensitivity and specificity of coronary angiography were 43% and 95%, respectively. With ultrasound, the average atherosclerotic plaque thickness was 1.3 +/- 0.6 mm and the cross-sectional area narrowing was 34 +/- 16%. Atherosclerotic involvement frequently was focal (85%), eccentric (mean eccentricity index, 87 +/- 8), and near arterial bifurcations. Donors of the transplant recipients with coronary atherosclerosis were older than those without atherosclerosis (37 +/- 12 versus 25 +/- 10 years, P = .001). Maximal intimal thickness correlated with donor age (r = .54, P = .0001). Multivariate analysis demonstrated that donor age (P = .0001), male sex of donor (P = .0006), and recipient age (P = .03) were independent predictors of atherosclerosis. Coronary atherosclerosis is frequently but inadvertently transmitted by means of cardiac transplantation from the donor to the recipient. Long-term outcomes of donor-transmitted coronary artery disease will require further evaluation.

903-9 Effectiveness of Recombinant Hirulog®in Reducing Restenosis After Balloon Angioplasty in the Atherosclerotic Rabbit

Thrombin may play a central role in restenosis after balloon angioplasty (BA), and angiographic and pathologic restenosis have been shown to be reduced in the rabbit model using recombinant desulfatohirudin, a selective thrombin inhibitor. We hypothesized that an intravenous infusion of hirulog, a 20 amino acid potent and selective thrombin inhibitor, given at the time of angioplasty would reduce restenosis in the atherosclerotic rabbit model. Focal femoral atherosclerosis was induced in 27 rabbits by air desiccation endothelial injury followed by a 2% cholesterol diet for 1 month. At BA (2.5 mm balloon with three 60-second, 10 atm inflations 60 seconds apart), rabbits received either heparin (150 units/kg bolus, n = 14) or hirulog (5 mg/kg bolus followed by 5 mg/kg/hr × 2 hours, n = 13). Angiograms performed before and after BA and at 28 days were analyzed quantitatively by two blinded observers. Rabbits were sacrificed 28 days after BA, and quantitative histomorphometric analysis was performed on all vessels. The angiographic mean luminal diameters (LD) in mm were: Pre-BA Post-BA 28 Days Heparin 1.1 ± 0.2 1.5 ± 0.2 * 1.0 ± 0.4 *† Hirulog 1.2 ± 0.1 1.6 ± 0.1 * 1.5 ± 0.2 † * p = &lt; 0.05 pre vs post, post vs 28 days † p = 0.0001 heparin vs hirulog at 28 days By histomorphometric analysis, percent cross-sectional area narrowing by plaque (CSAN-P) was 56 ± 24% and 42 ± 21% in heparin-and hirulog-treated vessels, respectively (p = 0.04). In addition, 14 of 21 heparin controls but only 7 of 23 hirulog vessels had &gt; 50% CSAN-P (p = 0.03, heparin vs hirulog). In conclusion, a 2-hour infusion of hirulog at the time of angioplasty reduced angiographic restenosis as well as cross-sectional area narrowing by plaque in this atherosclerotic rabbit model.

Geometric remodeling is not the principal pathogenetic process in restenosis after balloon angioplasty. Evidence from correlative angiographic-histomorphometric studies of atherosclerotic arteries in rabbits.

Restenosis after balloon angioplasty of coronary arteries is thought to be a proliferative response of the arterial wall to injury. Recently, it has been suggested that geometric remodeling of the arterial wall, rather than intimal fibromuscular hyperplasia, may be the major pathophysiological mechanism underlying restenosis. In this study, we evaluated the relative contribution of a geometric decrease in arterial size versus neointimal growth to luminal narrowing associated with restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits. Focal femoral atherosclerosis was induced by endothelial desiccation injury followed by a 2% cholesterol diet. After 1 month on the high cholesterol diet, the animals were subjected to one of four strategies: (1) balloon angioplasty, (2) balloon angioplasty followed by treatment with the factor Xa inhibitor antistasin, (3) combined laser and balloon angioplasty, or (4) no angioplasty. Animals were killed 2 hours or 28 days after angioplasty, and excised femoral artery segments were prepared for histomorphometric analysis. Angiography was performed serially before and immediately after angioplasty and before the animals were killed. An initial postprocedural gain in luminal diameter at sites of angioplasty was followed by a significant reduction in diameter by angiography and a significant increase in luminal cross-sectional area narrowing by plaque by histomorphometry 28 days after angioplasty compared to adjacent nonangioplastied segments of the same arteries, to nonangioplastied control arteries, or to angioplastied segments of animals treated with the factor Xa inhibitor antistasin. By contrast, the overall arterial size (cross-sectional area bounded by the external elastic lamina) at sites of restenosis was not significantly different from adjacent nonangioplastied segments in the majority of arteries excised at 28 days, and the mean overall arterial size at sites of restenosis was not significantly different from corresponding segments of nonangioplastied control arteries or from angioplastied segments of animals treated with antistasin. In the minority of angioplastied arteries in which the arterial size did change, most got larger. Geometric remodeling resulting in a decrease in overall cross-sectional arterial size does not appear to be the principal pathogenetic mechanism for restenosis after balloon angioplasty with or without laser in this experimental model.