Polymeric Surface Modifications of Tantalum Stents

Purpose:

To compare two kinds of polymer-coated tantalum stents with bare tantalum stents (control) to determine if the coatings can improve thromboresistance.

Methods:

Twenty-seven Fontaine-Dake stents were balloon expanded in three 8-mm × 80-cm.polytetrafluoroethylene (PTFE) grafts; 9 stents were bare tantalum (T); 9 were coated with polyetherurethane (PL); and 9 were coated with parylene (PA). There were 9 stents placed in each graft as follows: 3 tantalum, 3 polyetherurethane, and 3 parylene. In swine whose platelets had been radiolabeled with indium 111, the ends of each stented graft were connected to 14F femoral and venous sheaths to create an ex vivo fistula. Each graft was exposed to blood for 30, 60, and 120 minutes. At the end of each test period, the stented grafts were disconnected from the sheaths, flushed with saline until clear, and then flushed with formalin. The stents were removed from the grafts, and a radionuclide well counter recorded radionuclide counts from each stent type at each period of blood contact. These values were converted to platelet density per 1000 mUm2. Stents were then photographed and scanned with electron microscopy (EM) for qualitative analysis. Possible significant differences in platelet adhesion with the three types of stents (both between stent groups and within stent groups) were examined using a two-tailed Student's f-test.

Results:

There were significantly fewer platelets adsorbed on PA versus T at all time periods (p < 0.005); on PL versus T at 60 and 120 minutes (p < 0.005); and on PA versus PL at 30 and 120 minutes (p < 0.0005). There was no significant difference in platelet density within each stent group (p = 0.1). Mean platelet density (number of platelets per 1000 mUm2 ± SD) was as follows: at 30 minutes: T = 1891 ± 965; PL = 373 ± 193; and PA = 27 ± 3; at 60 minutes: T = 6226 ± 1621; PL = 1573 ± 793; and PA = 1185 ± 710; at 120 minutes: T = 5307 ± 591; PL = 3164 ± 318; and PA = 180 ± 100. Gross inspection of the 120-minute groups demonstrated focal areas of thrombus on T, less on PL, and none on PA. Scanning EM demonstrated extensive platelet accumulation covering T at all time periods, less on PL, and even less on PA.

Conclusions:

Polymeric surface modification of tantalum stents with parylene and/or polyetherurethane can improve the acute thromboresistance of these devices; parylene appears to be the more thromboresistant of the two coatings.

Peripherally inserted central catheters with distal versus proximal valves: prospective randomized trial

PURPOSE

To evaluate whether peripherally inserted central catheters (PICCs) with a proximal valve have any advantage compared to those with a distal valve in regard to the incidence of occlusion, infection, or malfunction.

MATERIALS AND METHODS

One hundred patients (mean age, 46 y) were randomized to receive either a distal-valved Bard Groshong catheter (n = 48) or a proximal-valved Catheter Innovations Pressure Activated Safety Valve catheter (n = 52). All catheters were 4-F, single-lumen PICCs. Catheters were placed under fluoroscopic (n = 82) or sonographic (n = 18) guidance. Most (91%) were placed for the administration of antibiotics. The placement procedure, maintenance, and weekly follow-up were the same for both catheters.

RESULTS

Percutaneous placement with the catheter tip in the central veins was successful in all patients. Mean dwell time was 36 days. There were 12 (25%) occlusive or infectious complications in the distal valve catheter group and six (11.5%) in the proximal valve group (P = .08). There were 25 fractures in 17 distal valve catheters (35.4%) and three (5.8%) proximal valve catheter fractures (P < .01).

CONCLUSION

There was a marked difference in durability between the valved catheters, in favor of the catheter with a proximal valve. There was also a trend for fewer occlusive and infectious complications with the proximal valve catheter.

Type III heart block with peripheral use of the Angiojet thrombectomy system

The authors describe the occurrence of type III heart block in a patient undergoing a transjugular intrahepatic portosystemic shunt recanalization with use of the AngioJet thrombectomy system.

Evaluation of silicone as an endovascular stent membrane: in vivo canine studies

PURPOSE

Comparative evaluation of the biological effects of a silicone-covered stent versus a bare-metal stent, in an animal model.

METHODS

Twelve stent implants were placed in the iliac arteries of six adult dogs. Each animal received one 8-mm x 20-mm silicone-covered stent (Permalume; Boston Scientific Vascular, Watertown, MA, USA), in the right iliac artery and one Wallstent (Boston Scientific Vascular) of the same diameter and length in the left iliac artery, during systemic anticoagulation. Angiography was performed before and after implantations. Animals were then allowed to recover and no platelet suppression was given during a 6-week interval, after which the animals were euthanized. The stented arteries were isolated and pressure-fixed in situ with 10% buffered formalin at a pressure of approximately 100 mmHg for a period of 1 hr. Two of 12 stented specimens were opened lengthwise and the luminal surfaces were photographed. Ten of 12 stented arterial segments were encased in methacrylate, then stained with hematoxylin and eosin. Neointimal thickness was quantified on histologic cross-section, for both bare and covered stents. The mean neointimal thicknesses were compared for significant difference using a student t-test.

RESULTS

All implants were widely patent at 6-week follow-up angiography. Histologic analysis showed bare metal stents covered by a thin uniform lining of neointima composed of smooth muscle cells in a hyaline matrix (mean thickness of 189 +/- 47 microm). Silicone covered stents were devoid of neointima. There was no chronic thrombus or mature endothelium noted anywhere upon the internal silicone surfaces of any of the specimens. There was no foreign body reaction to the silicone cover.

CONCLUSION

Short-term implantation of a silicone-lined Wallstent in canine iliac arteries is well tolerated. Silicone appears to be inert at 6 weeks in this experimental application.

Stent placement in the treatment of pulmonary artery stenosis secondary to fibrosing mediastinitis

This article describes an initial experience with stent placement in three patients with severe pulmonary artery stenosis secondary to fibrosing mediastinitis. All three patients were severely symptomatic on admission and all three were asymptomatic after treatment and remained symptom-free approximately 1 year after treatment.

Evaluation of local abciximab delivery from the surface of a polymer-coated covered stent: in vivo canine studies

PURPOSE

To determine the in vitro feasibility of abciximab absorption and elution from a polymer-coated, silicone-covered stent, and to determine the in vivo effect of local delivery of abciximab concerning endothelialization of a polymer-coated, silicone-covered stent in a canine model.

MATERIALS AND METHODS

Six polymer-coated, silicone-lined Wallstents were soaked in 2 mg/mL of concentrated solution of I131-labeled abciximab for a period as long as 48 hours. Quantification of abciximab absorption was determined by photon emission. Six maximally drug-loaded devices were then washed continuously with normal saline with use of a pustule pump apparatus. The quantity of residual abciximab was determined by photon emission for a period as long as 16 days. Eight similar devices (as described previously) were then implanted within the iliac arteries of four adult canines. Devices were identical except that four of eight were maximally loaded with abciximab. For each animal, one control implant was placed in the right iliac artery and one experimental implant (drug loaded) was placed in the left iliac artery, via right carotid cutdown. Animals were allowed to recover and no chronic medications were given. After an interval of 6 weeks, the animals were killed. Implants were isolated and perfused with 10% buffered formalin at a pressure of approximately 100 mm Hg for a period of 1 hour. Each implant was encased in methacrylate, sectioned into six equal segments, ground and polished, and stained with hematoxylin and eosin. Each slide was projected on a screen and the thickness of the neointima quantified. The mean neointima was determined for control and experimental groups, and compared for a potential significant difference with a Student t test.

RESULTS

Mean absorption of abciximab was 21.53 microg +/- 2.99 per device. Devices were fully saturated at 24 hours. Forty percent was absorbed at 1 hour, and 60% and 80% were absorbed at 4 hours and 12 hours, respectively. Regarding elution, 30% of abciximab was washed out after 1 hour. There was a gradual elution of the drug to 16 days, with approximately 40% remaining at the end of the term. Mean neointimal thickness was 995 microm +/- 597 for the experimental group and 1,738 microm +/- 1,042 for the control group. The difference was significant (P <.05).

CONCLUSIONS

Absorption and elution of abciximab from the surface of a covered stent is feasible. Local delivery of abciximab from the surface of this covered stent reduced the thickness of endothelial lining in the canine iliac artery compared to control.

Seat belt aorta: endovascular management with a stent-graft

PURPOSE

To report the endovascular treatment of a relatively uncommon type of deceleration injury to the abdominal aorta.

CASE REPORT

A 21-year-old backseat passenger was wearing a single lap belt without shoulder harness when the car was involved in a collision. He sustained a transverse (Chance) fracture of the third lumbar vertebra and a circumferential dissection of the infrarenal abdominal aorta with pseudoaneurysm. As an interim measure while a stent-graft was obtained, a Wallstent was deployed to tack down the dissection and prevent distal embolization. Thirty-six hours later, an AneuRx endograft was successfully implanted inside the Wallstent to seal the pseudoaneurysm. The patient's recovery was uneventful, and the endograft remains secure and the pseudoaneurysm excluded at 10 months after the accident.

CONCLUSIONS

Endovascular repair of "seat belt aorta" is a minimally invasive, straightforward method of management for this type of aortic injury. The potential for infection in a contaminated peritoneal cavity and the long-term outcome of this treatment have not been determined.

Retrospective comparison of the patency of Wallstents and Palmaz long-medium stents used for TIPS. Transjugular intrahepatic portosystemic shunts

PURPOSE

To compare patency rates of transjugular intrahepatic portosystemic shunts (TIPS) after placement of long-medium Palmaz stents or Wallstents.

METHODS

We performed a retrospective review of TIPS performed at our institution between December 1997 and December 1998. During this time period we placed long-medium Palmaz stents for TIPS procedures in 17 patients and Wallstents in 20 patients as the initial stent. Patency was determined on follow-up by ultrasound, angiography, or pathologic examination in the event of transplant.

RESULTS

Primary patency in the Palmaz stent group was 70.6% (12/17 patients) (follow-up 1-399 days, mean 127 days). Both primary assisted and secondary patency in the Palmaz group was 100% (17/17 patients) (follow up 1-399 days, mean 154 days). Primary patency in the Wallstent group was 50% (10/20 patients) (follow up 1-370 days, mean 65 days). Primary assisted patency in the Wallstent group was 80% (16/20 patients) (follow up 1-601 days, mean 141 days). Secondary patency in the Wallstent group was 100% (20/20 patients) (follow up 2-601 days, mean 142 days). Kaplan-Meier analysis of the two groups of patients yielded a primary patency of 266 days (standard error 45 days) for TIPS with the Palmaz stent and 139 days (standard error 45 days) for the Wallstent (p =.04). The 3, 6, and 12-month primary patency rates were .84, .63, and .42 respectively for the Palmaz stents and .36, .36, and .18 respectively for the Wallstent. There was no significant difference in primary assisted or secondary patency between the two stent groups. The mean tract curvature in the patients with Palmaz stents was 23.5 degrees (SD 18.2 degrees, range 0-69.0 degrees ) compared with 57 degrees (SD 34.5 degrees, range 7.0-144.0 degrees ) in patients with Wallstents (p =.01).

CONCLUSIONS

Our nonprospective, nonrandomized study suggests that TIPS created with the long-medium Palmaz stent have a higher primary patency than those created with the Wallstent in tracts that are relatively straight.

Primary placement of Palmaz long medium stents in transjugular intrahepatic portosystemic shunts

PURPOSE

To describe our results with primary placement of the long-medium Palmaz stent for transjugular intrahepatic portosystemic shunts (TIPS).

MATERIALS AND METHODS

Between December 1997 and December 1998 primary placement of long-medium Palmaz stents was performed for TIPS procedures in 17 patients. Patency was determined with ultrasound, angiography, or pathologic examination in the event of transplant.

RESULTS

Primary patency was achieved in 13 of 17 patients (76.5%) (follow up, 1-399 days; mean, 99 days). Secondary patency was achieved in 17 of 17 patients (100%) (follow-up, 1-399 days; mean, 110 days). Among the four patients who required revision, the mean time to revision from initial shunt creation was 81 days (range, 13-125 days). Two of these four patients had symptoms of worsening ascites as well as abnormal ultrasound findings prior to their revision; the other two patients were asymptomatic and had abnormal ultrasound findings only. Revisions were performed for intimal hyperplasia within the stent in three of the patients and acute thrombus within the stent in the remaining patient. Kaplan-Meier survival analysis for primary patency yielded mean survival time of 265 days (standard error, 52 days).

CONCLUSION

The long-medium Palmaz stent is a viable stent for creation of TIPS shunts.

Prospective randomized comparison of valved versus nonvalved peripherally inserted central vein catheters

OBJECTIVE

The purpose of this study was to evaluate whether a valved peripherally inserted central catheter (PICC) design would result in a lower incidence of occlusion, infection, and malfunction than a clamped catheter.

SUBJECTS AND METHODS

Three hundred sixty-two study patients (233 men, 129 women; mean age, 44 years) were randomized to receive a clamped (n = 182) or valved (n = 180) 5-French single-lumen PICC. Catheters were placed under fluoroscopic (n = 331) or sonographic guidance (n = 31). The valved PICC was flushed with saline solution, and the clamped PICC was flushed with a heparin-saline solution. All patients were prospectively followed up at least weekly for catheter status and complications.

RESULTS

Percutaneous placement with the catheter tip in the central veins was successful in 99% of patients. Mean dwell time was 34 days. Twenty-six occlusive or infectious complications occurred in the clamped catheter group and 12 in the valved catheter group (p = .02). The clamped and valved catheter groups had 13 and five occlusions, respectively (p = .06), and 12 and five catheter-related blood stream infections, respectively (p = .09). Most occlusions (68%) were treated successfully with urokinase, and site infection or sepsis was treated by catheter removal.

CONCLUSION

We found a statistically significant difference in the complication rate for the valved PICC compared with the clamped PICC. With the valved PICC, occlusion and infection were reduced, and patients having these catheters did not require heparin flushes.

Transcatheter arterial embolization for intractable epistaxis secondary to gunshot wounds

PURPOSE

To evaluate the efficacy of transcatheter arterial embolization for intractable epistaxis secondary to gunshot wounds.

MATERIALS AND METHODS

Seven patients with intractable epistaxis secondary to penetrating trauma (gunshot wounds) were studied with angiography and subsequently underwent embolization with particles (polyvinyl alcohol, gelatin sponge) and/or microcoils. Clinical follow-up included standard hemodynamic monitoring, serial hematocrit determinations, and clinical observation for recurrent bleeding.

RESULTS

Diagnostic angiography demonstrated evidence of acute arterial injury in all patients. All patients subsequently underwent embolization to complete angiographic stasis. Two patients had persistent bleeding following embolization. One of these patients required maintenance of his nasal packing for 7 days after embolization; no blood products were required during this time. The second patient's bleeding resolved following correction of his coagulopathy. No complications occurred in any of the patients.

CONCLUSIONS

Transcatheter arterial embolization for epistaxis secondary to gunshot wounds is efficacious in the acute setting when conservative management fails.

Treatment of inferior vena cava anastomotic stenoses with the Wallstent endoprosthesis after orthotopic liver transplantation

PURPOSE

To evaluate the efficacy of the Wallstent endoprosthesis for treatment of stenotic or occlusive inferior vena cava (IVC) lesions refractory to balloon angioplasty in patients after orthotopic liver transplantation.

MATERIALS AND METHODS

Wallstent endoprostheses were implanted in six patients with IVC anastomotic stenoses or occlusions that were refractory to balloon angioplasty. Follow-up included both duplex ultrasound (US) and clinical evaluations.

RESULTS

Ten stents were successfully implanted in six patients. Five of six patients (83%) demonstrated primary patency on duplex US for a mean period of 11 months (range, 4-17 months). One patient's symptoms recurred within 3 weeks after intervention. This patient underwent repeated stent placement. Follow-up duplex US in this patient demonstrated primary assisted patency at 7 months. Mean clinical follow-up was 12 months (range, 7-18 months). Other than the previously described case, no patient developed recurrent symptoms of IVC stenosis or occlusion. Two patients who experienced hemorrhagic complications secondary to anticoagulation were treated successfully.

CONCLUSIONS

The Wallstent endoprosthesis is a useful adjunct for treatment of IVC stenosis or occlusions in patients who have undergone orthotopic liver transplantation when these lesions are refractory to simple balloon angioplasty.

Renal artery dissection causing renal infarction in otherwise healthy men

Arterial dissection is usually associated with pathological states such as malignant hypertension, severe atherosclerosis, severe trauma, Marfan syndrome, or Ehlers-Danlos syndrome. However, we report three cases in which renal artery dissection occurred in otherwise healthy, normotensive men. In two cases, the onset of symptoms of renal artery dissection was coincident with an unusual degree of physical activity. In the third case, the symptoms occurred while the patient was sitting but during a stressful business meeting. In each case, the patient experienced severe unilateral flank pain. Urolithiasis was suspected, but intravenous pyelography showed only ipsilateral impaired renal cortical perfusion, and the urinalyses showed no hematuria. The diagnosis of renal artery dissection was established by arteriography in two cases and by nephrectomy in one case. The latter case showed fibromuscular dysplasia by arteriography performed after the nephrectomy. The other two cases showed no evidence of fibromuscular dysplasia. We conclude that spontaneous renal artery dissection can occur in otherwise healthy individuals. Our experience and the reports of others indicate that this condition occurs mainly in men, conservative (nonsurgical) management is generally indicated, and the long-term prognosis is generally excellent. In some patients, an unusual degree of physical exertion might be the cause of renal artery dissection.

Renal artery origins: best angiographic projection angles

PURPOSE

To determine the best projection angles for imaging the renal artery origins in profile.

MATERIALS AND METHODS

A mathematical model of the anatomy at the renal artery origins in the transverse plane was used to analyze the amount of aortic lumen that projects over the renal artery origins at various projection angles. Computed tomographic (CT) angiographic data about the location of 400 renal artery origins in 200 patients were statistically analyzed.

RESULTS

In patients with an abdominal aortic diameter no larger than 3.0 cm, approximately 0.5 mm of the proximal part of the renal artery and origin may be hidden from view if there is a projection error of +/-10 degrees from the ideal image. A combination of anteroposterior and 20 degrees and 40 degrees left anterior oblique projections resulted in a 92% yield of images that adequately profiled the renal artery origins. Right anterior oblique projections resulted in the least useful images.

CONCLUSION

An error in projection angle of +/-10 degrees is acceptable for angiographic imaging of the renal artery origins. Patients sex, site of interest (left or right artery), and local diameter of the abdominal aorta are important factors to consider.

Update on the use of percutaneous nephrostomy/balloon dilation for the treatment of renal transplant leak/obstruction

PURPOSE

Retrospective evaluation of the efficacy of percutaneous nephrostomy and nephroureteral stent placement for treatment of post-transplant ureteral leak, and percutaneous nephrostomy and balloon dilation for treatment of post-transplant ureteral obstruction.

PATIENTS AND METHODS

Data were reviewed for all patients who underwent percutaneous therapy for complications after renal transplantation between January 1985 and June 1995. A total of 61 patients with complications (leak, n = 17; obstruction, n = 44) had been treated. Patients underwent percutaneous nephrostomy followed by antegrade placement of a nephroureteral stent. In addition, all patients with obstruction also underwent ureteral balloon dilation. Follow-up ranged from 9 weeks to 24 months. Positive outcome was defined as nonsurgical closure of leak, significant improvement in renal function, and removal of the nephroureteral stent with maintenance of stable renal function.

RESULTS

Regarding ureteral leak, 10 of 17 patients (59%) healed after treatment. Seven patients (41%) did not respond and went on to surgical repair. All patients with early (n = 13) ureteral obstruction (< 3 months after transplantation), had improved renal function (P < .025). Sixty-two percent of patients with early obstruction were cured (tube out with stable renal function) and 38% went to surgery for ureteral repair. In patients with late (n = 31) obstruction (> 3 months after transplantation), renal function improved in only 58% (P < .01). Only 16% of patients with late obstruction were cured (tube out with stable renal function). Ureteral obstruction was persistent in the remaining patients and did not respond to multiple balloon dilations. All complications were minor and included 23 of 61 (38%) patients with urinary tract infections and nine of 61 (14%) patients with limited hematuria.

CONCLUSION

Percutaneous nephrostomy is very effective in improving renal function in patients with early obstruction. It is moderately successful in treating ureteral leak. Ureteral balloon dilatation is moderately effective for treatment of obstruction in the early (< 3 months) postoperative period. However, balloon dilation is minimally successful in curing ureteric obstruction occurring more than 3 months after transplantation.

Vascular stent prototype: in vivo swine studies

PURPOSE

Evaluation of implantation technique and biocompatibility of a new balloon-expandable peripheral vascular stent.

MATERIALS AND METHODS

Twenty-four stents, varying in diameter from 4 mm to 14 mm and length from 2 cm to 6 cm, were placed in eight microswine. After implantation, two of the animals were killed at 2 months and the remaining animals were killed at 6 months. All animals underwent premorbid angiography. The stents were then pressure fixed, harvested, and encased in methacrylate. The specimens were then sectioned by a diamond saw prior to staining. Individual specimens were then photographed, projected against a screen, and the neointimal thickness quantified by calibration with the diameter of the stent wire retained in the specimen.

RESULTS

Technical success (implantation) was 96% (one embolization). All stents were widely patent at 2- and 6-month follow-up. Histopathologic examination demonstrated a very thin neointima covering the stent wires, with a maximum thickness measuring 254 microns.

CONCLUSION

This new stent is safely implantable and biocompatible as tested in the arterial system of this animal model. Human clinical trials are indicated.

Prototype stent: in vivo swine studies in the biliary system

PURPOSE

To evaluate the safety of implantation and the biocompatibility of a new balloon-expandable stent in the biliary system of the swine model.

MATERIALS AND METHODS

Thirty stents, varying in diameter from 4 mm to 12 mm and in length from 2 cm to 6 cm, were placed in the bile ducts of 10 microswine. After implantation, one-third of the animal subjects were killed at 2 months and the rest, at 6 months. All animals underwent premorbid cholangiography. Stents were pressure fixed, harvested, and encased in methacrylate. Specimens were then sectioned with a diamond saw, prior to staining. Individual specimens were photographed for visualization of the histologic reaction.

RESULTS

Technical success (implantation) was 100%. All stents were widely patent at 2-month and 6-month follow-up. Histopathologic study demonstrated a very thin epithelial hyperplasia that formed between stent wires. This did not cover the stent wires.

CONCLUSION

This new stent is safely implantable and demonstrates minimal tissue reaction in the biliary system of the swine, when compared with other metallic biliary stents.

Polymeric surface modifications of tantalum stents

PURPOSE

To compare two kinds of polymer-coated tantalum stents with bare tantalum stents (control) to determine if the coatings can improve thromboresistance.

METHODS

Twenty-seven Fontaine-Dake stents were balloon expanded in three 8-mm x 80-cm polytetrafluoroethylene (PTFE) grafts; 9 stents were bare tantalum (T); 9 were coated with polyetherurethane (PL); and 9 were coated with parylene (PA). There were 9 stents placed in each graft as follows: 3 tantalum, 3 polyetherurethane, and 3 parylene. In swine whose platelets had been radiolabeled with indium 111, the ends of each stented graft were connected to 14F femoral and venous sheaths to create an ex vivo fistula. Each graft was exposed to blood for 30, 60, and 120 minutes. At the end of each test period, the stented grafts were disconnected from the sheaths, flushed with saline until clear, and then flushed with formalin. The stents were removed from the grafts, and a radionuclide well counter recorded radionuclide counts from each stent type at each period of blood contact. These values were converted to platelet density per 1000 microns 2. Stents were then photographed and scanned with electron microscopy (EM) for qualitative analysis. Possible significant differences in platelet adhesion with the three types of stents (both between stent groups and within stent groups) were examined using a two-tailed Student's t-test.

RESULTS

There were significantly fewer platelets adsorbed on PA versus T at all time periods (p < 0.005); on PL versus T at 60 and 120 minutes (p < 0.005); and on PA versus PL at 30 and 120 minutes (p < 0.0005). There was no significant difference in platelet density within each stent group (p = 0.1). Mean platelet density (number of platelets per 1000 microns 2 +/- SD) was as follows: at 30 minutes: T = 1891 +/- 965; PL = 373 +/- 193; and PA = 27 +/- 3; at 60 minutes: T = 6226 +/- 1621; PL = 1573 +/- 793; and PA = 1185 +/- 710; at 120 minutes: T = 5307 +/- 591; PL = 3164 +/- 318; and PA = 180 +/- 100. Gross inspection of the 120-minute groups demonstrated focal areas of thrombus on T, less on PL, and none on PA. Scanning EM demonstrated extensive platelet accumulation covering T at all time periods, less on PL, and even less on PA.

Use of polyetherurethane to improve the biocompatibility of vascular stents

PURPOSE

To investigate potential differential growth on neointima following overdilating arterial trauma with polyetherurethane-coated versus bare metallic stents in swine.

METHODS

Twelve specially constructed tantalum stents, 6 coated with polyetherurethane block copolymer and 6 uncoated, were overdilated by 25% in 12 normal renal arteries of six swine. The stents were harvested 8 weeks after implantation and prepared for histologic examination. Neointimal thickness was quantified and analyzed for significant differences between coated and uncoated prostheses.

RESULTS

All specimens demonstrated fractures of the internal elastic lamina consistent with vascular injury. There was significantly less neointimal formation (0.0001 < p < 0.05) in coated specimens as compared to uncoated controls in each test animal.

CONCLUSIONS

The vascular response to overdilating stent trauma appears to be moderated with the use of polyetherurethane block copolymer as compared to control.

Stent-induced intimal hyperplasia: are there fundamental differences between flexible and rigid stent designs?

PURPOSE

To evaluate possible differences in neointimal development resulting from overdilation of rigid versus flexible vascular stents.

MATERIALS AND METHODS

Twelve vascular sheaths were placed bilaterally through femoral arteries in six swine. After angiographic measurement, 12 stents (six flexible and six rigid) were balloon expanded to 8-mm diameters in 12 6-mm iliac arteries (approximately 30% overdilation). All stents were similar in surface area, gauge, and type of wire (tantalum). The primary difference was longitudinal flexibility (low hoop strength) versus rigidity (high hoop strength). Stents were studied with angiography and intravascular ultrasound 5 weeks after implantation. The animals were killed, and the stented segments were removed and examined histologically.

RESULTS

Rigid stents maintained larger diameters than flexible stents: mean, 6.52 mm versus 5.82 mm (mean difference, 0.70; standard deviation [SD], 0.47; confidence interval [CI], +/- 0.49; P < .05). In addition, rigid stents developed a thicker, eccentric neointimal reaction relative to flexible stents: mean 1.08 mm versus 0.74 mm (mean difference, 0.338; SD, 0.315; CI, +/- 0.331; P < .05).

CONCLUSION

Rigid stents maintain larger diameters over the long term relative to flexible stents when overdilated in normal swine arteries. However, a thicker neointima develops within the lumen of rigid stents at follow-up (greater late loss).

Decreased platelet adherence of polymer-coated tantalum stents

PURPOSE

To compare the acute thrombogenicity of polyurethane-coated stents with that of bare tantalum stents.

MATERIALS AND METHODS

Thirty stents (15 coated with polyurethane) were balloon expanded in 8-mm x 80-cm sections of polytetrafluoroethylene grafts (six stents per graft). Under sterile conditions, 8- and 10-F vascular sheaths were placed percutaneously in the femoral artery and vein of a 100-lb (45-kg) swine. Platelets were labeled with indium-111 and reinjected for quantitative assay. The stented grafts were connected to the arterial and venous sheaths to create an ex vivo fistula. Each fistula was opened for 5, 10, 30, 60, or 120 minutes, exposing heparinized blood to fully expanded stents. The fistulas were closed, flushed with saline until clear, and fixed with formalin. Stents were explanted, placed in a radionuclide well counter, and scanned with electron microscopy.

RESULTS

Quantitatively, there were considerably fewer platelets on coated versus uncoated stents. At 60 minutes, coated stents averaged 12.93 platelets per 1,000 microns 2 compared with 75.88 platelets per 1,000 microns 2 for bare metallic stents. At 120 minutes, there were 23.22 platelets/1,000 microns 2 versus 102.31 platelets/1,000 microns 2, respectively. Electron microscopy of coated stents demonstrated few scattered platelets at 5, 10, and 30 minutes. There was a uniform layer of platelets at 60 and 120 minutes. Uncoated stents demonstrated random areas of platelet clumping at 5, 10, and 30 minutes. At 60 and 120 minutes, uncoated stents showed extensive layering of platelets and fibrin.

CONCLUSION

Polyurethane coating decreases platelet adhesion, relative to bare tantalum, at all time intervals tested.

Tantalum balloon-expandable stent: in vivo swine studies

PURPOSE

The authors describe the experimental use of a balloon-expandable tantalum vascular stent in normal and atherosclerotic microswine.

MATERIALS AND METHODS

Thirty-one stents (15 iliac, 13 aorta, two femoral, one renal) were placed in 11 animals. Stents were placed in both normal and stenotic atherosclerotic arteries. The animals were killed and the stents explanted 2-32 weeks after placement. Arteriography was performed just prior to death in all cases.

RESULTS

All stents were patent arteriographically and on gross inspection. Histopathologic study showed a thin, smooth, endothelial-lined neointima over the segments with stents. This covering had a mean thickness of 2.9 x 10(-5) mm and appeared maximally developed 2-5 weeks after stent placement. The stent design incorporates the following engineering and clinical considerations: minimal profile and surface area and maximal expansion ratio, hoop strength, flexibility, fluoroscopic visibility, biocompatibility, and ease of placement. When compressed and mounted on the balloon catheter, the stent is flexible. This allows it to be easily maneuvered through tortuous or diseased vessels. On expansion, the stent becomes a semirigid tubular structure composed of multiple rhomboid cells. Stents with an expanded diameter of less than 11 mm can be introduced through a 7-F vascular sheath.

CONCLUSION

Initial results suggest that this stent successfully incorporates a number of theoretically desirable features for a vascular prosthesis, and it may offer some advantages over previously described devices.

Human surface electrogastrograms: ac and dc measurements

Both ac and dc abdominal electrical recordings were made on fasted and fed human subjects using a spatial array of 18 cutaneous, biopotential electrodes. Controlled skin puncture minimized cutaneous potentials. Pregelling electrodes minimized drift. The recording sessions were between two and three hours in length. We determined the optimal location for ac recording of a 3 cpm wave at a location on the midline approximately 5 cm below the xiphoid process. Seven cpm waves were also observed in one individual at the same location. The dc values were fed into a Hewlett Packard 1000 computer which interpolated the intermediate values and plotted two-dimensional contour plots which were examined visually. The right abdominal surface was typically 1.8 mV more negative than the left for prefeeding. The left abdominal surface was typically 4.6 mV more negative than the right for postfeeding. We propose an electrical model that explains these results during the fasted state.