Histopathologic phenomena at the site of percutaneous transluminal coronary angioplasty: the problem of restenosis

Accelerated restitution of endothelial integrity and endothelium-dependent function after phVEGF165 gene transfer

BACKGROUND

Delinquent reendothelialization (rET) has been shown to have a permissive, if not facilitatory, impact on smooth muscle cell proliferation. This inverse relation has been attributed to certain functions of the endothelium, including barrier regulation of permeability, thrombogenicity, and leukocyte adherence, as well as production of growth-inhibitory molecules. Accordingly, the present investigation was designed to test the hypothesis that an endothelial cell (EC) mitogen could serve as the basis for a novel gene therapy strategy designed to facilitate EC regeneration, reduce neointimal thickening, and promote recovery of EC dysfunction after balloon injury.

METHODS AND RESULTS

New Zealand White rabbits underwent simultaneous balloon injury and gene transfer of one femoral artery with phVEGF165, encoding the 165-amino acid isoform of vascular endothelial growth factor (VEGF), or pGSVLacZ. In each animal transfected with phVEGF165 or pGSVLacZ, the contralateral femoral artery was also subjected to balloon injury but not to gene transfer. For pGSVLacZ, rET remained incomplete at 4 weeks after transfection; in contrast, phVEGF165 produced prompt rET, which was 95% complete by 1 week. Furthermore, rET in the contralateral, balloon-injured, nontransfected limb of the VEGF group was similarly accelerated. Consequently, intimal thickening was diminished, thrombotic occlusion was less frequent, and recovery of EC-dependent vasomotor reactivity was accelerated in VEGF transfectants compared with control animals. A similar benefit was observed for the contralateral, balloon-injured, nontransfected limb.

CONCLUSIONS

Catheter-mediated, site-specific arterial gene transfer of phVEGF165 can accelerate rET at local and remote sites, leading to inhibition of neointimal thickening, reduction in thrombogenicity, and restoration of endothelium-dependent vasomotor reactivity. These findings support the notion that gene transfer encoding for an EC-specific mitogen may be useful for preventing the complications, including restenosis, of balloon angioplasty.

Coronary artery and saphenous vein graft remodeling: A review of histologic findings after various interventional procedures--Part III

Catheter balloon angioplasty is a well accepted form of nonsurgical treatment of acutely and chronically obstructed coronary artery vessels. It is also the centerpiece for various new intervention techniques. Their morphologic effects on the site of obstruction has been termed "remodeling." Part III of this six-part series focuses on intimal proliferation and chronic recoil in patients undergoing previous remodeling techniques by balloon angioplasty.

Gamma radiation effect on vascular smooth muscle cells in culture

PURPOSE

Prior work in our laboratory demonstrated that external gamma irradiation administered within 48 h following balloon catheter carotid artery injury in rats produced a marked inhibition of intimal hyperplasia and restenosis. The current study used smooth muscle cells (SMC) in vitro to examine the radiation dose response and to investigate the cellular mechanism by which radiation inhibits SMC proliferation.

METHODS AND MATERIALS

Quiescent rat aortic SMC in plasma were refed with whole blood serum to stimulate synchronous proliferation and immediately irradiated with single fraction doses of 1.25-20 Gy.

RESULTS

Comparison between a micronucleus assay and a clonogenic assay indicated a dose-dependent inhibition of SMC growth, with an ED50 at 2-3 Gy. The micronucleus assay also demonstrated a dose-dependent increase in apparent chromosomal damage at 72 h after irradiation. Inhibition of SMC growth by radiation did not correlate with changes in intracellular or released mitogenic activity. Furthermore, there was no evidence of apoptosis in irradiated SMC up to 96 h after treatment.

CONCLUSION

Radiation likely inhibits SMC proliferation after arterial injury by a dose-dependent mechanism of lethal and/or sublethal cellular injury leading to clonogenic cell death.

Stents wrapped in autologous vein: an experimental study

OBJECTIVES

A new type of coated stent, consisting of a conventional stent covered by an autologous vein graft, was developed at our institution.

BACKGROUND

Coated stents are under investigation to address stenting limitations. However, experimental implantation of coated stents covered by autologous tissue has not been reported.

METHODS

An autologous vein graft was removed and carefully prepared. Subsequently, a Palmaz stent was covered by the vein graft both internally and externally. Twenty-seven stents were implanted in the normal iliac arteries of 27 pigs weighing 18 to 33 kg. In 15 of the pigs, 15 noncoated Palmaz stents were implanted in the contralateral artery; these animals served as the control group. The animals were followed up angiographically for a period ranging from 7 days to 6 months. At the time of death, the stented segments were removed, and histomorphometric analysis was performed.

RESULTS

Autologous vein graft-coated stent preparation and implantation was feasible and uncomplicated. In both stents, angiographic follow-up revealed the absence of thrombosis, except for two cases of subacute thrombosis in the control group. The thickness of the intimal layer was greater in the coated stents and seems to be due to the existence of the internal vein layer ([mean +/- SD] 0.57 +/- 0.12 vs. 0.27 +/- 0.13 mm, p = 0.001). The arterial media of the coated stent segments was thinner than that in the control group (0.14 +/- 0.03 vs. 0.18 +/- 0.01 mm, p = 0.02).

CONCLUSIONS

The autologous vein graft-coated stent seems to be nonthrombogenic, and only minimal hyperplasia was observed in the pigs. Further studies are needed to explore the efficacy of this technique in humans.

Arterial remodeling after coronary angioplasty: a serial intravascular ultrasound study

BACKGROUND

Restenosis occurs after 30% to 50% of transcatheter coronary procedures; however, the natural history and pathophysiology of restenosis are still incompletely understood.

METHODS AND RESULTS

Serial (postintervention and follow-up) intravascular ultrasound imaging was used to study 212 native coronary lesions in 209 patients after percutaneous transluminal coronary angioplasty, directional coronary atherectomy, rotational atherectomy, or excimer laser angioplasty. The external elastic membrane (EEM) and lumen cross-sectional areas (CSA) were measured; plaque plus media (P+M) CSA was calculated as EEM minus lumen CSA. The anatomic slice selected for serial analysis had an axial location within the target lesion at the smallest follow-up lumen CSA. At follow-up, 73% of the decrease in lumen (from 6.6+/-2.5 to 4.0+/-3.7 mm2, P<.0001) was due to a decrease in EEM (from 20.1+/-6.4 to 18.2+/-6.4 mm2, P<.0001); 27% was due to an increase in P+M (from 13.5+/-5.5 to 14.2+/-5.4 mm2, P<.0001). Delta Lumen CSA correlated more strongly with delta EEM CSA (r=.751, P<.0001) than with delta P+M CSA (r=.284, P<.0001). Delta EEM was bidirectional; 47 lesions (22%) showed an increase in EEM. Despite a greater increase in P+M (1.5+/-2.5 versus 0.5+/-2.0 mm2, P=.0009), lesions exhibiting an increase in EEM had (1) no change in lumen (-0.1+/-3.3 versus 3.6+/-2.3 mm2, P<.0001), (2) a reduced restenosis rate (26% versus 62%, P<.0001), and (3) a 49% frequency of late lumen gain (versus 1%, P<.0001) compared with lesions with no increase in EEM.

CONCLUSIONS

Restenosis appears to be determined primarily by the direction and magnitude of vessel wall remodeling (delta EEM). An increase in EEM is adaptive, whereas a decrease in EEM contributes to restenosis.

Vascular repair mechanisms after directional atherectomy or percutaneous transluminal coronary angioplasty in atherosclerotic rabbit iliac arteries

Although directional atherectomy (DA) reduces the plaque burden, successful revascularization is not associated with a reduced restenosis rate when compared with percutaneous transluminal coronary angioplasty (PTCA). The purpose of this study was to compare and contrast the vascular response to DA-induced and PTCA-induced injury. Six to 8 weeks after induction of atherosclerosis, PTCA (n = 34) was performed in one iliac artery and DA in the other (n = 30). Arteries were obtained at 6 time points: 1, 3, 5, 7, 14, and 28 days. Eleven arteries that did not undergo an intervention acted as controls. Radiograms obtained before and after intervention and at euthanization were compared. Morphometric, histologic, and immunohistochemical analyses were performed. Both PTCA and DA resulted in an immediate increase in luminal diameter that subsequently decreased over the ensuing month. PTCA caused deep dissection (7 of 8 arteries), often extending to the adventitia, whereas stand alone DA resulted in deep cleft formation (4 of 5). Of the 30 arteries that underwent DA, 4 exhibited an increase in luminal diameter in the absence of tissue retrieval. Thrombus was observed in both the dissection planes and the clefts within the first 7 days, and cellular ingrowth was appreciated at 5 to 7 days. By 7 days the artery was repaired, and the histologic appearance of the arteries that had undergone PTCA could not be differentiated from the arteries that had undergone DA. Increased intimal and medial collagen and elastin was noted at 14 and 28 days. An increase in the area bordered by the external elastic lamina was observed in both groups. Although successful DA results in tissue removal and the production of a deep tissue cleft and PTCA causes a dissection, both produce a condition in which the arterial injury exposes the arterial media to blood, causing thrombus formation and inflammation with subsequent cellular accumulation into the thrombotic framework.

Remodeling rather than neointimal formation explains luminal narrowing after deep vessel wall injury: insights from a porcine coronary (re)stenosis model

BACKGROUND

Oversized balloon dilatation of normal porcine coronary arteries usually heals without stenosis formation.

METHODS AND RESULTS

With the purpose of developing a stenotic model and examining the mechanisms of luminal narrowing after angioplasty, we produced a circumferential deep vessel wall injury by inflating and withdrawing an oversized chain-encircled angioplasty balloon in the left anterior descending coronary artery (LAD) of 20 pigs. Three pigs died and did not complete the study. In 8 pigs (group 1), serial coronary arteriography was performed. The lumen diameter (mean+/-SD) before dilation was 3.4 +/- .4 mm; after dilation, 4.2 +/- 0.6 mm; and at follow-ups 2 and 4 weeks later, 1.6 +/- 0.4 mm (P<.0001). In 9 pigs (group 2) examined postmortem 3 weeks after dilatation, histology revealed that the injury was deep (out to adventitia) in all arteries and completely circumferential (360 degrees) in all but two arteries. Adventitia was markedly thickened as a result of neoadventitial formation. Injury correlated strongly with neointimal formation (middle LAD, r=.71, P=.00001, but neither injury nor neointima correlated with lumen size (r=.14, P=.46 and r=.34, P=.07, respectively); ie, neointimal formation did not explain late luminal narrowing. Lumen size, however, did correlate strongly with vessel size (r=.74, P=000005). The late loss in lumen diameter observed angiographically in group 1 substantially exceeded that caused by neointimal formation seen by histology in group 2.

CONCLUSIONS

The chain-encircled angioplasty balloon produced a circumferential deep vessel wall injury that healed by luminal narrowing. In this porcine model, arterial remodeling was more important than neointimal formation in late luminal narrowing.

Intracoronary low-dose beta-irradiation inhibits neointima formation after coronary artery balloon injury in the swine restenosis model

BACKGROUND

Neointima formation contributing to recurrent stenosis remains a major limitation of percutaneous transluminal angioplasty. Endovascular low-dose gamma-irradiation has been shown to reduce intimal thickening (hyperplasia) after balloon overstretch injury in pig coronary arteries, a model of restenosis. The objective of this study was to determine whether the use of a beta-emitting radioisotope for this application would have similar effects and to examine the dose-response relations with this approach.

METHODS AND RESULTS

Normal domestic pigs underwent balloon overstretch injury in the left anterior descending and left circumflex and coronary arteries. A flexible catheter was introduced by random assignment into one of these arteries and was afterloaded with a 2.5-cm ribbon of encapsulated 90Strontium/90Yttrium sources (90Sr/Y, a pure beta-emitter). It was left in place for a period of time sufficient to deliver one of four doses: 7, 14, 28, or 56 Gy, to a depth of 2 mm. Animals were killed 14 days after balloon injury, the coronary vasculature was pressure-perfusion fixed, and histomorphometric analysis of arterial cross sections was performed. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area to medial fracture length was inversely correlated with increasing radiation dose: control (no radiation), 0.47; 7 Gy, 0.34; 14 Gy, 0.20; 28 Gy, 0.08; and 56 Gy, 0.02 (r = -.78, P < .000001). Scanning electron microscopy demonstrated a confluent layer of endothelium-like cells both in control and in 14 Gy-irradiated arteries. There was neither evidence of significant necrosis nor excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in the irradiated groups. Furthermore, the exposure to the staff and the total body exposure to the pig with the beta source was a small fraction of the dose previously measured and calculated with 192Ir, a gamma-emitting radioisotope.

CONCLUSIONS

Administration of endovascular beta-radiation to the site of coronary arterial overstretch balloon injury in pigs with 90Sr/Y is technically feasible and safe. Radiation doses between 7 and 56 Gy showed evidence of inhibition of neointima formation. A dose-response relation was demonstrated, but no further inhibitory effect was seen beyond 28 Gy. These data suggest that intracoronary beta-irradiation is practical and feasible and may aid in preventing clinical restenosis.

Smooth muscle cell proliferation is proportional to the degree of balloon injury in a rat model of angioplasty

BACKGROUND

A variable degree of smooth muscle cell (SMC) proliferation after balloon injury has been reported in previous rat studies. It is unknown whether balloon injury induces c-fos expression and whether it is related to the degree of vascular injury in vivo. Therefore, we tested the hypothesis that proportional increases in neointimal formation and c-fos expression might be present after different degrees of balloon dilation.

METHODS AND RESULTS

Angioplasty of the carotid artery was performed with a balloon catheter. Vascular injury was evaluated at 0, 0.5, 1.0, 1.5, and 2 atm (n = 6 for all). In 40 additional rats, total RNA dot blots were performed to assess the effect of various degrees of balloon injury on c-fos expression. SMC proliferation proportional to the increases of inflation pressure was found between 0 and 2 atm with neointimal areas of 0.002 +/- 0.002, 0.069 +/- 0.014, 0.128 +/- 0.043, 0.190 +/- 0.010, and 0.255 +/- 0.041 mm2, respectively. When the degree of SMC proliferation (neointima and neointima/media ratio) was plotted against balloon inflation pressure, a linear relation was observed (r = .733, P < .001 and r = .755, P < .001, respectively). An increase in c-fos expression proportional to the degree of injury was found 30 minutes after injury.

CONCLUSIONS

Neointimal proliferation produced by balloon injury is related to balloon inflation pressure, supporting the concept of an SMC proliferative response proportional to the degree of injury. The increase in SMC proliferation is associated with a proportional increase in the early expression of the c-fos nuclear proto-oncogene.

Spontaneous regression of restenosis: an angiographic study

OBJECTIVES

This study was designed to examine the possibility that spontaneous regression in stenosis severity occurs over time in patients with restenosis after percutaneous transluminal coronary angioplasty.

BACKGROUND

The underlying mechanisms of restenosis are intimal hyperplasia and smooth muscle cell proliferation in response to vascular injury. We hypothesized that the initial hyperplastic response is followed by dynamic remodeling and eventual spontaneous regression, leading to stabilization or a reduction in stenosis severity.

METHODS

A total of 136 patients participated in a trial to evaluate the efficacy of fish oil versus placebo in preventing restenosis after angioplasty. One hundred thirteen patients completed this study with angiographic follow-up, of whom 56 had restenosis. Of these, 19 were asymptomatic and did not undergo repeat revascularization; 15 consented in a separate study to undergo repeat angiography, which was performed 6 to 25 months later to assess the possibility of regression.

RESULTS

There was a significant mean (+/- SD) decrease in lesion severity from 66.9 +/- 8.7% to 47.5 +/- 9.0% (p < 0.0001) and a significant mean increase in minimal lumen diameter from 0.91 +/- 0.31 mm to 1.44 +/- 0.35 mm (p < 0.0001). No patient showed progression of stenosis, but regression of restenosis, defined as a decrease in minimal lumen diameter > or = 0.2 mm, was noted in 12 of the patients.

CONCLUSIONS

Although all 15 study patients were asymptomatic, similar changes may occur in symptomatic patients. A trial of medical therapy may be appropriate in asymptomatic or mildly symptomatic patients before further interventions. This strategy would avoid unnecessary invasive procedures, prevent a "restenosis cycle" and result in significant cost savings.

Apoptosis in human atherosclerosis and restenosis

BACKGROUND

Apoptosis has been recognized in normal, including rapidly proliferating, cell populations and is inferred to be potentially responsible for the maintenance of stable cell numbers in tissues with various degrees of proliferative activity. Previous studies performed in rats indicated that despite the persistence of a relatively high level of injury-induced proliferative activity, total arterial smooth muscle content at 12 weeks remained unchanged from that measured at 2 weeks, suggesting that accrual of vascular smooth muscle cells is mitigated by cell death. The extent to which apoptosis may be observed in human atherosclerosis and/or restenosis, however, has not been previously established.

METHODS AND RESULTS

We performed immunohistochemical studies on 56 specimens retrieved from patients undergoing directional atherectomy for primary atherosclerotic lesions or recurrent arterial narrowing after percutaneous revascularization (restenosis). Immunohistochemical staining disclosed evidence of apoptosis in 35 (63%) of the 56 specimens studied. When present, immunohistochemical evidence of apoptosis was typically limited to < 2% of cells in the specimen. The finding of apoptosis, however, was not distributed equally among four groups of specimens studied. Specimens retrieved from patients with restenosis were more frequently observed to contain foci of apoptosis than specimens retrieved from patients with primary atherosclerotic lesions. Among 14 peripheral arterial specimens from patients with restenosis, 13 (93%) contained foci of apoptosis; in contrast, apoptosis was observed in only 6 (43%) of 14 peripheral specimens from patients with primary lesions (P = .0046). Among coronary arterial specimens, apoptosis was observed in 12 (86%) of 14 specimens from patients with restenosis versus 6 (29%) of 14 specimens from patients with primary obstructions (P < .0075).

CONCLUSIONS

Apoptosis is a feature of human vascular pathology, including restenotic lesions and, to a lesser extent, primary atherosclerotic lesions. The findings of the present study suggest that apoptosis may modulate the cellularity of lesions that produce human vascular obstruction, particularly those with evidence of more extensive proliferative activity.

Restenosis after experimental angioplasty. Intimal, medial, and adventitial changes associated with constrictive remodeling

Predicting and preventing arterial restenosis after angioplasty has failed despite considerable research into mechanisms and techniques. We examined the roles of chronic constriction, neointimal-medial growth, and adventitial changes in restenosis in atherosclerotic rabbits. Angioplasty was performed on femoral artery lesions 4 weeks after lesion induction by air drying and cholesterol-supplemented diet. Angiographic and histological evaluation was conducted 3 to 4 weeks after angioplasty. The angiographic minimum luminal diameter (MLD) increased from 1.31 +/- 0.21 to 1.73 +/- 0.41 mm after angioplasty. Loss in MLD by 3 to 4 weeks was 0.95 +/- 0.64 mm. Initial gain and late loss correlated (P = .008). Late residual stenosis, defined histologically as the difference between the luminal areas of a proximal reference site and lesion site normalized by the luminal area of the reference site, was 52 +/- 32%. Histological indices of chronic constriction, neointimal-medial growth, and adventitial growth were defined on the basis of the areas of these arterial wall layers at the lesion site relative to the reference site. Another parameter defined as the ratio of adventitial area to the area of intima+media at the lesion site allowed evaluation of the relative importance of these layers. Surprisingly, late residual stenosis correlated with chronic constriction (P = .0003) but not with neointimal-medial growth or adventitial growth. The ratio of adventitial area to the area of intima+media at the lesion site also correlated with chronic constriction (P = .01). These findings suggest that factors related to arterial remodeling rather than neointimal-medial growth may dominate the response to angioplasty.

Intracoronary irradiation markedly reduces neointimal proliferation after balloon angioplasty in swine: persistent benefit at 6-month follow-up

OBJECTIVES

This study examined the long-term efficacy of intracoronary irradiation for limiting neointimal proliferation after overstretch balloon angioplasty in a porcine model of restenosis. In addition, this study sought to identify any adverse late sequelae of this novel therapy for restenosis.

BACKGROUND

Restenosis after coronary angioplasty represents in part a proliferative response of vascular smooth muscle at the site of injury. We have shown previously that high dose intracoronary radiation induces focal medial fibrosis and markedly reduces neointimal proliferation early after balloon angioplasty in swine.

METHODS

Twenty-two juvenile swine underwent intervention at a target segment of the left coronary artery. In 11 swine, a 2-cm ribbon of iridium-192 was positioned at the target segment and 2,000 cGy was delivered to the vessel wall. Subsequently, overdilation balloon angioplasty was performed at the irradiated segment. In 11 control swine, overdilation balloon angioplasty was performed without previous irradiation. Twenty animals survived and underwent histopathologic analysis at 180 +/- 8 days.

RESULTS

Mean (+/- SD) neointimal area was 1.59 +/- 0.78 and 0.46 +/- 0.35 mm2 (p < 0.001) in control and irradiated animals, respectively. Mean percent area stenosis was 37.9 +/- 12.4% and 14.2 +/- 9.0% (p < 0.001) in the control and irradiated animals, respectively. Thus, by 6-month follow-up, intracoronary irradiation before balloon angioplasty had reduced the bulk of the neointimal lesion by 71.1% and reduced percent area stenosis by 62.5% compared with that in control animals. There was no evidence of radiation vasculopathy or myocardial damage at 6 months.

CONCLUSIONS

Intracoronary irradiation (2,000 cGy) produces persistent impairment of neointimal proliferation 6 months after balloon injury, with no evidence of late radiation sequelae.

Endovascular low-dose irradiation inhibits neointima formation after coronary artery balloon injury in swine. A possible role for radiation therapy in restenosis prevention

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty remains a major limitation of the long-term success of this procedure. Restenosis is a form of wound healing. Low-dose ionizing radiation has been effective in inhibiting exuberant wound healing responses in a variety of clinical situations.

METHODS AND RESULTS

Vascular neointimal lesions resembling human restenosis were created in the coronary arteries of normal pigs by overstretch balloon angioplasty injury. To test the effect of low-dose endovascular gamma radiation on lesion formation, a high-activity 192Ir source was introduced into one of the injured arteries in each animal and left in place for a period sufficient to deliver one of three doses: 350, 700, or 1400 cGy. To test potential benefits of delayed irradiation, 700 cGy was given in another group 2 days after injury. Animals were killed 14 days after balloon injury and the coronary vasculature was pressure-perfusion fixed. To test the late effect and safety of endovascular low-dose irradiation, 700 or 1400 cGy was given in miniswine coronary arteries after injury as well as in noninjured carotid arteries; this group was followed up for 6 months. Tissue sections were measured by computer-assisted planimetry. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area-to-medial fracture length (IA/FL) was inversely correlated with the different radiation doses: control, 0.59; 350 cGy, 0.38; 700 cGy, 0.42; and 1400 cGy, 0.17 (r = -0.75, P < .0001). Delay of 700-cGy irradiation for 2 days after injury significantly decreased neointima formation compared with the same dose given immediately after injury. Analysis of long-term specimens showed reduction of IA/FL in the arteries irradiated with 700 cGy (0.3, P = .009) and 1400 cGy (0.31, P = .001) compared with control arteries (0.50). There was no excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in pigs that received radiation compared with control animals.

CONCLUSIONS

Low-dose intracoronary irradiation delivered to the site of coronary arterial overstretch balloon injury in pigs inhibited subsequent intimal thickening (hyperplasia). A dose-response relationship was demonstrated, and delay of treatment for 48 hours appeared to augment the inhibitory effect. Six months of follow-up without fibrosis or arteriosclerosis demonstrated the durability of the beneficial effect in the treated group. These data suggest that intracoronary irradiation therapy may aid in preventing clinical restenosis.

Effect of alpha-tocopherol on restenosis after angioplasty in a model of experimental atherosclerosis

The ability of alpha-tocopherol to reduce restenosis after angioplasty was tested in a rabbit model in which angioplasty was performed on established atherosclerotic lesions. Lesions induced by 4 wk of cholesterol feeding after focal desiccation of femoral arteries were balloon dilated. 3 wk after angioplasty, angiographically determined minimum luminal diameters were less in the untreated group (0.80 +/- 0.51 mm) than in the group treated with oral alpha-tocopherol beginning 19 d before angioplasty (1.38 +/- 0.29 mm; P < 0.01). The cross-sectional area of the intima-media was greater in the untreated group (1.18 +/- 0.48 mm2) than in the alpha-tocopherol group (0.62 +/- 0.25 mm2, P < 0.0001). These differences were not due to vasoconstriction or altered plasma cholesterol. Alpha-tocopherol thus reduced restenosis after angioplasty in this model. In rabbit vascular smooth muscle cells, oxidized low density lipoprotein stimulated DNA synthesis. Alpha-tocopherol treatment inhibited DNA synthesis stimulated by oxidized low density lipoprotein, but not by serum. The findings are consistent with the hypothesis that oxidized lipids can stimulate hyperplasia and that antioxidants may limit hyperplasia by inhibiting either the oxidation or the proliferative effects of oxidants on cells.

Adult respiratory distress syndrome complicating intravenous infusion of low-molecular weight dextran

Respiratory failure is one of the most uncommon and serious adverse drug reactions. Low-molecular-weight-dextran (Dextran-40) is a useful adjunctive anti-platelet agent in the setting of coronary angioplasty and intracoronary stent placement. We report the occurrence of the adult respiratory distress syndrome following intravenous infusion of Dextran-40.

Differences in compensatory vessel enlargement, not intimal formation, account for restenosis after angioplasty in the hypercholesterolemic rabbit model

BACKGROUND

In de novo human atherosclerosis, compensatory vessel enlargement limits the effect of intimal plaque formation on lumen narrowing. We hypothesized that arterial remodeling may also play an important role in determining the chronic lumen size after angioplasty and tested this hypothesis using the hypercholesterolemic rabbit iliac artery angioplasty model.

METHODS AND RESULTS

Morphometric analysis of histological cross-sectional areas of vessels from animals killed immediately after angioplasty (acute group, n = 11) were compared with the same areas from animals killed 4 weeks after the procedure (chronic group, n = 37), when restenosis occurs in this model. The area circumscribed by the internal elastic lamina (IEL) increased by 20% from acute to 4 week follow-up after angioplasty (acute group, 2.36 +/- 0.45 mm2, chronic group, 2.84 +/- 0.89 mm2). Over the same time period, intimal area increased by 0.82 mm2. Despite this increase in intimal area, lumen area decreased by only 0.34 mm2 because of the compensatory enlargement of the IEL area. In the chronic group, polynomial regression analysis revealed a quadratic relation between intimal area and lumen area (R2 = .35, P < .001). A lumen area of 0.45 mm2 (the nadir of the quadratic relation) was used to divide the chronic group into two subgroups: restenotic (n = 21; lumen area, < 0.45 mm2) and nonrestenotic (n = 16; lumen area, > 0.45 mm2). By definition, there was a significant difference in lumen area between the two subgroups (0.15 +/- 0.15 mm2 for restenotic; 0.73 +/- 0.18 mm2 for nonrestenotic). Surprisingly, the intimal areas in the two subgroups were virtually identical (2.41 +/- 0.92 mm2 for restenotic, 2.49 +/- 0.69 mm2 for nonrestenotic, P = NS). The difference in the lumen area between restenotic and nonrestenotic vessels was a result of the significantly greater IEL area in the nonrestenotic subgroup (3.22 +/- 0.83 mm2 for nonrestenotic, 2.56 +/- 0.84 mm2 for restenotic, P < .05). In both restenotic and nonrestenotic vessels, the IEL area increased with increases in intimal area. In the restenotic arteries, the slope of this correlation was < 1, showing inadequate compensatory enlargement for the intimal plaque. In the nonrestenotic vessels, the slope was > 1, limiting the effect of intimal plaque on luminal narrowing.

CONCLUSIONS

These data indicate that the iliac artery in an atherosclerotic rabbit model compensates for intimal formation after angioplasty by vessel enlargement. Furthermore, the degree of vessel enlargement is more important than intimal area in determining the chronic lumen size.

Intracoronary irradiation markedly reduces restenosis after balloon angioplasty in a porcine model

OBJECTIVES

This study examined the effects of intracoronary irradiation on neointimal proliferation after overstretch balloon angioplasty in a normolipemic swine model of restenosis.

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty represents, in part, a proliferative response of vascular smooth muscle at the site of injury. We have previously shown that ionizing radiation, delivered by means of an intracoronary source, causes focal medial fibrosis. We therefore hypothesized that intracoronary irradiation delivered at the time of balloon angioplasty might impair the restenosis process.

METHODS

Nineteen juvenile swine underwent coronary angiography; a segment of the coronary artery was chosen as a target for balloon injury. In 10 swine, a ribbon of iridium-192 was positioned at the target segment, and 2,000 cGy was delivered at the vessel wall. Subsequently, overdilation balloon angioplasty was performed at the irradiated segment. In nine control swine, overdilation balloon angioplasty was performed without previous irradiation. Eighteen animals survived and were killed at 30 days. Histopathologic analysis was performed by a pathologist in blinded manner. The area of maximal lumen compromise within the target segment was analyzed by computer-assisted planimetry.

RESULTS

In the control group, mean (+/- SD) neointimal area was 0.84 +/- 0.60 mm2 compared with that in the irradiated group, 0.24 +/- 0.13 mm2 (p = 0.01). In the control group, mean percent area stenosis was 47.6 +/- 20.7%, whereas that in the irradiated group was 17.6 +/- 10.5% (p = 0.001). This represents a 71.4% reduction in neointimal area and a 63.0% reduction in percent area stenosis in the irradiated group. Adjacent coronary segments and surrounding myocardium were unaffected.

CONCLUSIONS

Intracoronary irradiation (2,000 cGy) delivered to a target porcine coronary segment before balloon overdilation markedly reduces neointima formation at 30 days and thus significantly impairs the restenosis process.

Differential neointimal response to coronary artery injury in pigs and dogs. Implications for restenosis models

Neointimal hyperplasia occurs in the coronary arteries after percutaneous revascularization procedures and is a reparative response that frequently causes recurrent stenosis. Prior animal studies have shown that neointimal tissue thickness is proportional to the depth of arterial injury. Because animal models are increasingly used to test therapeutic strategies against restenosis, the purpose of this study was to evaluate the degree of neointimal thickening formed in the coronary arteries of pigs compared with dogs in response to severe injury. Fourteen coronary arteries in six mongrel dogs and 18 coronary arteries in nine pigs underwent severe arterial injury using tantalum metal coils delivered on oversized angioplasty balloons. Animals were killed after 4 weeks, and all coronary arteries were pressure perfusion fixed. Mean histological injury scores and neointimal thicknesses for dogs were 1.9 +/- 0.3 and 0.30 +/- 0.11, respectively, compared with 2.1 +/- 0.7 and 0.71 +/- 0.36 for pigs. Thus, there was significantly less neointimal thickening in dogs compared with pigs (P < .001) despite no differences in injury (P = NS). The neointimal thickening differences translated into significantly different percent area stenoses: 55 +/- 24% for pigs versus 27 +/- 13% for dogs (P < .001). Linear regression modeled neointimal thickness versus injury assessed by an ordinal injury score proportional to the depth of injury for each species. This analysis confirmed the differences across multiple injury levels. The slope of the regression line for dogs was small, suggesting that no relation may exist between injury and neointimal thickness in this species. The pig may be a more appropriate model for the study of the genesis of stenosing neointima.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma irradiation inhibits neointimal hyperplasia in rats after arterial injury

BACKGROUND AND PURPOSE

Restenosis complicates a significant proportion of endovascular and open vascular procedures such as carotid endarterectomy. In contrast to the primary atheroma, restenosis is characterized by intimal hyperplasia of vascular smooth muscle cells. We hypothesized that gamma radiation would reduce restenosis by limiting intimal hyperplasia after arterial injury.

METHODS

To demonstrate the effect of gamma radiation on smooth muscle hyperplasia in vivo, a standardized bilateral carotid balloon catheter arterial injury was produced in 37 rats. A single dose of 750, 1500, or 2250 cGy (1cGy = 1 rad) gamma radiation was delivered to the right carotid artery at either 1 or 2 days after injury; the shielded contralateral carotid artery served as matched control. At 21 days after injury, vessels were perfusion-fixed in situ, and cross-sectional area of neointima was determined from axial sections using image analysis.

RESULTS

Marked reductions in neointimal cross-sectional area were demonstrated in vessels subjected to 1500- and 2250-cGy radiation at both 1 and 2 days after injury. A less prominent effect was noted for 750 cGy, reaching statistical significance only at 2 days after injury. By two-way ANOVA, radiation dose (P = .0002), timing of radiation delivery (P = .003), and an interaction between timing and dose (P = .0278) were significantly associated with reduction in neointimal cross-sectional area. At 1500 cGy, delivery of radiation 1 day after injury inhibited neointimal hyperplasia more prominently than the same dose 2 days after injury; a dose-response relation was evident at 1 day.

CONCLUSIONS

Radiation may be an important adjunctive therapy for reducing the incidence of restenosis after angioplasty or endarterectomy.

Relative significance of endothelium and internal elastic lamina in regulating the entry of macromolecules into arteries in vivo

A role for the internal elastic lamina (IEL), which separates the intima and media of an artery wall, as a restrictive barrier to macromolecular movement has been suggested in atherosclerotic lesion development or restenosis during angioplasty. The permeability coefficient of the IEL, however, has never been quantified in unperturbed vessels in vivo. Using a newly developed technique, we measured the concentration distributions in both intima and media of cationic (pI approximately 8.5) and anionic (pI approximately 6.3) isozymes of the 44-kD macromolecule horseradish peroxidase (HRP). Two mathematical models of arterial wall transport differing in their resolution of the intima were required to simulate the concentration distribution data and to estimate the parameters of interest. Optimal estimates of the permeability coefficients of the endothelium (PE) and IEL (PIEL) to HRP were determined by the best least-squares fit of the two models to experimental data. These estimates (anionic: PE = 0.050 +/- 0.021 microns/min, PIEL = 0.146 +/- 0.082 microns/min, n = 8; cationic: PE = 0.034 +/- 0.018 microns/min, PIEL = 0.110 +/- 0.047 microns/min, n = 8) indicate that the IEL is responsible for approximately 25% (anionic, 26 +/- 9%; cationic, 25 +/- 13%) of the resistance to HRP transport from the blood into the arterial media. Although both parameters were less for the cationic preparation, the differences were not significant, and the relative role of the IEL was similar for both molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary angioplasty from the perspective of atherosclerotic plaque: morphologic predictors of immediate success and restenosis

High restenosis rates continue to plague the overall efficacy of percutaneous transluminal coronary balloon angioplasty (PTCA). It is not surprising that predictions of long-term success or failure of PTCA based on coronary angiography are of limited value because these images provide only a circumscribed view of the arterial lumen and offer little insight into underlying plaque morphologic characteristics. Coronary atherosclerotic lesions are quite diverse with respect to plaque characteristics (eccentricity, concentricity, and extent of fibrosis, necrosis, and calcification) and cardiac ischemic syndromes (stable angina, unstable angina, myocardial infarction, and sudden cardiac death). It could thus be expected that dissimilar plaques will respond differently to balloon dilatation, and that plaque morphologic features may play an important role in the immediate and long-term outcome after PTCA. Histologic evaluation of de novo atherosclerotic plaques underscores the heterogeneity of coronary atherosclerosis. From pathologic examination of human coronary arteries subjected to PTCA during life, expansion of the arterial circumference via medial damage is required for an effective increase in lumen size. Eccentric plaques and plaques with a large necrotic core are more likely to be successfully dilated compared to concentric, fibrotic lesions. Intravascular ultrasound studies of PTCA have supported histologic findings. Restenosis involves the complex interaction of growth factors and cytokines, cellular elements (endothelial cells, smooth muscle cells, platelets, and inflammatory cells), and the extent of arterial injury. The effects of underlying plaque morphologic features on the vascular biology of restenosis requires further clarification.

Induction of neointimal hyperplasia by coronary angioplasty balloon overinflation: comparison of feeder pigs to Yucatan minipigs

We evaluated the use of simple balloon overinflation to induce neointimal hyperplasia in a porcine model of coronary artery restenosis. By using standard percutaneous transluminal coronary angioplasty techniques, left anterior descending (LAD) and/or left circumflex (LCX) coronary arteries of either juvenile feeder pigs or adult Yucatan minipigs were intentionally overinflated. Four weeks later, resultant neointimal hyperplastic responses (neointima/media area; NI/M) were quantitated morphometrically. At all ballooned sites neointimal hyperplasia occurred only when the internal elastic lamina (IEL) was ruptured; the degree of hyperplasia correlated directly with the injury index, that is, the percentage of IEL circumference that fractured (r = 0.74; n = 25; p < 0.05). Despite similar injury indexes in the LAD bed, there was a trend (p = 0.07; analysis of variance) toward greater NI/M ratios in the Yucatan minipig versus the feeder pig group (1.14 +/- 0.21 vs 0.73 +/- 0.09, n = 7/group). We found no such trend in the LCX bed, where the injury index (25.7% +/- 3.5%) was significantly greater than that of the LAD (18.2% +/- 1.2%, p < 0.05). If variations in balloon-induced vascular injury are accounted for, the technique of balloon overinflation of coronary arteries should prove useful in testing potential antirestenotic agents in either adult or juvenile pigs.

Usefulness of dobutamine echocardiography for detecting restenosis after percutaneous transluminal coronary angioplasty

To determine the usefulness of dobutamine stress echocardiography for detecting restenosis after percutaneous transluminal coronary angioplasty, the results of coronary arteriography and dobutamine stress echocardiography were compared in 103 patients 6 months after percutaneous transluminal coronary angiography. The dobutamine stress echocardiograms were obtained on the same day as the coronary arteriograms, which were analyzed by both quantitative and visual estimates of luminal narrowing. The angiographic restenosis rate was 44% by quantitative and 31% by visual estimates of stenosis. Dobutamine stress echocardiography was abnormal in 38% of previously dilated regions with restenosis and normal in 79% of previously dilated regions without restenosis by quantitative coronary angiography. Dobutamine stress echocardiography was concordant in 69% of 16 patients with multivessel disease compared with 40% of 41 patients with 1-vessel disease (p < 0.05). By quantitative coronary angiography, 64% of patients with significant disease in the left anterior descending artery were identified by dobutamine stress echocardiography compared to 12 and 24% of patients with disease in the left circumflex and right coronary arteries, respectively (p < 0.009). Concordance was seen in 79% of patients with baseline wall motion abnormalities compared with 54% of patients without baseline wall motion abnormalities. Dobutamine stress echocardiography has a low sensitivity but high specificity for detecting restenosis after coronary angioplasty, which may be explained in part by the high prevalence of 1-vessel disease in this patient population. The variables associated with significantly higher degrees of concordance were the presence of left anterior descending artery disease, multivessel disease, and baseline wall motion abnormalities.

Coronary restenosis: evaluation of a restenosis injury index in a swine model

To investigate the mechanisms of restenosis and detect useful interventions to prevent it, reliable quantitative measurements must be evaluated. Coronary arteries of domestic and minipigs (n = 18) were mechanically injured by balloon overstretching and killed at different intervals (2 to 25 weeks) after quantitative angiographic analysis. Morphometric measurements evaluated intimal hyperplasia at 0.59 +/- 0.42 mm without relation to artery size or balloon/artery ratio. Intimal hyperplasia, expressed as the ratio of neointimal area to total wall area (A), is directly related to the injury, assessed by the ratio of internal elastic lamina (IEL) fracture length to IEL circumference (B), r = 0.84, p = 0.002. Restenosis injury index, defined as A/B, provides a useful tool for the quantitative assessment of future angioplasty-related restenosis interventions.

Restenosis revisited: insights provided by quantitative coronary angiography

In this editorial, the problem of restenosis after coronary balloon angioplasty and other transluminal interventions is reviewed from the perspective of quantitative coronary angiography. The review is largely based on the experience of the Thoraxcentre in the application of quantitative angiography to the study of restenosis over the past decade, with incorporation and discussion of relevant and significant contributions from other groups. Current discrepancies in the angiographic definition of restenosis are highlighted and the use of percent diameter stenosis or MLD as the measurement parameter of choice is objectively addressed. Perspectives on the pathologic paradigm of restenosis are briefly reviewed as a basis from which to evaluate quantitative angiographic information provided by various studies. Particular attention is then paid, in chronologic fashion, to discussion and elaboration of insights to the restenosis process provided by quantitative angiographic studies, which have led to the introduction of some new methodological approaches to the comparison of short- and long-term angiographic luminal changes after various interventions. A word of caution on the potential pitfalls of quantitative angiographic studies is provided and counterbalanced with a discussion of clinical correlations of quantitative angiographic measurements. Finally, a proposal is made for the application of quantitative angiographic measurements to randomized clinical trials for the purpose of comparing new interventional devices.

Restenosis after coronary angioplasty

Coronary angioplasty is used to treat coronary disease in many patients. Indications for angioplasty have expanded since it was first performed, mainly as a result of improvement in equipment and techniques. One problem with coronary angioplasty is the phenomenon of renarrowing of the treated coronary lesion, a process called restenosis. The events that constitute restenosis appear to be a universal response to the arterial wall injury of angioplasty. They are currently characterized as follows: platelet adhesion and aggregation on the damaged endothelium and within deep splits into the tunica media; release of platelet-derived growth factors; inflammation of the mechanically injured medial zone; transformation of smooth muscle cells of the tunica media after their activation by several of the growth-promoting substances; migration and proliferation of transformed smooth muscle cells, with secretion of copious amounts of extracellular matrix material; and, finally, termination of the growth process with regrowth of endothelium over the injured area. A decade of research work has helped identify clinical correlates of restenosis after coronary angioplasty procedures. This work is hindered by lack of a uniform angiographic definition of restenosis. In addition, much of the information has come from small studies, with incomplete follow-up and retrospective orientation. Nevertheless, some data are available. Patient-related correlates include male gender, unstable angina, diabetes, and continued smoking after angioplasty. Lesion-related correlates include multilesional and multivessel procedures, higher postangioplasty residual stenosis, proximal vessel location, location in the left anterior descending artery, location in a vein graft, long lesions, and total occlusions. The only consistent procedure-related correlate has been incorrect sizing of the angioplasty balloon to the treated artery. For the purposes of individual patient care, clinical correlates are not helpful. No group of variables has been found to be associated with complete freedom from restenosis, and no group is completely predictive of restenosis. All patients undergoing angioplasty procedures require some follow-up through subsequent months and years. Symptom status and the results of noninvasive studies have been investigated for purposes of follow-up. Symptoms are virtually useless by themselves for predicting restenosis or its absence. When symptom status is combined with exercise thallium 201 scintigraphy performed 4 to 6 months after an angioplasty procedure, the two factors are less than ideal but have a negative predictive value of more than 90%. This means that more than 90% of patients who have neither symptoms nor evidence of ischemia by thallium 201 scintigraphy will not have angiographic restenosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Cutting balloon coronary angioplasty--initial clinical experience

The success of percutaneous transluminal coronary angioplasty is limited by acute occlusion and late restenosis. In 25 patients (20 men, 5 women, age range 36-81 years) coronary angioplasty was performed using a new cutting balloon into which 3-4 longitudinally orientated blades are incorporated so as to reduce the rate of severe dissections. In 12 patients stenoses were reduced from 83.9 +/- 7.8% to 28.4 +/- 10.7% (mean +/- SD) by the cutting balloon alone, using predilatation with a small conventional balloon in two cases. Thirteen other patients were additionally dilated with a conventional balloon because of a residual stenosis > 50% after cutting balloon angioplasty. Here the stenoses could be reduced from 78.1 +/- 8.7% to 29.1 +/- 11.3%. Six months follow-up angiography in 14 patients showed > 50% restenosis in two of seven patients dilated with a conventional balloon in addition to the cutting balloon, and in one of seven patients dilated with the cutting balloon alone but predilated with a small conventional balloon. These results show that coronary angioplasty by the new cutting balloon results in a stenosis reduction comparable with conventional balloons at a low complication rate. Available 6 months follow-up data show three restenoses in patients either pre- or postdilated by a conventional balloon and none in stand-alone cutting balloon cases.

Is the Watanabe heritable hyperlipidemic rabbit a suitable experimental model for percutaneous transluminal coronary angioplasty in humans? A light microscopic, immunohistochemical and ultrastructural study

OBJECTIVES

This study was designed to assess an experimental model for the study of mechanisms that underlie restenosis after percutaneous transluminal coronary angioplasty.

BACKGROUND

The Watanabe heritable hyperlipidemic (WHHL) rabbit lacks the receptor for low density lipoproteins, produces atherosclerotic lesions very similar to those in humans and, therefore, could serve as a suitable model.

METHODS

Percutaneous transluminal angioplasty was performed on the left subclavian artery of 10 homozygous rabbits. The animals were killed at a few hours or 3, 7, 14 or 28 days after the procedure. The artery was fixed by perfusion, and the site of angioplasty was examined by both light and electron microscopy with the use of conventional and immunohistochemical staining techniques.

RESULTS

Angioplasty had caused a flap-like or dissecting tear into the media. At day 3, cells within the preexisting media adjacent to the injury had the ultrastructural characteristics of synthetic smooth muscle cells. At day 7, spindle cells at the site of injury stained either negative or very weakly positive with a marker for actin; ultrastructurally, these cells had the synthetic phenotype. At day 14, the spindle cells showed a mix of contractile and synthetic phenotypes. The surface was partially covered by endothelial cells. At day 28, the dominant cell type was the contractile smooth muscle cell and the surface was completely covered by endothelial cells.

CONCLUSIONS

Both the injury and the response to injury after percutaneous transluminal angioplasty were almost identical to that seen in humans after coronary angioplasty. Thus, the WHHL rabbit appears to be an appropriate experimental model for use in further studies.

Effects of angiotensin converting enzyme inhibition on neointimal proliferation in a porcine coronary injury model

To assess the effectiveness of angiotensin converting enzyme inhibition in a proliferative porcine coronary restenosis model, 35 animals received orally administered trandolapril (10 mg) or captopril (200 mg) or no drug (control group) for 6 days before and 28 days after injury by oversized metallic coils in one or more coronary arteries. Twenty arterial lesions in the trandolapril group, 17 in the captopril group, and 18 in the control group were evaluated. There was no significant difference in neointimal thickness or percentage luminal area stenosis for the groups as a whole. However, in quantitative comparisons in which vessel injury score was used as a covariate, the fractional increase in mean neointimal thickness per unit of injury was significantly less for the trandolapril group (p = 0.019) but not for the captopril group when compared with control animals. In this model, neointimal proliferation from arterial injury was inhibited by angiotensin converting enzyme inhibition with trandolapril but only modestly. Such an effect may not be clinically significant.

Thrombin stimulates proliferation of cultured rat aortic smooth muscle cells by a proteolytically activated receptor

Thrombin has been implicated in the stimulation of smooth muscle cell (SMC) proliferation that contributes to post angioplasty restenosis. The present studies demonstrated that human alpha-thrombin was a potent and efficacious mitogen for cultured rat aortic SMC, stimulating an increase in 3H-thymidine incorporation, as well as an increase in cell number at 1 to 10 nM concentration. gamma-Thrombin, which is enzymatically active but lacks fibrinogen clotting activity, stimulated SMC mitogenesis but was approximately 10-fold less potent than alpha-thrombin. In contrast, D-phenylalanyl-L-propyl-L-arginyl-chloromethyl ketone-alpha-thrombin, which lacked enzymatic activity, had no mitogenic effect. Diisopropylfluorophosphate-alpha-thrombin failed to stimulate mitogenesis except at concentrations having equivalent enzymatic activity as that of alpha-thrombin at its threshold for mitogenesis. Thus, thrombin-induced proliferation was dependent on enzymatic activity. A 14-residue peptide (SFLLRNPNDKYEPF) corresponding to amino acids 42 through 55 of the human thrombin receptor (Vu, T. K., D. T. Hung, V. I. Wheaton, and S. R. Coughlin, 1991. Cell. 64:1057-1068) had full efficacy in stimulating SMC proliferation. Reversing the first two amino acids of this peptide abolished mitogenic activity. Northern analysis demonstrated that SMC expressed a single mRNA species that hybridized to a labeled thrombin receptor cDNA probe. These findings indicate that alpha-thrombin stimulates SMC proliferation via the proteolytic activation of a receptor very similar or identical to that previously identified.

Coronary intimal proliferation after balloon injury and stenting in swine: an animal model of restenosis

OBJECTIVES

This study was designed to compare the proliferative response in coronary arteries after tantalum stent placement or balloon injury in a normolipemic swine model of restenosis.

BACKGROUND

Restenosis remains a significant complication of percutaneous transluminal coronary angioplasty. Efforts to study restenosis have been hampered by the lack of a suitable animal model.

METHODS

In an attempt to create lesions resembling those of human restenosis, normolipemic swine underwent injury of either the left anterior descending or the left circumflex coronary artery with either balloon inflation or deployment of a tantalum stent. At 4 weeks, they were killed and the injured vessels processed for histopathologic analysis. Intimal area, lumen area and maximal intimal thickness were measured. The degree of stenosis was expressed as residual lumen area (lumen area/intimal area ratio).

RESULTS

Vessels injured by either method demonstrated significant intimal smooth muscle proliferation leading to reduction in lumen area. In the 18 stented vessels residual lumen area measured 0.64 +/- 0.18 and maximal intimal thickness measured 0.6 +/- 0.3 mm; in the 15 balloon-injured vessels these values were 0.75 +/- 0.18 and 0.4 +/- 0.3 mm, respectively (p less than 0.05). In addition, most stented vessels had reactive inflammatory infiltrates surrounding the stent wires composed of lymphocytes, histiocytes and many eosinophils.

CONCLUSIONS

These data indicate that coronary artery injury in swine with either balloon inflation or stenting leads to intimal smooth muscle cell proliferation similar to that seen in human restenosis. The degree of intimal proliferation appears to be greater after stenting than after balloon injury. Intracoronary stenting in swine is associated with a marked inflammatory reaction around the stent wires. These models may be helpful in planning systemic and local antirestenosis strategies.

Low-molecular-weight heparin reduces neointimal proliferation after coronary stent implantation in hypercholesterolemic minipigs

BACKGROUND

Intracoronary stents have been suggested as a method of reducing the restenosis rate after balloon angioplasty. Proliferation of vascular smooth muscle cells is a major contributing factor to the restenosis process. Heparin and some of its derivatives have been shown to inhibit smooth muscle cell proliferation. We investigated the effect of low-molecular-weight heparin on the proliferative response after implantation of a balloon-expandable tantalum stent in previously deendothelialized coronary artery segments of hypercholesterolemic minipigs.

METHODS AND RESULTS

Minipigs were fed a diet containing 2% cholesterol, starting 1 month before balloon denudation of the endothelium in a coronary artery. One month later, a stent was implanted at this site. Animals were killed after 4 weeks (group 1, n = 6) or 3 months (group 2, n = 6). Animals in group 3 (n = 6), also followed for 4 weeks after stenting, received subcutaneous low-molecular-weight heparin at a dose of 200-300 units/kg anti-factor Xa activity per day in addition to the chronic acetylsalicylic acid (100 mg/day) also administered to groups 1 and 2. Eighteen of 22 animals survived to the end of the study. Angiography revealed patent stents in all surviving animals. In group 1, histological analysis showed extensive neointimal proliferation around stent struts. Maximal neointimal thickness seen in group 1 averaged 0.93 +/- 0.11 mm, was lower after 3 months (0.8 +/- 0.14 mm) in group 2, but was significantly reduced (0.44 +/- 0.18 mm, p less than 0.01) in group 3.

CONCLUSIONS

These data show a significant reduction of the neointimal proliferative response to coronary stent implantation by low-molecular-weight heparin.

Excimer laser angioplasty in the atherosclerotic rabbit: comparison with balloon angioplasty

The early and late results of excimer laser angioplasty and balloon angioplasty were compared in atherosclerotic rabbit iliac arteries. Immediately after laser angioplasty (n = 13) with a bare 600 microns fiber, there was a 33% increase in angiographically measured minimum lumen diameter; after balloon angioplasty (n = 12), there was a 53% increase. Restenosis (defined as loss of at least 50% of the gain achieved by angioplasty) occurred in none of six laser-treated rabbits studied 1 month later, compared with four of six balloon-treated rabbits (p = 0.06). Planimetric measurements of cross sections of the arterial wall 1 month after angioplasty showed less intimal and medial tissue in laser-treated (1.8 +/- 0.2 mm2) than in the balloon-treated rabbits (3.0 +/- 0.4 mm2; p less than 0.05). Typical thermal effects were absent on microscopic examination of laser angioplasty sites. It is concluded that in this animal model, excimer laser irradiation results in an immediate increase in lumen diameter comparable with balloon angioplasty, but is associated with less residual atheromatous tissue than balloon angioplasty and a trend toward a lower rate of restenosis.

Contribution of localized calcium deposits to dissection after angioplasty. An observational study using intravascular ultrasound

BACKGROUND

Atherosclerotic plaque fracture and dissection of the arterial wall are frequent concomitants of the balloon angioplasty process. The composition and morphology of plaque within the vessel may be critical in determining the extent of plaque fracture and dissection during balloon angioplasty. To examine this potential association in the clinical setting, we studied patients with intravascular ultrasound imaging after balloon angioplasty.

METHODS AND RESULTS

Forty-one patients were studied with intravascular ultrasound after angioplasty in both peripheral and coronary arteries. Ultrasound images representing the target lesion cross section were digitized, stored on computer, and analyzed off-line. The presence of intralesional calcium and the relative size of dissection for each lesion was computed. Thirty-one patients (76%) had ultrasound evidence of significant dissection or plaque fracture immediately after balloon dilation. In 23 of 31 (74%) of the lesions, the ultrasound scans showed significant localized calcium deposits within the plaque substance. In 87% of these cases, the dissections were adjacent to the calcific portion of the vessel wall. In addition, the relative size of dissections referenced to the neolumen area were significantly larger (p less than or equal to 0.002) in the calcified vessels (27.5 +/- 12.3%) compared with the size of the dissections in lesions without calcium (11.2 +/- 5.8%).

CONCLUSIONS

The presence of calcium within the vessel wall appeared to be significantly associated with both the location and size of the dissected tissue arm from the vessel wall. These data suggest that localized calcium deposits have a direct role in promoting dissection, presumably by increasing shear stresses within the plaque.

Histologic findings in specimens obtained by percutaneous directional coronary atherectomy

Percutaneous directional coronary atherectomy is a second-generation, catheter-based technique for the treatment of coronary artery disease that provides a unique opportunity to study tissue obtained from coronary artery stenoses. We reviewed the histologic findings in 131 coronary atherectomy specimens from 116 patients, including 79 primary lesions and 52 restenosis lesions that developed after a prior coronary intervention. Although atherosclerotic plaque was seen in 95% of cases, an important observation was the finding of deep arterial wall components in the majority of patients, including media in 61% and adventitia in 31%. Despite the relatively common finding of deep wall components, this was not associated with acute clinical complications. Intimal hyperplasia was seen in 64% of cases, including 96% of restenosis lesions. However, intimal hyperplasia was also seen in 45% of primary lesions. The intimal hyperplasia in primary and restenosis lesions was histologically identical and was characterized by cells that showed staining for vimentin and muscle-specific actin, consistent with a myogenous and/or myofibroblastic phenotype. Restenosis was seen in 29 of 94 lesions (31%) with angiographic follow-up an average of 6.3 months after atherectomy. The risk of restenosis was not significantly related to the vessel treated, the nature of the lesion treated (ie, primary v restenosis lesion), or any of the histologic features evaluated. In conclusion, (1) deep arterial wall components are commonly observed in coronary atherectomy specimens without acute complications and (2) intimal hyperplasia is a sensitive, but not specific, marker for restenosis lesions.

Restenosis following coronary angioplasty

Restenosis is the most important problem limiting the success of coronary angioplasty. Clinically, restenosis is seen in approximately one-third of patients undergoing percutaneous transluminal coronary angioplasty. Several clinical and angiographic risk factors have been identified which may contribute to the development of restenosis. Histopathologic studies indicate that restenosis is characterized by intimal proliferation of smooth muscle cells in a loose connective tissue matrix. These intimal lesions are associated predominantly with the nonatheromatous portion of the vessel wall. Thinning of the media of the plaque-free wall and marked fragmentation of the internal elastic lamina are also seen. Traumatic injury of the vessel wall during angioplasty probably triggers a series of cellular and subcellular events which may ultimately lead to myointimal proliferation and restenosis. Although the exact mechanism by which this occurs is unknown, several factors may enhance smooth muscle cell growth and therefore may play a role in the development of restenosis. These include platelet deposition, mechanical stretching of the media, inflammation of the vessel wall, the activity of growth factors, and alterations in vessel geometry. These possible mechanisms of restenosis suggest several potential ways to limit the proliferative response to vascular injury. Anticoagulants and platelet antagonists, direct inhibitors of smooth muscle proliferation, anti-inflammatory agents, growth factor inhibitors, and new devices which improve final vessel geometry are currently being tested as methods to curb restenosis. Unfortunately, no treatment has yet been shown to reduce significantly the rate of restenosis following angioplasty. The problem of restenosis will most likely be solved by better understanding of the basic molecular and biologic phenomena involved in vascular injury and repair.

Restenosis 1 to 24 months after clinically successful coronary balloon angioplasty: a necropsy study of 20 patients

This report describes clinical, morphologic and histologic findings at necropsy late (range 1.6 to 24.1 months [average 8.2 months]) after clinically successful coronary balloon angioplasty in 20 patients with coronary angioplasty restenosis. Clinical evidence of restenosis occurred in 14 patients (70%), including 6 patients with sudden coronary death. Of the 20 patients, 14 (70%) had a cardiac cause of death and 6 (30%) had a noncardiac cause of death. Two major subgroups of histologic findings were observed: 1) intimal proliferation (60%), and 2) atherosclerotic plaque only (40%). Of the eight sites with atherosclerotic plaque only, six were eccentric lesions and two were concentric lesions. No morphologic evidence of previous angioplasty injury (cracks, breaks, tears) was observed in the eight patients with atherosclerotic plaque only. Proposed mechanisms for the development of intimal proliferation involve the reaction of smooth muscle cells and platelets, whereas elastic recoil of overstretched eccentric or concentric atherosclerotic lesions represents the most likely explanation for the findings in the latter subgroup. On the basis of these morphologic findings at angioplasty restenosis sites, specific treatment strategies for restenosis after coronary artery balloon angioplasty are proposed.