Platelet and fibrin deposition on coronary stents in minipigs: effect of hirudin versus heparin

Noncanonical Matrix Metalloprotease 1-Protease-Activated Receptor 1 Signaling Drives Progression of Atherosclerosis

OBJECTIVE

Protease-activated receptor-1 (PAR1) is classically activated by thrombin and is critical in controlling the balance of hemostasis and thrombosis. More recently, it has been shown that noncanonical activation of PAR1 by matrix metalloprotease-1 (MMP1) contributes to arterial thrombosis. However, the role of PAR1 in long-term development of atherosclerosis is unknown, regardless of the protease agonist.

APPROACH AND RESULTS

We found that plasma MMP1 was significantly correlated (R=0.33; P=0.0015) with coronary atherosclerotic burden as determined by angiography in 91 patients with coronary artery disease and acute coronary syndrome undergoing cardiac catheterization or percutaneous coronary intervention. A cell-penetrating PAR1 pepducin, PZ-128, currently being tested as an antithrombotic agent in the acute setting in the TRIP-PCI study (Thrombin Receptor Inhibitory Pepducin-Percutaneous Coronary Intervention), caused a significant decrease in total atherosclerotic burden by 58% to 70% (P<0.05) and reduced plaque macrophage content by 54% (P<0.05) in apolipoprotein E-deficient mice. An MMP1 inhibitor gave similar beneficial effects, in contrast to the thrombin inhibitor bivalirudin that gave no improvement on atherosclerosis end points. Mechanistic studies revealed that inflammatory signaling mediated by MMP1-PAR1 plays a critical role in amplifying tumor necrosis factor α signaling in endothelial cells.

CONCLUSIONS

These data suggest that targeting the MMP1-PAR1 system may be effective in tamping down chronic inflammatory signaling in plaques and halting the progression of atherosclerosis.

Melagatran attenuates fibrin and platelet deposition in a porcine coronary artery over-stretch injury model

Melagatran is the active form of the oral direct thrombin inhibitor, ximelagatran. The purpose of this study was to compare the effects of different doses of melagatran with heparin or placebo on platelet deposition and relative fibrin content after coronary angioplasty in pigs. After 125I-labelled fibrinogen and autologous 111Indium-labelled platelets had been infused a balloon injury was performed in the left anterior descending and the right coronary arteries. Pigs were randomized to receive either heparin 200 IU/kg bolus plus 20 IU/kg per h infusion (n = 7); melagatran 1 mg/kg bolus plus 0.33 mg/kg per h infusion (n = 7); melagatran bolus 0.5 mg/kg plus 0.17 mg/kg per h infusion (n = 7); melagatran 0.15 mg/kg bolus plus 0.05 mg/kg per h infusion (n = 6) or saline (n = 4). Seventy-five minutes after the angioplasty, the pigs were euthanized and the injured vessel segments were measured in a gamma counter. Compared with placebo, platelet deposition and relative fibrin content were reduced after both heparin and melagatran, in the latter case with a dose-response relationship. Melagatran reduced platelet deposition and relative thrombus size in a dose-dependent manner when compared with placebo after coronary angioplasty in pigs. No statistically significant difference between melagatran and heparin was found.

Detection of a coronary arterial thrombus by indium-111-oxine-labeled platelet scintigraphy

Coronary arteriography revealed significant left anterior descending coronary artery stenosis in a 72-year-old man with a history of myocardial infarction. Stenting of the stenotic vessel was performed. Twelve hours after stenting the patient complained of chest pain but emergent coronary arteriography did not show sign of any coronary arterial stenosis. Under suspicion of coronary thrombus formation, indium-111-oxine-labeled platelet scintigraphy was performed 5 days after stenting, and revealed accumulation of indium-111-oxine in the area corresponding to the stent implantation site.

There is no effect on remodeling of vascular wall 4 weeks after local delivery of antithrombin in a porcine model of coronary overstretching

BACKGROUND

Antithrombin III is an effective endogenous inhibitor of thrombin with antiproliferative and anti-inflammatory capabilities. Systematic administration of direct thrombin inhibitors as well as of antithrombin has proven effective at reducing formation of neointima after injury to vessel wall in various animal models. Local delivery of antithrombin attenuates deposition of platelets after balloon injury to porcine coronary vessels.

OBJECTIVE

To test our hypothesis that local delivery of antithrombin affects remodeling of vessel wall after balloon injury to the left anterior descending artery (LAD) in pigs.

METHODS

With a balloon:vessel diameter ratio of 1.5 deep vessel-wall injury was performed with conventional balloon angioplasty in the LAD in 16 pigs. After balloon injury the pigs were administered locally two doses of 2.5 ml antithrombin (250 U) or, as a control, two doses of 2.5 ml albumin (10 mg). All pigs were administered 200 U/kg bodyweight heparin before catheterization. The animals were then kept in stalls and fed normal grain. After approximately 4 weeks the animals were killed and lesions were assessed by computer-assisted image analysis. The areas of each vessel-wall layer and the percentage area stenosis were calculated. As a measure of injury, the length of rupture of the lamina elastica interna was measured.

RESULTS

The injury was found to be equally profound in pigs of these groups. There was no significant difference between the groups concerning the areas of vessel-wall layers. The percentage area stenosis was similar for pigs in these two groups (36.5 +/- 14.9% for pigs in the antithrombin group versus 35.4 +/- 16.2% for pigs in the control group, NS).

CONCLUSIONS

Local delivery of 250 U antithrombin to the LAD in pigs did not affect remodeling of the vessel wall 4 weeks after balloon injury.

Hirudin-based anticoagulant strategies for patients with suspected heparin-induced thrombocytopenia undergoing percutaneous coronary interventions and bypass grafting

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug reaction that is associated with thrombotic events of the venous and arterial circulatory systems stemming from an intense and well-characterized prothrombotic triad of platelet activation, coagulation cascade stimulation and vascular endothelial cell injury. Although heparin (or other sulfated mucopolysaccharide compound) cessation represents a vital first step in management, patients remain susceptible to life-threatening thrombosis for up to several weeks, providing a strong rationale for a 'proactive approach' to care that includes prompt initiation of an alternative anticoagulant strategy throughout the high-risk period. The importance of alternative options for anticoagulation is most evident in clinical situations wherein treatment is a recognized standard of care and prerequisite for an optimal outcome. The following review highlights the use of recombinant hirudin (lepirudin) among patients with suspected HIT requiring precutaneous coronary interventions (PCI) and coronary arterial bypass grafting.

Altered vascular injury responses in mice deficient in protease-activated receptor-1

Expression of protease-activated receptor-1 (PAR-1), a cell-surface receptor for thrombin, is increased in balloon-injured rat carotid artery and human atherosclerotic tissue. To examine the role of PAR-1 in vascular injury, we compared vascular injury responses in wild-type (WT) and PAR-1-deficient (PAR-1(-/-)) mice. Arterial injury was induced by inserting a flexible guidewire into the common carotid artery and withdrawing it 6 times with rotation. Bromodeoxyuridine, delivered subcutaneously by osmotic minipump, was used to measure cellular proliferation. Mice were perfusion-fixed at 1, 2, 5, 10, and 14 days after injury. Extensive endothelial damage, mural thrombosis, platelet adherence, and medial smooth muscle cell loss and necrosis were apparent at day 1 in both WT and PAR-1(-/-) mice. The incidence of thrombosis or platelet deposition in WT and PAR-1(-/-) mice declined from 100% at day 1 to 25% and 21%, respectively, at 14 days. Endothelial disruption, as assessed by Evan's blue uptake, was maximum at day 1 and declined by day 14. This apparent endothelial regrowth was similar in WT and PAR-1(-/-) mice. Significant medial thickening at 14 days after injury was similar in WT (from 22.8+/-1.7 to 30.7+/-1.9 microm) and PAR-1(-/-) (from 23.2+/-2.1 to 30.5+/-2.2 microm) mice. Medial area also increased in response to injury but to a lesser extent in PAR-1(-/-) mice (from 0.0250+/-0.0044 to 0.0312+/-0.0047 mm(2)) than in WT mice (from 0.0266+/-0.0040 to 0.0398+/-0.0050 mm(2)). Neointima was variable and occurred in 6 of 13 WT and 5 of 12 PAR-1(-/-) mice. However, intimal area tended to be less in PAR-1(-/-) mice (0. 0016+/-0.0007 mm(2)) compared with WT mice (0.0082+/-0.0032 mm(2)), although this difference did not achieve statistical significance (P=0.06). Cell density was significantly greater in normal carotids from PAR-1(-/-) (6.4+/-0.5 x 10(3)/mm(2)) compared with WT (4.3+/-0. 8 x 10(3)/mm(2)) mice and remained elevated after injury. Vessel and lumen diameters tended to increase in WT mice after injury, whereas vessel diameter was unchanged and lumen diameter actually decreased in PAR-1(-/-) mice. Cell proliferation in injured carotid arteries was similar in PAR-1(-/-) and WT mice. These data suggest that PAR-1(-/-) may play a role in vascular injury responses in this mouse model via possible effects on extracellular matrix regulation.

Local drug delivery of argatroban from a polymeric-metallic composite stent reduces platelet deposition in a swine coronary model

Thrombus formation after intracoronary stent implantation provides a stimulus for neointimal hyperplasia and if excessive can result in stent thrombosis. We tested the hypothesis that local delivery of an antithrombin drug from a polymeric-metallic stent inhibits platelet thrombus formation. An uncoated metal slotted tube, a jellyroll slotted metal stent with an Argatroban-loaded polymeric sleeve, and a jellyroll slotted metal stent with a drug-leached polymeric sleeve were randomly deployed into the coronary arteries of eight juvenile farm swine. Platelet deposition in the stented segments was determined at 2 hr using autologous 111Indium oxime-labeled platelets. Platelet deposition was significantly less in the Argatroban-loaded stents compared to the Argatroban-leached stents (1.40 x 10(8) platelets/cm2 vs. 26.8 x 10(8) platelets/cm2; P=0.005). When corrected for differences in the metal surface area exposed to blood, platelet deposition was significantly lower in the Argatroban-loaded stent (1.74+/-1.95 x 10(8)/cm2) compared to the Argatroban-leached stent (33.5+/-39.1 x 10(8)/cm2; P=0.005) and the uncoated metal stent (36.2+/-73.3 x 10(8)/cm2; P=0.006). In this coronary stent thrombosis model Argatroban has local antithrombotic properties when delivered with a polymer-metallic stent. Improved polymeric designs may reduce risk of thrombus deposition at the site of stent implantation.

[Diagnosis and differential therapy of mitral stenosis]

Clinical symptoms and diagnostic findings in patients with mitral stenosis are usually determined by the extent of the stenosis. Compared to a normal mitral valve area (MVA) of > 4 cm2, MVA in patients with severe mitral stenosis is usually reduced to < 1.5 cm2. In older patients symptoms are frequently influenced by concomitant diseases (e.g. atrial fibrillation, arterial hypertension or lung disease). An important diagnostic element besides anamnesis, auscultation, ECG and chest X-ray is echocardiography, which is required in order to measure non-invasively and reliably the mitral valve gradient (MVG), the MVA and morphologic changes to the valves, as well as concomitant valvular disease, ventricular functions and, where appropriate, left-atrial thrombi. In addition to the surgical treatment of patients with severe mitral stenosis, which has been an established procedure for 50 years, percutaneous balloon mitral valvuloplasty (MVP) has recently established itself as an alternative option. At the current time, the Inoue technique seems to display the most advantages. Following transseptal puncture, the Inoue balloon is guided transvenously into the left atrium and then into the left ventricle using a special support wire. The balloon is short and soft. Its special unfolding character enables it to be placed securely in the mitral valve without any risk of ventricular perforation (Figure 1). As with surgical commissurotomy, balloon valvuloplasty leads to a separation of fused commissures. This results in a significant reduction of MVG, accompanied by an increase in the MVA (Figure 2). The results and success of MVP are influenced by the morphology of the valves and the changes to the subvalvular apparatus. In randomized studies, the results of surgical commissurotomy were comparable with those of balloon mitral valvulotomy. In our hospital, an increase in MVA from 1.0 to 1.8 cm2 could be achieved in 899 patients (mean age 56 +/- 3 years). In younger patients with less significantly changed valves, the results were correspondingly more favorable than in older patients (Figure 3). Provided valve morphology is suitable, a relapse following previous surgical commissurotomy is not a contraindication for MVP. The MVP complication rate is very low in skilled hands: mortality is below 1%; mitral insufficiency occurs in 3 to 10% of interventions; we observed a severe mitral insufficiency in 5% of our patient group. Thromboembolic complications may be prevented after exclusion of atrial thrombi by transesophageal echocardiography. The occurrence of a hemodynamically significant atrial septum defect is a very rare event. The mid-term results (5 to 10 years) and the low restenosis rate following MVP in patients with suitable valves are comparable with those of surgical commissurotomy. In older patients with considerably changed, calcified and fibrotic valves, restenosis may be expected within 1 to 5 years. In these patients MVP represents no more than a palliative intervention in order to prolong the point of surgery, for example in patients where a concomitant aortic valve disease in itself is not yet an indication for surgery. Special indications are to be found in young patients with severe mitral stenosis yet few symptoms, in pregnant females and in emergency situations, as well as in patients with Grade II mitral stenosis with intermittent atrial fibrillation. Catheter therapy is much less invasive than surgery. In case of failure the patient still has the option of surgical therapy. Patients with morphologically significantly altered valves usually receive a valve replacement since an unsuccessful reconstruction would lead to a second operation within a very short time interval. Contraindications for MVP are thrombi in the left atrium, a previously existing > Grade II mitral regurgitation and marked, degenerative destruction of the subvalvular apparatus or extensive calcification of the valves. MVP thus represents a significant addi

Comparison of antiplatelet effects of aspirin, ticlopidine, or their combination after stent implantation

BACKGROUND

This study was performed to analyze the influence of either aspirin, ticlopidine, or their combination on platelet activation and aggregation parameters after stent implantation.

METHODS AND RESULTS

Sixty-one patients with successful implantation of a single Palmaz-Schatz stent in a native coronary artery were randomly assigned to either group A (aspirin 300 mg/d+ticlopidine 2X250 mg/d), group B (ticlopidine 2X250 mg/d), or group C (aspirin 300 mg/d). Platelet activation was evaluated on days 1, 7, and 14 by flow cytometry measurement of expression of CD62p (p-selectin) and the binding of fibrinogen to the platelet surface glycoprotein IIb/IIIa receptor. Platelet aggregation was induced by addition of ADP or collagen. Differences between treatment groups were compared by ANOVA. Between days 1 and 14, we observed a significant decrease in collagen-induced platelet aggregation in group A (62.2+/-2.5% versus 36.9+/-3.1%), whereas an increase was seen in group B (58.3+/-2.5% versus 67.7+/-3.2%) and no change was seen in group C (P<.0001). The ADP-induced aggregation declined significantly in group A (74.7+/-1.4% versus 55.3+/-2.6%), whereas a delayed reduction was seen in group B (72.0+/-3.0% versus 52.6+/-4.2%) and no change was seen in group C (P=.0017). The CD62p expression declined significantly in groups A (68.2+/-2.7% versus 41.3+/-2.7%) and B (64.8+/-2.9% versus 39.3+/-3.5%) but not in group C (P<.0001). Moreover, the fibrinogen binding decreased significantly in group A (61.0+/-4.3% versus 36.3+/-4.2%) and with delay in group B (58.3+/-2.2% versus 39.4+/-3.0%), whereas no alterations were seen in group C (P=.012).

CONCLUSIONS

Our results demonstrate synergistic and accelerated platelet inhibitory effects of ticlopidine plus aspirin in patients after stent implantation compared with a monotherapy with either ticlopidine or aspirin alone.

Abrupt vessel closure: changing importance, management, and consequences

Percutaneous coronary interventions have been performed for 20 years. Despite the success and progress of these interventions, abrupt vessel closure has been a dramatic adverse event of coronary interventions. Closure has frequently led to the major complications of death, myocardial infarction, and emergency coronary artery bypass. Because of the fear of this adverse event and its subsequent complications, the applicability of coronary interventions is sometimes limited. The pathologic characteristics of abrupt vessel closure have been recognized as predominantly caused by dissection, with vessel recoil and thrombus formation playing important secondary roles. The recognition of the lesions at risk for abrupt vessel closure has led to a strategy of lesion-specific device therapy to reduce complications. Similarly the role of antiplatelet and antithrombotic therapies have reduced complications. The earliest methods of dealing with abrupt closure was emergency coronary artery bypass surgery with significant rates of morbidity and mortality. With the advent of second-generation devices and techniques, particularly stents, the management of abrupt vessel closure has been simplified and alternatives to emergency coronary bypass are more available. This article will review the history and current status of the prevention and management of abrupt vessel closure and demonstrate that anticipation and management of this complication have been facilitated with reduction of subsequent complications and increased applicability of coronary interventions.

Inhibition of neointimal proliferation after coronary angioplasty by low-molecular-weight heparin (clivarine) and polyethyleneglycol-hirudin

Proliferation of medial smooth muscle cells (SMC) plays a major role in restenosis after coronary angioplasty and can be inhibited by heparin. Platelets stimulate SMC proliferation, and their aggregation after angioplasty can be reduced by the direct thrombin inhibitor hirudin. In a porcine coronary stent-angioplasty model (16 animals, 4 per group), we studied the effect of 3- and 14-day treatment with a novel long-lasting polyethyleneglycol-conjugated (PEG-hirudin, LU 57291), at a dose of 1 mg/kg intravenously (i.v.) and then subcutaneously once daily as compared with chronic low-molecular-weight heparin (LMWH) clivarine at a dose of 150 IU/kg as an intravenous bolus, followed by 10 IU/kg/h i.v. for 24 h, followed by 75 IU/kg twice daily, as compared with acute unfractionated heparin (100 IU/kg) as a control. Sixteen animals were randomly assigned to the four treatment groups. Four weeks after angioplasty, hearts were perfusion-fixed and six slices per angioplasty segment were analyzed for neointimal thickness and neointimal area (% of total vessel cross-sectional area). Maximal neointimal thickness was 1.10 +/- 0.2 mm in the control group (mean +/- SD, n = 9 arteries) and was significantly lower in both PEG-hirudin (0.62 +/- 0.22 and 0.86 +/- 0.18 mm, 11 and 10 arteries) and in clivarine-treated animals (0.75 +/- 0.33 mm, 11 arteries, p < 0.01). Similarly, neointimal area was smaller in PEG-hirudin groups (20 +/- 12 and 21 +/- 12%) and in the clivarine group (24.8 +/- 13.2%) as compared with the control group (41 +/- 17%, p < 0.02). We conclude that PEG-hirudin and clivarine reduce neointimal proliferation in a coronary stent-angioplasty model. Prolonged PEG-hirudin has no better effect than therapy limited to 3 days.

Comparison of the effects of the thrombin inhibitor r-hirudin in four animal models of neointima formation after arterial injury

Thrombin has been implicated as a contributing factor to restenosis after vessel reopening procedures. We compared the ability of the direct thrombin inhibitor recombinant (r-) hirudin to reduce neointimal growth in different animal models of arterial injury. Carotid arteries of rats, rabbits, and hypercholesterolemic minipigs were injured by withdrawal of an inflated balloon catheter. In addition, we used a double-lesion model in rabbits, which involved balloon angioplasty of a preexisting lesion induced by carotid denudation 4 weeks earlier. r-Hirudin was given in all four animal models as a short-term application (bolus of 1 mg/kg i.v. immediately before injury, followed by infusion of 1 mg.kg-1.h-1 for 2 hours, and an injection of 6 mg/kg SC). Additionally, we investigated the effects of prolonged treatment (intravenous infusion for 3 and 14 days) in rats. Inhibition of thrombin was monitored by determination of activated partial thromboplastin time, and histomorphometric analysis of the arteries was performed after 2 (rats) or 4 (rabbits and minipigs) weeks. In rabbits, short-term r-hirudin treatment reduced neointimal area by 59% (single-injury model, P = .05) and 44% (double-injury model, P = .02). In rats and minipigs no inhibition of neointimal growth was observed after short-term r-hirudin application. A 3- or 14-day infusion of r-hirudin in rats, however, resulted in 25% (P = .007) and 27% (P = .003) reductions in neointimal area, respectively. In conclusion, there is considerable interspecies variation in the time frame of susceptibility for reduction of neointimal growth by inhibition of thrombin after arterial injury. These results demonstrate the importance of testing potential antirestenotic treatments in an array of different animal models.

Relationship of vascular thrombosis and inflammatory leukocyte infiltration to neointimal growth following porcine coronary artery stent placement

BACKGROUND

Superficial and intramural thrombosis are reproducible histopathological features of the porcine coronary oversized stent injury model. Fibrin and its degradation products are chemotactic for mononuclear leukocytes, and promote the proliferation and migration of vascular smooth muscle cells (VSMC) in vitro. The goal of this study was to quantitate the serial histomorphologic evolution of thrombosis, leukocyte infiltration, VSMC proliferation and collagen accumulation following porcine coronary artery stent placement in a porcine model.

METHODS

Twenty-four normocholesterolemic swine underwent oversized balloon (3.5-4.0 mm) coronary angioplasty and tantalum metal stent placement. Twenty-six different arterial sites were injured, followed by serial sacrifice at day 4 (n = 6), 8 (n = 6), 14 (n = 6), and 28 (n = 6). Quantitative analysis of the neointima was performed using a high resolution video-microscopy interface and a validated histomorphometric software program. Alpha actin-positive VSMC density (per 10(4) micro(2) neointimal area) and collagen-specific picro-sirius red fluorescence (percent of neointima) were quantitated at sites adjacent to and distant from coronary artery stent placement.

RESULTS

The percent of total neointimal area occupied by resolving thrombus material was greater at days 4-8 compared to 14-28 days (59-63% vs. 1-2%; P = 0.001). Mononuclear leukocytes were also significantly increased at days 4 and 8 (92 +/- 1 and 70 +/- 8%) compared to days 14-28 (both 3 +/- 3%; P = 0.001), as a percentage of the total neointimal cellularity. Total neointimal cell density did not change (20 +/- 10, 12 +/- 6, 23 +/- 7 and 20 +/- 3 cells/10(4) micro(2); P-value, NS), despite progressive cross-sectional vascular area stenosis reduction from 7 +/- 3% at day 4 to 72 +/- 14% at day 28 (P = 0.001). Percent neointimal fibrinoid thrombus content and mononuclear leukocyte cellularity were correlated in this model (R = 0.81; P < 0.001). Peri-stent neointimal collagen staining exceeded that at vascular sites distant from porcine coronary stent placement by 14 days (29 +/- 6 vs. 15 +/- 3%), and remained greater at 28 days (35 +/- 11 vs. 16 +/- 12%) (both P < 0.05).

CONCLUSIONS

Quantitative serial histomorphometry of porcine coronary vascular stent delivery sites demonstrates early (4-8 day) neointimal mononuclear leukocyte infiltration which is histomorphologically and temporally related to intramural fibrinoid thrombosis. Significant vascular stenosis and collagen deposition occurs by 14-28 days at these vascular injury sites. These data suggest a local interaction between thrombotic and inflammatory elements in porcine coronary neointima following oversized stent injury.

Reduction in thrombotic events with heparin-coated Palmaz-Schatz stents in normal porcine coronary arteries

BACKGROUND

The use of stents improves the result after balloon coronary angioplasty. Thrombogenicity of stents is, however, a concern. In the present study, we compared stents with an antithrombotic coating with regular stents.

METHODS AND RESULTS

Regular stents were placed in coronary arteries of pigs receiving no aspirin (group 1; n = 8) or aspirin over 4 weeks (group 2, n = 10) or 12 weeks (group 3, n = 9). Stents coated with heparin (antithrombin III uptake, 5 pmol/stent) were placed in 7 pigs that did not receive aspirin (group 4). The other animals received aspirin and coated stents with a heparin activity of 12 pmol antithrombin III/stent (group 5, n = 10) or 20 pmol/stent (group 6, n = 10; group 7, n = 10). Quantitative arteriography was performed at implantation and after 4 (groups 1, 2, and 4 through 6) or 12 weeks (groups 3 and 7). In an additional 5 animals, five regular and five coated stents (20 pmol/stent) were placed and explanted after 5 days for examination of the early responses to the implants. Thrombotic occlusion of the regular stent occurred in 9 of 27 in groups 1 through 3. However, in 0 of 30 of the animals receiving high-activity heparin-coated stents (groups 5 through 7), thrombotic stent occlusion was observed (P < .001). Histological analysis at 4 weeks showed that the neointima in group 6 was thicker compared with its control group 2 (259 +/- 104 and 117 +/- 36 microns, P < .01), but at 12 weeks the thickness was similar (152 +/- 61 and 198 +/- 49 microns, respectively). Comparison at 5 days suggested delayed endothelialization of the coating.

CONCLUSIONS

High-activity heparin coating of stents eliminates subacute thrombosis in porcine coronary arteries.

Reduced acute thrombus formation results in decreased neointimal proliferation after coronary angioplasty

OBJECTIVES

We tested the hypothesis that reduced acute platelet deposition after angioplasty results in reduced late neointimal proliferation.

BACKGROUND

Platelet-mediated mechanisms contribute to smooth muscle cell proliferation and migration.

METHODS

Indium-111-labeled platelets were injected 16 h before coronary stent angioplasty in 10 Göttinger minipigs: group 1 (n = 5) = heparin (100-U/kg bolus) before angioplasty; group 2 (n = 5) = recombinant hirudin (CGP 39393, 1.0-mg/kg body weight bolus intravenously), followed by subcutaneous doses of 6 to 10 mg/kg every 8 h. Furthermore, stent angioplasty was performed in coronary arteries of 16 minipigs: group 3 (n = 5, nine stents) = 100 U/kg heparin only; group 4 (n = 5, 10 stents) = 1-mg/kg bolus hirudin before and 45 min after angioplasty; group 5 (n = 6, 11 stents) = hirudin (1-mg/kg intravenous bolus) before and 45 min after angioplasty, followed by 6 to 10 mg/kg subcutaneously every 8 h.

RESULTS

In segments with deep arterial injury, the number of platelets/angioplasty segment in group 2 after 72 h (mean 21, range 9.7 to 39.7 x 10(6)) was significantly less than that in group 1 (mean 375, range 72 to 787 x 10(6)). Morphometric analysis after 4 weeks showed no difference between groups in degree of vessel wall injury. Mean (+/- SD) neointimal thickness was 0.70 +/- 0.06 mm in group 3 and was significantly reduced in both group 4 (0.46 +/- 0.11 mm) and group 5 (0.48 +/- 0.21 mm).

CONCLUSIONS

The direct thrombin inhibitor hirudin significantly reduces platelet deposition up to 72 h after coronary stent angioplasty. A hirudin bolus alone as well as continued subcutaneous administration for 14 days substantially reduced neointimal proliferation compared with heparin 4 weeks after coronary stent angioplasty in minipigs.

Infarct size after acute myocardial infarction measured by quantitative tomographic 99mTc sestamibi imaging predicts subsequent mortality

BACKGROUND

99mTc sestamibi is a recently developed radioisotope that has been used to measure myocardium at risk and infarct size. The relation between these measurements and subsequent patient outcome has not yet been demonstrated.

METHODS AND RESULTS

Two hundred seventy-four consecutive patients with acute myocardial infarction underwent tomographic 99mTc sestamibi imaging on arrival at the hospital (to measure myocardium at risk before reperfusion therapy) and at hospital discharge (to measure the amount of salvaged myocardium and final infarct size). Defect size on the sestamibi images was quantified using a threshold value of 60% of peak counts from the circumferential count profile curves generated for five representative slices of the left ventricle. Patients were followed after hospital discharge to evaluate the association between final infarct size and subsequent mortality. The median defect size measured was 27% of the left ventricle at presentation to the hospital (range, 0% to 77%) and was 12% of the left ventricle at hospital discharge (range, 0% to 68%). Almost one half of the patients had a final infarct size of < or = 10%. The median amount of myocardium salvaged was 9% (range, -31% to 75%). During a median duration of follow-up of 12 months, there were 10 deaths (7 cardiac and 3 noncardiac) and 1 resuscitated out-of-hospital cardiac arrest. There was a significant association between infarct size and overall mortality (chi 2 = 8.66, P = .003) and cardiac mortality (chi 2 = 11.89, P < .001). Two-year mortality was 7% for patients whose infarct size was > or = 12% versus 0% for patients whose infarct size was < 12%. There also was a significant association between myocardium at risk and cardiac mortality (chi 2 = 6.87, P = .009). There was no association between myocardium at risk and overall mortality or between amount of myocardium salvaged and either overall mortality or cardiac mortality.

CONCLUSIONS

Larger infarct size measured by 99mTc sestamibi imaging after acute myocardial infarction is associated with increased mortality risk during short-term follow-up.

Intracoronary stenting without coumadin: one month results of a French multicenter study

In order to simplify post-coronary stenting treatment and to obtain a lower rate of complications, especially in bailout situations, seven French institutions treated 246 stented patients with 0.25 g/day of ticlopidine, 0.1 g/day of IV aspirin, and 2 days of heparin followed by low-molecular-weight heparin for 1 month. Fifty percent of patients had a planned stenting procedure, and 50% had an unplanned procedure, including 29 (11.8%) in bailout situations. Subacute occlusion occurred in three (1.2%) patients (one death, two non-Q-wave infarctions). During the 1 month follow-up period, another death was reported (non-stent-related), two elective coronary artery bypass grafts were performed, and three additional patients presented with non-Q-wave myocardial infarctions. Nine (3.7%) patients had a groin complication that required blood transfusion or surgical repair. These results suggest that while waiting for the technological advancements of stents, postprocedural treatment that includes a low dosage of ticlopidine, aspirin, and low-molecular-weight heparin is a very effective alternative to conventional poststenting therapy.

Neointima formation after vascular stent implantation. Spatial and chronological distribution of smooth muscle cell proliferation and phenotypic modulation

Intravascular stents have proved useful as angioplasty devices, but intimal hyperplasia after stent implantation remains an unsolved problem. In the present study, we analyzed the spatial and chronological distribution of proliferation and phenotypes of smooth muscle cells (SMCs) in rabbit aortas during the process of neointima formation after stent implantation (Gianturco's Z type) by immunohistochemistry for proliferating cell nuclear antigen (PCNA) and myosin heavy chain isoforms (SM1, SM2, and SMemb). Stent implantation induced regional injury in the arterial wall. Medial SMCs then began to proliferate adjacent to the injured SMCs, maximally on day 4 (PCNA index in the media: 3.9 +/- 3.4% [mean +/- SD]), and were modulated to the embryonic phenotype (SMemb-positive and SM2-negative). They migrated into the intima and proliferated most frequently on day 7 (PCNA index in the intima: 20.3 +/- 5.5%) and subsequently led to fibrocellular neointima formation at 2 weeks and later. At 1 month after implantation and later, SMC proliferation was rare, and the phenotype of intimal SMCs was gradually returning to the adult type (SMemb-negative and SM2-positive). Thus, this stent implantation model demonstrates that the regional effect on arterial wall by stenting leads to neointima formation through transient and regional proliferation and migration of SMCs and their phenotypic modulations.

Direct thrombin inhibitors in cardiovascular medicine

Currently used antithrombotics such as heparin have a number of potential limitations that may be overcome by the new class of agents that directly inhibit thrombin. These agents variously block the active catalytic and/or the anion binding exosites of the thrombin molecule and are potent and specific inhibitors of thrombin's many biological actions, as demonstrated by in vitro and animal models of thrombosis. Preliminary data indicate that the direct antithrombins are safe and efficacious in humans, and their use in acute coronary syndromes and coronary angioplasty in place of heparin has yielded promising early results. Phase III trials in these clinical settings are currently under way. Newer antithrombotics that inhibit thrombin generation and thrombin activity at various strategic points within the coagulation cascade are also in the early stages of development.

Decreased platelet deposition and smooth muscle cell proliferation after intramural heparin delivery with hydrogel-coated balloons

BACKGROUND

In vitro and in vivo studies have demonstrated both anticoagulant and antiproliferative effects of heparin. The purpose of this study was to assess the effect of local intramural delivery of heparin, using heparin-coated hydrogel balloons, on platelet deposition and early smooth muscle cell proliferation after in vivo balloon angioplasty.

METHODS AND RESULTS

The effects of local heparin delivery were assessed during balloon angioplasty of porcine peripheral arteries. All balloon dilatations were performed with oversized hydrogel balloons coated with a known quantity of heparin. Balloon dilatations in contralateral vessels with uncoated hydrogel balloons served as study controls. The pharmacokinetics of heparin delivery were assessed using 3H-heparin to quantitate heparin wash-off from the balloon surface, heparin delivery to the arterial wall, and intramural persistence of drug. Platelet deposition at 1 hour after balloon injury was quantified using 111In-labeled platelets. Smooth muscle cell proliferation was assessed 6 to 7 days after angioplasty with immunohistochemical staining for proliferating cell nuclear antigen. 3H-heparin wash-off from the hydrogel balloon surface occurred rapidly, with approximately 95% of the heparin coating disappearing within 10 seconds in the intact circulation. Approximately 2% of heparin on the balloon surface was delivered intramurally at the time of angioplasty. Intramural heparin dissipated rapidly, although small amounts of intramural heparin could still be detected for at least 48 hours. In comparison to control vessels, there was less 111In-platelet deposition (P = .002) and less medial smooth muscle cell proliferation (P = .03) in heparin-treated vessels.

CONCLUSIONS

Local intraluminal delivery of heparin at the time of balloon angioplasty with heparin-coated hydrogel balloons results in intramural deposition of drug that persists for at least 48 hours. This in vivo technique significantly decreases platelet deposition and early smooth muscle cell proliferation after angioplasty injury.

Hirudin: clinical potential of a thrombin inhibitor

Hirudin is the most potent and specific known inhibitor of thrombin, the enzyme that plays a key regulatory function in hemostasis and blood coagulation. The importance of thrombosis in cardiovascular disease has recently highlighted the limitations of existing antithrombotic drugs and the potential value of direct thrombin inhibition as an effective approach to antithrombotic therapy. Hirudin and a small peptidomimetic analog--hirulog--are being developed as alternatives to heparin for the treatment of unstable angina, for prevention of abrupt closure and restenosis following coronary angioplasty, for prevention of deep vein thrombosis after major orthopedic surgery, and as an adjunct to fibrinolytic therapy. Direct thrombin inhibitors have several potential advantages over heparin: They can inhibit thrombin bound to clots or extracellular matrices, which are relatively resistant to heparin; they do not require antithrombin III as a cofactor, which may lead to a more predictable dose response; and they are not inhibited by activated platelets, which release platelet factor 4 and other molecules that neutralize heparin. The results of early clinical studies suggest that hirudin and hirulog may be more efficacious and more predictable and may have fewer bleeding complications than heparin for several clinical indications.