Neal A. Scott

Seeding of intracoronary stents with immortalized human microvascular endothelial cells

Intracoronary stents are effective in decreasing the complications associated with acute closure during coronary angioplasty. A major complication associated with the use of coronary stents is acute thrombotic occlusion. It has been postulated that the stent loses its thrombogenic potential after it becomes covered with a layer of endothelial cells. Human dermal microvascular endothelial cells were transfected with a plasmid containing the simian virus 40 large T-antigen gene. Stents were placed in culture media with cells for 2 weeks. Seeding efficiency of the stent with the endothelial cells was assessed by scanning electron microscopy. Balloon-expandable coronary stents placed in cell culture with immortalized human microvascular endothelial cells showed near-complete coverage after 2 weeks. After balloon inflation, persistence of cells on the stent was noted only on the lateral aspect of the balloon-expanded stents. If these stents were placed in culture, complete recovery of the monolayer was noted after 3 days. Stents were then covered with endothelial cells and frozen for 4 days. After thawing, the cells adhered to the devices and divided to form a monolayer in tissue culture. Seeded balloon-expandable stents were frozen for 4 months, thawed, and then implanted in a pig coronary artery. Human endothelial cells were identified on the stent 4 hours after deployment. These studies demonstrate the feasibility of using a human microvascular endothelial cell line to seed an uncoated metal stent. The cells remain adherent to the stent, are functional after freezing, and remain on the stent at least 3 hours after intracoronary implantation.

Local delivery of an antithrombin inhibits platelet-dependent thrombosis.

BACKGROUNDnPlatelet-dependent thrombosis can be effectively inhibited by intravenous administration of direct thrombin antagonists. However, an increased propensity for abnormal bleeding has been associated with systemic administration of these agents. The goal of this study was to determine whether local delivery of a potent thrombin inhibitor, D-Phe-L-Pro-L-Arg chloromethyl ketone (PPACK), could inhibit platelet-dependent thrombosis without altering systemic hemostatic function.nnnMETHODS AND RESULTSnThrombus formation was measured by quantitative imaging of 111In-labeled platelet deposition on segments of thrombogenic vascular graft interposed in arteriovenous shunts in a porcine model. Intravenous administration of PPACK inhibited platelet deposition at a dose of 12.5 micrograms/kg per minute, which was associated with significant prolongations of both template bleeding times and activated partial thromboplastin times. By contrast, local infusion of PPACK at a dose of 0.02 micrograms/kg per minute (ie, a 600-fold smaller dose) into the fluid boundary layer at the interface between flowing blood and the thrombogenic segment produced equivalent inhibition of platelet deposition without prolonging either the bleeding time or the activated partial thromboplastin time. In addition, static exposure of a mural thrombus to solutions of PPACK at concentrations > or = 2.5 mg/mL for 15 minutes produced sustained inhibition of platelet-dependent thrombosis with no change in hemostatic measurements.nnnCONCLUSIONSnThese results indicate that local delivery of the direct antithrombin PPACK, by either boundary layer infusion or static application techniques, effectively inhibits platelet-dependent thrombosis at doses that are several orders of magnitude less than the systemic dose required for an equivalent antithrombotic effect. In contrast to the systemic administration of PPACK, local delivery produced maximal inhibition of thrombosis without alterations in hemostasis.

Local delivery of a synthetic antithrombin with a hydrogel-coated angioplasty balloon catheter inhibits platelet-dependent thrombosis☆

OBJECTIVESnThis study evaluated the efficacy of local administration of an antithrombin agent with a hydrogel-coated percutaneous transluminal coronary angioplasty balloon catheter.nnnBACKGROUNDnIntravenous infusion of antithrombin compounds has been shown to inhibit platelet-dependent thrombosis. However, hemorrhage is a common side effect associated with the systemic administration of antithrombin compounds.nnnMETHODSnThe potent, irreversible thrombin inhibitor D-Phe-L-Pro-L-Arginyl chloromethyl ketone (PPACK) was used to inhibit thrombus formation in chronic porcine arteriovenous shunts. Platelet deposition was quantitated with gamma camera imaging of 111In-labeled platelets.nnnRESULTSnIntravenous administration of PPACK in swine, in doses sufficient to maximally inhibit thrombus formation, was associated with prolongation of bleeding parameters. The inhibition of thrombosis associated with intravenous PPACK was dose related. The amount of intravenous PPACK necessary for maximal inhibition of thrombus formation for a period of 45 min was 16.9 mg. In contrast, local delivery of PPACK with a hydrogel-coated angioplasty balloon deployed at the site of the thrombus inhibited platelet deposition for at least 45 min after the balloon was removed. Using 3H-labeled PPACK, the calculated amount of PPACK delivered was 33.5 micrograms. There was no change in bleeding time or activated partial thromboplastin time when swine received an intravenous bolus greater than the total amount of PPACK adsorbed onto the balloon (70 micrograms).nnnCONCLUSIONSnThese results suggest that in this model, a hydrogel-coated coronary angioplasty balloon catheter can be used to deliver enough antithrombin agent to inhibit platelet-dependent thrombosis for at least 45 min at doses that are several orders of magnitude less than those required for systemic administration. In addition, local delivery can provide effective inhibition of thrombus formation without alteration of bleeding parameters.

Comparison of the thrombogenicity of stainless steel and tantalum coronary stents

This study was designed to compare the thrombogenicity of stainless steel and tantalum coronary stents of the same design. Stainless steel and tantalum coronary stents are being evaluated for their utility in treating acute closure and restenosis. A major disadvantage of stainless steel stents is radiolucency. To determine whether radioopaque tantalum stents may be safely substituted for stainless steel stents, we compared the relative thrombogenicity of these materials in stents of identical design. Total platelet and fibrin deposition on the stents were determined from measurements of indium 111-labeled platelet and iodine 125-labeled fibrinogen accumulation after deployment into exteriorized chronic arteriovenous shunts in seven untreated baboons. In another series of experiments, 111In-platelet deposition was compared 2 hours after stent implantation in coronary arteries of pigs. In baboons, platelet thrombus formation on stainless steel and tantalum stents was equivalent and plateaued at approximately 2.5 x 10(9) platelets after 1 hour (p > 0.05). Fibrin deposition averaged approximately 1 mg/stent and did not differ between the stainless steel and tantalum stents (p > 0.05). In the porcine coronary model there was no significant difference in 111In-labeled platelet deposition between the stainless steel and tantalum stents (p > 0.05). This result was confirmed by scanning electron microscopic analysis of the coronary stents. Based on these two models, we conclude that there is no significant difference in the thrombogenicity of stainless steel and tantalum wire coil stents.

Recent changes in the management and outcome of acute closure after percutaneous transluminal coronary angioplasty

The major cause of morbidity and mortality associated with percutaneous transluminal coronary angioplasty (PTCA) is acute closure. This study compared the clinical outcome of 2 groups of patients who experienced acute closure during PTCA. One group was treated during a period when intracoronary stents, laser balloons and perfusion balloons were available for treatment of acute closure (group II). These results were compared with the clinical outcome a group of similar patients who were treated for acute closure during a period that immediately preceded the availability of these devices (group I). One hundred sixty-six patients had acute closure in group I, whereas 156 patients experienced acute closure in group II. Baseline clinical characteristics were similar for both groups. There was no difference in ejection fraction, number of vessels diseased, degree of stenosis or number of vessels attempted between the 2 groups. Patients in group II had more balloon inflations and longer balloon inflation times when compared with patients in group I. Of the 156 patients in group II, 47% were treated with either an intracoronary stent, laser balloon or perfusion balloon. Group II patients had fewer Q-wave myocardial infarctions (9.1 vs 20.3%, p = 0.005). In addition, peak creatine phosphokinase levels (826 +/- 1,515 vs 517 +/- 1,050, p < 0.01) and mean residual stenosis (40.7 +/- 33.2 vs 58.0 +/- 34.4%, p < 0.0001) were also lower in group II patients. There was also less coronary artery bypass grafting during the same admission (38.6 vs 29.5%, p = 0.02) in group II patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension detection, treatment and control: a call to action for cardiovascular specialists.

Hypertension affects about 25% of the adult population in the United States, or about 50 million people [(1,2)][1]. Over the past 30 years great strides have been made in improving awareness, treatment and control of high blood pressure [(1)][1]. These advances in blood pressure control have

Local intracoronary heparin delivery with a microporous balloon catheter

Arterial thrombosis plays a major role in the pathogenesis of acute coronary syndromes such as unstable angina and acute myocardial infarction. Heparin is efficacious in treating both disorders; however, systemically administered heparin is associated with bleeding complications. Local intracoronary delivery of heparin may be a safer, more effective method of administration. This study was performed to determine the fate of heparin infused with a specially designed catheter for local intracoronary delivery. To quantitate heparin delivery, tritiated-labeled heparin was dissolved in a solution of unlabeled heparin (1,000 U/ml). A microporous balloon catheter was placed in the left anterior descending (LAD) and left circumflex arteries of anesthetized pigs (n = 15), and 1 ml of the heparin solution was infused. The animals were euthanized within 1 hour, and the treated arteries and controls were harvested, processed, and the tritiated activity was measured. To assess the distribution of the heparin in the arterial wall, 1 ml of fluorescein-isothiocyanate (FITC)-labeled heparin was locally delivered into the walls of the LAD and left circumflex arteries with the microporous balloon catheter. To visualize the dynamic fluid transfer of the device, a microporous balloon catheter was inflated in the LAD, and 1 ml of diluted contrast medium was infused under cinefluoroscopy. The arteries treated with tritiated-labeled heparin contained 0.6% +/- 0.2% of the infused heparin dose. Control arteries contained 0.01% of the administered heparin. Animals that were infused with FITC-labeled heparin displayed fluorescence throughout all layers of the artery, especially in the adventitia. In animals that were injected with 1 ml of diluted contrast medium through the microporous balloon, a relatively large amount of the infusate appeared in the arterial lumen proximal to the balloon. In conclusion, these results suggest that heparin can be delivered to coronary arteries with a microporous balloon catheter. However, <1% of the infused dose can be found in the artery 1 hour after delivery. Infused heparin is distributed throughout the arterial wall, but most of the infused solution appears in the arterial lumen proximal to the inflated balloon and is probably washed downstream after balloon deflation.

In vitro and in vivo evaluation of the site-specific administration of d-phenylalanyl-l-prolyl-l-arginyl chloromethyl ketone (PPACK): a powerful thrombin inhibitor

Abstract d -Phenylalanyl- l -prolyl- l -arginyl chloromethyl ketone (PPACK) was incorporated into thin films of ethylene vinyl acetate copolymer (EVA, 33% vinyl acetate content). The release devices sustained the release of PPACK for approximately 120 min and delivered approximately 47 μg of PPACK/cm 2 /h in vitro at 4°C. The chemical degradation of PPACK was evaluated by HPLC and by 1 H-NMR spectroscopy. In spite of its low chemical stability, PPACK could be released from the polymeric matrix without apparent degradation. As a functional test of the release of PPACK from a polymer, the ability to inhibit platelet deposition on a metallic coronary stent was tested in vivo in a clinically relevant baboon model. In control experiments, the stent itself as well as stents in contact with plain films of EVA were found to be highly thrombogenic. However, when the coronary stent was placed in contact with a polymer film loaded with PPACK, there was a marked diminution in the number of platelets deposited on the stent for the duration of the 2-h experiment. Those studies provide the first experimental confirmation of the concept that the intraarterial, site-specific release of a thrombin inhibitor can reduce platelet deposition on an artificial polymeric surface in vivo.

Hypertension detection, treatment and control

Hypertension affects about 25% of the adult population in the United States, or about 50 million people [(1,2)][1]. Over the past 30 years great strides have been made in improving awareness, treatment and control of high blood pressure [(1)][1]. These advances in blood pressure control have

Inhibition of platelet deposition with local delivery of heparin using a double balloon catheter

Heparin is an effective agent in the treatment of unstable angina and myocardial infarction. The clinical utility of heparin is limited by bleeding complications. This study was performed to determine whether static delivery of heparin could effectively inhibit further platelet deposition. Thrombogenic graft segments were incorporated into chronic arteriovenous shunts in pigs. Autologous platelets were labeled with 111Indium. Platelet deposition was quantitated with gamma camera imaging. The grafts were exposed to blood flow for 15 min in order to induce platelet deposition on the thrombogenic surface. Heparin was delivered locally either by direct exposure or with a double balloon catheter. After a 15 minute exposure period, the heparin solution was removed and subsequent platelet deposition was monitored for 90 minutes. Heparin, administered with the double balloon catheter in doses as low as 12.5 U, effectively inhibited further platelet deposition. An intravenous injection of 100 U of heparin, the highest dose use for local delivery, did not perturb bleeding time or the activated partial thromboplastin time. In conclusion, platelet deposition can be inhibited with static local delivery of heparin at doses that are not associated with systemic bleeding.